Search

Purpose: The J-sign is a clinical evaluation tool that assesses for patellar maltracking and is considered positive if lateral translation of the patella in extension, in the pattern of an inverted J is observed. This study aims to determine the association of clinical J-sign with imaging features noted on dynamic kinematic computed tomography (DKCT)., Methods: A retrospective review was conducted by reviewing the clinical records of all patients aged 18 years or younger who had a CT patellar tracking scan done between 1 January 2005 to 31 December 2016 in a single institution. Patients who had the presence or absence of a 'J-sign' evaluated clinically were included. Radiographic parameters evaluated using the axial cuts include the patellar tilt angle, congruence angle, Dejour's classification, femoral sulcus angle, trochlear groove depth, and Wiberg's classification. Patients were then divided into two groups based on the presence or absence of J-sign on clinical examination. The radiographic measurements were then analyzed for association with the presence or absence of J-sign on clinical examination., Results: Patients with a positive J-sign had an increased patellar tilt of 23.3° ± 14.2° and an increased congruence angle of 47.1° ± 28.5° when measured in extension as compared to a patellar tilt of 18.3° ± 10.8° and a congruence angle of 32.1° ± 20.8° in patients with a negative J-sign ( p  = 0.024 and 0.004, respectively). Comparisons of the change in congruence angles with the knee in full extension and at 20° flexion also yielded significantly higher change of 28.0° ± 20.4° in patients with a positive J-sign as compared to 11.9° ± 17.5° in patients with a negative J-sign. Patients with a positive J-sign also had an increased TT-TG distance of 17.6 ± 5.6 mm as compared to a TT-TG distance of 14.7 ± 6.9 mm in patients with a negative J-sign ( p  = 0.01)., Conclusion: Patients with a positive J-sign had an increased patellar tilt and an increased congruence angle when measured in extension. Increased TT-TG distance was also significantly associated with positive J-sign. Patients with a positive J-sign also had a greater change in their congruence angle when measured with the knee in full extension and at 20° of flexion.

Background: For the normal functioning of the patellofemoral joint (PF), the relationship between the patella and the trochlear groove must be compatible., Purpose: To investigate the relationship between patellofemoral joint morphology (PFM) and patellar chondromalacia., Material and Methods: Overall, 136 knees of patients aged 20-55 years examined between March 2020 and March 2021 were included in this study. In all patients, trochlear sulcus angle, trochlear sulcus depth, trochlear facet asymmetry, patella alta (Insall-Salvati [IS] index), and patellar facet asymmetry were measured. Of these cases, 66 knees with an abnormality detected in any of the measurements for PFM were included in the case group. Moreover, 70 knees with demonstrating normal PFM measurements were included in the control group., Results: The incidence and grade of chondromalacia was higher in the case group than in the control group ( P  < 0.001). Between the patients with and without chondromalacia trochlear sulcus angle (mean = 138.25° ± 10.02° vs. 132.58° ± 7.24°; P = 0.001), IS index (mean = 1.25 ± 0.21 vs. 1.16 ± 0.15; P = 0.014), patellar facet asymmetry (mean = 0.77 ± 0.09 vs. 0.73 ± 0.12; P = 0.039), trochlear sulcus depth (mean = 5.39 ± 1.42 mm vs. 6.27 ± 1.04 mm; P < 0.001), and trochlear facet asymmetry (mean = 0.67 ± 0.11 vs. 0.71 ± 0.09; P = 0.023) measurements, there was a significant difference., Conclusion: The presence of at least one of the measures indicating pathology in PFM is associated with the presence and severity of chondromalacia., Competing Interests: Declaration of conflicting interestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Purpose: To propose a new measurement, the patellar shift ratio (PSR), for characterising lateral patellar shift; to determine its diagnostic accuracy in predicting recurrent patellar dislocation (RPD); and to identify the effect of patellar tilt and morphology on shift measurements., Methods: Variables including the PSR, bisect offset (BSO), BSO adjusted by trigonometric analysis, linear patellar displacement (LPD) distance and congruence angle were measured on axial computed tomography (CT). Furthermore, PSR was classified into grades determined by the threshold generated by receiver operating characteristic (ROC) curves. Youden's index was used to identify the ideal threshold on the curve. The area under the ROC curve (AUC) values and likelihood ratios were calculated to assess diagnostic performance in predicting RPD. Correlation analysis was conducted to identify the effects of lateral tilt and the Wiberg index on lateral shift. Intra- and interobserver reliability were evaluated using the intraclass correlation coefficient., Results: The study included 54 RPD patients and 54 controls matched by sex and age. The threshold for PSR was 24.3% (sensitivity, 96.30%; specificity, 85.19%). AUCs were categorised as excellent for all protocols (P < 0.001). The positive likelihood ratio of the PSR for predicting RPD was 6.50. PSR was categorised in terms of lateral trochlear quadrants consisting of 25% increments. Lateral patellar tilt showed a strong positive correlation with BSO (P < 0.001); moderate correlations with PSR, LPD distance and adjusted BSO (P ≤ 0.001); and a weak correlation with congruence angle (P = 0.034). The Wiberg index presented a positive moderate correlation with BSO (P < 0.001), while no correlation was found with PSR, LPD distance, or congruence angle (n.s.). All parameters showed good repeatability (intraobserver) and reproducibility (interobserver)., Conclusions: The PSR showed excellent diagnostic performance as indicated by likelihood ratios, measurement accuracy (being relatively resistant to the effects of tilt and the Wiberg index), and intra- and interobserver reliability. The optimal PSR threshold for predicting RPD risk was 24.3%, and the grade of PSR (normal, 1-4) was also a reliable and easily calculated predictor of RPD. This quantifying method to characterise lateral patellar shift is an alternative useful method for clinical assessments of RPD patients and for research on patellofemoral congruence., Level of Evidence: Level III., (© 2022. The Author(s) under exclusive licence to European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA).)

Purpose: To characterize patellofemoral morphology, determine radiological cutoff values based on computed tomography (CT) images, and clarify predominant anatomic risk factors in young patients with recurrent patellar dislocation (RPD)., Methods: A total of 212 knees (age 23.0 ± 5.3 years, female: male = 110:102) with CT-confirmed RPD were enrolled for analysis. The control group was matched by age and sex (2:1). Patellofemoral and trochlear morphology, patellofemoral alignment, and other parameters were assessed by CT. Standardized methods were used for measurements. Receiver operating characteristic (ROC) curves and the areas under the ROC curve (AUCs) were used to assess accuracy in diagnosing RPD. The index of union (IU) was employed to identify a cutoff value for risk. A binary logistic regression model (Forward, LR) was constructed, and standardized coefficients were calculated to compare the relative strength of different predictors. Factors included in the model were employed to calculate distributions in the studied population., Results: The majority of measurements showed a significant difference between the RPD and control groups when comparing mean values. The AUC value was favorable for sulcus depth and significantly better than that for other trochlear morphology parameters (P < 0.0001). Cutoff values were 0.58 for the Wiberg index, 153.3° for the sulcus angle, 3.6 mm for the sulcus depth, 1.94 for the trochlear width ratio, 16.2° for the lateral trochlear inclination, 17.2° for the patellar lateral tilt, 25.5° for the congruence angle, 1.2 for the patellar height [Caton-Deschamps index (CDI)], 6.1° for the knee rotation, and 16.4 mm for the tibial tubercle-trochlear groove (TT-TG) distance. A binary logistic regression model (χ 2  = 20.826, P = 0.008) including the Wiberg index, sulcus depth, congruence angle, patellar height (CDI), and TT-TG distance was constructed for RPD (P ≤ 0.015), which showed excellent diagnostic performance, as indicated by an AUC of 0.989 (95% CI, 0.979 to 0.998). Sulcus depth showed the strongest relationship with RPD, followed by the congruence angle and Wiberg index, as indicated by the standardized coefficients - 1.43, 1.02, and 0.97, respectively. Eighty-seven percent of the RPD population had sulcus depth ≤ 3.6 mm., Conclusions: This study provides a systematic reference of cutoff values based on CT data. The combination of five anatomic risk factors (sulcus depth, congruence angle, Wiberg index, TT-TG distance, and CDI) may be an excellent predictor of RPD as initial risk assessment. Sulcus depth, as the most frequently observed anatomic risk factor, showed the best diagnostic performance among trochlear morphological parameters and the strongest relationship with RPD, followed by the congruence angle and Wiberg index. In clinical practice, the sulcus depth, congruence angle, Wiberg index, TT-TG distance, and CDI with the proposed cutoff values can be used in combination to evaluate RPD. When assessing trochlear morphology, sulcus depth is recommended as the best radiological parameter., Level of Evidence: Level III., (© 2022. The Author(s) under exclusive licence to European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA).)

Purpose: The femoral anteversion angle is considered to be the same as femoral torsion; however, the femoral anteversion angle is strongly influenced by the femoral posterior condylar morphology. It remains unclear whether the femoral anteversion angle and axial orientation of the femoral trochlea can predict patellar instability. This study aimed to redefine the femoral inherent torsion, verify whether the femoral anteversion angle reflects the femoral inherent torsion, and compare the validity and calculate the cut-off values of the femoral anteversion angle and femoral trochlear axial orientation for predicting patellar instability., Methods: Seventy-three patients with patellar instability and 73 matched controls underwent computed tomography to measure the femoral anteversion angle, femoral inherent torsion, and femoral trochlear axial orientation. Pearson's product moment correlation coefficients and linear regression were calculated to determine correlations between measurements. Receiver operating characteristic curves and nomograms were plotted to evaluate the predictive validity of the femoral anteversion angle and femoral trochlear axial orientation for patellar instability., Results: All measurements showed excellent intra- and inter-observer reliability. Compared with the control group, the patellar instability group had a significantly larger femoral anteversion angle (25.4 ± 6.4° vs. 20.2 ± 4.5°) and femoral inherent torsion (18.3 ± 6.7° vs. 15.8 ± 3.4°), and significantly smaller femoral trochlear axial orientation (58.1 ± 7.3° vs. 66.9 ± 5.1°). The femoral anteversion angle and femoral trochlear axial orientation had area under the receiver operating characteristic curve values of 79 and 84%, respectively, and cut-off values of 24.5° and 62.7°, respectively. The calibration curve and decision curve analysis showed that the femoral trochlear axial orientation performed better than the femoral anteversion angle in predicting patellar instability. There was a strong correlation between the femoral anteversion angle and femoral inherent torsion (r > 0.8). Linear regression analysis of the femoral inherent torsion with the femoral anteversion angle as the prediction variate showed moderate goodness-of-fit (adjusted R 2  = 0.69)., Conclusion: The femoral anteversion angle moderately reflects the femoral inherent torsion. The femoral trochlear axial orientation is better than the femoral anteversion in predicting patellar instability in terms of predictive efficiency, consistency with reality, and net clinical benefit. These findings warn orthopaedists against overstating the role of the femoral anteversion angle in patellar instability, and suggest that the femoral trochlear axial orientation could aid in identifying at-risk patients and developing surgical strategies for patellar instability., Level of Evidence: III., (© 2022. The Author(s) under exclusive licence to European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA).)

