Background 

Any abnormal structures that contribute to the narrowing of the ischiofemoral space could induce ischiofemoral impingement. Bernese periacetabular osteotomy (PAO) medializes the hip center and, therefore, decreases contact stress on the cartilage in developmental dysplasia of the hip (DDH). However, medialization of the hip center might also narrow the ischiofemoral space, which may increase the risk of postoperative ischiofemoral impingement in patients with acetabular dysplasia who are undergoing PAO. Furthermore, the dysplastic hip has less ischiofemoral space and less space for the quadratus femoris. A few studies have focused on the amount of medialization of the hip center, but the proportion of postoperative ischiofemoral impingement after PAO has not been investigated.

Questions/purposes 

(1) What proportion of patients develop ischiofemoral impingement after undergoing unilateral PAO for DDH? (2) What radiographic factors are associated with postoperative ischiofemoral impingement in patients who underwent PAO for DDH? (3) How much hip center medialization is safe so as to avoid postoperative ischiofemoral impingement during PAO?

Methods 

Between 2014 and 2016, we treated 265 adult patients who had symptomatic residual acetabular dysplasia (lateral center-edge angle less than 20°) using PAO. During that time, we generally offered PAO to patients with acetabular dysplasia when the patients had no advanced osteoarthritis (Tönnis grade < 2). Of those, we considered only patients who underwent primary PAO without femoral osteotomy as potentially eligible. Based on that, 65% (173 of 265) were eligible; a further 9% (24 of 265) were excluded due to leg length discrepancy, spine disorders, or joint replacement in the contralateral side, and another 6% (17 of 265) of patients were lost before the minimum study follow-up of 2 years or had incomplete datasets, leaving 50% (132 of 265) for analysis in this retrospective study at a mean of 2.70 ± 0.71 years. The diagnosis of ischiofemoral impingement was defined by symptoms, MRI, and diagnostic ischiofemoral injection. We ascertained the percentage of patients with this diagnosis to answer the first research question. To answer the second question, we divided the patients into two groups: PAO patients with ischiofemoral impingement and PAO patients without ischiofemoral impingement. The demographic data and preoperative imaging parameters of patients in both groups were compared. There were statistical differences in acetabular version, ischial angle, neck-shaft angle, the presence of positive coxa profunda sign, McKibbin index, ischiofemoral space, quadratus femoris space, anterior acetabular section angle, and the net amount of hip center medialization. To investigate potential factors associated with postoperative ischiofemoral impingement in patients who underwent PAO, these factors underwent binary logistic regression analysis. To answer the third question, the cutoff value of the net amount of hip center medialization was evaluated using receiver operator characteristic curve and the Youden index method.

Results 

We found that 26% (35 of 132) of PAO dysplastic hips had postoperative ischiofemoral impingement. After controlling for confounding variables such as acetabular version, ischial angle, femoral neck version, McKibbin index, and ischiofemoral space, we found that an increasing neck-shaft angle (odds ratio 1.14 [95% confidence interval 1.01 to 1.29]; p = 0.03), a positive coxa profunda sign (OR 0.13 [95% CI 0.03 to 0.58]; p < 0.01), and an increasing net amount of hip center medialization (OR 2.76 [95% CI 1.70 to 4.47]; p < 0.01) were associated with postoperative ischiofemoral impingement in patients with DDH who underwent PAO (R² = 0.73). The cutoff values of neck-shaft angle was 138.4°. The cutoff values of the net amount of hip center medialization was 1.9 mm.

Conclusions 

Postoperative ischiofemoral impingement could occur in patients with acetabular dysplasia who have undergone PAO after hip center medialization. An increasing neck-shaft angle, a positive coxa profunda sign on preoperative imaging, and excessive medialization of the hip center are factors associated with ischiofemoral impingement development in these patients. Therefore, we suggest that physicians measure the ischiofemoral space on a preoperative CT when patients with DDH have an increasing neck-shaft angle (> 138.4°) or a positive coxa profunda sign on radiological imaging. During PAO, the amount of hip center medialization should be carefully controlled to keep these patients from developing postoperative ischiofemoral impingement.

Level of Evidence 

Level III, therapeutic study.

