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Background: Since the introduction of the first total knee designs, a frequent design goal has been to reproduce normal knee motion. However, studies of many currently used total knee designs, have shown that this goal has not been achieved. We proposed that Guided Motion total knee designs, could achieve more anatomic motion than present standard designs., Methods: Several Guided Motion knees for application without cruciate ligaments were designed using a computer method where the bearing surfaces were generated by the motion required. A knee testing machine was constructed where physiological forces including compressive, shear and torque were applied during knee flexion. The neutral path of motion and the laxity about the neutral path were measured. This evaluation method was a modification of the ASTM standard Constraint Test., Results: The motions of the Guided Motion knees and a standard PS knee were compared with the anatomic motion of knee specimens determined in an earlier study The Guided Motion knees showed motion patterns which were closer to anatomic than the PS knee., Conclusions: The results provided justification for carrying out further evaluations of functional conditions, using either knee simulators or computer modelling. If anatomic motions could be reproduced in vivo, it is possible that clinical outcomes could be improved., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Purpose: Given the goal of achieving optimal correction and alignment after knee arthroplasty or high tibial osteotomy, literature focusing on the inter-individual variability of the native knee, tibia and femur with regards to the coronal or sagittal alignment is lacking. The aim of this study was to analyse normal angular values in the healthy middle-aged population and determine differences of angular values according to inter-individual features. The first hypothesis was that common morphological patterns may be identified in the healthy middle-aged non-osteoarthritic population. The second hypothesis was that high inter-individual variability exists with regards to gender, ethnicity and alignment phenotype., Methods: A CT scan-based modelling and analysis system was used to examine the lower limb of 758 normal healthy patients (390 men, 368 women; mean age 58.5 ± 16.4 years) with available data concerning angular values and retrieved from the SOMA database. The hip-knee-ankle angle (HKA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), posterior distal femoral angle (PDFA), posterior proximal tibial angle (PPTA) and non weight-bearing joint line convergence angle (nwJLCA) were then measured for each patient. Results were analysed for the entire cohort and based on gender, ethnicity and phenotype., Results: The mean HKA was 179.4° ± 2.6°, LDFA: 85.8° ± 2.0°, MPTA: 85.6° ± 2.4°, PDFA: 85.2° ± 1.5°, PPTA: 83.8° ± 2.9° and nwJLCA: 1.09° ± 0.9°. Gender was associated with higher LDFA and lower HKA for men. Ethnicity was associated with greater proximal tibial vara and distal femoral valgus for Asian patients. Patients with an overall global varus alignment had more tibia vara and less femoral valgus than patients with an overall valgus alignment., Conclusion: Even if significant differences were found based on subgroup analysis (gender, ethnicity or phenotype), this study demonstrated that neutral alignment is the main morphological pattern in the healthy middle-aged population. This neutrality is the result from tibia vara compensated by an ipsilateral femoral valgus., Level of Clinical Evidence: III, retrospective cohort study.

Background: Total knee arthroplasty (TKA) design continues to be refined. As part of the pre-clinical design process, kinematic evaluation under ideal circumstances must be simulated. Previously, this was accomplished mechanically through the use of elastomeric bumpers and human cadaver models, which can be costly and time-intensive. With improved technology, a six-axis joint simulator now allows for virtual ligament reconstruction. The aim of this study was to create and evaluate a virtual posterior cruciate ligament (PCL) model to simulate native knee kinematics for component testing in TKA., Methods: Three human cadaveric knee specimens were utilized, each mounted in a six-axis joint simulator and the femoral and tibial ligament insertion points digitized. Ligament stiffness and kinematics were first tested with the intact knee, followed by retesting after PCL transection. Knee kinematic testing was then repeated, and the virtual PCL was reconstructed until it approximated that of the intact knee by achieving less than 10% random mean square (RMS) error., Results: A virtual three-bundle PCL was created. The RMS error in anterior-posterior motion between the virtually reconstructed PCL and the intact knee ranged from six to eight percent for simulated stair climbing in the three knee specimens tested, all within our target goal of less than 10%., Conclusion: This study indicated that a virtually reconstructed three-bundle PCL with a joint simulator can replicate knee kinematics. Such an approach is valuable to obtain clinically relevant kinematics when testing cruciate-retaining total knee arthroplasty under force control., Competing Interests: Declaration of competing interest This project was funded and completed as part of the Stryker Resident and Fellow Research Program., (Copyright © 2019 Elsevier B.V. All rights reserved.)