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Current surgical practices in total knee arthroplasty (TKA) have advanced and include significant changes and improvements in alignment philosophies, femorotibial implant conformities, and ligament management to replicate in vivo knee kinematics. While corrective measures have emphasized sagittal plane alignment to restore normal flexion-extension (F-E) motion and coronal plane ligament balance, internal-external (I-E) rotation kinematics in the axial plane have been largely neglected. Recent in vivo evidence indicates that the combination of factors necessary to closely restore native tibial rotation as the knee flexes and extends is kinematic alignment (KA), which resurfaces the patients pre-arthritic knee without releasing ligaments, an insert with medial 1:1 ball-in-socket conformity and a lateral flat surface, and posterior cruciate ligament (PCL) retention. However, the inherent anterior-posterior (A-P) stability provided by the medial 1:1 ball-in-socket limits the surgeons ability to select the correct insert thickness using manual laxity testing. Accordingly, this review presents the design and validation of an instrument called an insert goniometer that measures I-E tibial rotation for inserts that differ in thickness by 1 mm and uses rotation limits at extension and 90° flexion to select the optimal insert thickness. The optimal thickness is the one that provides the greatest external tibial orientation in extension and internal tibial orientation at 90° flexion without lift-off of the insert.

Purpose: Resecting the posterior cruciate ligament (PCL) increases posterior laxity and increases the flexion gap more than the extension gap in the native (i.e. healthy) knee. These two effects could lead to significant anterior displacement of the medial femoral condyle in kneeling following total knee arthroplasty even when using a tibial insert with a high degree of medial conformity. Using an insert with ball-in-socket medial conformity and a flat lateral articular surface, the primary purpose was to determine whether the medial femoral condyle remained stable with and without PCL retention during kneeling. Methods: Two groups of patients were studied, one with PCL retention (22 patients) and the other with PCL resection (25 patients), while kneeling at 90º flexion. Following 3D model-to-2D image registration, A-P displacements of both femoral condyles were determined relative to the dwell point of the medial socket. Results: With PCL resection versus PCL retention, the medial femoral condyle was 5.1 ± 3.7 mm versus 0.8 ± 2.1 mm anterior of the dwell point (p < 0.0001). Patient-reported function scores were comparable (p ≥ 0.1610) despite a significantly shorter follow-up of 7.8 ± 0.9 months with PCL retention than 19.6 ± 4.9 months with PCL resection (p < 0.0001). Range of motion was 126 ± 8° versus 122 ± 6° with and without PCL retention, respectively (p = 0.057). Conclusion: Surgeons that use a highly conforming tibial insert design can stabilize the medial femoral condyle during kneeling by retaining the PCL. In patients with PCL resection, the 9 mm high anterior lip of the insert with ball-in-socket medial conformity was insufficient to prevent significant anterior displacement of the medial femoral condyle when weight-bearing on the anterior tibia. [ABSTRACT FROM AUTHOR]

PURPOSE: In total knee arthroplasty (TKA) with posterior cruciate ligament (PCL) retention, the medial and lateral insert conformity that restores in vivo native (i.e., healthy) knee tibial rotation and high function without causing stiffness is unknown. The purpose was to determine whether a ball-in-socket (B-in-S) medially conforming (MC) and flat lateral insert implanted with unrestricted kinematic alignment (KA) TKA and PCL retention restores tibial rotation to native. METHODS: One group of 25 patients underwent unrestricted KA TKA with manual instruments. Another group of 25 patients had native knees. Single-plane fluoroscopy imaged each knee while patients performed step-up and chair rise activities. Following 3D model-to-2D image registration, anterior-posterior (A-P) positions of the femoral condyles were determined. Changes in A-P positions with flexion were used to determine tibial rotation. RESULTS: At maximum flexion, mean tibial rotations of KA TKA knees were comparable to native knees (Step up: 12.3° ± 4.4° vs. 13.1° ± 12.0°, p = 0.783; Chair Rise: 12.7° ± 6.2° vs. 12.6° ± 9.5º, p = 0.941). However, paths of rotation differed in that screw home motion was less evident in KA TKA knees. At 8 months follow-up, the median Forgotten Joint Score was 69 points (range 65 to 85), the median Oxford Knee Score was 43 points (range 40 to 46), and mean knee flexion was 127º ± 8°. CONCLUSIONS: The ball-in-socket medial, flat lateral insert and PCL retention implanted with unrestricted KA TKA restored in vivo native knee tibial rotation at maximum flexion for each activity and high function without stiffness. Providing high A-P stability, this implant design might benefit patients desiring to return to demanding work and recreational activities. LEVEL OF EVIDENCE: Therapeutic - Level II.

PurposeBecause different targets are used for internal-external rotation, an asymmetric baseplate designed for mechanical alignment may lead to under-coverage and concomitant posterior rim loading in the lateral compartment following unrestricted kinematic alignment (KA) TKA. Recognizing that such loading can lead to premature wear and/or subsidence, our aim was to determine the cause(s) so that occurrence could be remedied. Our hypothesis was that baseplate design features such as asymmetric shape when aligned in KA would consistently contribute to posterior rim loading in the lateral compartment.MethodsBased on analysis of fluoroscopic images of 50 patients performing dynamic, weight bearing deep knee bend and step up and of postoperative CT images, five possible causes were investigated. Causes included internal rotation of the baseplate when positioned in KA; posterior position of the lateral femoral condyle at extension; internal tibial rotation with flexion; internal rotational deviation of the baseplate from the KA rotation target; and posterior slope.ResultsThe incidence of posterior rim loading was 18% (9 of 50 patients). When positioned in KA, the asymmetric baseplate left 15% versus 10% of the AP depth of the lateral compartment uncovered posteriorly for posterior rim loading and non-posterior rim loading groups, respectively (p = 0.009). The lateral femoral condyle at extension was more posterior by 4 mm for the posterior rim loading group (p = 0.003).ConclusionsPosterior rim loading in the lateral compartment was caused in part by the asymmetric design of the tibial baseplate designed for mechanical alignment which was internally rotated when positioned in KA thus under-covering a substantial percentage of the posterior lateral tibia. This highlights the need for new, asymmetric baseplates designed to maximize coverage when used in KA.Level of evidenceIII.

