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Objective: The lateral patellofemoral ligament (LPFL) is part of the lateral retinaculum cut during arthroscopic or open release. We investigated its anatomic and morphometric characteristics., Materials and Methods: We identified the LPFL insertion point on the condyle in vertical and sagittal planes in 32 adult cadaveric knees. We measured its length and width at the insertion point. We located the midpoint of this point and measured from it to the distal and posterior condylar ends. We measured anterior-posterior and proximal-distal lateral condylar lengths. We evaluated the insertion point shape on the lateral femoral condyle. Degree of relationship between variables was assessed using Pearson's correlation coefficient. p < 0.05 was considered statistically significant., Results: The LPFL mean length was 23.2 mm, and mean width at the insertion point was 15.6 mm. Regarding its insertion into the lateral condyle, central insertions were more frequent (vertical plane: 53.1% central and sagittal plane: 75% central). A significant positive correlation was evident between the LPFL length and width at the insertion point (p = 0.05). Thus, the LPFL length was proportional to its width at the insertion point. A significant positive correlation was found between the anterior-posterior condylar length and width of the LPFL at the insertion point (p = 0.017). Therefore, greater anterior-posterior condylar length equates to a larger area of insertion on the condyle., Conclusion: Greater width of the LPFL at the insertion point corresponds to greater LPFL and anterior-posterior lateral condylar lengths., (Copyright © 2016 Turkish Association of Orthopaedics and Traumatology. Production and hosting by Elsevier B.V. All rights reserved.)

This study aimed to compare trochlear morphology seen in magnetic resonance imaging between patients with chondromalacia patella and age-matched control patients without cartilage lesion. Trochlear morphology was evaluated using the lateral trochlear inclination, medial trochlear inclination, sulcus angle and trochlear angle on the axial magnetic resonance images. Consequently, an association between abnormal trochlear morphology and chondromalacia patella was identified in women. In particular, women with flattened lateral trochlea are at an increased risk of patellar cartilage structural damage., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Background: The incidence of primary lateral patellar dislocation (LPD) in children aged 9 to 14 years is 0.6 to 1.2 per 1000. Causation is assumed to be multifactorial, including anatomic variants of the patellofemoral (PF) joint that result in a higher risk of LPD. No publication has compared the morphology of the PF joint and anatomic patellar instability risk factors (APIFs) in a primary LPD population versus controls, defining children by skeletal maturity., Purpose: To characterize the PF morphology and APIFs (trochlear dysplasia, abnormal lateral patellar tilt, elevated tibial tubercle-trochlear groove [TT-TG] distance, patella alta) through magnetic resonance imaging (MRI) measurements in skeletally immature children with and without a primary LPD and to identify (potential) distinctive differences between these 2 groups., Study Design: Cross-sectional study; Level of evidence, 3., Methods: A prospective series of 103 skeletally immature children aged 9 to 14 years with an MRI-confirmed primary LPD were matched with a control group of 69 children. The PF morphology and APIFs were assessed during a 2.5-year period with standardized MRI using sagittal and axial views., Results: In the LPD group, 79% had 2 to 4 APIFs compared with 7% in the control group. All major measurements of trochlear dysplasia were significantly different between the 2 groups. The mean central condylar height was significantly higher in the LPD group compared with the control group, resulting in a lower trochlear depth (2.3 vs 4.5 mm, respectively) and higher sulcus angle (156.7° vs 141.1°, respectively). The LPD group had significantly higher values of patellar height, Caton-Deschamps index (1.33 vs 1.15, respectively), lateral patellar tilt (21.1° vs 8.5°, respectively), and TT-TG distance (13.9 vs 9.8 mm, respectively) compared with the control group. The main divergent APIF was trochlear dysplasia (defined as trochlear depth <3 mm), seen in 74% of the LPD group compared with 4% of the control group. Elevated TT-TG distance as a single APIF was never present in the LPD group; patellar tilt was only seen in the LPD group. The most common APIF in the control group was patella alta (36%)., Conclusion: There was a significant difference in mean values of all established APIFs between the children with a first-time LPD and the controls. Trochlear dysplasia was the main APIF, and together with lateral patellar tilt (≥20°), they had the strongest association with LPD.

Objective: To investigate the anatomic morphology of the patellar ridge and how it matches the femoral trochlea in patellar tracking., Method: We selected 40 volunteers, 20 males (age, 28 ± 5 years) and 20 female (age, 27 ± 6 years), who were completely asymptomatic with normal knee structures. We measured the right or left legs of volunteers, and the region from the distal femur to the tibial tuberosity was scanned by computed tomography (CT) with flexion at 0°, 30°, 60°, and 90°. CT data was reconstructed using image analysis software (Mimics). Variables such as the angle between the patellar ridge and patellar long axis, the tibial external rotation angle, as well as the best matching position between the patellar ridge and femoral trochlea at different knee flexion angles were measured. A single experienced orthopedic surgeon performed all the measurements, and the surgeon was blinded to the subject identifying information. We analyzed the differences between the various angles using a one-way analysis of variance. The differences between genders were analyzed using the t test., Results: The intraclass correlation coefficient (ICC) values were greater than 0.81 for all measurements, and the ICC value is almost in perfect agreement. The angle between the patellar ridge and the patellar long axis was 11.13° ± 4.1°. The angle in male participants was 10.87° ± 4.5° and it was 12.09° ± 3.7° in female participants. There were significant differences between each angle (0°, 30°, 60°, and 90°). The angles between the patellar ridge and femoral trochlear groove did not greatly increase with the knee flexion. The tibial internal rotation angle also showed a gradually increase at knee flexion of 0°-60°, and a gradually decrease at 60°-90°. The best-fit point between the patellar ridge and femoral trochlear groove gradually increased along with the knee flexion. There were no significant differences between male and female participants at all angles ( P < 0.05)., Conclusion: The anatomic morphology of the patellar ridge allows better matching between the patellar ridge and femoral trochlea during knee flexion, which is an important mechanism for the regulation of patellar tracking., (© 2016 Chinese Orthopaedic Association and John Wiley & Sons Australia, Ltd.)

Introduction: Patellofemoral instability is a complex anatomical phenomena that requires deep understanding. The cause for instability could be a result of an anatomical defect or a soft tissue pathology. A thorough patient history, physical examination and imaging are paramount for a correct diagnosis and for deciding on the correct treatment. The proper treatment is often debatable. Conservative treatment is suitable for acute dislocation but has a high failure rate in chronic instability, which usually necessitates surgical treatment. The common surgical treatments today focus on fixing anatomical defects, relieving patients' symptoms of instability and giving them the opportunity to return to the level of activity suitable for them. In this literature review we summarize the relevant anatomy, biomechanics, clinical evaluation and treatment options for patellofemoral instability.

Purpose: To correlate the location of the medial patellofemoral ligament femoral fixation site in knees suffering a chronic lateral patellar instability, by using radiographic references and by using the most important anatomic reference point (i.e. the adductor tubercle) identified by means of 3-dimensional (3D) surface reconstructions by computed tomography (CT) imaging., Methods: Thirty consecutive knee 3D-CT examinations at 0º of knee extension were obtained from patients (20 females, 10 males; median age of 23.5 years; range, 14-48 years) treated for chronic lateral patellar instability with at least two documented patellar dislocations. For each knee, three virtual 7-mm-diameter femoral tunnels were created. One of the tunnels used an anatomic fixation landmark (anatomic fixation), while the other two used established radiologic methods. We calculated the percentage of the anatomic tunnel covered by the tunnel created according to the method described by Schoettle, and the percentage of the anatomic tunnel covered by the tunnel created according to the method described by Stephen. These percentages were compared using paired Student's t test., Results: The percentage of anatomic tunnel area covered by the femoral tunnel created using Schoettle's method was 36.7 ± 25.2 %. When using Stephen's method, the percentage of overlap with the anatomic femoral tunnel was 25.5 ± 21.5 %. There were no significant differences between the two radiographic methods (n.s.)., Conclusion: None of the standard radiographic methods allowed a precise anatomic femoral placement. Conventional radiographic identification of the femoral graft placement site is only an approximation and should not be the sole basis for femoral attachment location., Level of Evidence: IV.

