Posterior stabilized total knee arthroplasty reproduces natural joint laxity compared to normal in kinematically aligned
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KNEE ARTHROPLASTY
Posterior stabilized total knee arthroplasty reproduces natural joint laxity compared to normal in kinematically aligned total knee arthroplasty: a matched pair cadaveric study In Jun Koh1,2 · Christen E. Chalmers3 · Charles C. Lin4 · Soo Bin Park1 · Michelle H. McGarry5 · Thay Q. Lee5 Received: 21 May 2020 / Accepted: 30 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Purpose As the goal of kinematic aligned (KA) total knee arthroplasty (TKA) is to preserve soft tissue tension to the native knee, many KA surgeons recommend cruciate-retaining (CR) prosthesis. However, how a posterior-stabilizing (PS) prosthesis affects the biomechanics of a KA TKA remains unclear. This cadaveric study tested the hypothesis that a PS prosthesis in KA TKA would produce biomechanics similar to CR prosthesis and KA TKA with a PS prosthesis would produce more native knee biomechanics than mechanical aligned (MA) TKA with PA prosthesis. Methods Fourteen cadaver knees (7 pairs) were mounted on a knee-testing system to measure knee motion during flexion. For each pair, 1 knee was assigned to KA TKA and the other to MA TKA. In the KA TKA group, the native knee, CR TKA, and PS TKA were tested sequentially. MA TKA was performed using conventional measured resection techniques with a PS prosthesis. All kinematics were measured and compared with the native knee before and after surgery. Results A PS prosthesis restored femoral rollback similar to a CR prosthesis. CR TKA showed less lateral rollback at knee flexion ≤ 60° than the native knee. There were no differences in soft tissue tensions among the native knee, CR, and PS prosthesis, except in varus tension at 30° of flexion. Varus tension of CR TKA was larger than those of PS TKA and the native knee after KA TKA with 1 degree, a third trial was performed; the mean values between the two trials were used. The femoral and tibial anatomical reference system included the transepicondylar axis (TEA) for the mediolateral (ML) axis of the femur and the transtibial axis (TTA). This was the longest ML axis of the tibia and connected the medial and lateral anatomical digitizing markers. Knee motion was assessed by measuring the medial and lateral femoral rollback during flexion. The medial and lateral rollback were calculated as the backward movement of each medial and lateral femoral epicondyle on the transverse plane of the tibia during flexion. As defining the physiologic neutral position in a cadaveric knee is inherently challenging, laxity measurements were defined as the resultant anterior–posterior (AP) displacement, varus-valgus angular displacement, and the internal–external rotational displacement of the tibia relative to the femur when a 60-N load was applied [5]. To quantify varus and valgus laxity, MicroScribe measurements were obtained with a 60-N load applied to the varus then valgus directions. To assess anterior–posterior translation, a 60-N load was directed anteriorly then posteriorly. For rotational laxity, 60 N was app
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