This paper introduces a method for measuring 3D tibiofemoral kinematics using a multi-channel A-mode ultrasound system under dynamic conditions. The proposed system consists of a multi-channel A-mode ultrasound system integrated with a conventional motion capture system (i.e., optical tracking system). This approach allows for the non-invasive and non-radiative quantification of the tibiofemoral joint's six degrees of freedom (DOF). We demonstrated the feasibility and accuracy of this method in the cadaveric experiment. The knee joint's motions were mimicked by manually manipulating the leg through multiple motion cycles from flexion to extension. To measure it, six custom ultrasound holders, equipped with a total of 30 A-mode ultrasound transducers and 18 optical markers, were mounted on various anatomical regions of the lower extremity of the specimen. During experiments, 3D-tracked intra-cortical bone pins were inserted into the femur and tibia to measure the ground truth of tibiofemoral kinematics. The results were compared with the tibiofemoral kinematics derived from the proposed ultrasound system. The results showed an average rotational error of 1.51 ± 1.13° and a translational error of 3.14 ± 1.72 mm for the ultrasound-derived kinematics, compared to the ground truth. In conclusion, this multi-channel A-mode ultrasound system demonstrated a great potential of effectively measuring tibiofemoral kinematics during dynamic motions. Its improved accuracy, nature of non-invasiveness, and lack of radiation exposure make this method a promising alternative to incorporate into gait analysis and prosthetic kinematic measurements later. [ABSTRACT FROM AUTHOR]

Introduction: Previous reports using cadaveric knees and musculoskeletal computer simulation have shown that kinematically aligned (KA) total knee arthroplasty (TKA) provides more natural and physiological tibiofemoral kinematic patterns than mechanically aligned (MA) TKA. These reports suggested that the modification of joint line obliquity improve the knee kinematics. This study aimed to determine whether joint line obliquity change the intraoperative tibiofemoral kinematics in TKA candidates with knee osteoarthritis. Methods: Thirty consecutive knees with varus osteoarthritis that underwent TKA using a navigation system were evaluated. Two types of trial components were prepared: (1) MA TKA model: component trial in which articulating surface was parallel to the bone cut surface (2) KA TKA model: the femoral component trial, which mimicked the KA TKA method of Dossett et al. was designed 3° valgus and 3° internal rotation to the femoral bone cut surface, and the tibial component trial was designed 3° varus to the tibial bone cut surface. These two trials were set on the same knees during the operation, and the tibiofemoral rotational kinematics and varus–valgus laxity were measured from 0° to 120° of knee flexion using a navigation system. Results: The joint gap was 20 ± 2 mm and 3° ± 1° varus in extension and 20 ± 2 mm and 3° ± 1°varus in flexion. The differences in femoral component rotation between KA TKA and MA TKA were not statistically significant for any knee flexion angle. The differences in varus–valgus laxity between KA TKA and MA TKA were also not statistically significant for any knee flexion angle. Conclusion: Although the degree of joint line obliquity varies widely in various KA TKA methods, this study, which mimicked the method of Dossett et al. showed that the modification of joint line obliquity did not change the tibiofemoral kinematics and stability of the knee joint in TKA candidates with knee osteoarthritis. [ABSTRACT FROM AUTHOR]

Purpose : For a new tibial insert design with ball-in-socket (B-in-S) medial conformity (MC), posterior cruciate ligament (PCL) retention, and flat lateral articular surface (B-in-S MC + PCL), this study determined whether internal tibial rotation and knee flexion were limited and clinical outcome scores were lower during weight-bearing activities relative to an insert with intermediate (I) (i.e., less than ball-in-socket) medial conformity (I MC + PCL). Methods: Twenty-five patients were treated with bilateral unrestricted, caliper-verified kinematic alignment (KA) total knee arthroplasty (TKA) with an I MC + PCL insert and B-in-S MC + PCL insert in opposite knees. Each patient performed weight-bearing deep knee bend, step up, and chair rise under single-plane fluoroscopy. Analysis following 3D model-to-2D image registration determined internal tibial rotation. For each TKA, knee flexion was measured and patients completed clinical outcome scoring questionnaires. Results: Internal tibial rotation did not differ between conformities during chair rise and step up (p = 0.3419 and 0.1030, respectively). During deep knee bend, internal tibial rotation between 90° and maximum flexion was 3° greater in the B-in-S MC + PCL group (18° vs 15°) (p = 0.0290). Mean knee flexion (p = 0.3115) and median Forgotten Joint Score (FJS), Oxford Knee Score (OKS), and Western Ontario and McMasters Universities Arthritis Index (WOMAC) scores (p = 0.2100, 0.2154, and 0.4542, respectively) did not differ between conformities. Conclusion: An insert with ball-in-socket medial conformity, which maximizes anteroposterior (AP) stability, did not limit internal tibial rotation and knee flexion and did not lower patient-reported outcomes when implanted with unrestricted caliper-verified KA and PCL retention. The high AP stability provided by the medial ball-in-socket might interest those surgeons exploring the treatment of the active patient with a desire to return to high-level and athletic activities. [ABSTRACT FROM AUTHOR]