The medial patellofemoral complex (MPFC) is the term used to describe the primary soft tissue stabilizer of the patella, which consists of fibers that attach to the patella (medial patellofemoral ligament, or MPFL), and the quadriceps tendon (medial quadriceps tendon femoral ligament, or MQTFL). Despite the variability of its attachment on the extensor mechanism, the midpoint of this complex is consistently at the junction of the medial quadriceps tendon with the articular surface of the patella, indicating that either patellar or quadriceps tendon fixation can be used for anatomic reconstruction. Multiple techniques exist to reconstruct the MPFC, including graft fixation on the patella, quadriceps tendon, or both structures. Various techniques using several graft types and fixation devices have all reported good outcomes. Regardless of the location of fixation on the extensor mechanism, elements critical to the success of the procedure include anatomic femoral tunnel placement, avoiding placing undue tension on the graft, and addressing concurrent morphological risk factors when present. This infographic reviews the anatomy and techniques for the reconstruction of the MPFC, including graft configuration, type, and fixation, while addressing common pearls and pitfalls in the surgical treatment of patellar instability., (Copyright © 2023 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

Post-traumatic knee osteoarthritis is attributed to alterations in joint morphology, alignment, and biomechanics triggered by injury. While magnetic resonance (MR) imaging-based measures of joint morphology and alignment are relevant to understanding osteoarthritis risk, time consuming manual data extraction and measurement limit the number of outcomes that can be considered and deter widespread use. This paper describes the development and evaluation of a semi-automated software for measuring tibiofemoral and patellofemoral joint architecture using MR images from youth with and without a previous sport-related knee injury. After prompting users to identify and select key anatomical landmarks, the software can calculate 37 (14 tibiofemoral, 23 patellofemoral) relevant geometric features (morphology and alignment) based on established methods. To assess validity and reliability, 11 common geometric features were calculated from the knee MR images (proton density and proton density fat saturation sequences; 1.5 T) of 76 individuals with a 3-10-year history of youth sport-related knee injury and 76 uninjured controls. Spearman's or Pearson's correlation coefficients (95% CI) and Bland-Altman plots were used to assess the concurrent validity of the semi-automated software (novice rater) versus expert manual measurements, while intra-class correlation coefficients (ICC 2,1 ; 95%CI), standard error of measurement (95%CI), 95% minimal detectable change, and Bland-Altman plots were used to assess the inter-rater reliability of the semi-automated software (novice vs resident radiologist rater). Correlation coefficients ranged between 0.89 (0.84, 0.92; Lateral Trochlear Inclination) and 0.97 (0.96, 0.98; Patellar Tilt Angle). ICC estimates ranged between 0.79 (0.63, 0.88; Lateral Patellar Tilt Angle) and 0.98 (0.95, 0.99; Bisect Offset). Bland-Altman plots did not reveal systematic bias. These measurement properties estimates are equal, if not better than previously reported methods suggesting that this novel semi-automated software is an accurate, reliable, and efficient alternative method for measuring large numbers of geometric features of the tibiofemoral and patellofemoral joints from MR studies.

Background: The medial patellofemoral complex (MPFC) is a structure composed of the medial quadriceps tendon-femoral ligament (MQTFL) superiorly and the medial patellofemoral ligament (MPFL) inferiorly. The pediatric MPFL anatomy has been well described, but the precise anatomy of the MQTFL has only recently been described and studied in skeletally immature patients., Purpose: To describe the anatomic relationship between the MQTFL and its insertion on the quadriceps tendon and patella in pediatric specimens., Study Design: Descriptive laboratory study., Methods: A total of 22 pediatric cadaveric knee specimens were dissected to analyze attachment of the MQTFL to the quadriceps tendon and patella. Dissection was facilitated using lateral parapatellar arthrotomy followed by eversion of the extensor mechanism to evaluate MQTFL fibers from its undersurface., Results: The mean specimen age was 7.4 years. Specimens were divided based on age into a younger cohort (1-2 years), middle cohort (4-8 years), and older cohort (9-12 years). The quadriceps tendon attachment (QTA) of the MQTFL proximal to the patella extended a median of 5.0 mm in the younger cohort, 11.4 mm in the middle cohort, and 12.0 mm in the older cohort, with significant differences found between the younger and middle cohorts ( P < .047) and the younger and older cohorts ( P < .001). The QTA as a percentage of patellar articular height averaged 44.4% across all specimens. The vertical height of the patella measured a median of 14.0 mm, 22.3 mm, and 27.3 mm in the younger, middle, and older cohorts, respectively., Conclusion: This study expands on the recently described anatomy of the pediatric MPFC to quantify the anatomic relationship between the MQTFL attachment to the quadriceps tendon and patella in a more clinically relevant cohort of donor specimens., Clinical Relevance: As access to pediatric cadaveric tissue is extremely limited, a better understanding of MPFC and MQTFL anatomy will support surgeons in preoperative planning and intraoperative considerations for their approach to MQTFL and MPFL reconstruction. This may facilitate improved anatomic surgical stabilization of the patellofemoral joint in pediatric patients.

Introduction: Trochleoplasty is a surgical procedure used to treat patellar instability by modifying the trochlear groove. Analysis of the groove with a handheld scanner would enable accurate real-time planning and facilitate tailormade correction. We aimed to measure trochlear depth, sulcus angle, trochlear facet ratio, trochlear angle and lateral trochlear inclination angle and to establish inter- and intra-rater reliability for knee models to determine reliability and repeatability., Methods: The trochlear grooves of three knee models were scanned by two investigators. Three-dimensional reference models were created and surface-matched. Custom software was used to determine the desired parameters. The intraclass correlation coefficient (ICC) was used to determine test-retest reliability and the parameter results for each model that showed best reproducibility., Results: There was good interobserver reliability (trochlear depth, 1.0mm; sulcus angle, 2.7°; trochlear angle, 4.0°; lateral trochlear inclination angle, 4.0°), except in the trochlear facet ratio (32.0%) of one knee model. With outliers removed, the ICC was moderate to excellent in 73.34% of measurements, with trochlear depth showing the best reproducibility., Discussion: This feasibility study showed a handheld scanner in conjunction with supporting software can measure trochlear parameters with good to excellent inter- and intra-observer reliability.

The patella is the largest sesamoid bone of the skeleton. It is strongly involved in the knee, improving output force and velocity of the knee extensors, and thus plays a major role in locomotion and limb stability. However, the relationships between its structure and functional constraints, that would enable a better understanding of limb bone functional adaptations, are poorly known. This contribution proposes a comparative analysis, both qualitative and quantitative, of the microanatomy of the whole patella in perissodactyls, which show a wide range of morphologies, masses, and locomotor abilities, in order to investigate how the microanatomy of the patella adapts to evolutionary constraints. The inner structure of the patella consists of a spongiosa surrounded by a compact cortex. Contrary to our expectations, there is no increase in compactness with bone size, and thus body size and weight, but only an increase in the tightness of the spongiosa. No particular thickening of the cortex associated with muscle insertions is noticed but a strong thickening is observed anteriorly at about mid-length, where the strong intermediate patellar ligament inserts. The trabeculae are mainly oriented perpendicularly to the posterior articular surface, which highlights that the main stress is anteroposteriorly directed, maintaining the patella against the femoral trochlea. Conversely, anteriorly, trabeculae are rather circumferentially oriented, following the insertion of the patellar ligament and, possibly also, of the quadriceps tendon. A strong variation is observed among perissodactyl families but also intraspecifically, which is in accordance with previous studies suggesting a higher variability in sesamoid bones. Clear trends are nevertheless observed between the three families. Equids have a much thinner cortex than ceratomorphs. Rhinos and equids, both characterized by a development of the medial border, show an increase in trabecular density laterally suggesting stronger stresses laterally. The inner structure in tapirs is more homogeneous despite the absence of medial development of the medial border with no "compensation" of the inner structure, which suggests different stresses on their knees associated with a different morphology of their patellofemoral joint., (© 2021 Anatomical Society.)

The relationship between three-dimensional shape and patellofemoral mechanics is complicated. The Wiberg patella classification is a method of distinguishing shape differences in the axial plane of the patella that can be used to connect shape differences to observed mechanics. This study uses the Wiberg patella classification to differentiate variance in a statistical shape model describing changes in patella morphology and height. We investigate how patella morphology influences force distribution within the patellofemoral joint. The Wiberg type I patella has a more symmetrical medial and lateral facet while the type III patella has a larger lateral facet compared to medial. The second principal component of the statistical shape model described shape variation that qualitatively resembled the different Wiberg patellas. We generated patellofemoral morphologies from the statistical shape model and integrated them into a musculoskeletal model with a twelve degrees-of-freedom knee. We simulated an overground walking trial with these morphologies and recorded patellofemoral mechanics and ligament forces. An increase in patellar ligament force corresponded with an increase in patella height. Wiberg type III patellas had a sharper patella apex which related to lower ratios of quadriceps tendon forces to patellar ligament forces. The change in pivot point of the patella affects the ratio of forces as well as the patellofemoral reaction force. This study provides a better understanding of how patella morphology affects fundamental patella mechanics which may help identify at-risk populations for pathology development., (Copyright © 2021 by ASME.)

