Purpose

The Oxford unicompartmental knee replacement (UKR) has a fully congruent mobile bearing to minimise wear. However, with younger higher demand patients, wear remains a concern. The aim of this study was to quantify the wear rate of Phase 3 Oxford UKR bearings over the course of 5 years and to identify the factors that influence it.

Methods

40 medial Oxford UKRs recruited for a randomised study of cemented and cementless fixation were studied with Radiostereometric analysis (RSA) at 1 week, 3 months, 6 months, 1 year, 2 years, and 5 years post-operatively and bearing thickness was calculated. Penetration, defined as the change in thickness compared to the 1-week measurement, was determined. Creep (early penetration) and wear (late penetration at a constant rate) were calculated. The influence of demographic factors, Oxford Knee Score (OKS), Tegner score, fixation and bearing overhang (determined by RSA) on wear was analysed.

Results

After 6 months the penetration rate was constant, indicating that wear alone was occurring. The wear rate was 0.07 mm/year (SD 0.03). The creep was 0.06 mm with about 95% occurring during the first 3 months. There was no significant relationship between fixation (cemented/cementless), age, component size, OKS and Tegner score with wear rate. Increasing BMI was associated with decreasing wear (p = 0.042). 37/40 bearings overhung the tibia to some extent and 23/40 overhung the tibia medially. An increase in the area of overhang (p = 0.036), amount of medial overhang (p = 0.028) and distance between the bearing and tibial wall (p = 0.019) were associated with increased wear. Bearings that did not overhang (0.06 mm/year) had less wear (p = 0.025) than those that did (0.08 mm/year). There was no relationship (p = 0.6) between the femoral contact area and wear.

Conclusion

During the first three to six months after implantation, the bearing becomes 0.06 mm thinner due to creep. The combined wear rate of the upper and lower surfaces of the bearing is constant (0.07 mm/year). The wear is lower if the bearing does not overhang the tibia so surgeons should aim for the bearing to be close to the tibial wall. The orientation of the femoral component does not influence wear.

Level of evidence

Retrospective Study, Level III.

中文翻译：

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活动轴承单髁膝关节置换术后聚乙烯蠕变和磨损低。

目的

牛津单室膝关节置换术 (UKR) 具有完全一致的移动轴承，可最大限度地减少磨损。然而，随着年轻患者的需求较高，磨损仍然是一个问题。本研究的目的是量化牛津 UKR 第 3 阶段轴承在 5 年内的磨损率，并确定影响它的因素。

方法

在术后 1 周、3 个月、6 个月、1 年、2 年和 5 年，采用放射立体测量分析 (RSA) 研究了 40 名用于骨水泥和非骨水泥固定随机研究的 Oxford UKR 内侧，并计算了轴承厚度。渗透，定义为与 1 周测量值相比的厚度变化，已确定。计算蠕变（早期渗透）和磨损（以恒定速率延迟渗透）。分析了人口统计学因素、牛津膝关节评分 (OKS)、Tegner 评分、固定和轴承悬垂（由 RSA 确定）对磨损的影响。

结果

6 个月后，穿透率保持不变，表明仅发生磨损。磨损率为 0.07 毫米/年 (SD 0.03)。蠕变为 0.06 毫米，大约 95% 发生在前 3 个月。固定（水泥/非水泥）、年龄、组件尺寸、OKS 和 Tegner 评分与磨损率之间没有显着关系。增加 BMI 与减少磨损相关 ( p  = 0.042)。37/40 轴承在一定程度上伸出胫骨，23/40 轴承在内侧伸出胫骨。外伸面积 ( p  = 0.036)、内侧外伸量 ( p  = 0.028) 以及轴承与胫骨壁之间的距离 ( p  = 0.019) 的增加与磨损增加有关。没有悬垂（0.06 毫米/年）的轴承磨损较少（p  = 0.025）比那些做了（0.08 毫米/年）。 股骨接触面积和磨损之间没有关系（p = 0.6）。

结论

在植入后的前三到六个月内，由于蠕变，轴承变薄了 0.06 毫米。轴承上下表面的综合磨损率是恒定的（0.07 毫米/年）。如果轴承不突出胫骨，则磨损较低，因此外科医生应将轴承瞄准胫骨壁。股骨部件的方向不影响磨损。

证据级别

回顾性研究，III 级。