Hasegawa Masahiro, Sudo Akihiro, Uchida Atsumasa
Department of Orthopaedic Surgery, Mie University Faculty of Medicine, 2-174 Edobashi, Tsu City, Mie 514-8507, Japan.
Clin Orthop Relat Res. 2004 Aug(425):163-7. doi: 10.1097/00003086-200408000-00022.
Disassembly of bipolar cups with a self-centering system occurred in six patients (seven hips; five women, one man) and the cause of the failure was evaluated. The mean age of the patients at the time of arthroplasty was 49.7 years (range, 27-85 years), and mean weight was 48.4 kg (range, 37-65 kg). The mean time to failure was 7.5 years (range, 4.8-9.2 years). Before failure, all implants functioned well and none of the patients had sustained trauma. Retrieval study showed that the cause of failure of the locking mechanism with a self-centering system was severe polyethylene abrasion at the rim attributable to impingement and deformity of the locking ring. After the locking ring detached, the inner head dislocated from the outer head resulting in a varus position of the outer head in the acetabulum. If the deformed locking ring did not detach, the inner head could dislocate, with the varus outer head remaining in the acetabulum. The incidence of this failure was 11%. This disassembly is not a rare occurrence numerous years after a well-functioning bipolar hemiarthroplasty, even with the self-centering system.
6例患者（7髋；5名女性，1名男性）出现了带有自定心系统的双极杯组件拆卸情况，并对失败原因进行了评估。接受关节置换术时患者的平均年龄为49.7岁（范围27 - 85岁），平均体重为48.4千克（范围37 - 65千克）。失败的平均时间为7.5年（范围4.8 - 9.2年）。在失败前，所有植入物功能良好，且患者均未遭受过外伤。取出研究表明，带有自定心系统的锁定机制失败的原因是由于锁定环的撞击和变形导致边缘处严重的聚乙烯磨损。锁定环脱落后，内头从外头脱位，导致外头在髋臼内处于内翻位置。如果变形的锁定环未脱落，内头可能脱位，外头内翻仍留在髋臼内。这种失败的发生率为11%。即使采用了自定心系统，在功能良好的双极半髋关节置换术多年后，这种组件拆卸情况并不罕见。
