Tyagi Vineet, Akinbo Oluwaseun
Department of Orthopaedics and Rehabilitation, Yale School of Medicine, New Haven, CT, USA.
J Orthop Case Rep. 2017 Mar-Apr;7(2):21-24. doi: 10.13107/jocr.2250-0685.732.
The concept of a dual mobility (DM) cup has been in existence for more than 40 years and was initially popularized in Europe. Only recently has it started to garner attention in the United States. Its design, consisting of a small femoral head articulating within a larger polyethylene (PE) insert, which articulates with an outer shell, has found increasing use in patients that are at risk for post-operative dislocations. This case report describes a case of recurrent total hip arthroplasty (THA) dislocation managed with the implantation of a DM cup with an acute intraprosthetic dislocation of the DM construct.
A 52-year-old woman underwent an uneventful left THA through a posterior approach. Within 6 weeks of her surgery, she had four dislocations, managed with closed reductions. She then underwent an open revision of her acetabular component with conversion to a DM construct. 5 weeks after her revision, she had another dislocation treated with closed reduction in the operating room, with the resultant eccentric location of the femoral head in the acetabular component. Computed tomography (CT) confirmed intraprosthetic dislocation with the PE liner lodged in the gluteal tissue. She was taken to the operating room with a plan to revise her acetabular component to another DM construct, but with an increase in the anteversion despite initial anteversion being "appropriate" on CT imaging. Intraoperatively, the PE liner was embedded in gluteal tissue as depicted on the CT. The abductors were intact. There was no impingement in extension and maximal external rotation when trialed with a conventional head/liner construct. A new DM construct was then implanted.
Intraprosthetic dislocation is a rare occurrence and unique complication to DM constructs. It is not common in the short-term setting postoperatively to our knowledge, and this case report represents an early report of intraprosthetic dislocation in the literature. Care should be taken during reduction of dislocated DM constructs to avoid intraprosthetic dislocations. Open revisions can be managed with revisions to another DM construct or to a constrained liner construct to maximize stability.
双动（DM）杯的概念已经存在了40多年，最初在欧洲流行。直到最近它才开始在美国受到关注。其设计包括一个较小的股骨头在一个较大的聚乙烯（PE）衬垫内活动，该衬垫与一个外壳相连接，在有术后脱位风险的患者中应用越来越多。本病例报告描述了一例复发性全髋关节置换术（THA）脱位，通过植入DM杯进行治疗，术中DM结构发生急性假体内部脱位。
一名52岁女性通过后路顺利进行了左侧THA手术。术后6周内，她发生了4次脱位，均通过手法复位处理。随后她接受了髋臼组件的翻修手术，转换为DM结构。翻修术后5周，她再次脱位，在手术室进行了手法复位，结果股骨头在髋臼组件中位置偏心。计算机断层扫描（CT）证实假体内部脱位，PE衬垫嵌入臀肌组织。她被送往手术室，计划将髋臼组件翻修为另一种DM结构，但尽管CT成像显示初始前倾角“合适”，术中前倾角仍有所增加。术中，PE衬垫如CT所示嵌入臀肌组织。外展肌完整。使用传统的股骨头/衬垫结构进行试验时，伸展和最大外旋时无撞击。然后植入了一种新的DM结构。
假体内部脱位是DM结构罕见且独特的并发症。据我们所知，在术后短期内并不常见，本病例报告是文献中关于假体内部脱位的早期报告。在复位脱位的DM结构时应小心，以避免假体内部脱位。开放性翻修可以通过翻修为另一种DM结构或限制性衬垫结构来进行，以最大限度地提高稳定性。