Abstract Purpose In total knee arthroplasty (TKA) with posterior cruciate ligament (PCL) retention, the medial and lateral insert conformity that restores in vivo native (i.e., healthy) knee tibial rotation and high function without causing stiffness is unknown. The purpose was to determine whether a ball‐in‐socket (B‐in‐S) medially conforming (MC) and flat lateral insert implanted with unrestricted kinematic alignment (KA) TKA and PCL retention restores tibial rotation to native. Methods One group of 25 patients underwent unrestricted KA TKA with manual instruments. Another group of 25 patients had native knees. Single‐plane fluoroscopy imaged each knee while patients performed step‐up and chair rise activities. Following 3D model‐to‐2D image registration, anterior–posterior (A‐P) positions of the femoral condyles were determined. Changes in A‐P positions with flexion were used to determine tibial rotation. Results At maximum flexion, mean tibial rotations of KA TKA knees were comparable to native knees (Step up: 12.3° ± 4.4° vs. 13.1° ± 12.0°, p = 0.783; Chair Rise: 12.7° ± 6.2° vs. 12.6° ± 9.5º, p = 0.941). However, paths of rotation differed in that screw home motion was less evident in KA TKA knees. At 8 months follow‐up, the median Forgotten Joint Score was 69 points (range 65 to 85), the median Oxford Knee Score was 43 points (range 40 to 46), and mean knee flexion was 127º ± 8°. Conclusions The ball‐in‐socket medial, flat lateral insert and PCL retention implanted with unrestricted KA TKA restored in vivo native knee tibial rotation at maximum flexion for each activity and high function without stiffness. Providing high A‐P stability, this implant design might benefit patients desiring to return to demanding work and recreational activities. Level of evidence Therapeutic – Level II.

Knowledge of anterior–posterior (AP) movement of the femoral condyles on the tibia in healthy knees serves to assess whether an artificial knee restores natural movement. Two methods for identifying AP positions and hence condylar movements include: (1) the flexion facet center (FFC) and (2) the lowest point (LP) methods. The objectives were to determine (1) agreement between the two methods and (2) whether addition of articular cartilage and/or smoothing significantly affects AP positions. Magnetic resonance (MR) images of healthy knees were obtained from eleven subjects, who subsequently performed a dynamic, weight-bearing deep knee bend under fluoroscopy. Four different types of MR models of the distal femur were created: femur, smoothed femur, femur with articular cartilage, and femur with smoothed articular cartilage. In the medial and lateral compartments for the femur with smoothed articular cartilage at 0 deg flexion, mean AP positions of the LPs were 7.7 mm and 5.4 mm more anterior than those of the FFCs, respectively (p < 0.0001, p = 0.0002) and limits of agreement were ±5.5 mm. In the flexion range 30 deg to 90 deg, differences in mean AP positions were 1.5 mm or less and limits of agreement were bounded by ±2.4 mm. Differences in mean AP positions between model types were <1.3 mm for both LPs and FFCs. Since omitting articular cartilage from three-dimensional (3D) models of the femur minimally affected AP positions, faster and less expensive imaging techniques such as computed-tomography (CT) can be used to generate 3D bone models for kinematic analysis. In addition, the LP method is preferred over the FFC method because of its inherent accuracy in indicating the AP position of the instant center of curvature of the femoral condyles which varies with the knee in extension versus flexion. [ABSTRACT FROM AUTHOR]

Background: Anterior cruciate ligament (ACL) injury can lead to changes in tibiofemoral kinematics during gait, but the detailed short-term kinematic changes after ACL injury are still unknown. Purpose: To measure tibiofemoral kinematics during gait in ACL-deficient (ACLD) knees over time after ACL injury. Study Design: Controlled laboratory study. Methods: The authors categorized 76 patients with unilateral ACLD knees into 4 groups based on the time from injury: <3 months (group 1), 3 to 6 months (group 2), >6 to 12 months (group 3), and >12 months (group 4). The controls were 20 participants with ACL-intact knees. Changes in the knee kinematics and range of motion during gait were compared among ACLD groups and those with ACL-intact knees. Results: Compared with controls, the range of motion of flexion in group 1 was significantly lower (6°; P =.033), and the mean knee flexion was significantly increased (0.7°-3.4°) in groups 1 to 4 (all P ≤.004). There was more internal tibial rotation (2.9°-4.3°) in group 1 and 2, and more anterior tibial translation (4.3 mm) in group 1 during the stance or swing phases than in controls (P ≤.049 for all). The mean internal tibial rotation and anterior tibial translation significantly decreased from group 1 to group 4 (P <.001 for both). Compared with controls, the mean medial tibial translation was significantly greater (1.2-2.5 mm) in all groups, and more medial tibial translations (2.4-3.7 mm) were observed during the stance phase in groups 1, 3, and 4 (P ≤.047 for all). Conclusion: ACLD knees displayed a motion impairment walking strategy within 3 months, and a higher-flexion walking strategy increased with time after injury. Excessive anterior translation and internal rotation of the tibia tended to return to normal, while excessive medial translation of the tibia increased in ACLD knees after 6 months postinjury. These results may provide new insight into the compensatory mechanisms and risk factors for premature osteoarthritis in ACLD knees. [ABSTRACT FROM AUTHOR]

