Department of Orthopedics and Rehabilitation (E.J.S., H.D.T.-A., N.G., R.W., J.E.G., and M.C.W.) and Department of Engineering (H.D.T.-A. and J.E.G.), University of Iowa, Iowa City, Iowa.
J Bone Joint Surg Am. 2018 Oct 17;100(20):e131. doi: 10.2106/JBJS.17.01631.
BACKGROUND: Femoral cam deformity is frequently present in patients with acetabular dysplasia. Computational modeling can be used to identify how this deformity affects joint mechanics. Our purpose was to identify the relationship between cam deformity and joint contact stress after periacetabular osteotomy (PAO). We hypothesized that cam deformity is associated with an increase in peak joint contact stress after PAO. METHODS: This was a retrospective review of patients treated for hip dysplasia with PAO without femoral osteochondroplasty. Patient-specific hip models created from preoperative and postoperative computed tomography (CT) scans were evaluated using discrete element analysis to determine maximum joint contact stress after PAO. Twenty hips with a postoperative increase in maximum contact stress were compared with 20 that demonstrated decreased maximum contact stress. Hips were assessed for cam deformity on cross-sectional imaging. Radiographic measures of acetabular dysplasia before and after PAO were assessed and compared with the change in maximum contact stress after PAO. RESULTS: There was a moderate relationship between the change in maximum contact stress and the α angle (r = 0.31; p = 0.04), and the average α angle in the hips with increased maximum contact stress was significantly different from that in the hips with decreased joint contact stress (51° ± 11.4° versus 42° ± 5.1°; p = 0.04). All 6 hips with an α angle of >60° demonstrated increased joint contact stress. CONCLUSIONS: Cam deformity is common in patients with hip dysplasia. In our study, α angles of >60° were associated with increased postoperative joint contact stress. The α angle should be assessed preoperatively, and deformity should be addressed for optimal joint mechanics after PAO. CLINICAL RELEVANCE: A reduction in joint contact stress is a proposed mechanism for the increased joint longevity following periacetabular osteotomy for hip dysplasia. Impingement from abnormal femoral offset negatively impacts clinical outcome, but this finding has not been evaluated from a biomechanical perspective previously and a threshold for performing femoral osteochondroplasty has not been established previously. This study provides biomechanical evidence supporting surgical management of femoral cam deformity for an α angle of >60°.
背景：股骨髋臼撞击症患者常存在股骨凸轮畸形。计算模型可用于确定该畸形如何影响关节力学。我们的目的是确定髋臼周围截骨术（PAO）后凸轮畸形与关节接触应力之间的关系。我们假设凸轮畸形与 PAO 后关节接触峰值应力增加有关。
方法：这是一项回顾性研究，研究对象为接受 PAO 治疗而未行股骨骨软骨切除术的髋关节发育不良患者。使用离散元分析对术前和术后 CT 扫描创建的患者特定髋关节模型进行评估，以确定 PAO 后最大关节接触应力。将术后最大接触应力增加的 20 髋与最大接触应力降低的 20 髋进行比较。在横断面上评估髋关节凸轮畸形。评估髋臼发育不良的放射学指标，并与 PAO 后最大接触应力的变化进行比较。
结果：最大接触应力的变化与α角呈中度相关（r=0.31；p=0.04），最大接触应力增加的髋关节的平均α角与最大接触应力降低的髋关节明显不同（51°±11.4°与 42°±5.1°；p=0.04）。所有 6 个α角>60°的髋关节均表现为关节接触应力增加。
结论：凸轮畸形在髋关节发育不良患者中很常见。在我们的研究中，α角>60°与术后关节接触应力增加有关。术前应评估α角，并应在 PAO 后解决畸形，以获得最佳的关节力学效果。
临床相关性：髋关节发育不良行髋臼周围截骨术后关节寿命延长的一个推测机制是关节接触应力降低。异常股骨偏心距引起的撞击会对临床结果产生负面影响，但以前从未从生物力学角度对此进行评估，也没有建立过进行股骨骨软骨切除术的阈值。本研究提供了支持对>60°α角的股骨凸轮畸形进行手术治疗的生物力学证据。
J Bone Joint Surg Am. 2018-10-17
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