Purpose: Increasing knowledge on the treatment of patellar dislocation has resulted in the development of new surgical techniques for patella stabilisation. National incidence and trends in surgery for patellar dislocation were examined using data from the Finnish National Hospital Discharge Register (NHDR). The hypothesis was that an increased understanding of the pathophysiology of patellar instability has increased the popularity of reconstructing damaged structures and modification of anatomical risk factors., Methods: Data from the years 1997-2016 were collected from the NHDR database using ICD-10 diagnostic codes and the Nomesco Classification of Surgical Procedures (NCSP) codes. Surgical procedures were categorised into subgroups representing the main surgical approaches of patellar dislocation. Total incidence of surgery for patellar dislocation and change in incidence during the study period were calculated., Results: A total of 9702 operations for patellar dislocation were performed during the study period. Median (IQR) patient age at time of primary surgery was 23 (18-34) years. The total incidence of surgeries remained stable across the study period at of 8.9 per 100,000 person-years. Incidences of ligament reconstruction, femoral osteotomies and osteochondral fragment reimplantation operations multiplied during the study period. Ligament reconstruction procedures were the most performed operations at the end of the study period., Conclusion: The incidence of surgical procedures for patellar dislocation remained unchanged during the years 1997-2016. Ligament reconstruction procedures increased in popularity. Surgical techniques have shifted towards the reconstruction of damaged structures and the modification of congenital anatomical risk factors for patellar dislocation. Diversified surgical techniques have enabled the tailoring and combining of stabilizing procedures according to the patient's individual anatomy.

A range of surgical techniques and osteochondral interventions have been developed for early stage chondral/osteochondral repair interventions in the knee however, methods for functional, pre-clinical assessment of these therapies are limited. In this study, a method for simulating physiological loading and motion in the porcine patellofemoral joint was developed using a 6-axis simulator. As an example of how the method can be used, the influence of surgical positioning of osteochondral allografts in the patella on cartilage wear, deformation and damage and graft stability was investigated in this porcine patellofemoral joint model. The functional performance of allografts implanted either optimally (flush with the cartilage surface) or 1 mm proud of the cartilage surface was compared to a positive control (stainless steel pin implanted 1 mm proud of the cartilage surface), a negative control (no intervention) and a defect model. Allografts implanted flush with the surrounding cartilage could restore the articulating surface of the patella resulting in low wear, damage and deformation of the opposing cartilage surface, similar to that of the negative control group. Implanting the graft proud of the patella surface resulted in cartilage lesions on the femoral trochlea (ICRS grade 2) and a cartilage volume difference of 2.0 ± 3.9 mm3; the positive controls resulted in more severe lesions, a higher volume difference (14.2 ± 7.4 mm3) which in some cases exposed subchondral bone (ICRS grade 4). Defects in the patella caused deformation of the opposing cartilage surface. All grafts implanted in the patella subsided over the duration of the study. This study demonstrated a method that can be used to evaluate osteochondral repair strategies in the patellofemoral joint applying physiological loading and motions., Competing Interests: I have read the journal’s policy and the authors of this manuscript have the following competing interests: John Fisher is a consultant to DePuy Synthes Joint Reconstruction, Invibio, Tissue Regenix and Simulation Solutions. Eileen Ingham is a consultant to DePuy Synthes and Tissue Regenix and is a shareholder in Tissue Regenix. Research funding and support have been received by the University of Leeds in related areas in which the authors are directly involved as investigators from the following companies: Simulation Solutions, DePuy Synthes, Invibio, Biocomposites, NHS Blood and Transplant, Mathys, Corin, MatOrtho. We can confirm that this does not alter our adherence to all PLOS ONE policies on sharing data and materials. The data will be openly available in the University of Leeds data repository.

Background: Three-dimensional (3D) imaging and analysis offer new possibilities in preoperative diagnostics and surgical planning. Simultaneous 3D analysis of the joint angles and the patellofemoral anatomy allow for a realistic assessment of bony pathologies in patients with patellofemoral complaints. This study aims to develop a standardized and validated assessment of the 3D patellofemoral morphology and to establish reference ranges., Methods: Thirteen patellofemoral anatomic landmarks were defined on 3D bone models of the lower limbs based on computer tomography data and evaluated regarding inter- and intra-observer variability. Further, 60 3D models of the lower limbs of young subjects without any previous knee operation/injury were assessed and rescaled reference values for relevant patellofemoral indices were obtained., Results: The mean inter- and intra-observer deviation of all landmarks was below 2.3 mm. The interobserver intraclass correlation coefficient (ICC) was between 0.8 and 1.0 and the intra-observer ICC between 0.68 and 0.99 for all patellofemoral parameters. The calculated reference ranges are: Insall-Salvati index 1.0-1.4; patella tilt 6-18°; patella shift -4 to 3 mm; patella facet angle 118-131°; sulcus angle 141-156°; trochlear depth 3-6 mm; tibial-tuberosity to trochlear groove distance(TT-TG) 2D 14-21 mm; TT-TG 3D 11-18 mm; lateral trochlear inclination 13-23°; trochlear facet angle 43-65°., Conclusion: The demonstrated 3D analysis of the patellofemoral anatomy can be performed with high inter- and intra-observer correlation. Applying the obtained reference ranges and using existing 3D assessment tools for lower limb alignment, a preoperative 3D analysis and planning for complex knee procedures now is possible., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Background: Medial patellofemoral ligament (MPFL) reconstruction is one of the main treatments for lateral patellar translation. Based on intraoperative true lateral radiographs, the accepted methods for femoral MPFL tunnel location are potentially inaccurate. Direct assessment of anatomic characteristics during surgery through palpation of the anatomic landmarks involving the saddle sulcus might help eliminate tunnel malposition., Hypothesis: The saddle sulcus is a reliable osseous landmark where the MPFL attaches for tunnel placement., Study Design: Descriptive laboratory study., Methods: A total of 9 fresh-frozen unpaired human cadaveric knees were dissected; MPFL insertion point and relative osseous structures were marked. Three-dimensional images and transformed true lateral radiographs were obtained for analysis; 3 previously reported radiographic reference points for MPFL femoral tunnel placement were determined on all images and compared with the anatomic insertion., Results: A saddle sulcus consistently existed where the MPFL was attached, located at 11.7 ± 5.9 mm from the apex of the adductor tubercle (AT) to the medial epicondyle (ME), 62.8% of the average distance between the apexes of the AT and ME, and 5.6 ± 2.8 mm perpendicular-posterior to the border connecting the AT and ME. The reported radiographic reference points were located at average distances of 6.2 ± 3.2 mm (Schöttle method), 5.9 ± 2.3 mm (Redfern method), and 7.3 ± 6.6 mm (Fujino method) from the saddle sulcus center on the true lateral radiographs., Conclusion: The saddle sulcus was a reliable landmark where the MPFL was anatomically attached, located approximately 12 mm from the AT to the ME (approximately 60% along a line from the AT to the ME) and 6 mm perpendicular-posterior to the border connecting the apexes of the AT and ME. Additionally, the saddle sulcus position presented variability on the femoral aspect of different knees. All of the average direct distances from the sulcus to the reference radiographic points exceeded 5 mm, and tunnel localizations on a true lateral radiograph were inaccurate., Clinical Relevance: This study demonstrates the potential precise position of the saddle sulcus, according to the ME and AT, as a reliable anatomic landmark for MPFL femoral tunnel location. Radiographic reference points were not accurate during MPFL reconstruction. Direct palpation of the landmarks might be effective for femoral MPFL tunnel placement.

Background: The relationship between the medial patellofemoral ligament (MPFL) and the distal femoral physis has been reported in multiple studies., Purpose: To determine the distance from the MPFL central origin on the distal femur to the medial distal femoral physis in skeletally immature participants., Study Design: Systematic review., Methods: A systematic review was performed according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Multiple databases were searched for studies investigating the anatomic origin of the MPFL on the distal femur and its relationship to the medial distal femoral physis in skeletally immature participants. Study methodological quality was analyzed with the Anatomical Quality Assessment tool, with studies categorized as low risk, high risk, or unclear risk of bias. Continuous variable data were reported as mean ± SD. Categorical variable data were reported as frequency with percentage., Results: Seven articles were analyzed (298 femurs, 53.7% male patients; mean age, 11.7 ± 3.4 years). There was low risk of bias based on the Anatomical Quality Assessment tool. The distance from the MPFL origin to the distal femoral physis ranged from 3.7 mm proximal to the physis to 10.0 mm distal to the physis in individual studies. Six of 7 studies reported that the MPFL origin on the distal femur lies distal to the medial distal femoral physis in the majority of specimens. The MPFL originated distal to the medial distal femoral physis in 92.8% of participants at a mean distance of 6.9 ± 2.4 mm., Conclusion: The medial patellofemoral ligament originates distal to the medial distal femoral physis in the majority of cases at a mean proximal-to-distal distance of 7 mm distal to the physis. However, this is variable in the literature owing to study design and patient age and sex.