Accurate knowledge of knee joint motion is needed to evaluate the effects of implant design on functional performance and component wear. We conducted a randomized controlled trial to measure and compare 6‐degree‐of‐freedom (6‐DOF) kinematics and femoral condylar motion of posterior‐stabilized (PS), cruciate‐retaining (CR), and medial‐stabilized (MS) knee implant designs for one cycle of walking. A mobile biplane X‐ray imaging system was used to accurately measure 6‐DOF tibiofemoral motion as patients implanted with PS (n = 23), CR (n = 25), or MS (n = 26) knees walked over ground at their self‐selected speeds. Knee flexion angle did not differ significantly between the three designs. Relative movements of the femoral and tibial components were generally similar for PS and CR with significant differences observed only for anterior tibial drawer. Knee kinematic profiles measured for MS were appreciably different: external rotation and abduction of the tibia were increased while peak‐to‐peak anterior drawer was significantly reduced for MS compared with PS and CR. Anterior‐posterior drawer and medial‐lateral shift of the tibia were strongly coupled to internal‐external rotation for MS, as was anterior‐posterior translation of the contact center in the lateral compartment. MS exhibited the least amount of paradoxical anterior translation of the femur relative to the tibia during knee flexion. The joint center of rotation in the transverse plane was located in the lateral compartment for PS and CR and in the medial compartment for MS. Substantial differences were evident in 6‐DOF knee kinematics between the healthy knee and all three prosthetic designs. Overall, knee kinematic profiles observed for MS resemble those of the healthy joint more closely than PS and CR. [ABSTRACT FROM AUTHOR]

This study is to compare the knee kinematic measurements between the novel portable skin marker-based motion analysis system (Opti-Knee®) and a conventional system (Vicon®). Nineteen subjects were recruited and asked to perform stair descent with lower limb placed with skin markers. Knee kinematic data was computed from the trajectories of the skin markers. Pearson's correlation coefficient and Root-mean-square deviation (RMSD) were used to analyse the data. For the waveform, sagittal plane rotation is strongly positive correlated between systems, while for axial and coronal plane rotation, it was moderately to strongly positive correlated in both normal (ACLN) and ACL-deficient (ACLD) group. Substantial difference between two groups was found in correlation of abduction/adduction in both stance and swing phase, as well as in external/internal rotation in all selected regions of interest. Moreover, the RMSD was larger in ACLN than in ACLD in three planes of rotation. The capability of Opti-Knee® in tracking lower limb sagittal plane rotation was comparable to Vicon®. However, for coronal and axial plane rotation, although the correlation to Vicon® in kinematic waveforms was moderately high, their ROM and peak values substantially deviated from the values in Vicon®. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the technical feasibility of measuring relative positions and orientations of the tibia with respect to the femur in an in-vitro experiment by using a 3D-tracked A-mode ultrasound system and to determine its accuracy of angular and translational measurements. As A-mode ultrasound is capable of detecting bone surface through soft tissue in a non-invasive manner, the combination of a single A-mode ultrasound transducer with an optical motion tracking system provides the possibility for digitizing the 3D locations of bony points at different anatomical regions on the thigh and the shank. After measuring bony points over a large area of both the femur and tibia, the bone models of the femur and tibia that were segmented from CT or MRI images were registered to the corresponding bony points. Then the relative position of the tibia with respect to the femur could be obtained and the angular and translational components could also be measured. A cadaveric experiment was conducted to assess its accuracy compared to the reference measurement obtained by optical markers fixed to intra-cortical bone pins placed in the femur and tibia. The results showed that the ultrasound system could achieve 0.49 ± 0.83°, 0.85 ± 1.86° and 1.85 ± 2.78° (mean ± standard deviation) errors for Flexion–Extension, Adduction–Abduction and External–Internal rotations, respectively, and −2.22 ± 3.62 mm, −2.80 ± 2.35 mm and −1.44 ± 2.90 mm errors for Anterior–Posterior, Proximal–Distal and Lateral–Medial translations, respectively. It was concluded that this technique is feasible and facilitates the integration of arrays of A-mode ultrasound transducers with an optical motion tracking system for non-invasive dynamic tibiofemoral kinematics measurement. [ABSTRACT FROM AUTHOR]

Introduction: Lateral retinacular release (LRR) is a common procedure during total knee arthroplasty (TKA), especially if patellar maltracking is observed intraoperatively. The impact of LRR on patellofemoral kinematics is well-examined, but the influence on femorotibial kinematics requires more elucidation. Therefore, the aim of this study was to evaluate the effects of LRR on femorotibial kinematics in vitro.Materials and Methods: A fixed bearing TKA was implanted in six human knee specimens. Femorotibial kinematics were measured dynamically through the use of a custom-constructed knee rig which flexes the knee from 20° to 120° under weight bearing conditions. Measurements were performed before and after LRR. LRR was performed completely including transection of synovium, retinaculum and tractus fibers. For the registration of tibiofemoral kinematics a 3-dimensional-ultrasound-based motion analysis system was used.Results: LRR revealed a significant reduction of femoral rollback at the lateral compartment (9.4 ± 5.0 vs 7.8 ± 9.4 mm; p < 0.01), whereas the present decrease of femoral rollback at the medial compartment was not significant (3.4 ± 4.7 vs 2.3 ± 5.9 mm; p = 0.34). Accordingly, LRR significantly reduced internal rotation of the tibia (0.8°; p < 0.01).Conclusion: The results suggest that LRR significantly decreases lateral femoral rollback as well as internal rotation of the tibia, probably by changing the tension of the iliotibial band. When performing a LRR in clinical routine, surgeons should be aware of altering not only patellofemoral kinematics but also the femorotibial kinematics. [ABSTRACT FROM AUTHOR]