Purpose: To describe and quantify the variability of the attachments of the medial patellofemoral ligament (MPFL)., Methods: Thirty-three cadaveric knees were dissected, and the MPFL was identified from the articular side after anterior reflection of the extensor mechanism and removal of the synovium. The width of the MPFL at its femoral origin and anterior attachment was measured using digital calipers once by 1 examiner. The percentage of fibers that attached to the patella versus the quadriceps tendon was calculated relative to the width of the total attachment. The length of the MPFL fibers was measured from the femoral origin to (1) the patella and (2) the quadriceps tendon and compared using paired t tests., Results: Four knees had no identifiable MPFL fibers, and 1 was excluded because of the presence of osteophytes. In 28 knees, the mean width of the MPFL was 10.7 ± 1.8 mm at the femoral origin and 30.4 ± 5.5 mm at the patellar attachment. One knee had all MPFL fibers attaching to the patella, and another had all fibers attaching to the quadriceps tendon. The remainder had attachments to both structures, with 57.3% ± 19.5% (range, 0% to 100%) of fibers attaching to the patella. Mean length of the MPFL fibers was 62.6 ± 5.2 mm from the femoral origin to the patella and 69.7 ± 5.5 mm from the femoral origin to the quadriceps tendon (7.1-mm difference; P < .0001)., Conclusions: MPFL fibers vary in their width and percentage of attachments to the patella and quadriceps tendon. Further studies are needed to identify the appropriate fixation points to re-create the anatomy and isometry of the MPFL during reconstruction for patellar stabilization., Clinical Relevance: Variability in the anatomy of the MPFL suggests that optimal anatomic graft placement may vary during reconstruction of this ligament., (Copyright © 2016 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

The purpose of this study was to compare two different methods of medial patellar femoral ligament (MPFL) reconstructions: isometric and anatomic. These were then compared with the native MPFL. Fourteen fresh frozen cadaveric knees were carefully dissected to expose the MPFL. The patella was laterally translated 10 mm using an Instron and values were recorded for the intact ligament and the reconstructions. Neither the anatomic nor the isometric reconstructions completely restored the biomechanical properties of the intact MPFL. There were fewer differences between the isometric reconstruction and the intact specimens. The higher forces and stiffer constructs that occurred with the anatomic reconstruction may suggest that this reconstruction technique could overconstrain the patellofemoral joint., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Background: The medial patellofemoral ligament varies in attachment of its fibers to the patella and vastus intermedius tendon. Our aim was to identify and describe its anatomic midpoint. To account for the variability of the attachment site, we refer to it as the medial patellofemoral complex., Methods: Using AutoCAD software, we identified the midpoint of the medial patellofemoral complex attachment on photographs of 31 cadaveric knee dissections. The midpoint was referenced relative to the superior articular surface of the patella (P1) and was described in terms of the percentage of the patellar articular length distal to this point. A second point, at the junction of the medial border of the vastus intermedius tendon with the superior articular border of the patella, was identified (P2). The distances of the midpoint to P1 and P2 were calculated and were compared using paired t tests., Results: Twenty-five images had appropriate quality and landmarks for digital analysis. The midpoint of the medial patellofemoral complex was located a mean (and standard deviation) of 2.3% ± 15.8% of the patellar articular length distal to the superior pole and was at or proximal to P1 in 12 knees. In all knees, the midpoint was at or proximal to P2. After exclusion of 2 knees with vastus intermedius tendon attachments only, the medial patellofemoral complex midpoint was closer to P2 (5.3% ± 8.6% of the patellar articular length) than to P1 (9.3% ± 8.5% of the patellar articular length) (p = 0.06)., Conclusions: The midpoint of the medial patellofemoral complex was 2.3% of the articular length distal to the superior pole of the patella. Additionally, we describe an anatomic landmark at the junction of the medial border of the vastus intermedius tendon and the articular border of the patella that approximates the midpoint of this complex., Clinical Relevance: Our study shows that the anatomic midpoint of the attachment of the medial patellofemoral complex is proximal to the junction of the medial vastus intermedius tendon and the articular border of the patella, suggesting that graft placement may be more anatomic on the vastus intermedius tendon rather than on the patella., (Copyright © 2016 by The Journal of Bone and Joint Surgery, Incorporated.)

Background: Patellofemoral joint osteoarthritis is common, although circumstances dictating its evolution and pathogenesis remain unclear. Advances in surgical technique have improved the ability to modify long-bone alignment in the coronal, sagittal, and axial planes. However, to our knowledge, there is no significant long-term data available in regard to the relationship between anatomic alignment parameters most amenable to surgical modification and patellofemoral joint osteoarthritis., Methods: Five-hundred and seventy-one cadaveric skeletons were obtained from the Hamann-Todd osteological collection. Mechanical lateral distal femoral angle, medial proximal tibial angle, tibial slope, femoral version, tibial torsion, the position of the tibial tubercle relative to the width of the tibial plateau, trochlear depth, and patellar size were measured using validated techniques. A previously published grading system for patellofemoral joint arthritis was used to quantify macroscopic signs of degenerative joint disease., Results: Increasing age (standardized beta 0.532, p<0.001), female gender (standardized beta 0.201, p=0.002), and decreasing mechanical lateral distal femoral angle (standardized beta -0.128, p=0.025) were independent correlates of increased patellofemoral joint osteoarthritis. A relatively more laterally positioned tibial tubercle trended towards predicting patellofemoral joint osteoarthritis (standardized beta 0.080, p=0.089)., Conclusions: These findings confirm that patellofemoral joint osteoarthritis is strongly associated with increasing age and female gender. Valgus alignment of the distal femur, a relatively more lateral location of the tibial tubercle, and a shallower trochlear grove appear to have modest effects on the development of patellofemoral joint osteoarthritis., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Purpose: To determine differences in tibial tubercle-trochlear groove (TT-TG) distance between patients with a history of noncontact anterior cruciate ligament (ACL) injury and an uninjured control group., Methods: MRI studies of 60 patients (age range, 14 to 25 years) with ACL-deficient (ACLD) knees were compared with 60 intact-ACL controls. All patients underwent MRI after a noncontact sports injury. TT-TG distances were measured on proton density-weighted axial images. Independent t-tests were used to determine differences in TT-TG distance between the ACLD and control groups., Results: The mean TT-TG distance in the ACLD group was 12.07 mm (95% confidence interval [CI], 11.11 to 13.02), compared with 10.44 mm (95% CI, 9.64 to 11.24) in the control group. The mean TT-TG distance in the male ACLD group was 12.95 mm (95% CI, 11.39 to 14.51), compared with 10.87 mm (95% CI, 9.52 to 12.21) in the male control group. The mean TT-TG distance in the female ACLD group was 11.48 mm (95% CI, 10.24 to 12.71), compared with 10.04 mm (95% CI, 9.06 to 11.02) in the female control group. There were statistically significant differences in TT-TG distance between the ACLD and control groups (P = .011) and between the male ACLD and control groups (P = .041)., Conclusions: In adolescents and young adults, the TT-TG distance was statistically larger in knees with noncontact ACL tears than in intact-ACL control knees. When the groups were stratified on the basis of sex, only the male patients showed a statistical difference, with a 2.08 mm increase in TT-TG distance between the ACLD and intact-ACL patients. No difference in TT-TG distance was found between the ACLD and control groups for female patients. Despite the findings of this study, the clinical significance of an increased TT-TG distance as an isolated risk factor for noncontact ACL injury remains unanswered., Level of Evidence: Level III, case-control study., (Copyright © 2016 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