Purpose: To investigate alterations in technique for medial patellofemoral ligament (MPFL) reconstruction in the setting of patella alta and describe the effect of these alterations on MPFL anatomometry., Methods: Ten cadaveric knees were used. Four candidate femoral attachment sites of MPFL were tested. The attachment sites were Schottle's point (SP), 5 mm distal to SP, 5 mm proximal to SP, and 10 mm proximal to SP. A suture anchor was placed at the upper 40% of the medial border of the patella with the emanating suture used to simulate the reconstructed ligament. MPFL maximum length change was calculated through a range of motion between 0° and 110°. Recordings at all 4 candidate femoral attachments sites were repeated after a flat tibial tubercle osteotomy and transfer to achieve alta as measured by the Caton-Deschamps Index (CDI) of 1.3, 1.4, and 1.5., Results: The 10 specimens had an average CDI of 0.99, range 0.87 to 1.16. In the native tibial tubercle condition, SP was more isometric through 20° to 70° range of motion, or anatomometric, than any other candidate femoral attachment location. With patella alta with a CDI of 1.3 and 1.4, attachment site 5 mm proximal to SP exhibited more anatomometry than SP. With patella alta with a CDI of 1.5, attachment site 10 mm proximal to SP exhibited more anatomometry than SP., Conclusions: Increased patella alta significantly alters MPFL anatomometry. With increasing degrees of patella alta, more proximal candidate femoral attachment sites demonstrate decreased change in length compared with SP. None of the varied femoral attachments produced anatomometry over the entirety of the flexion range from 20° to 70°, suggesting that in cases of significant patella alta, proximalization the femoral attachment site of MPFL reconstruction may be necessary to achieve an anatomometric MPFL reconstruction., Clinical Relevance: A standardized, isolated MPFL reconstruction may be prone to failure in the setting of patella alta, given the anisometry demonstrated. Alternative femoral attachment sites for MPFL reconstruction should be considered in these patients., (Copyright © 2020 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

Purpose: To analyze whether preoperative patellofemoral anatomy is associated with clinical improvement and failure rate after isolated patellofemoral arthroplasty (PFA) using a modern inlay-type trochlear implant., Methods: Prospectively collected 24 months data of patients treated with isolated inlay PFA (HemiCAP ® Wave, Arthrosurface, Franklin, MA, USA) between 2009 and 2016, and available digitalized preoperative imaging (plain radiographs in three planes and MRI) were retrospectively analyzed. All patients were evaluated using the WOMAC score, Lysholm score, and VAS pain. Patients revised to TKA or not achieving the minimal clinically important difference (MCID) for the total WOMAC score or VAS pain were considered failures. Preoperative imaging was analyzed regarding the following aspects: Tibiofemoral OA, patellofemoral OA, trochlear dysplasia (Dejour classification), patellar height (Insall-Salvati index [ISI]; Patellotrochlear index [PTI]), and position of the tibial tuberosity (TT-TG and TT-PCL distance)., Results: A total of 41 patients (61% female) with a mean age of 48 ± 13 years could be included. Fifteen patients (37%) were considered failures, with 5 patients (12%) revised to TKA and 10 patients (24%) not achieving MCID for WOMAC total or VAS pain. Failures had a significantly higher ISI, and a significantly lower PTI. Furthermore, the proportion of patients with a pathologic ISI (> 1.2), a pathologic PTI (< 0.28), and without trochlear dysplasia were significantly higher in failures. Significantly greater improvements in clinical outcome scores were observed in patients with a higher preoperative grade of patellofemoral OA, ISI ≤ 1.2, PTI ≥ 0.28, TT-PCL distance ≤ 21 mm, and a dysplastic trochlea., Conclusion: Preoperative patellofemoral anatomy is significantly associated with clinical improvement and failure rate after isolated inlay PFA. Less improvement and a higher failure rate must be expected in patients with patella alta (ISI > 1.2 and PTI < 0.28), absence of trochlear dysplasia, and a lateralized position of the tibial tuberosity (TT-PCL distance > 21 mm). Concomitant procedures such as tibial tuberosity transfer may, therefore, be considered in such patients., Level of Evidence: Level III, retrospective analysis of prospectively collected data.

Purpose: To report the shape and orientation of the medial patellofemoral complex (MPFC) footprint on the medial femur and describe the difference between the proximal (medial quadriceps tendon femoral ligament, MQTFL) and distal (medial patellofemoral ligament, MPFL) fibers., Methods: In 20 cadaveric knees, the MPFC footprint on the medial femur was exposed. Images of the medial femur were analyzed using ImageJ software. The length and width of the MPFC footprint were described to the nearest 0.1 mm; the angle of its long axis was described relative to the axis of the femoral shaft (0.1°). The footprint's most proximal and distal margins were described in relation to the adductor tubercle and medial epicondyle. The differences between each were compared using paired t tests., Results: 17 knees from 10 cadavers were included in this study. The MPFC footprint had a length of 11.7 ± 1.8 mm and a width of 1.7 ± 0.4 mm. The long axis of the footprint was at an angle 14.6° ± 16.6° anterior to the axis of the femoral shaft. The most proximal (MQTFL) fibers originated 7.4 ± 3.8 mm anterior and 1.8 ± 4.7 mm distal to the adductor tubercle and 4.1 ± 2.9 mm posterior and 8.4 ± 5.6 mm proximal to the medial epicondyle. The most distal (MPFL) fibers originated 4.9 ± 4.2 mm anterior and 12.7 ± 4.3 mm distal to the adductor tubercle, as well as 7.1 ± 2.4 mm posterior and 0.5 ± 5.6 mm distal to the medial epicondyle. The distal margin of the femoral MPFC footprint was 10.9 ± 1.7 mm distal (p < .001) and 2.6 ± 3.2 mm more posterior (p = .005) than the proximal margin., Conclusions: The femoral footprint of the MPFC has a length almost 7 times greater than its width, with the distal margin being 10.9 mm distal and 2.6 mm posterior to the proximal margin., Clinical Relevance: This differential anatomy within the femoral origin suggests that MPFL and MQTFL reconstruction may require separate positions of femoral fixation to recreate the anatomy of these fibers., (Copyright © 2020 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

Purpose: The aim of the present study was to evaluate the effect of patellofemoral joint morphology and patellar alignment (lateral patellar tilt and sagittal patellar tilt) on the presence and stage of CP, and identify the differences between sexes., Methods: MRI of 243 patients [146 men (60.1%)] were evaluated retrospectively. Patients were grouped as normal group without chondromalacia, group with mild chondromalacia (grades 1-2) and group with severe chondromalacia (grades 3-4). Sagittal patellofemoral alignment was assessed by the angle between the patella and patellar tendon (P-PTA), and the angle between the quadriceps tendon and patella (Q-PA). Patellar tilt was assessed by lateral patellar tilt angle (LPTA). In addition, patellofemoral joint morphology was evaluated by measuring trochlear depth (TD), trochlear sulcus angle (TSA) and patella angle (PA)., Results: P-PTA, Q-PA, LPTA and TD values were significantly lower in patients with severe chondromalacia than in patients with both normal and mild chondromalacia (P < 0.001). TSA values were significantly higher in patients with severe chondromalacia than those with both normal and mild chondromalacia (P < 0.001). TSA was higher and TD was lower in women compared to men (P < 0.001). LPTA and P-PTA were lower in women compared to men, and the difference was significant. There was no difference in PA between the two sexes., Conclusions: Patellar cartilage degeneration increases with trochlear dysplasia. There is a strong correlation between patellar malalignment (lateral patellar tilt and sagittal patellar tilt) and chondromalacia patella. Women are more prone to developing CP than men.

Purpose: To define the contributions of the of the medial patellofemoral ligament (MPFL) and medial quadriceps tendon femoral ligament (MQTFL) to lateral patellar translation as the knee moves through a 90° arc of motion., Methods: Six pairs of bilateral cadaveric knee specimens (12 knees) were dissected and potted in perfect lateral position using fluoroscopy. An eye screw was placed in the midpoint on the lateral aspect of the patella. Each knee underwent testing in 4 conditions after sequential sectioning: intact, lateral retinacular release, randomized MQTFL or MPFL sectioning, and complete proximal medial patellar restraint (PMPR) sectioning. With a custom machined jig, all knees were tested at 0, 10, 20, 30, 45, 60, and 90° of flexion on an MTS machine with 20N of lateral patellar force applied and displacement recorded., Results: PMPR extensor mechanism insertion on all specimens was identified 50% on the quadriceps tendon and 50% on the proximal aspect of the medial patella. Isolated MPFL sectioning resulted in significantly increased lateral displacement compared to the lateral release state at all flexion angles tested except 0°. There was significantly increased lateral patellar displacement with complete sectioning compared with isolated proximal sectioning at all degrees of knee flexion except 0°. However, complete sectioning following isolated MPFL sectioning did not demonstrate significance at any angle., Conclusions: Compared with the MQTFL, the MPFL is primarily responsible for resistance to lateral patellar translation throughout a 0° to 90° arc of motion. The MPFL provides a similar resistance to lateral patellar displacement as the fully intact PMPR; however, the MQTFL may contribute to resistance in full extension., Clinical Significance: Proximal medial patellar restraint reconstruction techniques involving both the patellar and quadriceps insertion have been described; however, the unique contributions of the native anatomy to lateral patellar restraint have not been investigated., (Copyright © 2020 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

Purpose: To evaluate the potential relationship between the tibial tubercle-trochlear groove (TT-TG) distance and the femoral anteversion of different segments of the femur in patients with patellar dislocation., Methods: A total of 60 patients with a diagnosis of patellar dislocation were included in our study. Patients with previous knee surgeries, previous fractures, or lack of necessary radiologic examinations were excluded from our study. The data of computed tomography scanning within a week before the surgery was used to measure the TT-TG distance, total anteversion, proximal anteversion, diaphyseal anteversion, distal anteversion, and tibial torsion. All the data were obtained from the picture archiving and communication system (PACS) workstation. The Pearson correlation analysis was performed to confirm the potential relationship between TT-TG distance and femoral anteversion of different segments. The intraclass correlation coefficient was used to assess the interobserver reliability of measurements., Results: The TT-TG distance was significantly correlated with the diaphyseal anteversion (r = -0.305, P = 0.008) and distal anteversion (r = 0.365, P = 0.004). The total anteversion was associated with proximal anteversion (r = 0.392, P = 0.02) and diaphyseal anteversion (r = 0.631, P < 0.001). The intraclass correlation coefficient showed the measurements of included parameters were presented with excellent agreement., Conclusion: Our study showed that patients with high diaphyseal anteversion and distal anteversion tend to had a higher TT-TG distance but the value of total and proximal femoral anteversion were independent of the value of TT-TG distance., Level of Evidence: Level IV therapeutic case series., (Copyright © 2019 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

Purpose: Patellar height measurements on lateral radiographs are dependent on knee flexion which makes standardisation of measurements difficult. This study described a plain radiographic measurement of patellar sagittal height which reflects patellofemoral joint kinematics and can be used at all degrees of flexion., Methods: The study had two parts. Part one involved 44 normal subjects to define equations for expected patellar position based on the knee flexion angles for three new patellar height measurements. A mixed model regression with random effect for individual was used to define linear and polynomial equations for expected patellar position relating to three novel measurements of patella height: (1) patellar progression angle (trochlea), (2) patellar progression angle (condyle) and (3) sagittal patellar flexion. Part two was retrospective and involved applying these measurements to a surgical cohort to identify differences between expected and measured patellar position pre- and post-operatively., Results: All three measurements provided insight into patellofemoral kinematics. Sagittal patellar flexion was the most useful with the least residual error, was the most reliable, and demonstrated the greatest detection clinically., Conclusions: Clinically applied radiographic measurements have been described for patellar height which reflect the sagittal motion of the patella and can be used regardless of the degree of flexion in which the radiograph was taken. The expected sagittal patellar flexion linear equation should be used to calculate expected patellar height., Level of Evidence: IV.