We investigated the effects of isolated meniscectomy on tibiofemoral skeletal kinematics and cartilage contact arthrokinematics in vivo . We recruited nine patients who had undergone isolated medial or lateral meniscectomy, and used a dynamic stereo-radiography (DSX) system to image the patients’ knee motion during decline walking. A volumetric model-based tracking process determined 3D tibiofemoral kinematics from the recorded DSX images. Cartilage contact arthrokinematics was derived from the intersection between tibial and femoral cartilage models co-registered to the bones. The kinematics and arthrokinematics were analyzed for early stance and loading response phase (30% of a gait cycle), comparing the affected and intact knees. Results showed that four patients with medial meniscectomy had significantly greater contact centroid excursions in the meniscectomized medial compartments while five patients with lateral meniscectomy had significantly greater cartilage contact area and lateral shift of contact centroid path in the meniscectomized lateral compartments, comparing to those of the same compartments in the contralateral intact knees. No consistent difference however was identified in the skeletal kinematics. The current study demonstrated that cartilage-based intra-articular arthrokinematics is more sensitive and insightful than the skeletal kinematics in assessing the meniscectomy effects. [ABSTRACT FROM AUTHOR]

Background: Although retaining the posterior cruciate ligament (PCL) is advantageous in unrestricted kinematically aligned TKA, it is often excised with a medial stabilized implant. The primary objectives were to determine whether PCL retention using an insert with ball-in-socket (B-in-S) medial conformity to maximize A-P stability promotes internal tibial rotation and flexion while providing high patient-reported outcome scores., Methods: Two cohorts of 25 patients each were treated with unrestricted kinematically aligned (KA) TKA using a tibial insert with B-in-S medial conformity and a flat lateral articular surface. One cohort retained the PCL; the other had it excised. Patients performed deep knee bend and step-up exercises during fluoroscopic imaging. Following 3D model-to-2D image registration, anterior-posterior (A-P) positions of the femoral condyles and tibial rotation were determined., Results: For deep knee bend, mean internal tibial rotation with PCL retention was significantly greater at maximum flexion (17.7° ± 5.7° versus 10.4° ± 6.5°, p < 0.001) and significantly greater at 30°, 60°, and 90° flexion as well (p ≤ 0.0283). For step-up, mean internal tibial rotation with PCL retention was significantly greater at at 15°, 30°, and 45° flexion (p ≤ 0.0049) but was marginally not significantly greater at 60° (i.e. maximum) flexion (12.3° ± 4.4° versus 10.1° ± 5.4°, p = 0.0794). Mean flexion during active knee flexion with PCL retention was significantly greater (127° ± 8° versus 122° ± 6°, p = 0.0400). Both cohorts had high median Oxford Knee, WOMAC, and Forgotten Joint Scores that were not significantly different (p = 0.0918, 0.1448, and 0.0855, respectively) CONCLUSION: Surgeons that perform unrestricted KA TKA should retain the PCL with an insert that has B-in-S medial conformity, as this maintains extension and flexion gaps while also promoting internal tibial rotation and knee flexion as well as providing high clinical outcome scores., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: S.M. Howell is a paid consultant for Medacta and receives royalties from Medacta. M. L. Hull receives research support from Medacta USA, Inc and the Orthopaedic Research and Education Foundation. He is also on the Editorial Board of the Journal of Biomechanics. Ed O’Donnell holds stock in Novocare., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Quantification of clinically meaningful tibiofemoral motions requires a joint coordinate system (JCS) with motions free from kinematic crosstalk errors. The objectives were to use a JCS with literature-backed functional axes (FUNC) and a JCS recommended by the International Society of Biomechanics (ISB) to determine tibiofemoral kinematics of the native (i.e., healthy) knee, determine variability associated with each JCS, and determine whether the FUNC JCS significantly reduced kinematic crosstalk errors compared to the ISB JCS. Based on a kinematic model consisting of a three-cylindric joint chain, the FUNC JCS included functional flexion-extension (F-E) and internal-external (I-E) tibial rotation axes. In contrast, the ISB JCS included F-E and I-E axes defined using anatomic landmarks. Single-plane fluoroscopic images in 13 subjects performing a weighted deep knee bend were analyzed. Tibiofemoral kinematics using the FUNC JCS fell within the physiological range of motion in all six degrees-of-freedom. Internal tibial rotation averaged 13 deg for the FUNC JCS versus 10 deg for the ISB JCS and motions in the other four degrees-of-freedom (collectively termed off-axis motions) were minimal as expected based on biomechanical constraints. Off-axis motions for the ISB JCS were significantly greater; maximum valgus rotation was 4 deg and maximum anterior and distraction translations were 9 mm and 25 mm, respectively, which is not physiologic. Variabilities in off-axis motions were significantly greater with the ISB JCS (p < 0.0002). The FUNC JCS achieved clinically meaningful kinematics by significantly reducing kinematic crosstalk errors and is the more suitable coordinate system for quantifying tibiofemoral motions., (Copyright © 2023 by ASME.)