Background: Several factors are believed to contribute to patellofemoral joint function throughout knee flexion including patellofemoral (PF) kinematics, contact, and bone morphology. However, data evaluating the PF joint in this highly flexed state have been limited. Therefore, the purpose of this study was to evaluate patellofemoral contact and alignment in low (0°), moderate (60°), and deep (140°) knee flexion, and then correlate these parameters to each other, as well as to femoral morphology., Methods: Sagittal magnetic resonance images were acquired on 14 healthy female adult knees (RSRB approved) using a 1.5 T scanner with the knee in full extension, mid-flexion, and deep flexion. The patellofemoral cartilage contact area, lateral contact displacement (LCD), cartilage thickness, and lateral patellar displacement (LPD) throughout flexion were defined. Intra- and inter-rater repeatability measures were determined. Correlations between patellofemoral contact parameters, alignment, and sulcus morphology were calculated., Results: Measurement repeatability ICCs ranged from 0.94 to 0.99. Patellofemoral cartilage contact area and thickness, LCD, and LPD were statistically different throughout all levels of flexion (p<0.001). The cartilage contact area was correlated to LPD, cartilage thickness, sulcus angle, and epicondylar width (r=0.47-0.72, p<0.05)., Discussion: This study provides a comprehensive analysis of the patellofemoral joint throughout its range of motion., Conclusions: This study agrees with past studies that investigated patellofemoral measures at a single flexion angle, and provides new insights into the relationship between patellofemoral contact and alignment at multiple flexion angles., Clinical Relevance: The study provides a detailed analysis of the patellofemoral joint in vivo, and demonstrates the feasibility of using standard clinical magnetic resonance imaging scanners to image the knee joint in deep flexion., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Objective: To verify whether the tibial tuberosity-trochlear groove distance (TT-TG) and the tendinous-cartilaginous TT-TG (the distance between the patellar tendon and trochlear groove: PT-TG) are identical using computed tomography (CT) and magnetic resonance imaging (MRI) techniques., Subjects and Methods: The TT-TG and PT-TG distances were measured on the same knee samples by three observers (two measurements per observer) using CT and MRI scans collected retrospectively. The reproducibility of the measurements was assessed using the interclass correlation coefficient (ICC). The means and standard deviations of four measurements were calculated for each patient. A paired t-test was used to assess differences between measurements., Results: Fifty knee samples (32 with patellar instability and 18 with other conditions) were evaluated. The inter- and intraobserver reliability was excellent for all four measurements (>0.8). On average, the TT-TG distance on MRI was 3.1-3.6 mm smaller than that on CT, and the PT-TG distance on MRI was 1.0-3.4 mm larger than the TT-TG distance on MRI., Conclusion: The osseous TT-TG and tendinous-cartilaginous PT-TG distances determined by CT and MRI were not identical.

Background: The restoration of an adequate patellar thickness is a key to the successful outcome of knee arthroplasty. This study investigated the relationship between the thickness of the native patellar and medial-lateral patellar width using magnetic resonance imaging (MRI)., Methods: 75 MRI scans of young adults, with an average age of 27 (range 16-40) were studied. Exclusion criteria included a diagnosis of degenerative joint disease, patello-femoral pathology or age under 16/over 40 (170 patients). The bony thickness of the patellar, the chondral thickness and patellar width were measured, as was the location of maximal patellar thickness. Inter/intraobserver variability was calculated and correlation analysis was performed., Results: We found a strong correlation between patellar width and thickness (bone plus cartilage) (Pearson 0.75, P<0.001). The mean width to thickness ratio was 1.8:1 (standard deviation 0.1, 95% confidence interval 1.78-1.83). Without cartilage the ratio was 2.16:1 (SD 0.15, 95% CI 2.11-2.21), correlation was moderate (Pearson 0.59, P<0.001). The average maximal patellar cartilage thickness was 4.1mm (SD 1.3)., Conclusion: The strong correlation and narrow confidence intervals for the ratio of patellar width to thickness, suggest that patellar width might be used as a guide for accurate restoration of patellar thickness during total knee or patello-femoral replacement. After removing osteophytes we would recommend a ratio of 1.8:1. Further work is required to establish whether there is a relationship between anterior knee pain post total knee arthroplasty and an abnormal patellar width:thickness ratio., Level of Evidence: Level III., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Purpose: The aim of the present study was to investigate the influence of knee flexion and weight bearing on the Tibial Tuberosity-Trochlear Groove (TTTG) distance., Materials and Methods: Magnetic resonance imaging of the knee was carried out in 8 healthy volunteers. An open 0.25 T scanner equipped with a C-shaped permanent tilting magnet allowing examinations in weight-bearing conditions was used for the present investigation. A 3D gradient-echo sequence with axial slice orientation was obtained in a lying and an upright position with the knee straight and at 30° of knee flexion. The medial, central and lateral trochlear heights as well as the TTTG were determined., Results: The mean medial trochlear height was 76.2 ± 4%, the central trochlear height was 72.2 ± 3%, and lateral trochlear height was 82.9 ± 3 %. The mean TTTG distance was 11.6 ± 4.4 mm in lying position at 0° knee flexion and 7.3 ± 2.9 mm (n.s.) at 30° knee flexion. Under weight bearing, the mean TTTG was significantly smaller at both 0° knee flexion 6.3 ± 3.2 mm (p = 0.040) and 30° knee flexion 4.9 ± 3.9 mm (p = 0.006) compared to the lying position with 0° knee flexion., Conclusion: Tibial Tuberosity-Trochlear Groove distance depends on both knee flexion angle and weight bearing. The latter only seems to be of relevance in full extension.

Purpose: The design of the trochlear compartment is crucial in patellofemoral arthroplasty (PFA), because 78% of patients with isolated patellofemoral arthritis present concomitant trochlear dysplasia with patellar maltracking and therefore remain predisposed to post-operative patellar subluxation and dislocation. The study investigated whether current PFA implants are designed with anatomic trochlear parameters such as the sulcus angle, lateral facet height and groove orientation., Methods: Five trochlear components of commercially available PFA implants were scanned, and the generated three-dimensional surfaces were measured using engineering design software. The mediolateral trochlear profiles were plotted at various flexion angles (0°, 15°, 30° and 45°) to deduce the following variables: sulcus angle, height of lateral facet and trochlear groove orientation., Results: Four specimens had sulcus angle>144° in the 45° of flexion, and all five specimens had sulcus angle>143° in 30° of flexion. Three specimens had a facet<5 mm high through the entire range of early flexion (0°-30°), and two specimens had a facet<5 mm high beyond early flexion (30°-45°). The trochlear groove was oriented laterally in all specimens (range 1.6°-13.5°)., Conclusion: Current PFA trochlear components are not always designed with anatomic parameters, and some models exhibit characteristics of trochlear dysplasia. Surgeons are therefore advised to implant components with a deep sulcus, particularly in patients with history of patellofemoral disorders, and to adapt the surgical technique and extensor mechanism if the component implanted has a shallow sulcus, to ensure normal patellar tracking., Level of Evidence: III.

Patellofemoral disorders are common. There is a broad spectrum of disease, ranging from patellofemoral pain and instability to focal cartilage disease and arthritis. Regardless of the specific condition, abnormal anatomy and biomechanics are often the root cause of patellofemoral dysfunction. A thorough understanding of normal patellofemoral anatomy and biomechanics is critical for the treating physician. Recognizing and addressing abnormal anatomy will optimize patellofemoral biomechanics and may ultimately translate into clinical success., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Patella instability can cause significant pain and functional limitations. Several factors can predispose to patella instability, such as ligamentous laxity, increased anterior TT-TG distance, patella alta, and trochlear dysplasia. Acquired factors include MPFL injury or abnormal quadriceps function. In many cases, first-time dislocation can successfully be managed with physical therapy and other nonoperative management; however, more than one dislocation significantly increases the chance of recurrence. Surgical management can improve stability, but should be tailored to the injuries and anatomic risk factors for recurrent dislocation. Isolated lateral release is not supported by current literature and increases the risk of iatrogenic medial instability. Medial repair is usually reserved for patients with largely normal anatomy. MPFL reconstruction can successfully stabilize patients with medial soft tissue injury but is a technically demanding procedure with a high complication rate and risks of pain and arthrosis. Tibial tubercle osteotomy can address bony malalignment and also unload certain articular cartilage lesions while improving stability. Trochleoplasty may be indicated in individuals with a severely dysplastic trochlea that cannot otherwise be stabilized. A combination of procedures may be necessary to fully address the multiple factors involved in causing pain, loss of function, and risk of recurrence in patients with patellar instability., (Copyright © 2014 Elsevier Inc. All rights reserved.)