Purpose: There is still lack of knowledge regarding the variability of patellofemoral alignment in healthy, non-osteoarthritic knees, without patellofemoral instability. Therefore, a systematic review of the existing literature was performed to evaluate the variability of patellofemoral alignment., Methods: Patellofemoral alignment of the knee was defined by the following parameters: sulcus angle (SA), femoral trochlear depth (FTD), patellar tilt angle (PTA), lateral patellofemoral angle (LPFA), lateral femoral trochlear inclination (LFTI) and tibial tubercle-trochlear groove distance (TT-TG). The electronic databases MEDLINE and EMBASE were searched from database inception to search date (January 11, 2019) and screened for relevant studies. The PRISMA guidelines were followed. Articles reporting PF alignment measurements of healthy knees in patients between 15 years and 47 years were included., Results: A total of 15 studies met the inclusion criteria. The studies reported mean values and standard deviations for the SA between 118.7° ± 7 and 168°; for the FTD between 3.4 mm ± 1.1 and 7.1 mm ± 1.8; for the PTA between 0.7° ± 4.99 and 17.05° ± 4.3; for the LPFA between 6.26° ± 4.1 and 11.1° ± 4.0; for the LFTI between 16.3° ± 2.8 and 22.1° ± 1.9; and for the TT-TG between 9.8 mm ± 4.6 and 17.3 mm ± 5.3., Conclusion: Patellofemoral alignment in the healthy knee is extremely variable. A more precise knowledge of the complex relationship between the patella and the trochlea may help to better diagnose PF disorders and eventually help in selecting the correct therapy. Furthermore, standardised imaging protocols and measurement techniques for patellofemoral parameters are needed., Level of Evidence: III.

Background: Despite the critical role the trochlea plays in patellofemoral (PF) pathology, the development of the trochlea is poorly understood. The purpose of this study was 2-fold: (1) Describe quantitative osseous and soft tissue anatomy of the patella and trochlea in skeletally immature cadaveric specimens utilizing known measurements used in PF instability, and (2) evaluate additional measurement techniques in the sagittal plane as they relate to PF morphologic development., Methods: Thirty-one skeletally immature fresh frozen cadaveric knees between the ages of 2 and 11 years old were evaluated using 0.625 mm computed tomography scans. In the axial plane, measurements included condylar height asymmetry, trochlear facet asymmetry, trochlear depth, osseous sulcus angle, cartilaginous sulcus angle, patella sulcus angle, and tibial tubercle-trochlear groove distance. In the sagittal plane, measurements included previously undescribed measurements of trochlear length and condylar height asymmetry which are based on the anterior femoral cortex., Results: Analysis of trochlear morphology using condylar height asymmetry (both axial and sagittal), trochlear facet asymmetry, and trochlear depth and length demonstrated an increase in the size of the medial and lateral trochlea as age increased. There was more variability in the change of size of the medial trochlea (height, length, and facet length) than the lateral trochlea. The osseous sulcus angle, cartilaginous sulcus angle, and patella sulcus angle decreased (became deeper) with age until after 8 years and then plateaued., Conclusions: This cadaveric analysis demonstrated that there is an increase in the medial and lateral trochlear height as age increased by all measurements analyzed. The findings also demonstrate that the shape of the patella and trochlea change concurrently, which suggests that there may be interplay between the 2 during development. These new sagittal measurement techniques evaluating the medial, central, and lateral trochlear height and length with respect to age may help guide clinicians when investigating patellar instability in skeletally immature patients., Levels of Evidence: Level IV.

Trochlear dysplasia has been recognized as a dominant anatomic risk factor in patients with recurrent patellar instability. Sulcus-deepening trochleoplasty is a very effective and powerful procedure for correcting trochlear dysplasia and, specifically, eliminating the supratrochlear spur. However, it must be emphasized that trochleoplasty is not appropriate for patients with mild trochlear dysplasia or those without a large supratrochlear spur or bump. We discuss the characteristics and classification of trochlear dysplasia and discuss specific indications for sulcusdeepening trochleoplasty.

The important medial patellar ligamentous restraints to lateral dislocation are the proximal group (the medial quadriceps tendon femoral ligament and the medial patellofemoral ligament) and the distal group [medial patellotibial ligament (MPTL) and medial patellomeniscal ligament (MPML)]. The MPTL patellar insertion is at inferomedial border of patella and tibial insertion is in the anteromedial tibia. The MPML originates in the inferomedial patella, right proximal to the MPTL, inserting in the medial meniscus. On the basis of anatomy and biomechanical studies, the MPTL and MPML are more important in 2 moments during knee range of motion: terminal extension, when it directly counteracts quadriceps contraction. In a systematic review on MPTL reconstructions 19 articles were included detailing the clinical outcomes of 403 knees. All were case series. Overall, good and excellent outcomes were achieved in >75% of cohorts in most studies and redislocations were <10%, with or without the association of the medial patellofemoral ligament. The MPTL is a relevant additional tool to proximal restraint reconstruction in select patient profiles; however, more definitive clinical studies are necessary to better define surgical indications.

Patellofemoral disorders including pain and instability are common orthopedic problems, particularly in the adolescent population. Patellofemoral pain is usually anterior, poorly localized, and diffuse. Because of its multifactorial etiology, patellofemoral pain can be clinically challenging to diagnose and manage. With regards to instability, predisposing factors include trochlear dysplasia, patella alta, patellar tilt, and an elevated tibial tuberosity and trochlea groove distance. Initially, nonoperative management is recommended to treat patellofemoral maladies such as overload, maltracking, and acute first-time dislocations. However, tibial tubercle transfer (TTT) is commonly used to address cases of symptomatic malalignment and overload and recurrent patellar instability. The tubercle can be translated in multiplanar directions to correct patellar height, maltracking associated with instability, and to offload chondral defects. A thorough understanding of the anatomy and biomechanics of the patellofemoral joint is essential for optimizing results after TTT. Individualizing the direction and degree of tubercle transfer on the basis of patient parameters is critical to producing successful long-term results after surgery. This article will review the indications for performing a TTT and highlight the various techniques.

The main objectives of this study were to expand the moving-axis joint model concept to the patellofemoral joint and evaluate the patellar motion against experimental patellofemoral kinematics. The experimental data was obtained through 2D-to-3D bone reconstruction of EOS images and segmented MRI data utilizing an iterative closest point optimization technique. Six knee model variations were developed using the AnyBody Modeling System and subject-specific bone geometries. These models consisted of various combinations of tibiofemoral (hinge, moving-axis, and interpolated) and patellofemoral (hinge and moving-axis) joint types. The newly introduced interpolated tibiofemoral joint is calibrated from the five EOS quasi-static lunge positions. The patellofemoral axis of the hinge model was defined by performing surface fits to the patellofemoral contact area; and the moving-axis model was defined based upon the position of the patellofemoral joint at 0° and 90° tibiofemoral-flexion. In between these angles, the patellofemoral axis moved linearly as a function of tibiofemoral-flexion, while outside these angles, the axis remained fixed. When using a moving-axis tibiofemoral joint, a hinge patellofemoral joint offers (-5.12 ± 1.23 mm, 5.81 ± 0.97 mm, 14.98 ± 2.30°, -4.35 ± 1.95°) mean differences (compared to EOS) while a moving-axis patellofemoral model provides (-2.69 ± 1.04 mm, 1.13 ± 0.80 mm, 12.63 ± 2.03°, 1.74 ± 1.46°) in terms of lateral-shift, superior translation, patellofemoral-flexion, and patellar-rotation, respectively. Furthermore, the model predictive capabilities increased as a direct result of adding more calibrated positions to the tibiofemoral model (hinge-1, moving-axis-2, and interpolated-5). Overall, a novel subject-specific moving-axis patellofemoral model has been established; that produces realistic patellar motion and is computationally fast enough for clinical applications., (Copyright © 2019. Published by Elsevier Ltd.)

Purpose: The scientific literature concerning the anatomy of medial soft-tissue stabilizers of the patella is growing exponentially. Much of the surgical literature has focused on the role of the medial patellofemoral ligament (MPFL) and techniques to reconstruct it, yet our understanding of its anatomy has evolved during the past several years. Given this, we report on the current understanding of medial patellofemoral anatomy and implications for reconstruction., Methods: Current and historical studies of medial patellar anatomy were reviewed, which include the MPFL and medial quadriceps tendon femoral ligament (MQTFL), as well as that of the distal medial patellar restraints, the medial patellotibial ligament (MPTL) and medial patellomeniscal ligament (MPML). In addition to the reported findings, the authors' anatomic descriptions of each ligament during their dissections were identified and recorded., Results: Despite the name of the MPFL, which implies that the ligament courses between the femur and patella, recent studies have highlighted the proximal MPFL fibers that attach to the quadriceps tendon, known as the MQTFL. The MPFL and MQTFL have also been referred to as the medial patellofemoral complex, reflecting the variability in anatomical attachment sites. The MPFL accounts for only half of the total restraint to lateral patellar displacement, and the remaining contributions to patellar stability are derived from the combination of the MPTL and MPML, which function primarily in greater degrees of knee flexion., Conclusion: The understanding of the complexity of the medial patellar stabilizers continues to evolve. Although MPFL reconstruction is gaining wide acceptance as a procedure to treat patellar instability, it is important to recognize the complex and changing understanding of the anatomy of the medial soft-tissue stabilizers and the implications for reconstruction., Level of Evidence: V.

