Murotani Yoshiki, Kuroda Yutaka, Goto Koji, Kawai Toshiyuki, Matsuda Shuichi
Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, Shogoin, Kawahara-cho 54, Sakyo-ku, Kyoto, 606-8507, Japan.
J Med Case Rep. 2018 Nov 6;12(1):331. doi: 10.1186/s13256-018-1886-6.
Dislocation following total hip arthroplasty is mainly caused by malposition. However, the coexistence of neuromuscular disorders is also considered a risk for dislocation due to excessive hip joint laxity. To minimize risk of dislocation, preoperative planning using combined anteversion has been widely used. The recommended combined anteversion angle (the total of cup and stem anteversion angles) is 50 ± 10°.
A 33-year-old Japanese woman underwent elective total hip arthroplasty due to osteonecrosis of the femoral head associated with corticosteroid pulse therapy for myasthenia gravis. Intraoperatively, no tendency of dislocation was found when simulating an evoking position under general anesthesia. In postoperative X-ray and computed tomography scans, cup inclination, cup anteversion, and stem anteversion angles were 37°, 13°, and 35° respectively. The resulting combined anteversion was 48°, which was set as the target along with accurate placement. Her postoperative course was normal and she was discharged without adverse events. Three months postoperatively, due to worsening of myasthenic weakness in her lower extremities while resting, she tended to raise her left limb up using both hands for sitting up. An anterior dislocation occurred when her legs were in a figure-of-four position. She was brought to an emergency department, and reduction of dislocation was performed. It was inferred that myasthenic crisis in the affected limb enabled excessive passive motion due to joint hyperlaxity. At the end of 2016, elective total hip arthroplasty on the contralateral side was performed. Cup anteversion, stem anteversion, and the combined anteversion angles were 27°, 24°, and 51° respectively. We instructed her to exercise care during passive leg movement, which may worsen her myasthenic condition. She returned to a normal life and was able to walk long distances without a cane. No recurrence of dislocation was seen at final follow-up.
Even if accurate component orientation is attained in total hip arthroplasty, patients with neuromuscular disorders such as myasthenia gravis have a potential risk of muscle weakness in the affected limb. Therefore, physicians' instructions and patients' careful attention are required to prevent dislocation due to excessive hip joint laxity under conditions of motor weakness.
全髋关节置换术后脱位主要由位置不当引起。然而，神经肌肉疾病的并存也被认为是由于髋关节过度松弛而导致脱位的一个风险因素。为了将脱位风险降至最低，使用联合前倾角的术前规划已被广泛应用。推荐的联合前倾角（髋臼和股骨柄前倾角之和）为50°±10°。
一名33岁的日本女性因股骨头坏死接受择期全髋关节置换术，该股骨头坏死与重症肌无力的皮质类固醇脉冲治疗有关。术中，在全身麻醉下模拟诱发位置时未发现脱位倾向。术后X线和计算机断层扫描显示，髋臼倾斜角、髋臼前倾角和股骨柄前倾角分别为37°、13°和35°。由此得出的联合前倾角为48°，连同准确的植入位置一起被设定为目标。她的术后病程正常，无不良事件出院。术后三个月，由于休息时下肢重症肌无力加重，她在坐起时倾向于用双手抬起左下肢。当她的双腿呈“4”字位时发生了前脱位。她被送往急诊科并进行了脱位复位。据推测，患侧肢体的重症肌无力危象因关节过度松弛而导致过度被动运动。2016年底，对侧进行了择期全髋关节置换术。髋臼前倾角、股骨柄前倾角和联合前倾角分别为27°、24°和51°。我们告知她在被动腿部运动时要小心，因为这可能会加重她的重症肌无力状况。她恢复了正常生活，能够不用拐杖长距离行走。最后一次随访时未见脱位复发。
即使在全髋关节置换术中实现了假体组件的精确定向，患有重症肌无力等神经肌肉疾病的患者患侧肢体仍有肌肉无力的潜在风险。因此，需要医生的指导和患者的密切关注，以防止在运动无力的情况下因髋关节过度松弛而导致脱位。