The relationship of patellofemoral congruency with chondromalacia patellae (CP) was retrospectively evaluated. Lateral patellar tilt angle (LPTA), sulcus angle (SA), trochlear depth (TD), and patella angle (PA) were measured at 301 knee magnetic resonance images and compared between groups with and without CP. In the CP group, LPTA and TD were significantly low (P<.01), SA was high (P<.01), while PA showed no difference (P>.05). The parameters were also compared between groups with mild and severe CP, and no significant difference was found (P>.05). Our results demonstrate that patellar tilt and trochlear dysplasia are related to the presence but not the degree of CP., (Copyright © 2014 Elsevier Inc. All rights reserved.)

The patellofemoral (PF) joint is a complex articulation, with interplay between the osseous and soft tissue structures to maintain the balance between knee mobility and stability. Disorders of the PF joint can be a source of anterior knee pain (AKP). In this article, radiographic and magnetic resonance imaging of the PF joint are reviewed, including normal anatomy, imaging techniques, and imaging-based measurements. Common imaging findings associated with AKP are reviewed, including symptomatic normal variants, tendinopathy, apophysitis, osteoarthritis, chondromalacia patella, trochlear dysplasia, excessive lateralization of tibial tuberosity, patellar maltracking, patellar dislocation and fractures, anterior bursitis, Morel-Lavallée effusions, and fat pad edema., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Modeling ligaments as three-dimensional strings is a popular method for in vivo estimation of ligament length. The purpose of this study was to develop an algorithm for automated generation of non-penetrating strings between insertion points and to evaluate its feasibility for estimating length changes of the medial patellofemoral ligament during normal knee flexion. Three-dimensional knee models were generated from computed tomography (CT) scans of 10 healthy subjects. The knee joint under weight-bearing was acquired in four flexion positions (0°-120°). The path between insertion points was computed in each position to quantify string length and isometry. The average string length was maximal in 0° of flexion (64.5 ± 3.9 mm between femoral and proximal patellar point; 62.8 ± 4.0 mm between femoral and distal patellar point). It was minimal in 30° (60.0 ± 2.6 mm) for the proximal patellar string and in 120° (58.7 ± 4.3 mm) for the distal patellar string. The insertion points were considered to be isometric in 4 of the 10 subjects. The proposed algorithm appears to be feasible for estimating string lengths between insertion points in an automatic fashion. The length measurements based on CT images acquired under physiological loading conditions may give further insights into knee kinematics.

Purpose: The purposes of this study were to examine patellar height at preoperation and postoperation, and compare the change of patellar height between opening wedge high tibial osteotomy (HTO) and closed wedge HTO by using Insall-Salvati (IS) ratio and our original method., Methods: Twenty patients (26 knees) were included. There were 6 males (6 knees) and 14 females (20 knees). Sixteen knees underwent closed method and 10 knees underwent opening method. Patellar height was measured at preoperation, immediately after the operation (postoperation) and 1 year after the operation according to IS ratio and modified Blumensaat (MB) ratio. We defined MB ratio as the ratio of distance from Blumensaat line to the midpoint of patellofemoral joint of patella against the length of Blumensaat line., Results: In opening wedge HTO, though IS ratio significantly increased postoperatively compared with preoperative IS ratio, IS ratio at 1 year after operation was not significantly different from preoperative values. MB ratio at postoperation and that at 1 year after the operation significantly decreased compared with preoperative MB ratio. In closed wedge HTO, there was no difference between preoperative and postoperative values of both IS ratio and MB ratio., Conclusions: In the postoperative period after opening wedge HTO, IS ratio was significantly increased, whereas MB ratio was decreased. We recommend that patients with low preoperative MB ratio must be treated with closed wedge HTO.

Purpose: To develop and validate short axial and sagittal MRI scans (<1min) to assess in vivo patellofemoral contact areas in loaded knee flexion., Materials and Methods: Contact area was assessed in four cadaver knee specimens from axial and sagittal scans using two contact area extraction techniques (delineation and intersection) and three calculation techniques (slice thickness multiplication, linear interpolation, and spline interpolation). Error was expressed as the mean absolute and percentage difference from a dye staining-based reference standard. Intrareader and intrasubject repeatability, expressed as the mean standard deviation, was determined., Results: Contact area assessments from the sagittal MRI scans using the delineation and slice thickness multiplication technique had the smallest error (47.7 ± 38.1 mm(2) or 10.7%). The intrareader repeatability from assessments using the sagittal scans was smaller than those using the axial scans when the delineation method was used (<9.4 ± 4.3 mm(2) and <15.4 ± 14.1 mm(2) , respectively). The intrasubject repeatability of the assessment from the sagittal scan was less than 39.9 ± 23.0 mm(2) ., Conclusion: This protocol yields assessments of contact area in less than 1 minute that have errors similar to those made using scans many times longer and can be used in series with kinematic scans to carry out simultaneous assessments in vivo to study patellofemoral joint disease., (Copyright © 2013 Wiley Periodicals, Inc.)

Background: The tibial tubercle-trochlear groove (TT-TG) distance is a useful tool in guiding surgical management for patients with recurrent lateral patellar instability. Current recommendations for tibial tubercle transfer are based on TT-TG distance thresholds derived from adult populations. Recurrent patellar instability, however, frequently affects children, but normal and pathological TT-TG values have not been established for pediatric patients. The objectives of this study were to (1) confirm that magnetic resonance imaging (MRI) measurements for TT-TG distance in a pediatric population are reliable and reproducible, (2) determine whether the TT-TG distance changes with age, (3) define normal TT-TG distances in a pediatric population, and (4) confirm that a subgroup of pediatric patients with patellar instability have higher TT-TG distances., Methods: Six hundred and eighteen MRIs were retrospectively collected for patients who were nine months to sixteen years old. Each MRI was measured twice in a blinded, randomized manner by each reviewer. Patient age, sex, knee laterality, magnet strength, underlying diagnosis, and pertinent previous surgical treatments were all recorded separately from the measurements. MRIs that were unreadable and those of patients who had previous extensor mechanism surgery, preexisting deformity, or destructive neoplasms were excluded., Results: There was excellent intraobserver and interobserver reliability of TT-TG distance measurements. TT-TG distance was associated with the natural logarithm of age (p < 0.001). A percentile-based growth chart was created to demonstrate this relationship. The median TT-TG distance for patients without patellar instability in this pediatric population was 8.5 mm (mean and 95% confidence interval, 8.6 ± 0.3 mm). Patients with patellar instability had higher TT-TG distances (median, 12.1 mm; p < 0.001). TT-TG distance measured nearly 2 mm less on MRIs performed with a 3-T magnet than on those acquired with a 1.5-T magnet (p < 0.001)., Conclusions: TT-TG distance changes with chronologic age in the pediatric population. As such, we developed a percentile-based growth chart in order to better depict normal TT-TG distances in the pediatric population. Like many issues in pediatric orthopaedics, an age-based approach for directing surgical treatment may be more appropriate for skeletally immature individuals with recurrent lateral patellar instability.