Purpose: The goal of this study was to evaluate the anatomy of the medial patellar retinaculum and the medial patellofemoral ligament (MPFL) to provide an anatomical validation of a pediatric reconstruction technique., Methods: Fifteen knees were dissected to study the MPFL and its relationship with the medial patellar retinaculum and the femoral insertion of the medial collateral ligament (MCL). The distances between the insertions of the MPFL of eight knees, and the patellar insertion of the MPFL and the femoral insertion of the MCL of four knees, were measured during the flexion to evaluate the isometricity of the native and reconstructed MPFL., Results: The medial patellar retinaculum includes four structures: the fascia, fibrous expansions of the vastus muscles, the MPFL and the medial patellomeniscal ligament. The femoral insertion of the MPFL was located just behind the femoral insertion of the MCL in 12 knees. During flexion, the distance between the insertion on the upper patella and the femoral insertion of the MPFL increased while the distance between the insertion on the lower patella and the femoral insertion of the MPFL decreased. The variation in the distances measured during the flexion was greater between the MPFL insertions (n sup  = 6.5 mm, n inf  = 6.5 mm) than between the patellar insertion of the MPFL and the femoral insertion of the MCL (n' sup  = 2.5 mm, n' inf  = 5.75 mm)., Conclusion: The MPFL is not isometric. Even though the results were obtained from knees of elderly specimens, this study demonstrates reconstruction of the MPFL should take into account its anatomy and biomechanical role in the knee.

Objectives: To measure the medial and lateral retinaculum thickness in individuals with and without patellofemoral pain using ultrasound and to assess associations with the symptom duration and function., Methods: Medial and lateral patellofemoral joint retinaculum thicknesses of 32 knees (16 with patellofemoral pain and 16 asymptomatic) were measured with B-mode ultrasound at 0.5, 1, and 1.5 cm from the patella border. Participants with patellofemoral pain completed a Kujala questionnaire, and both groups underwent a single-leg squat performance assessment. Two-way analyses of variance (site × group) determined the overall effect, and Cohen d values were calculated to describe the magnitude of the difference for each measurement., Results: The groups were matched for age, height, and weight. Compared to controls, participants with patellofemoral pain had thicker lateral (overall effect, P = .03) and medial (overall effect, P < 0.01) retinacula. No correlations between retinaculum thickness and Kujala scores (lateral retinaculum, r = 0.106 [0.5 cm], -0.093 [1 cm], and -0.207 [1.5 cm]; and medial retinaculum, r = 0.059, 0.109, and -0.219), symptom duration (lateral retinaculum, r = 0.001, -0.041, and 0.302; and medial retinaculum, r = -0.027, -0.358, and -0.346), or single-leg squat performance scores (lateral retinaculum, r = 0.051, 0.114, and 0.046; and medial retinaculum, r = -0.119, -0.292, and 0.011) were observed., Conclusions: Increased lateral and medial retinaculum thickness in individuals with patellofemoral pain compared to controls identifies structural changes that may be associated with the pathogenesis of patellofemoral pain. The absence of a significant correlation between retinaculum thickness and the symptom duration or function further shows a lack of an association between structure and function in individuals with patellofemoral pain., (© 2018 by the American Institute of Ultrasound in Medicine.)

Purpose: Because fluoroscopy is often used in graft placement during patellar stabilization surgery, the purpose of this study was to describe the radiographic landmarks for the anterior attachment midpoint of the medial patellofemoral complex (MPFC)., Methods: Seventeen fresh-frozen cadaveric knees were dissected, and the MPFC was exposed from the articular side after a lateral parapatellar approach. The midpoint of the anterior attachment of the MPFC was identified using a ruler and marked with a pin. Lateral fluoroscopic images of the patella were then obtained and analyzed using digital analysis software. The distance from the superior articular pole to the pin was divided by the length of the articular surface to describe the location of the pin as a percentage of patellar articular length., Results: Of the 17 cadaveric knees, 2 were excluded because of lack of MPFC fibers. In the remaining 15 knees, the mean (±standard deviation) proximal-distal width of the attachment to the patella and/or vastus intermedius tendon was 41 ± 10 mm, spanning from 15 ± 6 mm proximal to the superior pole of the patella to 27 ± 8 mm distal to it. When viewed on lateral fluoroscopic images, the MPFC midpoint was 19% ± 14% of the patellar articular length from the superior articular pole., Conclusions: In this study, the radiographic landmarks that correlate to the anatomic midpoint of the anterior MPFC attachment are 19% ± 14% of the articular surface from the superior pole of the patella., Clinical Relevance: Recent reports on medial patellofemoral ligament anatomy now include fibers that extend to the quadriceps tendon, summarized as the MPFC. With the inclusion of these fibers, the midpoint of the anterior MPFC attachment is more proximal than that of the medial patellofemoral ligament alone. Because fluoroscopy is often used intraoperatively to guide graft placement, this study correlates radiographic landmarks with anatomic findings of the MPFC midpoint on its attachment to the extensor mechanism., (Copyright © 2019 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

The patellofemoral joint is thought to be a common source for knee pain. Improper alignment and function of the patellofemoral joint can lead to abnormal contact pressures, which may explain patients' symptoms. In this review, the authors examine techniques for measuring patellofemoral joint contact pressures and summarize the relevant patellofemoral joint anatomy and contact pressures in normal knee kinematics. Finally, they discuss the results of studies investigating contact pressure changes in cases of patellar instability. This includes both reconstruction of the medial patellofemoral ligament and tibial tubercle osteotomy. [Orthopedics. 2019; 42(2):e172-e179.]., (Copyright 2019, SLACK Incorporated.)

Purpose: To describe the unclarified characteristics of medial patellofemoral ligament and its relation to neighboring structures., Methods: Sixteen fresh-frozen human knees were dissected in using outside-in and inside-out combined technique. The patellar side attachment was observed from the inside view and femoral side from outside view., Results: The medial patellofemoral ligament was described a complex and multiconnected structure. The femoral side included the upper and lower portion, of which the upper portion attached on the femur with mean width 7.5 ± 1.1 mm and its superficial fibers extended to the adductor magnus tendon and the medial gastrocnemius tendon, and of which the lower portion appeared a right-triangle connected to the MCL without bony attachment. From inside view, the patellar attachment consisted of the bony and non-bony parts. The width of bony attachment was measured mean 16.3 ± 3.8 mm, and the non-bony attachment was found attached on the vastus intermedius tendon with mean width 21.7 ± 4.8 mm. The average thickness was 0.4 ± 0.1 mm and the length were inside assessed mean 67.9 ± 6.1 mm., Conclusion: The medial patellofemoral ligament which dissected a complicated structure with bony and non-bony attachment and multi-connected to neighboring structures on both patella and femur side appears as a polygon-shaped complex structure.

Background: Abnormalities in the trochlea-patella-tibia relationship have been shown to be risk factors for recurrent patellofemoral instability, although no current measurements quantify patellar containment in the trochlea. Standard measurements, such as tibial tubercle-trochlear groove (TT-TG) distance, do not account for the containment of the patella by the trochlea. Our goal was to develop a measurement to assess how well the trochlea contained the extensor mechanism., Hypothesis: A novel measurement describing the amount of the patellar tendon lateral to the lateral trochlear ridge (PT-LTR) would be a reliable measurement and significantly greater among patients with patellofemoral instability., Study Design: Cohort study (diagnosis); Level of evidence, 2., Methods: The authors analyzed radiology records from 2005 to 2014 for patients aged 5 to 18 years with and without patellofemoral dislocations who had knee magnetic resonance imaging (MRI). Two blinded reviewers evaluated 215 MRI studies. Standard and novel morphology measurements were calculated for each knee and compared in a case-control design. Interobserver reliability of each measure was assessed by the intraclass correlation coefficient. Predictability for patellofemoral dislocation was calculated with 2-tailed independent-samples Student t tests. Discriminative capacity was calculated with receiver operating characteristic analyses and area under the curve (AUC). An optimal measurement cutoff with resultant sensitivity and specificity was calculated., Results: Standard measurements of TT-TG distance, tangential axial width of the patella (TAWP), and tangential axial trochlear width (TATW) had excellent agreement between raters; lateral femoral condyle length had good agreement; and the novel measurement-width of the tendon beyond the lateral femoral condyle (PT-LTR)-also had excellent agreement. These underwent predictability and discriminative capacity analyses. TT-TG, TAWP, TATW, and PT-LTR were significant predictors of patellofemoral instability. In receiver operating characteristic analysis, TAWP had an AUC of 0.65, below the 0.8 threshold. TATW had an AUC of 0.814 and, when <32.5 mm, was 76% sensitive and 77% specific for dislocations. TT-TG demonstrated an AUC of 0.806. TT-TG ≥13.5 mm was 76% sensitive and 76% specific for dislocations. PT-LTR demonstrated an AUC of 0.876 and, when ≥5.55 mm, was 73% sensitive and 89% specific for patellofemoral dislocation., Conclusion: PT-LTR is reliable, predictable, and discriminative for patellofemoral dislocations. This measurement had sensitivity similar to that of TT-TG but with higher specificity.

