Department of Orthopedic Surgery, Physical Medicine and Rehabilitation, University Hospital, Ludwig-Maximilians-University (LMU), Campus Großhadern, Marchioninistr. 15, 81377, Munich, Germany.
ECOM-Excellent Center of Medicine, Arabellastr, 17, 81925, Munich, Germany.
Knee Surg Sports Traumatol Arthrosc. 2020 Sep;28(9):3016-3021. doi: 10.1007/s00167-019-05761-3. Epub 2019 Nov 5.
Higher revision rates were shown in varus- or valgus-positioned tibias in unicompartmental knee arthroplasty (UKA), but more than 15% of UKA prostheses are implanted with more than 5° of varus or valgus. This study aimed to analyze the wear rate in UKA when implanting the tibial component in either varus or valgus position versus a neutral placement at 90° to the tibial anatomical axis. The study hypothesized that a 5° varus or valgus positioning of the tibial plateau will generate less wear compared to a neutral alignment.
Wear was experimentally analyzed on a medial anatomical fixed-bearing unicompartmental knee prosthesis (Univation, Aesculap, Germany) in vitro with a customized, four-station, servohydraulic knee wear simulator, reproducing the walking cycle. The forces, loading and range of motion were applied as specified in the ISO 14243-1:2002, 5 million cycles were analyzed. The tibial components of the medial prostheses were inserted in a neutral position, with 5° varus, and 5° valgus (n = 3, each group).
The wear rate decreased significantly with a 5° varus positioning (6.30 ± 1.38 mg/million cycles) and a 5° valgus positioning (4.96 ± 2.47 mg/million cycles) compared to the neutral position (12.16 ± 1.26 mg/million cycles) (p < 0.01 for the varus and the valgus position). The wear area on the inlay was slightly reduced in the varus and valgus group.
A varus or valgus "malpositioning" up to 5° will not lead to an increased wear. Wear was even less because of the reduced articulating contact area between the inlay and the femur. A slight varus positioning of the tibial component (parallel to the anatomical joint line) positioning can be advocated from a point of wear.
Experimental study.
在单髁膝关节置换术中，胫骨呈内翻或外翻位时，翻修率较高，但超过 15%的单髁膝关节置换术假体存在 5°以上的内翻或外翻。本研究旨在分析在胫骨解剖轴成 90°角时，将胫骨组件分别置于内翻、外翻或中立位置时，单髁膝关节置换术中的磨损率。该研究假设胫骨平台 5°的内翻或外翻定位会产生比中立对齐更少的磨损。
在体外使用定制的四工位伺服液压膝关节磨损模拟器对内侧解剖固定轴承单髁膝关节假体（Aesculap，德国 Univation）进行磨损实验分析，该模拟器可模拟行走周期。按照 ISO 14243-1：2002 的规定施加力、负荷和运动范围，分析 500 万次循环。内侧假体的胫骨部件分别以中立、5°内翻和 5°外翻的位置插入（每组 3 个，每个位置）。
与中立位置（12.16 ± 1.26mg/百万次循环）相比，5°内翻定位（6.30 ± 1.38mg/百万次循环）和 5°外翻定位（4.96 ± 2.47mg/百万次循环）的磨损率显著降低（p < 0.01）。内翻和外翻组的镶嵌物磨损面积略有减少。
在 5°以内的内翻或外翻“错位”不会导致磨损增加。由于镶嵌物和股骨之间的接触面积减小，磨损甚至更少。从磨损的角度来看，胫骨组件的轻微内翻定位（与解剖关节线平行）是可以提倡的。
实验研究。