Background: The osseous morphology of the patellofemoral joint is an independent factor that affects the biomechanics of patellofemoral instability., Objective: The purpose of this study is to determine age- and gender-related differences in the osseous morphology of the patellofemoral joint in children during skeletal maturation., Materials and Methods: This study was approved by the institutional review board and was HIPAA-compliant. We included 97 children and young adults (age range 5-22 years; 51 girls and 46 boys, mean ages 14.3 years and 13.7 years, respectively). We studied 1.5-T knee MR exams, measuring the osseous morphology of the patellofemoral joint (lateral trochlear inclination, trochlear facet asymmetry, trochlear depth, patellar height ratio, tibial tubercle-trochlear groove distance, and lateral patellofemoral angle) for each MR exam. We compared measurements to published values for patellofemoral instability. Physeal patency (open or closing/closed) was determined on MR. We assessed the associations between MR osseous measurements and gender, age and physeal patency using Wilcoxon rank sum test and least square means regression models., Results: The osseous patellofemoral joint morphology measurements were all within a normal range. There were no significant correlations between MR osseous measurements and age, gender or physeal patency., Conclusion: During skeletal maturation, age and gender do not affect the osseous morphology or congruency of the patellofemoral joint.

Background: Patellar malalignment is thought to be an etiological factor with respect to the development of patellofemoral pain. Although previous studies have suggested that the geometry of the femoral trochlea and the height of the patella play an important role in determining patellar alignment, no investigation has systematically examined these relationships during weight bearing. The aim of this study was to determine whether patellar height and/or trochlear geometry predicts patellar alignment (lateral patellar displacement and lateral patellar tilt) during weight bearing., Methods: MR images of the patellofemoral joint were acquired from 36 participants during weight bearing (25% of body weight) at 4 knee flexion angles (0°, 20°, 40° and 60°). Using the axial images, patellar alignment (lateral displacement and tilt) and femoral trochlear geometry (sulcus angle and inclination of the lateral femoral trochlea) were measured. Patellar height (Insall-Salvati ratio) was measured on reconstructed sagittal plane images., Results: Stepwise regression analysis revealed that at 0° of knee flexion, the height of the patella was the best predictor of lateral patellar tilt while the lateral trochlea inclination angle was the best predictor of lateral patellar displacement. Lateral trochlear inclination was the best predictor of patellar lateral displacement and tilt at 20°, 40° and 60° of knee flexion., Conclusion: Similar to a previous study performed under non-weight bearing condition, our findings suggest that lateral trochlear inclination is an important determinant of patellar alignment in weight bearing., Level of Evidence: Level III., (© 2013. Published by Elsevier B.V. All rights reserved.)

Objective: To assess the intraobserver, interobserver, and test-retest reproducibility of minimum joint space width (mJSW) measurement of medial and lateral patellofemoral joints on standing "skyline" radiographs and to compare the mJSW of the patellofemoral joint to the mean cartilage thickness calculated by quantitative magnetic resonance imaging (qMRI)., Materials and Methods: A couple of standing "skyline" radiographs of the patellofemoral joints and MRI of 55 knees of 28 volunteers (18 females, ten males, mean age, 48.5 ± 16.2 years) were obtained on the same day. The mJSW of the patellofemoral joint was manually measured and Kellgren and Lawrence grade (KLG) was independently assessed by two observers. The mJSW was compared to the mean cartilage thickness of patellofemoral joint calculated by qMRI., Results: mJSW of the medial and lateral patellofemoral joint showed an excellent intraobserver agreement (interclass correlation (ICC) = 0.94 and 0.96), interobserver agreement (ICC = 0.90 and 0.95) and test-retest agreement (ICC = 0.92 and 0.96). The mJSW measured on radiographs was correlated to mean cartilage thickness calculated by qMRI (r = 0.71, p < 0.0001 for the medial PFJ and r = 0.81, p < 0.0001 for the lateral PFJ). However, there was a lack of concordance between radiographs and qMRI for extreme values of joint width and KLG. Radiographs yielded higher joint space measures than qMRI in knees with a normal joint space, while qMRI yielded higher joint space measures than radiographs in knees with joint space narrowing and higher KLG., Conclusions: Standing "skyline" radiographs are a reproducible tool for measuring the mJSW of the patellofemoral joint. The mJSW of the patellofemoral joint on radiographs are correlated with, but not concordant with, qMRI measurements.

The current study was performed to evaluate the accuracy of computational assessment of the influence of the orientation of the patellar tendon on the patellofemoral pressure distribution. Computational models were created to represent eight knees previously tested at 40 deg, 60 deg, and 80 deg of flexion to evaluate the influence of hamstrings loading on the patellofemoral pressure distribution. Hamstrings loading increased the lateral and posterior orientation of the patellar tendon, with the change for each test determined from experimentally measured variations in tibiofemoral alignment. The patellar tendon and the cartilage on the femur and patella were represented with springs. After loading the quadriceps, the total potential energy was minimized to determine the force within the patellar tendon. The forces applied by the quadriceps and patellar tendon produced patellar translation and rotation. The deformation of each cartilage spring was determined from overlap of the cartilage surfaces on the femur and patella and related to force using linear elastic theory. The patella was iteratively adjusted until the extension moment, tilt moment, compression, and lateral force acting on the patella were in equilibrium. For the maximum pressure applied to lateral cartilage and the ratio of the lateral compression to the total compression, paired t-tests were performed at each flexion angle to determine if the output varied significantly (p &lt; 0.05) between the two loading conditions. For both the computational and experimental data, loading the hamstrings significantly increased the lateral force ratio and the maximum lateral pressure at multiple flexion angles. For the computational data, loading the hamstrings increased the average lateral force ratio and maximum lateral pressure by approximately 0.04 and 0.3 MPa, respectively, compared to experimental increases of 0.06 and 0.4 MPa, respectively. The computational modeling technique accurately characterized variations in the patellofemoral pressure distribution caused by altering the orientation of the patellar tendon.

While various factors have been assumed to affect knee joint biomechanics, few data have been reported on the function of the extensor mechanism in deep flexion of the knee. This study analyzed the patellofemoral joint contact kinematics and the ratio of the quadriceps and patellar tendon forces in living subjects when they performed a single leg lunge up to 150 deg of flexion. The data revealed that in the proximal-distal direction, the patellofemoral articular contact points were in the central one-third of the patellar cartilage. Beyond 90 deg of flexion, the contact points moved towards the medial-lateral edges of the patellar surface. At low flexion angles, the patellar tendon and quadriceps force ratio was approximately 1.0 but reduced to about 0.7 after 60 deg of knee flexion, implying that the patella tendon carries lower loads than the quadriceps. These data may be valuable for improvement of contemporary surgical treatments of diseased knees that are aimed to achieve deep knee flexion.

Purpose: The aim of this study was to investigate the attachment of the medial patellofemoral ligament (MPFL) using cadaver specimens and establish an anatomic basis for optimal MPFL reconstruction to achieve better patella stability., Methods: Sixteen knees of eight cadavers were used in this study. The relationship of the MPFL with quadriceps muscles was investigated from outside after removal of the distal part of the vastus medialis and the rectus femoris and then evaluated from intra-articular side after release of lateral margin of the vastus lateralis muscle, patella and patella tendon., Results: The proximal fibres of MPFL were mainly attached to the vastus intermedius tendon, without tight adhesion to the vastus medialis. The distal fibres of MPFL were interdigitated with the deep layer of the medial retinaculum that was attached to the medial margin of the patella tendon., Conclusion: These findings imply that MPFL, which was directly attached to the vastus intermedius and patella and indirectly continued to the patella tendon, could keep pulling them medially as one unit and consequently make the patella move smoothly on the trochlea during whole movement of the knee. Clinically, dysfunction of both proximal and distal MPFL fibres should be considered in the diagnosis and treatment of patella instability after traumatic patella dislocation. MPFL reconstruction with both fibres has a possibility to lead ideal function of MPFL and better instability of the patella.