Purpose: Although controversy still remains, isolated patellofemoral arthroplasty recently gained in popularity as a treatment option for patellofemoral osteoarthritis. It has compared to total knee arthroplasty the advantage of preserving the tibiofemoral articulation, which in theory would allow the preservation of natural tibiofemoral kinematics. Today, however, no data exist to support this assumption. This study was therefore performed in order to investigate the effect of isolated patellofemoral arthroplasty on the native three-dimensional tibiofemoral kinematic behaviour and whether a change in patellar thickness would have an influence. Methods: Six fresh-frozen cadavers were fixed on a custom-made mechanical knee rig. Full 3D kinematics was analysed during passive flexion-extension cycles, open chain extension, with and without mechanical resistance, as well as deep knee squats, using infrared motion capture cameras and retroflective markers. Measurements were taken for the native knee and after prosthetic trochlear resurfacing with and without patellar resurfacing in three different patellar thicknesses. Results: Compared to the natural knee, patellofemoral arthroplasty resulted in significant changes in tibiofemoral kinematics, which were most pronounced in the most loaded motor tasks. Increased internal tibial rotation was noted in the mid- and high flexion ranges, reaching at 120° of flexion a mean difference of 4.5° ± 4.3° ( p < 0.0001) during squat motion, over the whole flexion range during open chain motion and in deeper flexion beyond 50° (mean at 70°, 1.9° ± 3.7°) during resisted open chain. During squats, also, a more posterior translation of the lateral femoral condyle was observed. The effect was accentuated in case of patella overstuffing, whereas kinematics was closer to normal with patellar thinning. Conclusion: Isolated patellofemoral arthroplasty alters natural tibiofemoral kinematics, and the effects become more pronounced in case of increased patellar thickness. Therefore, it might be recommended to aim for a slight over-resection of patellar bone if sufficient bone stock is available. [ABSTRACT FROM AUTHOR]

This manuscript presents a new subject-specific musculoskeletal dynamic modeling approach that integrates high-accuracy dynamic stereo-radiography (DSX) joint kinematics and surface-based full-body motion data. We illustrate this approach by building a model in OpenSim for a patient who participated in a meniscus transplantation efficacy study, incorporating DSX data of the tibiofemoral joint kinematics. We compared this DSX-incorporated (DSXI) model to a default OpenSim model built using surface-measured data alone. The architectures and parameters of the two models were identical, while the differences in (time-averaged) tibiofemoral kinematics were of the order of magnitude of 10° in rotation and 10 mm in translation. Model-predicted tibiofemoral compressive forces and knee muscle activations were compared against literature data acquired from instrumented total knee replacement components (Fregly et al., 2012) and the patient's EMG recording. The comparison demonstrated that the incorporation of DSX data improves the veracity of musculoskeletal dynamic modeling. [ABSTRACT FROM AUTHOR]

Abstract: This study assessed the accuracy of surface-measured OpenSim-derived tibiofemoral kinematics in functional activities. Ten subjects with unilateral, isolated grade II PCL deficiency performed level running and stair ascent. A dynamic stereo radiography (DSX) system and a Vicon motion capture system simultaneously measured their knee or lower extremity movement. Surface marker motion data from the Vicon system were used to create subject-specific models in OpenSim and derive the tibiofemoral kinematics. The surface-measured model-derived tibiofemoral kinematics in all six degrees of freedom (DOFs) were then compared with those measured by the DSX as the benchmarks. The differences between surface- and DSX-measured tibiofemoral kinematics were found to be substantial: the overall mean (±SD) RMS differences during running were 9.1±3.2°, 2.0±1.2°, and 6.4±4.5° for the flexion–extension, abduction–adduction, and internal–external rotations, respectively, and 7.1±3.2mm, 8.8±3.7mm, and 1.9±1.2mm for anterior–posterior, proximal–distal, and medial–lateral translations, respectively. The differences were more pronounced in relatively higher speed running than in stair ascent. It was also found that surface-based measures significantly underestimated the mean as well as inter-subject variability of the differences between PCL-injured and intact knees in abduction–adduction, internal–external rotations, and anterior–posterior translation. [Copyright &y& Elsevier]

Abstract: The purpose of our study was to test the hypothesis that when a shear force was applied posteriorly to the loaded knee in vivo, there would be no relative motion between the tibia and the medial femoral condyle. Siemens 7Tesla high-resolution MRI machine was used to scan eight healthy male volunteers with the knee at 15° of flexion. Two scans were obtained: the first with a compressive force of 660N along the tibial long axis and a second with the compressive force and a posterior shear force of 36N applied to the tibia. Solid models were created of the femur, tibia, and menisci for both loading conditions. The tibial models were superimposed enabling the displacements of the femur and menisci to be determined, relative to a fixed tibia. On average, the lateral femoral condyle displaced anteriorly by 0.66mm but the medial femoral condyle displaced posteriorly by 0.36mm. This indicated an axial rotation with a center between the lateral and medial condyles, but closer to the medial. The menisci displaced with the femoral condyles, but there was no indication that the medial meniscus was contributing to the pivoting action. This study supported the concept of medial anterior–posterior stability under weight-bearing conditions, but with structures other than the medial meniscus providing the stability. This study has application to the treatment of knee injuries and to knee arthroplasty design. [Copyright &y& Elsevier]

Abstract: This study investigated passive translational and rotational stability properties of the intact knee joint, after bicruciate-retaining bi-compartmental knee arthroplasty (BKA) and after posterior cruciate retaining total knee arthroplasty (TKA). Fourteen human cadaveric knee specimens were used in this study, and a robotic manipulator with six-axis force/torque sensor was used to test the joint laxity in anterior–posterior translation, valgus–varus, and internal–external rotation. The results show the knee joint stability after bicruciate-retaining BKA is similar to that of the native knee. On the other hand, the PCL-retaining TKA results in inferior joint stability in valgus, varus, external rotation, anterior and, surprisingly, posterior directions. Our findings suggest that, provided functional ligamentous structures, bicruciate-retaining BKA is a biomechanically attractive treatment for joint degenerative disease. [Copyright &y& Elsevier]