Purpose: An initial episode of patellar instability poses a treatment challenge given the absence of a valid, reproducible, and universally applicable predictor of recurrence. Recently, a series of patellar instability ratios (PIRs) were described. Each ratio consisted of the traditional tibial tubercle to trochlear groove (TT-TG) distance normalized to patient-specific measures. The purpose of this study was to investigate the reliability and validity of these novel measures., Methods: Eighty-seven patients experiencing a first-time lateral patellar dislocation were identified in a retrospective manner. Magnetic resonance imaging (MRI) studies obtained at the time of injury were reviewed. The TT-TG distance, patellar width (PW), trochlear width (TW), patellar length (PL), and trochlear length (TL) were obtained by two observers in a blinded, randomized fashion. Measurement reliability was assessed using intra-class correlation coefficients (ICCs). Patients were divided into those having a single dislocation (Group 1) and those experiencing recurrent instability (Group 2). The ability of the TT-TG distance and each PIR to predict recurrent instability was assessed by calculating odds ratios (ORs) with 95% confidence intervals (CIs). Sensitivity and specificity were also calculated for each measure., Results: Excellent inter-rater agreement was observed with ICCs > 0.75 for all patellofemoral joint measurements obtained on MRI. The TT-TG distance alone was predictive of recurrent patellar instability with an OR of 8.9 (p < 0.001). However, the isolated TT-TG distance had the lowest sensitivity at 25.6%. Among ratios, a TT-TG/PL ≥ 0.5 was the most predictive of recurrent instability with an ORs of 6.1 (p = < 0.001). A TT-TG/TL ≥ 0.8 was also predictive of recurrence (OR 4.9, p = 0.027) and had the highest sensitivity of any measure at 94.9%., Conclusion: The results of the current study support the reproducibility and predictive ability of PIRs. While a TT-TG ≥ 20 mm was the strongest predictor of recurrent patellar instability, it was a relatively insensitive measure. Sensitivity may be improved by normalizing the TT-TG distance to patient-specific axial and sagittal plane patellofemoral measurements on MRI. Ultimately, PIRs are reproducible measures that may serve as an additional tool when clinically assessing the unstable patellofemoral joint., Level of Evidence: III.

Successful outcome following total knee arthroplasty (TKA) with patella resurfacing is partly determined by the restoration of patellofemoral (PF) function and recovery of the quadriceps mechanism. The current study compared two patellar TKA geometries (medialized dome and anatomic) to determine their impact on PF mechanics and quadriceps function. In-vivo, subject-specific patellar mechanics were evaluated using a sequential experimental and modeling approach. First, stereo radiography, marker-based motion capture, and force plate data were collected for TKA patients (10 dome, 10 anatomic) performing a knee extension and lunge. Second, subject-specific, whole-body, musculoskeletal models, including 6 degrees-of-freedom (DOF) knee joint kinematics, were created for each subject and activity to predict quadriceps forces. Last, finite element models of each subject and activity were created to predict PF kinematics, patellar loading, moment arm, and patellar tendon angle. Differences in mechanics between dome and anatomic patients were highlighted during load-bearing (lunge) activity. Anatomic subjects demonstrated greater PF flexion angles (avg. 11 ± 3°) compared to dome subjects during lunge. Similar to the natural knee, contact locations on the patella migrated inferior to superior as the knee flexed in anatomic subjects, but remained relatively superior in dome subjects. Differences in kinematics and contact location likely contributed to altered mechanics with anatomic subjects presenting greater load transfer from the quadriceps to the patellar tendon in deep flexion (>75°), and dome subjects demonstrating larger contact forces during lunge. Although there was substantial patient variability, evaluations of PF mechanics suggested improved quadriceps function and more natural kinematics in the anatomic design. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1910-1918, 2018., (© 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.)

Patellar instability in children and adolescents is a challenging subset to treat. Varied forms of instability, ranging from episodic dislocation to fixed dislocation, have been recognized. It is of utmost importance for the treating physician to recognize these different patterns of instability and their associated risk factors, as more complex patterns of instability would require more extensive surgical procedures. Medial patellofemoral ligament (MPFL) reconstruction, by itself, may not suffice or may not be appropriate for the more complex instability patterns. Appropriate and early treatment of such instability in children would allow for functional progression and possible remodeling of the trochlea. However, early treatment has the associated risk of growth disturbances when surgical procedures are performed around open physis or if adult-type bony procedures are performed in children. Recent knowledge about the relationship between trochlea, MPFL femoral attachment, and distal femoral physis could help to advance safe surgical care for these patients. This article reviews the pathophysiology, risk factors, and the existing classification systems for patellar instability in children and adolescents. It focuses on varied surgical techniques, which are unique to the pediatric population, and summarizes the outcomes of these surgical techniques., Competing Interests: Authors’ Disclosure Statement: The authors report no actual or potential conflict of interest in relation to this article.

Purpose: This study aimed to investigate the natural morphology of the femoral trochlear groove based on quantitative measurement., Methods: Computed tomographic femur models of 50 male and 50 female healthy Chinese adults (30-60 years) were analysed using three-dimensional software. Coaxial cutting planes (15° increments) rotating about the trochlear groove axis from the proximal to distal point were created, followed by the deepest point of the trochlear groove marked at each cross section. The shape, position, and orientation of the trochlear groove were analysed., Results: The trochlear groove was located laterally relative to the mechanical axis and consisted of the laterally oriented proximal part and medially oriented distal part. Based on the turning points located on different cross sections, the trochlear groove was classified into four types: types 45°, 60°, 75°, and 90°. The mediolateral position relative to the mechanical axis was types 45°, 60°, 75°, and 90°, from the lateral to medial side, while the distal parts of them extended along the same path. The orientation of the trochlear groove was relatively consistent and smooth, which oriented at approximately 1° medially between two adjacent segments, except at approximately 10° medially at the turning point., Conclusion: The trochlear groove tracking varies greatly amongst a population that is mainly categorized into four types. This study may be helpful for better understanding of the natural trochlear groove anatomy, prosthetic design modification, and provide the reference value for studying patellofemoral diseases such as patellar maltracking and trochlear dysplasia., Level of Evidence: Prospective study, Level II.

Objective: We aimed to (1) determine reference values for trochlear morphology and patellofemoral (PF) alignment in adults without magnetic resonance imaging (MRI)-defined PF full thickness cartilage damage or knee pain; and (2) evaluate dose-response patterns for these measures with prevalent MRI-defined PF structural damage and/or knee pain., Design: The Framingham Community Cohort is a population-based sample of ambulatory adults aged ≥50 years. We evaluated six morphology and alignment measures using MRI (n = 985), and reported reference values (mean ± 2SD) in a subsample without MRI-defined PF full thickness cartilage damage or knee pain (n = 563). With restricted cubic spline Poisson regression, we evaluated dose-response patterns of each of the six measures with prevalent MRI-defined PF structural damage or joint pain. Our primary outcome was full thickness cartilage damage., Results: For dose-response curves, prevalence ratios (PR) increased monotonically for all measures except patellar tilt, which rose with both lateral and medial tilt. Associations were generally strongest in the lateral PF compartment. PR for the strongest predictors of full thickness cartilage damage reached clinical relevance (PR > 1.5) at sulcus angle (SA) ≥135.0°; patellar tilt angle at ≤1.0° and ≥15.0°; and bisect offset ≥57.0%. Lateral trochlear inclination (LTI) achieved PR > 1.5 at ≤23.0° for full thickness cartilage damage with pain., Conclusions: SA, patellar tilt, and bisect offset were most strongly associated with full thickness cartilage damage. LTI, patellar tilt and bisect offset had stronger associations with the addition of pain. These findings contribute to better identifying a subset of patients who may benefit from mechanically based interventions., (Copyright © 2017 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.)

Purpose To determine the relationship of patellofemoral joint alignment and trochlear morphology to superolateral Hoffa fat pad (SHFP) edema on magnetic resonance (MR) images in older adults with or at risk for osteoarthritis of the knee. Materials and Methods Institutional review board approval and written informed consent were obtained from all subjects. The Multicenter Osteoarthritis Study is a prospective cohort study of older adults with or at risk for osteoarthritis of the knee. Subjects were recruited from Birmingham, Alabama, and Iowa City, Iowa. In this cross-sectional study, patellofemoral joint alignment (bisect offset, patellar tilt angle, and Insall-Salvati ratio), trochlear morphology (sulcus angle, lateral and medial trochlear inclination, and trochlear angle) and SHFP edema were assessed on MR images of the knee. Measures of alignment and morphology were divided into quartiles, and SHFP was determined to be present or absent. Separate logistic regression models were used to determine the relationship of each measure of alignment and morphology to the presence of SHFP edema, with adjustments for age, sex, and body mass index. Results SHFP edema was present in 152 (13.4%) of the 1134 knees that were included. When compared with knees with measurements in the lowest quartile, knees with measurements in the highest quartile for trochlear angle, bisect offset, and Insall-Salvati ratios were 1.6 (95% confidence interval [CI]: 1.0, 2.6), 2.3 (95% CI: 1.3, 4.0), and 8.9 (95% CI: 4.7, 16.9) times more likely to show SHFP edema, respectively. No relationship was found between other measures and SHFP edema. Conclusion A more anterior trochlear facet, a more laterally displaced patella, and knees with patella alta were significantly associated with SHFP edema on MR images in subjects with or at risk for osteoarthritis of the knee. © RSNA, 2017.

Purpose: To describe the anatomy of the medial patellofemoral ligament (MPFL) and its relationship to the Adductor Magnus (AM) tendon as well as the behaviour exhibited in length changes during knee flexion., Methods: Ten cadaveric knees were dissected. The length from the superior and inferior patellar origin of the MPFL to its femoral insertion was measured at different degrees of knee flexion (0°, 30°, 60°, 90° and 120°). The same measures were made from both patellar origins of the MPFL up to the femoral insertion of the AM. The distance between the insertion of the AM and the Hunter canal was also measured., Results: In general, isometry up to 90° was seen in all measures of the MPFL and those of the AM. The most isometric behaviour was seen in 2 measures: the length of the AM femoral insertion up to the inferior origin of the MPFL on the patella and the length of the femoral insertion of the MPFL up to the inferior origin of the MPFL on the patella. Similar behaviour was seen regardless of the anatomical or quasi-anatomical femoral point of attachment (n.s.). The distance from the AM tendon to the Hunter canal had a mean value of 78.6 mm (SD 9.4 mm)., Conclusion: The behaviour exhibited during the changes in the length of the anatomical femoral footprint of the MPFL and the AM is similar. Neurovascular structures were not seen at risk. This is relevant in the daily clinical practice since the AM tendon might be a suitable point of insertion for MPFL reconstruction.