The results of mathematic modelling of work of femoropatellar joint in normal conditions and in the presence of dysplastic deformity were adduced. There was established, that a knee joint (KJ) by its external appearance and function constitutes a classic cam mechanism. Biomechanical scheme of interaction between the femoral bone processus and patella was elaborated. In accordance to scheme of cam mechanism its experimental roentgenometric investigations were performed. According to statistical analysis performed, in conditions of dysplasia in femoropatellar joint the changes in the KJ occur, which may cause its blockade; the patella position in the KJ depends on peculiarities of anatomical structure of the femoral bone processuses.

Acute patellofemoral dislocation is the most common acute knee disorder in children and adolescents. The predisposing factors for acute patellar dislocation are multifactorial. Unless associated with substantial articular cartilage damage, nonsurgical management is typically used to treat a first-time acute patellofemoral dislocation in a skeletally immature athlete. In the setting of recurrent instability, surgical reconstruction is usually recommended. Surgical treatment of patellofemoral instability in the skeletally immature athlete is evolving from nonanatomic extensor mechanism surgical procedures to anatomic restorative procedures based on reconstitution of the medial patellofemoral ligament. The current goal of surgery is to restore the normal anatomy of the patellofemoral joint. Proper patient selection and attention to technical details are important in achieving good outcomes.

Purpose: Excellent results of anteromedialization of the tibial tuberosity for recurrent patellar dislocation have been reported; however, the contribution of the preoperative anatomic factors to postoperative patellar instability has not been well established. The purpose of this study was to investigate the mid-term results and the incidence of postoperative patellar instability after Fulkerson procedure for recurrent patella dislocation, and to determine the radiologic predictor of the postoperative patellar instability., Methods: Sixty-two knees of 41 patients underwent Fulkerson procedure with or without lateral retinacular release for recurrent patellar dislocation and were followed-up for 85-155 months. Predisposing anatomic factors for recurrent patellar dislocation were evaluated preoperatively, including valgus knee alignment (femorotibial angle), patella alta (Insall-Salvati ratio), trochlear dysplasia (trochlear depth), lateral patellar displacement (congruence angle) and lateral malposition of the tibial tuberosity (tibial tuberosity-trochlear groove distance). The relationship between the measurements of anatomic factors and postoperative patellar instability, which was defined by the patellar re-dislocation or residual apprehension after surgery, was analyzed., Results: The Fulkerson score and the Kujala score were significantly improved from the median of 65 (35-80) points and 68 (36-82) points preoperatively to 95 (60-100) points and 92 (57-100) points at the final follow-up, respectively. Three knees (4.8%) experienced postoperative patellar re-dislocation and 4 knees (6.5%) showed the positive apprehension sign at the final follow-up. The statistical analysis showed that the postoperative patellar instability correlated with only patella alta., Conclusion: Patella alta was the only predictor of postoperative patellar instability after Fulkerson procedure. These results indicated that isolated Fulkerson procedure should not be indicated for recurrent patellar dislocation with severe patella alta., Level of Evidence: Case-control study, Level III.

Boundary lubrication is characterized by sliding surfaces separated by a molecularly thin film that reduces friction and wear of the underlying substrate when fluid lubrication cannot be established. In this study, the wear and replenishment rates of articular cartilage were examined in the context of friction coefficient changes, protein loss, and direct imaging of the surface ultrastructure, to determine the efficiency of the boundary lubricant (BL) layer. Depletion of cartilage lubricity occurred with the concomitant loss of surface proteoglycans. Restoration of lubrication by incubation with synovial fluid was much faster than incubation with culture media and isolated superficial zone protein. The replenishment action of the BL layer in articular cartilage was rapid, with the rate of formation exceeding the rate of depletion of the BL layer to effectively protect the tissue from mechanical wear. The obtained results indicate that boundary lubrication in articular cartilage depends in part on a sacrificial layer mechanism. The present study provides insight into the natural mechanisms that minimize wear and resist tissue degeneration over the lifetime of an organism., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Purpose: We investigated the contact pressure and area of the patellofemoral joint both before and after different meniscectomies to provide a biomechanical basis for selecting meniscectomy and its clinical application for meniscus injuries., Methods: Six fresh cadaveric knees were used in the study. Using Staubli robots and an ultra-low-min-type pressure-sensitive tablet, changes in contact area and stress in the patellofemoral joint were measured at various flexion angles following different parts and degrees of meniscectomy., Results: The patellofemoral contact area enlarged with the increase of knee flexion angle. From the values obtained from contact areas and average contact pressure of the patellofemoral joint, we found no significant difference between partial meniscectomy and intact knees, but a significant difference was found between total meniscectomy and intact knees. The contact area after lateral meniscectomy was statistically less than that of intact knees. The mean patellofemoral contact pressure after lateral meniscectomy was larger than in intact knees at each angle of flexion. No significant difference in contact area was observed between intact knees and medial meniscectomy. The average patellofemoral contact pressure after medial meniscectomy was larger than in intact knees from 0° ~ 30° of knee flexion, and no significant differences were found between intact knees and medial meniscectomy while knee bending from 60° to 90°., Conclusions: Different meniscectomies result in high contact pressure or disordered distribution of contact pressure, which may be the cause of postoperative patellofemoral degenerative arthrosis.

A detailed 3D anatomical model of the patellofemoral joint was developed to study the tracking, force, contact and stability characteristics of the joint. The quadriceps was considered to include six components represented by 15 force vectors. The patellar tendon was modeled using four bundles of viscoelastic tensile elements. Each of the lateral and medial retinaculum was modeled by a three-bundle nonlinear spring. The femur and patella were considered as rigid bodies with their articular cartilage layers represented by an isotropic viscoelastic material. The geometrical and tracking data needed for model simulation, as well as validation of its results, were obtained from an in vivo experiment, involving MR imaging of a normal knee while performing isometric leg press against a constant 140 N force. The model was formulated within the framework of a rigid body spring model and solved using forth-order Runge-Kutta, for knee flexion angles between zero and 50 degrees. Results indicated a good agreement between the model predictions for patellar tracking and the experimental results with RMS deviations of about 2 mm for translations (less than 0.7 mm for patellar mediolateral shift), and 4 degrees for rotations (less than 3 degrees for patellar tilt). The contact pattern predicted by the model was also consistent with the results of the experiment and the literature. The joint contact force increased linearly with progressive knee flexion from 80 N to 210 N. The medial retinaculum experienced a peak force of 18 N at full extension that decreased with knee flexion and disappeared entirely at 20 degrees flexion. Analysis of the patellar time response to the quadriceps contraction suggested that the muscle activation most affected the patellar shift and tilt. These results are consistent with the recent observations in the literature concerning the significance of retinaculum and quadriceps in the patellar stability.

Trochlear dysplasia is a risk factor for patellofemoral instability. Trochleoplasty involves reshaping the trochlear groove to provide increased patellofemoral stability. We obtained post-operative radiographs, MRI, and outcome scores in 6 patients who underwent this procedure. All 6 of the patients were satisfied with their outcome following trochleoplasty with no recurrent instability events. Mean bony sulcus angles decreased from 148 degrees to 129 degrees. However, 4 of the 6 patients reported anterior knee pain. Similar to previously published studies, trochleoplasty can reliably improve patellofemoral stability in patients with severe trochlear dysplasia, but a high percentage of patients will have pain postoperatively.