Background: Tibial tuberosity realignment surgery is performed to improve patellofemoral alignment, but it could also alter tibiofemoral kinematics.Hypothesis: After tuberosity realignment in the malaligned knee, the reoriented patellar tendon will pull the tuberosity back toward the preoperative position, thereby altering tibiofemoral kinematics.Study Design: Controlled laboratory study.Methods: Ten knees were tested at 40°, 60°, and 80° of flexion in vitro. The knees were loaded with a quadriceps force of 586 N, with 200 N divided between the medial and lateral hamstrings. The position of the tuberosity was varied to represent lateral malalignment, with the tuberosity 5 mm lateral to the normal position; tuberosity medialization, with the tuberosity 5 mm medial to the normal position; and tuberosity anteromedialization, with the tuberosity 10 mm anterior to the medial position. Tibiofemoral kinematics were measured using magnetic sensors secured to the femur and tibia. A repeated measures analysis of variance with a post hoc Student-Newman-Keuls test was used to identify significant (P < .05) differences in the kinematic data between the tuberosity positions at each flexion angle.Results: Medializing the tibial tuberosity primarily rotated the tibia externally compared with the lateral malalignment condition. The largest average increase in external rotation was 13° at 40° of flexion, with the increase significant at each flexion angle. The varus orientation also increased significantly by an average of 1.5° at 40° and 80°. The tibia shifted significantly posteriorly at 40° and 60° by an average of 4 mm and 2 mm, respectively. Shifting the tuberosity from the medial to the anteromedial position translated the tibia significantly posteriorly by an average of 2 mm at 40°.Conclusion: After tibial tuberosity realignment in the malaligned knee, the altered orientation of the patellar tendon alters tibiofemoral kinematics.Clinical Relevance: The kinematic changes reduce the correction applied to the orientation of the patellar tendon and could alter the pressure applied to tibiofemoral cartilage. [ABSTRACT FROM AUTHOR]

Background: The actual in vivo tibiofemoral and patellofemoral kinematics of the posterior cruciate ligament (PCL)-reconstructed knee joint are unknown. Hypothesis: Current single-bundle PCL reconstruction is unable to correct the abnormal tibiofemoral and patellofemoral kinematics caused by rupture of the ligament. Study Design: Controlled laboratory study/case series; Level of evidence, 4. Methods: Seven patients with an isolated PCL injury in 1 knee and the contralateral side intact were included in the study. Magnetic resonance and dual fluoroscopic imaging techniques were used to compare the tibiofemoral and patellofemoral kinematics between the intact contralateral (control group), PCL-deficient, and PCL-reconstructed knee during physiologic loading with a single-legged lunge. Data were collected preoperatively and 2 years after single-bundle reconstruction. Results: The PCL reconstruction reduced the abnormal posterior tibial translation in PCL-deficient knees to levels not significantly different from those of the intact knee. Posterior cruciate ligament deficiency resulted in an increased lateral tibial translation between 75° and 120° of flexion, and reconstruction was unable to restore these values to normal. No differences were detected among the groups in varus-valgus and internal-external rotation. The PCL reconstruction reduced the increased patellar flexion of PCL-deficient knees between 90° and 120° of knee flexion and the lateral shift at 120°. The abnormal patellar rotation and tilt seen in PCL deficiency at flexion angles of 75° and greater persisted after reconstruction. Conclusion: Single-bundle PCL reconstruction was successful in restoring normal anteroposterior translation of the tibia, as well as the patellar flexion and shift. However, single-bundle PCL reconstruction was unable to achieve the same success in mediolateral translation of the tibia or in the patellar rotation and tilt. Clinical Relevance: The persistent abnormal mediolateral translation of the tibia, as well as decreased patellar rotation and tilt, provide a possible explanation for the development of cartilage degeneration after reconstruction of an isolated PCL injury. [ABSTRACT FROM AUTHOR]

Abstract: This study determined in-vitro anterior cruciate ligament (ACL) force patterns and investigated the effect of external tibial loads on the ACL force patterns during simulated weight-bearing knee flexions. Nine human cadaveric knee specimens were mounted on a dynamic knee simulator, and weight-bearing knee flexions with a 100N of ground reaction force were simulated; while a robotic/universal force sensor (UFS) system was used to provide external tibial loads during the movement. Three external tibial loading conditions were simulated, including no external tibial load (termed BW only), a 50N anterior tibial force (ATF), and a 5Nm internal rotation tibial torque (ITT). The tibial and femoral kinematics was measured with an ultrasonic motion capture system. These movement paths were then accurately reproduced on a robotic testing system, and the in-situ force in the ACL was determined via the principle of superposition. The results showed that the ATF significantly increased the in-situ ACL force by up to 60% during 0–55° of flexion, while the ITT did not. The magnitude of ACL forces decreased with increasing flexion angle for all loading conditions. The tibial anterior translation was not affected by the application of ATF, whereas the tibial internal rotation was significantly increased by the application of ITT. These data indicate that, in a weight-bearing knee flexion, ACL provides substantial resistance to the externally applied ATF but not to the ITT. [Copyright &y& Elsevier]

