It is usually assumed that the severity of varus osteoarthritis (OA) of the knee is correlated with the axis deviation of the limb. Despite this, there is currently no clear radiographic definition to define a so-called ‘high degree’ varus knee, which is characterized by a pronounced lateral ligamentous laxity. The purpose of this study was to radiographically determine if the lateral joint line opening (LJLO) is an indicative parameter when defining so-called high grade varus knees. Two hundred forty Full length radiographs of patients with end-stage varus osteoarthritis who were scheduled for Total knee arthroplasty (TKA) were evaluated. The Hip-knee-ankle-angle (HKA-angle), Joint-line-convergence-angle (JLCA) and the lateral joint line opening were measured. The lateral joint line opening is the shortest distance between the lateral tibial plateau and the deepest point of the lateral femoral condyle. Linear regression models were used to investigate the relationships between the radiographic measurements. Hip-knee-angle-angle, joint-line-conversion-angle, and lateral joint line opening were all positively correlated (p < 0.001). An increase of 1 mm lateral joint line opening causes an increase of 0.6° joint-line-conversion-angle (p = 0.029) below a cut-off point of 4.7 mm. For lateral opening values beyond 4.7 mm, the gradient increased to 1.2 (p < 0.001). A lateral joint line opening of 4.7 mm corresponds to a hip-knee-ankle-angle of 6.0° (95% CI [5.5; 6.5]). A lateral joint line opening of more than 5 mm in end-stage OA knees is indicative of increased lateral joint laxity. Those knees can be radiographically classified as so-called ‘high-grade’ varus knees. Therapeutic study, Level III.

中文翻译：

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外侧关节线开口：高等级膝关节内翻的影像学指示参数

通常认为膝关节内翻性骨关节炎（OA）的严重程度与肢体轴偏斜相关。尽管如此，目前还没有明确的放射学定义来定义所谓的“高度”内翻膝，其特征是明显的外侧韧带松弛。本研究的目的是通过射线照相确定外侧关节线开口 (LJLO) 是否是定义所谓的高级内翻膝时的指示性参数。评估了计划进行全膝关节置换术 (TKA) 的终末期内翻骨关节炎患者的 240 张全长 X 光片。测量了髋-膝-踝-角（HKA-角）、关节线会聚角（JLCA）和外侧关节线开口。外侧关节线开口是外侧胫骨平台与股骨外侧髁最深点之间的最短距离。线性回归模型用于研究射线照相测量之间的关系。髋-膝-角-角、关节-线-转换-角和外侧关节线开口均呈正相关（p < 0.001）。横向关节线开口增加 1 mm 会导致在 4.7 mm 的截止点以下增加 0.6° 关节线转换角 (p = 0.029)。对于超过 4.7 mm 的横向开口值，梯度增加到 1.2 (p < 0.001)。4.7 mm 的外侧关节线开口对应于 6.0° 的髋-膝-踝-角 (95% CI [5.5; 6.5])。末期 OA 膝关节外侧关节线开口超过 5 毫米表明外侧关节松弛度增加。这些膝关节在放射学上可以归类为所谓的“高级”内翻膝。治疗研究，III 级。