Castelhano Rute, Deo Sunny
Department of Trauma and Orthopaedics, The Great Western Hospitals NHS Foundation Trust, Swindon, United Kingdom.
J Orthop Case Rep. 2021 Apr;11(4):52-55. doi: 10.13107/jocr.2021.v11.i04.2150.
The design of some knee replacements includes the use of a mobile polyethylene bearing which can potentially dislocate away from the main bearing surfaces. This is particularly the case in unicompartmental or partial knee replacements (UKRs), and the most widely used UKR currently has this feature. Bearing dislocations are typically very painful and disabling, but not always, as in the case we present.
We report the case of a patient presenting at a 1 -year follow- up following a mobile bearing UKR. At this consultation, the patient reported a smooth initial recovery but with on-going pain and swelling in the posterior aspect of his knee for 3 months, diagnosed as a soft- tissue strain.
Radiographs at 1 year follow-up appointment showed that the polyethylene insert was dislocated posteriorly towards the popliteal fossa with metal components in direct contact. At revision surgery, this was confirmed as a chronic dislocation with severe metallosis requiring revision to a total knee replacement.
We report a case of a posterior dislocation of a mobile polyethylene bearing of a partial / unicompartmental knee replacement UKR with delayed definitive treatment due to mis-diagnosis at the time of onset of symptoms and signs. The key lesson is that plain radiographs should be obtained promptly for any local issue in knee replacement patients.
一些膝关节置换设计包括使用可移动的聚乙烯轴承，其有可能从主要轴承表面脱位。在单髁或部分膝关节置换（UKR）中尤其如此，目前使用最广泛的UKR就有这一特点。轴承脱位通常非常疼痛且会导致功能障碍，但并非总是如此，就像我们所呈现的病例那样。
我们报告一例在进行可移动轴承UKR术后1年随访时出现的患者情况。在此次会诊时，患者报告最初恢复顺利，但膝关节后方持续疼痛和肿胀3个月，诊断为软组织拉伤。
1年随访时的X线片显示，聚乙烯衬垫向后脱位至腘窝，金属部件直接接触。在翻修手术中，证实这是一例慢性脱位，伴有严重金属沉着病，需要翻修为全膝关节置换。
我们报告一例单髁/部分膝关节置换UKR的可移动聚乙烯轴承后脱位病例，由于症状和体征出现时误诊，导致确定性治疗延迟。关键教训是，对于膝关节置换患者的任何局部问题，应及时进行X线平片检查。
