Prevention of dislocation in hip arthroplasty 髋关节置换术关节脱位的预防AbstractDislocation following primary and revision hip surgery is a common complication.The cause is often multi-factorial including patient factors, surgeon factors, implant design, implant orientation, and soft tissue factors. This article looks at ways of reducing the rate of hip dislocati on.摘要 脱位是初次全髋关节置换及翻修后常见的并发症。引起脱位的原因是多因素的包括患者方面的因素、外科 手术医生的因素、假体的设计、组件的方向及软组织因素。本文旨在探求减少脱位的相关预防措施。 IntroductionDislocation occurs between 0.3% and 10% after primary total hip replacements and up to 28% af ter revision hip replacement1. It is most likely to occur in the first three months after surgery, but the cumulative risk increases over the years following implant insertion. While half of those p atients who dislocate do so only once, the remainder suffer recurrent instability and often require furthersurgical intervention2. The morbidity and cost of revision surgery for instability is consider able and clinical outcome scores and global outcome assessments in patients who have suffered d islocation of their hip are significantly worse than those without3 and do not improve despite su ccessful revision surgery.引言初次全髋关节置换脱位发生率为 0.3%10%，而翻修关节脱位率高达 28% 1。脱位发生最常于术后3 个月这内，但随着假体在体内时间的延长，脱位的累积风险增加。在脱位的患者当中，有一半人只出现一 次脱位，另一半则因为反复不稳出现多次脱位，常常需要手术干预2。对这些脱位患者的治疗往往要花费 大量的代价，与那些没有脱位患者相比较，出现过脱位及成功翻修患者的髋关节功能均相对较差3。 The cause of dislocation is most often multi-factorial. Every hip replacement has the potential to d islocate and through careful pre-operative assessment, implant choice, component positioning, and surgical technique the risk of dislocation can be reduced. Therefore assessment of patients, risk is an important part of pre-operative planning.引起脱位的原因常常是多因素的。髋关节置换都存有潜在的脱位风险因素，假体的设计、组件的位置及外 科技术都有引起术后脱位风险发生，因此，对患者应进行全面仔细的术前评估是术前计划重要的组成部分。 This article reviews the risk factors and mechanisms leading to hip dislocation, intra-operative tech niques, and the available implants that can improve the stability of a hip replacement.本文对引起脱位风险因素进行综述，并分析其脱位机制，术中的相关技巧及假体的选择均有可能改善髋关 节置换术后的稳定性。An illustrative case of recurrent dislocation 一髋关节反复脱位的典型病例This case highlights the challenges posed when treating patients with recurrent dislocation. 此病例充分说明的治疗髋关节置换术后反复不稳所带来的挑战。A 72-year-old man with a previous history of acetabular fracture underwent a left total hip replac ement (Figures 1 and 2). He subsequently had several episodes of posterior hip dislocation (Figur e 3). Even after revision surgery using a larger diameter head and increased head length (Figure 4), he continued to dislocate (Figure 5). A second revision involved acetabular component exchange with a constrained liner (Fi gure 6) but this too failed (Figure 7). At a third revision the liner was removed, a metal shell cemented into the existing cup (Figure 8) and an even larger head was inserted to maximise the head neck ratio but this too dislocated (Figure 9).Figure 2 Primary Hybrid Total Hip Replacement (THRJ.男，72 岁，既往有过左髋臼骨折史，左侧已行全髋关节置换（图1,2）。术后患者经历了多资髋关节脱位（图 3）。即使在翻修时增大头的直径、使用大股骨头，仍然发生了脱位（图 4,5）。二次翻修使有限制性髋臼衬垫 仍然再次出现脱位（图6,7）。第三次翻修时，将衬垫取出，改用金屩的骨水泥壳嵌入臼杯-（图8）,并使用 更大的股骨头，将头颈率增至最大，但最终脱位仍没有幸免（图 9）。Figure 3 Dislocated Primary THR.匚忖In this case each revision operation addressed only a single aspect in the hip arthroplasty that co uld potentially prevent further instability. The final revision (Figure 10) addressed multiple issues; component position by revising both cup and stem, the head/neck ratio was maximised, a constrai ned liner and a trochanteric advancement osteotomy to address soft tissue deficiency. Thereafter t here was no further instability. The same principles form the cornerstones of prevention of disloca tion.figure 5 Dislocated revision THR.本例患者，在每次脱位后都对某一单因素进行了翻修，说明引起脱位的原因是多因素的（图 10），最终的翻修包括组件的位置（包括臼杯与柄），头颈率最大化，限制性髋臼衬执，大粗隆截骨前移改善软组织张力。 此后，没有再出现髋关节脱位，这些原则构成了预防关节脱位的基石。Ftgure 7 Dislocated constrained 匚omponent.DXY.匚忖img/imgQY厂忖Fgure 8 3rd revision THR with large diameter metal-on-rrietat bearing.img/imDX丫 CNFigure 9 Further instability following 3rd revision surgery, gFigure 10 Successful 4th revision surgery with exchange of both acetabular and femoral components, a laree diameter 匚onstrained bearingDXY.CIT and an advancement trochanteric osteotomy to tension soft tissues.Mechanism of dislocation脱位发生机制The general underlying mechanism of dislocation is impingement at the maximumextent of the primary arc of movement at the articulation interface (Figure 11). Levering-out of th e joint follows and when this exceeds the “excursion distance” or“jump -distance” of the bearing th en dislocation occurs. Jump distance is typically half the diameter of the femoral head and