Background: The aim of anterior cruciate ligament reconstruction is to reduce excess joint laxity, hoping to restore normal tibiofemoral kinematics and therefore improve joint stability. It remains unclear if successful ACL reconstruction restores normal tibiofemoral kinematics and whether it is this that is associated with a good result. Study: Case series. Purpose: To assess the kinematics of the anterior cruciate ligament_reconstructed knee using open-access MRI. Methods: Tibiofemoral motion was assessed using open-access MRI, weightbearing through the arc of flexion from 0° to 900° in 10 patients with isolated reconstruction of the anterior cruciate ligament (hamstring autograft) in one knee and a normal contralateral knee. Midmedial and midlateral sagittal images were analyzed in all positions of flexion in both knees to assess the tibiofemoral relationship. Sagittal laxity was also assessed by performing the Lachman test while the knees were scanned dynamically using open-access MRI Results: The amount of excursion between the tibial and femoral joint surfaces was similar between the normal and reconstructed knees, but the relationship of tibia to femur was always different for each position of knee flexion assessed-the lateral tibia being about 5 mm more anterior in the anterior cruciate ligament-reconstructed knees. This anterior tibial position is statistically significantly different at 00 (P < .0006), 20° (P = .0004), 450 (P = .002), and 900 of flexion (P < .006). Anteroposterior laxity was similar between normal and anterior cruciate ligament-reconstructed knees. Conclusion: Anterior cruciate ligament reconstruction reduces sagittal laxity to within normal limits but does not restore normal tibiofemoral kinematics despite a successful outcome. [ABSTRACT FROM AUTHOR]

The complexity of human tibiofemoral joint motion is now better understood with the advancement of new methodologies to measure tibiofemoral kinematics in vivo. Marker clusters anchored to stainless steel bone pins inserted directly into the femur and tibia provide the most sensitive and accurate means for directly measuring skeletal tibiofemoral joint motion. Despite its invasiveness, this technique has been successful, although complications have been reported with the femoral pin and its insertion site. The purpose of this technical report is twofold: to review the difficulties with the femoral pin and its insertion site from a historical perspective, and to identify the load force required from biological tissue to permanently deform the pin. In addition, proposals in the advancement of this method are discussed in the context of reducing impingement with the femoral pin and the Iliotibial band. Because stainless steel exhibits plastic behaviour with no sharp yield point, Apex self-drilling/self-tapping bone pins underwent incremental loading on an Instron materials testing machine. Loads were transmitted perpendicular to the pin with the threads partially exposed and fully secured in vice. Since the accuracy of our combined stereophotogrammetry and Optoelectric motion analysis was less than 0.4 mm, it was decided that plastic deformation occurred after deflections of 0.4 mm. With exposed threads, deflections larger than 0.4 mm were observed at 150 N and 100 N when loads were applied at 15 mm and 20 mm from the vice (representative of where the tissue came in contact with the pin). Loads greater than 200 N produced deflections less than 0.2 mm when threads were fully inserted. The 90 Hz resonant frequency for the marker cluster-bone pin complex is beyond the spectrum of human movement and can be lowpass filtered. To reduce impingement and pin bending, one solution may be to implant pins with a shorter threaded section. By completely penetrating the bone, only the smooth surface of the pin is exposed which is more resistant to bending. Otherwise pins with larger diameters and longer longitudinal incisions about the femoral insertion site are an alternative. Lengthening the longitudinal incisions about the insertion site, and correctly aligning and inserting the femoral pin between the Iliotibial band and quadriceps tendon may diminish impingement. Performing dynamic open chain flexion and extension movements while on the operating table may aid in aligning the pin at the incision site. This may stretch the IT band and quadriceps tendon and may guide the femoral pin into a more optimal position prior to it being inserted into the cortex of the bone. [ABSTRACT FROM AUTHOR]

Objective. To determine whether knee flexion influenced bony contact movements during flexion.Design. Accurate three-dimensional (3D) measurements of tibiofemoral bony contact points in vivo was performed using magnetic resonance imaging technology at 0°, 30° and 60° of flexion.Background. Magnetic resonance imaging is an accurate non-invasive tool for visualizing muscles, tendons, and bone, and provides precise 3D co-ordinates.Methods. Magnetic resonance imaging recordings were made from the right knee of 16 subjects with no history of knee dysfunction at 0°, 30° and 60° of flexion. Joint contact movements were reported as changes of the contact point''s position on the medial and lateral tibial condyle with respect to a fixed reference point for each flexion angle.Results. The dominant motion of the centroid of the contact area was posterior with a concomitant inferior and lateral displacement when flexing from 0–30°. Increased flexion to 60° the contact points moved slightly anterior, superior and continued laterally. Comparing movements between the medial and lateral compartments, larger displacement magnitudes were observed laterally. Additionally, tibial rotations of 3–5° were noted relative to the femur.Conclusion. Based on magnetic resonance imaging co-ordinates and the rotated anatomical reference frame, the geometric equations to derive the contact point between the tibiofemoral articulating surfaces is a viable means to investigate tibiofemoral bony contact movement.RelevanceContact areas and pressure distributions have been reported using cadaveric specimens but interpretation of the results is limited. Other investigations have been restricted to sagittal plane movement. Using kinematic magnetic resonance imaging, accurate non-invasive 3D recordings of the normal knee at increments of flexion are possible. The normative baseline date can be compared against that of the pathological knee, such as cruciate ligament injury or the status of post-operative meniscectomy in order to examine skeletal joint motion and stability. [Copyright &y& Elsevier]