Sah Alexander P, Estok Daniel M
Department of Orthopaedics, Massachusetts General Hospital, 55 Fruit Street, WHT 535, Boston, MA 02114-3117, USA.
J Bone Joint Surg Am. 2008 Mar;90(3):506-16. doi: 10.2106/JBJS.G.00479.
Revision hip arthroplasty is associated with a dislocation rate that is three to five times greater than the rate following primary hip replacement. Conversion of a hip hemiarthroplasty to a total hip replacement is a revision arthroplasty, but it differs from revisions of total hip arthroplasties because a native acetabulum is replaced and the subsequent prosthetic femoral head is smaller. It was our purpose to determine whether the risk of dislocation following conversion surgery is the same as or greater than that following revision total hip replacement.
From 1994 to 2005, eighty-nine hemiarthroplasties were converted to a total hip arthroplasty in seventy-seven patients, and the results were compared with those of 115 first-time revision total hip replacements following a primary total hip replacement in 111 patients. A retrospective chart review was performed, and radiographic measurements were obtained. The patient demographics were similar between the two groups. The percentages of patients who had undergone revision of only the acetabular component as compared with both components as well as the percentages of those who had received a modular femoral stem as compared with a nonmodular stem were also similar between the two groups.
Postoperatively, the femoral head size and the positioning of the acetabular component were similar between the two groups. The acetabular components were significantly larger (p < 0.001) in the group in which a total hip arthroplasty had been revised because they required additional acetabular reaming for placement of a new component. There were significantly more dislocations after the conversion procedures (22%) than after the revisions of the total hip arthroplasties (10%) (p < 0.018). Within both groups, the size of the acetabular component, the intraoperative range of motion, and the positioning of the acetabular component were similar between the hips that dislocated and those that did not. However, smaller femoral head components were at greater risk for dislocation after conversion surgery than after revision of a total hip arthroplasty.
A substantial reduction of the size of the prosthetic femoral head is unique to conversion arthroplasty and appears to play a role in instability after the revision surgery. While the smallest heads dislocated in the conversion group, a larger femoral head did not ensure stability. The increased dislocation risk with conversion surgery requires emphasis on soft-tissue balance and avoidance of excessive downsizing of the femoral head in an attempt to maximize hip stability.
髋关节翻修置换术的脱位率比初次髋关节置换术后的脱位率高三到五倍。髋关节半关节成形术转换为全髋关节置换术是一种翻修置换术，但它与全髋关节置换术的翻修不同，因为它替换了天然髋臼，且后续的人工股骨头较小。我们的目的是确定转换手术后的脱位风险是否与全髋关节置换术翻修后的脱位风险相同或更高。
1994年至2005年，77例患者的89例半关节成形术被转换为全髋关节置换术，并将结果与111例患者初次全髋关节置换术后的115例首次翻修全髋关节置换术的结果进行比较。进行了回顾性病历审查，并获得了影像学测量结果。两组患者的人口统计学特征相似。两组中仅翻修髋臼组件与翻修两个组件的患者百分比，以及接受模块化股骨干与非模块化股骨干的患者百分比也相似。
术后，两组的股骨头大小和髋臼组件的位置相似。在全髋关节置换术翻修的组中，髋臼组件明显更大（p < 0.001），因为放置新组件需要额外的髋臼扩孔。转换手术后的脱位明显多于全髋关节置换术翻修后（22%对10%）（p < 0.018）。在两组中，脱位髋关节与未脱位髋关节之间的髋臼组件大小、术中活动范围和髋臼组件位置相似。然而，转换手术后较小的股骨头组件比全髋关节置换术翻修后脱位风险更高。
人工股骨头尺寸大幅减小是转换置换术所特有的，似乎在翻修手术后的不稳定中起作用。虽然转换组中最小的股骨头发生了脱位，但较大的股骨头并不能确保稳定性。转换手术增加的脱位风险需要强调软组织平衡，并避免股骨头过度缩小以尽量提高髋关节稳定性。
