Background

Studies on the causes and factors affecting dislocation after total hip arthroplasty have revealed conflicting results. The purpose of this study was to evaluate the factors affecting impingement and dislocation after total hip arthroplasty, using a 3-dimensional dynamic motion analysis.

Methods

The CT data of 53 patients (53 hips: anterior dislocation; 11 cases, and posterior dislocation; 42 cases) who experienced hip dislocation after total hip arthroplasty with posterior approach, and 120 control patients (120 hips) without dislocation were analyzed. Parameters related to implant alignment, offset and leg length were evaluated. The impingement type was also analyzed using a software.

Findings

Considering implant settings affecting dislocation, patients at risk for posterior dislocation had decreased stem anteversion, combined anteversion, femoral offset, and leg length. Nevertheless, patients at risk for anterior dislocation had only lower leg length, and these patients may also be at risk for a higher incidence of recurrent dislocation. Bony impingement occurred in almost half of the cases with posterior dislocation, while implant impingement was associated with anterior dislocation. Importantly, anterior dislocation was not as common as posterior dislocation even in cases with occurrence of posterior impingement.

Interpretation

Bony impingement substantially affects dislocation even in the situation where the implant position and alignment are determined by the so-called “safe zone”, especially on the anterior side, while implant impingement affects anterior dislocation. The restoration of anterior offset (i.e., prescribed by the stem anteversion and femoral offset) and combined anteversion is critical for avoidance of posterior dislocation after total hip arthroplasty.

中文翻译：

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全髋关节置换术后撞击和脱位的影响因素-计算机模拟分析。

背景

对影响全髋关节置换术后脱位的原因和因素的研究显示出相互矛盾的结果。这项研究的目的是使用3维动态运动分析来评估影响全髋关节置换术后撞击和脱位的因素。

方法

分析了53例全髋关节置换术后后路脱位后发生髋关节脱位的患者（53髋：前脱位； 11例，后脱位； 42例）的CT数据，并分析了120例无脱位的对照患者（120髋）。评估与植入物对齐，偏移和腿长有关的参数。还使用软件分析了撞击类型。

发现

考虑到植入物的设置会影响脱位，处于后脱位风险的患者的茎前倾，联合前倾，股骨偏移和腿长减少。然而，有前脱位风险的患者的下肢长度较短，这些患者也可能有复发脱位的较高风险。骨骼撞击几乎发生在后脱位的病例中，而植入物撞击与前脱位有关。重要的是，即使发生后部撞击，前脱位也不如后脱位常见。

解释

即使在植入物的位置和对齐方式由所谓的“安全区”（尤其是在前侧）确定的情况下，骨撞击也会严重影响脱位，而植入物的撞击会影响前脱位。对于完全髋关节置换术后避免后脱位，恢复前侧偏移（即由茎前倾和股骨偏移规定）和联合前倾至关重要。