Recurrent patellar dislocation is observed in many patients treated nonoperatively following primary dislocation. Injury to the medial patellofemoral ligament (MPFL) is reported in the majority of patients following dislocation. There is an increased interest in repair or reconstruction of the MPFL for patients experiencing recurrent instability. The femoral attachment of the MPFL is critical in determining graft behavior following reconstruction. The femoral attachment can be determined by referencing local anatomy, fluoroscopic imaging or on the basis of desired graft-length changes. This article reviews the anatomy of the MPFL, with a focus on its femoral insertion site as it pertains to anatomic, isometric, and anisometric reconstruction. [Orthopedics. 2017; 40(4):e583-e588.]., (Copyright 2017, SLACK Incorporated.)

Complications in the patellofemoral (PF) joint of patients with total knee replacements include patellar subluxation and dislocation, and remain a cause for revision. Kinematic measurements to assess these complications and evaluate implant designs require the accuracy of dynamic stereo-radiographic systems with 3D-2D registration techniques. While tibiofemoral kinematics are typically derived by tracking metallic implants, PF kinematic measurements are difficult as the patellar implant is radiotransparent and a representation of the resected patella bone requires either pre-surgical imaging and precise implant placement or post-surgical imaging. Statistical shape models (SSMs), used to characterize anatomic variation, provide an alternative means to obtain the representation of the resected patella for use in kinematic tracking. Using a virtual platform of a stereo-radiographic system, the objectives of this study were to evaluate the ability of an SSM to predict subject-specific 3D implanted patellar geometries from simulated 2D image profiles, and to formulate an effective data collection methodology for PF kinematics by considering accuracy for a variety of patient pose scenarios. An SSM of the patella was developed for 50 subjects and a leave-one-out approach compared SSM-predicted and actual geometries; average 3D errors were 0.45±0.07mm (mean±standard deviation), which is comparable to the accuracy of traditional segmentation. Further, initial imaging of the patella in five unique stereo radiographic perspectives yielded the most accurate representation. The ability to predict the remaining patellar geometry of the implanted PF joint with radiographic images and SSM, instead of CT, can reduce radiation exposure and streamline in vivo kinematic evaluations., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Objective: The purpose of this study was to determine the variability of distances between four distinct anatomic landmarks used for the evaluation of patellofemoral alignment while implementing controlled changes in patient positioning during MRI., Materials and Methods: Limited MRI was performed of 12 knees in healthy volunteers (10 men, two women; mean age, 28 years) with the knees in four different positions. The four landmarks used were TT (the most anterior point of the osseous tibial tubercle), TG (the nadir of the cartilaginous trochlear groove), PT (the center of the patellar tendon insertion on the tibia), and PCL (the medial border of the posterior cruciate ligament at its insertion along the posterior tibia). TT-TG, PT-TG, TT-PCL, and PT-PCL distances were measured on the MR images. Each distance was measured with the knee at maximum patient comfort (rest), full extension, 15° of flexion, and 30° of flexion. Linear mixed models with random intercepts were implemented to determine variability between measurements and knee position., Results: In general, measurements based on anatomic landmark and knee position varied greatly. The greatest variability in different knee positions was seen in mean TT-TG and PT-TG distances ± SD (TT-TG: rest, 18.1 ± 7.9 mm; full extension, 17.3 ± 5.3 mm; 15° of flexion, 11.4 ± 5.7 mm; 30° of flexion, 11.7 ± 6.0 mm; intraclass correlation coefficient [ICC] = 0.539; PT-TG: rest, 18.1 ± 6.3 mm; full extension, 17.9 ± 4.7 mm; 15° of flexion, 13.2 ± 5.2 mm; 30° of flexion, 11.8 ± 4.3 mm; ICC = 0.633). In contrast, knee position did not significantly affect distances for TT-PCL and PT-PCL (TT-PCL: rest, 23.5 ± 6.8 mm; full extension, 20.5 ± 5.5 mm; 15° of flexion, 22.8 ± 6.2 mm; 30° of flexion, 22.8 ± 6.7 mm; ICC = 0.484; PTPCL: rest, 23.4 ± 5.3 mm; full extension, 21.5 ± 4.5 mm; 15° of flexion, 22.3 ± 4.3 mm; 30° of flexion, 23.1 ± 4.8 mm; ICC = 0.509)., Conclusion: On MRI, TT-PCL and PT-PCL measurements have significantly less variability compared with TT-TG and PT-TG measurements, regardless of knee position. Although further studies are warranted, the use of TT-PCL and PT-PCL measurements may offer more reliable assessment of tibial tubercle lateralization and patellofemoral alignment.

Background: The cross-sectional morphology of the prosthetic knee is crucial to understanding patellar motion and quadriceps strength after total knee arthroplasty. However, few comparative evaluations of the cross-sectional morphology of the femoral trochlea have been performed in the native knee and currently available femoral implants, and the relationship between the trochlear anatomy of prosthetic components and post-operative patellofemoral complications remains unclear. We aimed to investigate the differences in cross-sectional morphology of the femoral trochlea between native knees and prosthetic femoral components., Methods: Virtual total knee arthroplasty was performed, whereby four different femoral components (medial-pivot, Triathlon, NRG and NexGen) were virtually superimposed onto three-dimensional models of 42 healthy femurs. The following morphological parameters were measured in three cross-sections (0, 45 and 90°) of the femoral trochlea: sulcus height, lateral tilt angle, medial tilt angle and sulcus angle. Only statistically significant differences are described further (p < 0.05)., Results: In the 0° cross-section, sulcus height was smaller in the native knee than in the Triathlon, NRG and NexGen components; all prosthetic components had smaller lateral tilt angles and larger medial tilt angles. In the 45° cross-section, sulcus height was larger in the native knee than in the medial-pivot, Triathlon and NexGen components; both lateral and medial tilt angles were smaller in the prosthetic components. In the 90° cross-section, sulcus height was smaller in the native knee than in the medial-pivot component; all prosthetic components had a larger lateral tilt angle and smaller medial tilt angle. In all cross-sections, the sulcus angle was smaller in the native knee., Conclusions: The discrepancy between native and prosthetic trochlear geometries suggests altered knee mechanics after total knee arthroplasty, but further cadaveric, computational or fluoroscopic investigations are necessary to clarify the implications of this observation. Our findings can be used to optimize biomechanical guidelines for total knee arthroplasty (patellar resurfacing or non-resurfacing) in Chinese individuals so as to decrease the risk of patellar lateral dislocation, to maintain stability and to optimize extensor kinematics.

Objectives: To assess the relationship between injury patterns of medial patellofemoral ligament (MPFL) and anatomical variants and patellar cartilage lesions after acute lateral patellar dislocation (LPD) in children., Methods: MR images were obtained in 140 children with acute LPD. Images were acquired and evaluated using standardised protocols., Results: Fifty-eight cases of partial MPFL tear and 75 cases of complete MPFL tear were identified. Injuries occurred at an isolated patellar insertion (PAT) in 52 cases, an isolated femoral attachment (FEM) in 42 cases and an isolated mid-substance (MID) in five cases. More than one site of injury was identified in 34 cases. Compared with Wiberg patellar type C, Wiberg patellar type B predisposed to complete MPFL tear (P = 0.042). No correlations were identified between injury patterns of MPFL and trochlear dysplasia, patellar height and tibial tuberosity-trochlear groove distance (P > 0.05). Compared with partial MPFL tear, complete MPFL tear predisposed to Grade-IV and Grade-V patellar chondral lesion (P = 0.02). There were no correlations between incidence of patellar cartilage lesion and injury locational-subgroups of MPFL (P = 0.543)., Conclusions: MPFL is most easily injured at the PAT in children. Wiberg patellar type B predisposes to complete MPFL tear. Complete MPFL tear predisposes to a higher grade of patellar chondral lesion., Key Points: • MPFL is most easily injured at its patellar insertion in children. • Wiberg patellar type B predisposes to complete MPFL tear. • No correlations between injury patterns of MPFL and other three anatomical variants. • Complete MPFL tear predisposes to higher grade patellar chondral lesion. • No correlations between injury locations of MPFL and patellar cartilage lesion.

Background: Patellofemoral joint biomechanics contribute to anterior knee pain, instability, and dysfunction following total knee arthroplasty (TKA). Information about specific factors leading to anterior knee pain and dysfunction is currently limited. Changes in patellofemoral joint offset (PFO) refers to a mismatch between the preoperative and postoperative anteroposterior geometry of the patellofemoral joint. It remains unclear whether these changes lead to adverse outcomes in TKA., Methods: A retrospective radiographic review of 970 knees pre-TKA and post-TKA was completed to correlate the radiographic and clinical outcomes of changing the PFO using a posterior-stabilized single knee design with patellar resurfacing., Results: A total of 970 patients were reviewed. Postoperatively, the anterior femoral offset, anteroposterior femoral size, and anterior patellar offset were changed in 40%, 60%, and 71% of knees, respectively, compared to preoperative values. The Western Ontario and McMasters Osteoarthritis Index total score as well as subscale scores for pain and function were not significantly affected by an increase or decrease in PFO. Similarly, Knee Society Scores and range of motion were not significantly affected. Increased anterior patellar offset was, however, associated with increased postoperative patellar tilt. Postoperative patellar tilt was not correlated with adverse patient satisfaction scores or loss of range of motion., Conclusion: Changes in PFO (decreased, maintained, or increased) are common post-TKA and are not associated with a difference in clinical outcomes. Increases in anterior patellar offset led to increased patellar tilt, which was not associated with adverse patient satisfaction scores., (Copyright © 2016 Elsevier Inc. All rights reserved.)