中文翻译：

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哪些因素与髋关节发育不良的伯尔尼髋臼周围截骨术后坐骨股骨撞击相关？

背景 

任何导致坐骨股骨间隙变窄的异常结构都可能诱发坐骨股骨撞击。伯尔尼髋臼周围截骨术 (PAO) 将髋关节中心置于内侧，因此可以减少髋关节发育不良 (DDH) 软骨上的接触应力。然而，髋关节中心的内侧化也可能使坐骨股骨间隙变窄，这可能会增加接受 PAO 的髋臼发育不良患者术后发生坐骨股骨撞击的风险。此外，发育不良的髋关节的坐骨股骨空间和股方肌空间也较小。一些研究关注髋中心内侧化的量，但尚未调查 PAO 术后坐骨股骨撞击的比例。

问题/目的 

(1) 在接受单侧 PAO 治疗 DDH 后，有多少比例的患者出现坐骨股骨撞击？(2) 哪些影像学因素与因 DDH 接受 PAO 的患者术后坐骨股骨撞击相关？(3) 髋关节中心内移多少是安全的，以避免 PAO 术后发生坐骨股骨撞击？

方法 

2014年至2016年间，我们使用PAO治疗了265名有症状的残余髋臼发育不良（外侧中心边缘角小于20°）的成年患者。在那段时间里，我们通常为髋臼发育不良患者提供 PAO，前提是患者没有晚期骨关节炎（Tönnis 等级 < 2）。其中，我们认为仅接受原发性 PAO 而未进行股骨截骨术的患者可能符合资格。据此，65%（265 人中的 173 人）符合资格；另有 9%（265 名患者中的 24 名）由于腿长差异、脊柱疾病或对侧关节置换而被排除，另外 6%（265 名中的 17 名）患者在最低研究随访 2 个月之前就丢失了。年或数据集不完整，留下 50%（265 人中的 132 人）在这项回顾性研究中进行分析，平均时间为 2.70 ± 0.71 年。坐骨股骨撞击症的诊断是通过症状、MRI 和诊断性坐骨股骨注射来确定的。我们确定了患有此诊断的患者的百分比来回答第一个研究问题。为了回答第二个问题，我们将患者分为两组：伴有坐骨股骨撞击的PAO患者和不伴有坐骨股骨撞击的PAO患者。比较两组患者的人口统计学数据和术前影像学参数。髋臼版本、坐骨角、颈干角、是否存在髋深征阳性、McKibbin指数、坐骨股骨间隙、股方肌间隙、髋臼前切面角度、髋中心内侧净量等差异均有统计学意义。为了调查与接受 PAO 的患者术后坐骨股骨撞击相关的潜在因素，对这些因素进行了二元 Logistic 回归分析。为了回答第三个问题，使用受试者工作特征曲线和约登指数法评估髋中心内侧化净量的截止值。

结果 

我们发现 26%（132 例中的 35 例）PAO 发育不良的髋关节术后发生坐骨股骨撞击。在控制了髋臼版本、坐骨角度、股骨颈版本、McKibbin 指数和坐骨股骨空间等混杂变量后，我们发现颈干角度不断增加（比值比 1.14 [95% 置信区间 1.01 至 1.29]；p = 0.03 ）、髋深征阳性（OR 0.13 [95% CI 0.03 - 0.58]；p < 0.01）和髋中心内侧净量增加（OR 2.76 [95% CI 1.70 - 4.47]；p < 0.01）与接受 PAO 的 DDH 患者术后坐骨股骨撞击相关（R ² = 0.73）。颈轴角的截止值为138.4°。髋中心内侧化净量的截止值为 1.9 mm。

结论 

髋臼发育不良患者在髋中心内侧化后接受 PAO 术后可能会发生坐骨股骨撞击。颈干角增大、术前影像显示髋深征阳性以及髋中心过度内侧化是这些患者发生坐骨股骨撞击的相关因素。因此，我们建议当 DDH 患者颈干角增大（> 138.4°）或放射影像显示髋深征阳性时，医生在术前 CT 上测量坐骨股骨间隙。在 PAO 期间，应仔细控制髋中心内侧的量，以防止这些患者发生术后坐骨股骨撞击。

证据水平 

III级，治疗研究。