Purpose: The purpose of this study was to analyse true lateral radiographs of children and adolescents to determine the relation of the origin of the MPFL and the distal femoral physis considering the complex anatomy of the physis. The hypothesis was that the femoral insertion of the MPFL is distal to the growth plate., Methods: Antero-posterior and true lateral radiographs from PACS computer records of 27 patients with a history of patellofemoral instability were assessed. To determine the femoral origin of the MPFL, the method by Schöttle et al. and the method by Redfern et al. were applied independently. On the anteroposterior radiograph, the distance between the medial most part of the physis and the central part of the physis was measured to quantify the concave curvature of the physis. To cross-reference the femoral insertion of the MPFL onto an ap view, the projected MPFL origin-physis distance was subtracted from the distance between the most medial part of the physis and the central part of the physis., Results: The projected median origin of the MPFL as measured on a lateral radiograph was located 3.2 mm (1.2-5.8 mm) proximal to the physis. The median distance between the most medial part of the physis and the physeal line on the anteroposterior radiograph was 9.9 mm (4.1-12.0 mm). Subtracting the two measured values, the median origin of the MPFL as seen on the ap view was 6.4 mm (2.9-8.5 mm) distal to the femoral physis., Conclusion: Considering the concave curvature of the distal femoral physis, it can be assumed that the femoral insertion of the MPFL is distal to the femoral physis. As a too proximal insertion of the graft can cause unintentional tightening of the MPFL in knee flexion, these results have to be considered when performing reconstruction of the MPFL in children and adolescents with open growth plates.

Purpose: The objective of this study is to evaluate patellofemoral joint imaging on magnetic resonance imaging (MRI) in asymptomatic subjects to assess normal values and to test statistical correlation and reliability of MRI scan., Methods: An analysis of 51 standard MRI examinations was performed. Sulcus angle (SA), patellar axis (PA), lateral patellofemoral angle (LPFA), and lateral patellofemoral length (LPL) were measured. None of the patients suffered from patellofemoral complaints. Patients with patella alta and significant hydrops were excluded. The measurements were assessed with a 2-week interval by two raters under blinded conditions. Statistical analysis was applied by an independent analyst., Results: The mean SA referenced 142.4 ± 6.9°, PA 5.3 ± 3.8°, LPFA 13 ± 4.4°, and LPL 0.8 ± 2.9 mm. Inter-observer variability showed high correlation for LPL and PA, as the repeatability coefficient was high (LPL; 1.49 (LN), 5.7 (ST) and PA; 4.1 (LN), 5.8 (ST). Also, intra-observer variability showed good correlation for LPL and PA., Conclusion: The results represent patellofemoral values in the normal population. They indicate that MRI is a reliable imaging technique to determine lateral patellofemoral length and patellar axis. Lateral patellofemoral angle and sulcus angle showed a poor correlation and should not be used for decision making., Level of Evidence: Development of diagnostic criteria in a consecutive series of patients and a universally applied "gold" standard, Level II.

Functionally, the knee comprises 2 articulations-the patellofemoral and tibiofemoral. Stability of the joint is governed by a combination of static ligaments, dynamic muscular forces, meniscocapsular aponeurosis, bony topography, and joint load. The surgeon is ill equipped to undertake surgical treatment of a dislocated knee without a sound footing in the anatomic complexities of this joint. We review the normal anatomy of the knee, emphasizing connective tissue structures and common injury patterns.

Finite element methods have been applied to evaluate in vivo joint behavior, new devices, and surgical techniques but have typically been applied to a small or single subject cohort. Anatomic variability necessitates the use of many subject-specific models or probabilistic methods in order to adequately evaluate a device or procedure for a population. However, a fully deformable finite element model can be computationally expensive, prohibiting large multisubject or probabilistic analyses. The aim of this study was to develop a group of subject-specific models of the patellofemoral joint and evaluate trade-offs in analysis time and accuracy with fully deformable and rigid body articular cartilage representations. Finite element models of eight subjects were used to tune a pressure-overclosure relationship during a simulated deep flexion cycle. Patellofemoral kinematics and contact mechanics were evaluated and compared between a fully deformable and a rigid body analysis. Additional eight subjects were used to determine the validity of the rigid body pressure-overclosure relationship as a subject-independent parameter. There was good agreement in predicted kinematics and contact mechanics between deformable and rigid analyses for both the tuned and test groups. Root mean square differences in kinematics were less than 0.5 deg and 0.2 mm for both groups throughout flexion. Differences in contact area and peak and average contact pressures averaged 5.4%, 9.6%, and 3.8%, respectively, for the tuned group and 6.9%, 13.1%, and 6.4%, respectively, for the test group, with no significant differences between the two groups. There was a 95% reduction in computational time with the rigid body analysis as compared with the deformable analysis. The tuned pressure-overclosure relationship derived from the patellofemoral analysis was also applied to tibiofemoral (TF) articular cartilage in a group of eight subjects. Differences in contact area and peak and average contact pressures averaged 8.3%, 11.2%, and 5.7% between rigid and deformable analyses in the tibiofemoral joint. As statistical, probabilistic, and optimization techniques can require hundreds to thousands of analyses, a viable platform is crucial to component evaluation or clinical applications. The computationally efficient rigid body platform described in this study may be integrated with statistical and probabilistic methods and has potential clinical application in understanding in vivo joint mechanics on a subject-specific or population basis.

Objective: to investigate if the cartilaginous surface and corresponding osseous contour of the patellofemoral joint match in the axial plane for providing theoretical basis with evaluating alignment of patellofemoral joint and designing the part of patellofemoral joint in knee prosthesis., Methods: from January 2009 to March 2010, 9 human cadaver knees were prepared, which chandra of patellofemoral joint didn't degenerate. Each specimen was sectioned in the axial plane at 20° to 30° knee flax. The cross-sections revealed characteristics in the bony anatomy and corresponding articular surface geometry of the patellofemoral joint in the axial plane. Evaluating parameters included osseous patella congruence angle (OPCA), chondral patella congruence angle (CPCA), patella chondral convex point parameter (PCCPP), patella subchondral osseous convex point parameter (PSOCPP), the parameters of the deepest (chondral or osseous) point of the intercondylar sulcus. After that, the osseous and cartilaginous contours and subchondral osseous contours of the patella in the axial plane were analyzed through MRI data of 11 patients who didn't degenerate in patellofemoral joint cartilage. Parameters as same as cadaver knees were compared., Results: data from specimens of OPCA was (-4.5 ± 1.1)°, CPCA was (0.5 ± 0.8)°, PCCPP was 1.13 ± 0.11, PSOCPP was 1.67 ± 0.14, PCDPIS was 1.35 ± 0.28, PODPIS was 1.38 ± 0.33. Date from MRI of OPCA was (-3.8 ± 1.4)°, CPCA was (0.7 ± 1.0)°, PCCPP was 1.05 ± 0.21, PSOCPP was 1.73 ± 0.18, PCDPIS was 1.41 ± 0.21, PODPIS was 1.37 ± 0.27. The patella exhibited significant differences in the bony vs. chondral anatomy (P < 0.05), but the intercondylar sulcus nearly match in the bony vs. chondral anatomy., Conclusions: the cartilaginous surface and corresponding osseous contour of the patella don't match in the patellofemoral joint axial plane, but that of the trochlea nearly matches. This is very important for accurately evaluating alignment of patellofemoral joint because the normal osseous alignment of patellofemoral joint don't represent the normal alignment and helpful for designing the part of patellofemoral joint in knee prosthesis.

