Abstract

Purpose

The primary aim of this study was to investigate the potential benefit of stress radiographs for diagnosis of unstable total knee arthroplasty (TKA) and to identify clinically relevant cut-off values to differentiate between unstable and stable TKAs.

Methods

Data of 40 patients with 49 cruciate retaining (CR) TKA who underwent stress radiographs as part of the diagnostic algorithm in a painful knee clinic were prospectively collected. Anterior and posterior stress radiographs were done in 90° and 15° flexion, varus-valgus stress radiographs in 0° and 30° knee flexion. Knee laxity was measured in mm and degrees by two independent observers using standardized landmarks. Intra- and inter-observer single measure intraclass correlations were between 0.92 to 1 and 0.89 to 1, respectively. For evaluation and investigation of the potential cut-off values, two groups of patients with and without revision surgery due to instability were compared. Radiographic measures of standardized z values according to the group without revision due to instability were used to calculate average and maximum laxity z-scores.

Results

Knees undergoing revision TKA due to instability showed significantly (p < 0.001) lower (KSS) pain/function scores (94 ± 6.3, range 80–100; control group: 112 ± 19.2, range 80–148) and total KSS scores when compared to the control group. The laxity values of patients with instability were significantly higher in terms of mean values (p < 0.01) when compared to the control group. The maximum laxity z-score showed the strongest difference between the groups (R² = 0.26, p < 0.001). The following cut-off values indicating need of revision due to instability were established: in 90° (15°) flexion—anterior translation 5.2 mm (22.4 mm), posterior translation 16.6 mm (13.2 mm); varus stress in 0° (20°–30°) flexion—inlay gap 5.2 mm (6.1 mm) or joint angle 6.1° (6.8°); valgus stress in 0° (20°–30°) flexion—inlay gap 4.6 mm (5.7 mm) or joint angle 5.2° (7.1°).

Conclusion

Standardized stress radiographs are helpful tools for diagnosis of instability after TKA. The established cut-off values help to guide decision making in this challenging group of patients. However, laxity values should not be considered as the only criteria for diagnosis of unstable TKA.

Level of evidence

IV.

中文翻译：

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全膝关节置换术后不稳定膝关节的应力X线照片阈值

摘要

目的

这项研究的主要目的是研究应力射线照相对不稳定的全膝关节置换术（TKA）的诊断的潜在益处，并确定临床上相关的临界值，以区分不稳定和稳定的TKA。

方法

前瞻性地收集了40例49例交叉保留（CR）的TKA患者的数据，这些患者在膝关节疼痛诊所接受了放射线照相作为诊断算法的一部分。前后屈曲X线片分别在屈曲90°和15°时进行，内翻外翻应力X射线片在屈曲0°和30°时进行。两位独立的观察者使用标准化的界标以毫米和度为单位测量膝盖的松弛度。观察者内和观察者间单项测量的类内相关性分别在0.92至1和0.89至1之间。为了评估和调查潜在的临界值，比较了两组因不稳定性而接受和不接受翻修手术的患者。标准化z射线照相测量 根据不稳定性而未进行修订的组的数值用于计算平均和最大松弛度z得分。

结果

因不稳定性而接受翻修TKA的膝关节 疼痛/功能评分（94±6.3，范围80–100；对照组：112±19.2，范围80–148）显着（p <0.001）较低（KSS），总KSS评分到对照组。 与对照组相比，不稳定患者的松弛度值均值明显更高（p <0.01）。最大松弛度z评分显示两组之间的差异最大（R ²  = 0.26，p <0.001）。确定了以下临界值，这些值指示由于不稳定性而需要翻修：在90°（15°）屈曲时，前移5.2 mm（22.4 mm），后移16.6 mm（13.2 mm）；屈曲0°（20°–30°）时的内翻应力-镶嵌间隙5.2 mm（6.1 mm）或关节角度6.1°（6.8°）；外翻应力在0°（20°–30°）屈曲时-间隙4.6 mm（5.7 mm）或关节角5.2°（7.1°）。

结论

标准化的应力射线照相是诊断TKA后不稳定性的有用工具。既定的临界值有助于指导这一具有挑战性的患者群体的决策。但是，松弛度值不应被视为诊断不稳定TKA的唯一标准。

证据水平

IV。