Purpose: To investigate the effects of anterior cruciate ligament (ACL) deficiency and nonanatomic single-bundle (SB) and anatomic double-bundle (DB) ACL reconstruction on the contact characteristics of the patellofemoral (PF) joint., Methods: By use of a materials testing system, 7 fresh-frozen human cadaveric knees were tested. The following states were tested: ACL-intact knee, nonanatomic SB ACL reconstruction, anatomic DB ACL reconstruction, and ACL-deficient knee. Hamstring autografts were used. PF contact pressures and areas were measured with pressure-sensitive film at 30°, 60°, and 90° of knee flexion with a constant 100-N load on the quadriceps tendon., Results: The total contact area of ACL-deficient and nonanatomic SB ACL-reconstructed knees (123.8 ± 63.9 and 149.6 ± 79.3 mm(2), respectively) significantly decreased when compared with those of the intact knee (206.1 ± 83.6 mm(2)) at 30° of knee flexion. The lateral-facet peak pressure of ACL-deficient and nonanatomic SB ACL-reconstructed knees (1.12 ± 0.52 and 1.22 ± 0.54 MPa, respectively) significantly decreased when compared with those of the intact knee (0.68 ± 0.38 MPa) at 90° of knee flexion. Anatomic DB ACL reconstruction restored the contact pressures and areas to values similar to those of the intact knee (no significant difference)., Conclusions: ACL deficiency resulted in a significant decrease in the total and medial PF contact areas and in an increase in the lateral PF contact pressure. Anatomic DB ACL reconstruction more closely restored normal PF contact area and pressure than did nonanatomic SB ACL reconstruction., Clinical Relevance: Our findings suggest that the changes in the PF contact area and pressures in ACL deficiency and after nonanatomic SB ACL reconstruction may be one of the causes of PF osteoarthritis or other related PF problems found at long-term follow-up. Anatomic DB ACL reconstruction may reduce the incidence of PF problems by closely restoring the contact area and pressure., (Copyright © 2010 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

Objective: To examine the relationship between patella alta and the prevalence and worsening at followup of structural features of patellofemoral joint (PFJ) osteoarthritis (OA) on magnetic resonance imaging (MRI)., Methods: The Multicenter Osteoarthritis Study is a cohort study of persons ages 50-79 years with or at risk for knee OA. Patella alta was measured using the Insall-Salvati ratio (ISR) on the baseline lateral radiograph, and cartilage damage, bone marrow lesions (BMLs), and subchondral bone attrition (SBA) were graded on MRI at baseline and at 30 months of followup in the PFJ. We examined the association of the ISR with the prevalence and worsening of cartilage damage, BMLs, and SBA in the PFJ using logistic regression., Results: A total of 907 knees were studied (mean age 62 years, body mass index 30 kg/m(2), ISR 1.10), 63% from female subjects. Compared with knees in the lowest ISR quartile at baseline, those in the highest quartile had 2.4 (95% confidence interval [95% CI] 1.7-3.3), 2.9 (95% CI 2.0-4.3), and 3.5 (95% CI 2.3-5.5) times the odds of having lateral PFJ cartilage damage, BMLs, and SBA, respectively, and 1.5 (95% CI 1.1-2.0), 1.3 (95% CI 0.9-1.8), and 2.2 (95% CI 1.4-3.4) times the odds of having medial PFJ cartilage damage, BMLs, and SBA, respectively. Similarly, those with high ISRs were also at risk for worsening of cartilage damage and BMLs over time than those with low ISRs., Conclusion: A high ISR, indicative of patella alta, is associated with structural features of OA in the PFJ. Additionally, the same knees have an increased risk of worsening of these same features over time.

It is widely recognized that the tracking of patella is strongly influenced by the geometry of the trochlear groove. Nonetheless, quantitative baseline data regarding correlation between the three-dimensional geometry of the trochlear groove and patellar tracking under in vivo weight-bearing conditions are not available. A combined magnetic resonance and dual fluoroscopic imaging technique, coupled with multivariate regression analysis, was used to quantify the relationship between trochlear groove geometry (sulcus location, bisector angle, and coronal plane angle) and in vivo patellar tracking (shift, tilt, and rotation) during weight-bearing knee flexion. The results showed that in the transverse plane, patellar shift was strongly correlated (correlation coefficient R=0.86, p<0.001) to mediolateral location of the trochlear sulcus (raw regression coefficient β(raw)=0.62) and the trochlear bisector angle (β(raw)=0.31). Similarly, patellar tilt showed a significant association with the trochlear bisector angle (R=0.45, p<0.001, and β(raw)=0.60). However, in the coronal plane patellar rotation was poorly correlated with its matching geometric parameter, namely, the coronal plane angle of the trochlea (R=0.26, p=0.01, β(raw)=0.08). The geometry of the trochlear groove in the transverse plane of the femur had significant effect on the transverse plane motion of the patella (patellar shift and tilt) under in vivo weight-bearing conditions. However, patellar rotation in the coronal plane was weakly correlated with the trochlear geometry.

Knowledge of patellofemoral joint biomechanics is important for understanding sex-related dimorphism in patellofemoral pathologies and advancement of related treatments. We evaluated the hypotheses that sex differences exist in patellar tendon (PT) orientation and patellar tracking during weight-bearing knee flexion and that they relate to differences in tibiofemoral rotation. The PT orientation and patellar tracking were measured in healthy subjects (18 male, 13 female) during weight-bearing knee flexion, using magnetic resonance and dual fluoroscopic imaging. These data were analyzed for sex differences and correlation with previously reported tibiofemoral rotation data. The results indicated a significant effect of sex on PT orientation, particularly at low flexion angles. In females, the PT was oriented more anteriorly in the sagittal plane, more medially in the coronal plane, and showed greater external tilt in the transverse plane of the tibia (p < 0.05). Significant correlations between tibiofemoral rotation and PT orientation (p < 0.01) indicated that sex differences in coronal and transverse plane orientation of the PT relate to differences in tibiofemoral rotation. Patellar tracking did not show significant sex differences or correlation to tibiofemoral rotation. Further studies are warranted to determine implications for patellofemoral pathologies and treatments like total knee arthroplasty.

Anatomical open reduction is the choice treatment method in patellar fractures and the sole approach to study the cartilage surface healing is arthroscopy. This study is to evaluate the cartilage healing, long after the complete union of the fractures and the long-term effects of simple transverse patellar fractures with perfect results on patellofemoral cartilage surface. Free of charge standard diagnostic arthroscopy was done on 22 patients whose simple transverse pattelar fractures had happened at least 3 years ago with the mean age of 36.4 years. Fractures had happened at least 3 years ago and all cases had excellent union results. The data collected from cartilage surface studies were recorded. No other statistical tests were used except for X2 test to study the relation between clinical and radiological findings and arthroscopies. The elapsed time from the fracture occurrence to the arthroscopy was 39.2 months, at least 36 months. Five patients (22.6%) showed complete cartilage healing in cartilage surface arthroscopy and 10 patients (45.2%) proved to have Grade I chondral lesions. Four patients had Grade II chondral lesions and 3 patients had Grade III chondral lesions along with fibrillation. In 2 patients mirror cartilage lesions were observed in the opposite trochlea. In 3 patients with normal radiological signs, step-off was observed on cartilage surface. There was no relation between clinical signs and radiological characteristics of the patients with the healing on cartilage surface (p = 0.84). Having a diagnostic arthroscopy in an appropriate time after fusion, especially during extracting the metal instrument, is effective on evaluating patient's prognosis. Extracting metal instruments along with the simultaneous chondroplasty has low cost and complications, though leading to a decrease in the prevalence of secondary osteoarthritis and probably the eruptive swelling due to the debris released from probable fibrillations.

One difficulty in revision total knee arthroplasty (TKA) is the management of distal femoral bone defects in which a joint line elevation (JLE) is likely to occur. Although JLE has been associated with inferior clinical results, the effect that an elevated joint line has on knee contact forces has not been investigated. To understand the clinical observations and elaborate the potential risk associated with a JLE, we performed a virtual TKA on the musculoskeletal models of four subjects. Tibio- and patellofemoral joint contact forces (JCF) were calculated for walking and stair climbing, varying the location of the joint line. An elevation of the joint line primarily affected the patellofemoral joint with JCF increases of as much as 60% of the patient's body weight (BW) at 10-mm JLE and 90% BW at 15-mm JLE, while the largest increase in tibiofemoral JCF was only 14% BW. This data demonstrates the importance of restoring the joint line, as it plays a critical role for the magnitudes of the JCFs, particularly for the patellofemoral joint. JLE caused by managing distal femoral defects with downsizing and proximalizing the femoral component could increase the patellofemoral contact forces, and may be a contributing factor to postoperative complications such as pain, polyethylene wear, and limited function.

We have reviewed the literature to establish the role of lateral retinacular release in the management of disorders of the extensor apparatus of the knee. The scientific evidence for intervention is explored and reports on outcome are discussed.