We observed decreased pain and improved hip function at last followup. This included a decrease in the incidence of a positive anterior impingement test or pain and an improvement of internal rotation, abduction, and the Merle d’Aubigné-Postel score (Table 4). Internal rotation in flexion is typically decreased in hips with FAI  and improvement after surgical correction has been reported [5, 7, 23, 29]. Additionally, improvement in flexion has been reported in these studies [5, 7, 23, 29] but could not be seen in the current study (Table 4). However, we found postoperative improvement in abduction (Table 4), which has not been described so far. In a study using computer-animated hip motion, decreased abduction was found for hips with FAI along with decreased internal rotation in flexion . Improved clinical scores have been found for both labral reattachments and resection (Table 6) [1, 5, 11, 16, 21, 23]. Espinosa et al.  found a superior Merle d’Aubigné-Postel score for hips with labral reattachment compared with labral resection after surgical hip dislocation. Larson et al.  compared the results of labral reattachment and resection for hips after hip arthroscopy using the HHS. A good to excellent result was found in 92% of hips with reattachment and in 68% of hips with resection. In contrast, Laude et al.  found no difference for the clinical results comparing labral reattachment and resection. An improvement in pain has been reported for both labral reattachment and resection (Table 6) [3, 5, 7, 11, 21, 33]. However, Larson et al.  reported superior results in pain reduction (using the visual analog scale) comparing labral reattachment and resection after hip arthroscopy. At followup, we found comparable results for the WOMAC [1, 16, 29], HHS [6, 21, 23, 33, 34], SF-12 [1, 29], and UCLA  scores reported in the literature for studies with a variable percentage of labral reattachment (Table 6).
At a minimum 5-year followup, a minority of seven hips (7%) demonstrated progression of OA. This is consistent with results in the literature [11, 29]. In the current study at a 5-year followup, 91% of the hips presented without progression of OA with a good or excellent clinical score without conversion to a THA (Fig. 2). The early results of surgical hip dislocation without labral reattachment [3, 27] are inferior compared with more recent studies including labral reattachment in some or all hips (Fig. 4). As expected, studies reporting the results after arthroscopic treatment have shorter maximum followup compared with those with open treatment (Fig. 4). Nevertheless, the survivorships are comparable to those after surgical hip dislocation (Fig. 4).
We found new predictive factors for failure after surgical hip dislocation, all indicating postoperative acetabular undercoverage (Fig. 3). This likely is the result of too radical acetabular rim trimming or a false indication of acetabular trimming in hips without excessive acetabular coverage (Fig. 5). The strongest predictors for failure were all associated with postoperative undercoverage (extrusion index > 28%, acetabular index > 14°, LCE angle < 22°) or age > 40 years at operation (Table 5). The great majority of failures occurred if one or more of the radiographic parameters describing acetabular coverage were outside a previously described normal range (Fig. 3) . Normative radiographic data  can help a surgeon to decide whether rim trimming is possible without the risk of acetabular undercoverage and can be used to quantify the maximal amount of resection possible. Intraoperatively, rim trimming should be performed according to the preoperative planning until impingement-free ROM is achieved. Care must be taken not to trim all the damaged acetabular cartilage per se because this could result in acetabular undercoverage. Known negative predictive factors are preoperative advanced OA [22, 27, 32, 34] and increased age . In contrast to our results with increased weight or body mass index (BMI) being inversely related to failure of the procedure, Naal et al.  found a lower BMI in patients with hips that converted to a THA than for those with a preserved joint (21 versus 24 kg/m2).
Our study showed that surgical hip dislocation for treatment of FAI including labral reattachment improved hip function and clinical scores at a mean of 6-year followup. In over 90% of the patients, this treatment provided a good to excellent clinical result, no progression of OA, and no need for conversion to a THA at 5-year followup. Seven hips (7%) had to be converted to a THA. Preoperative advanced age, advanced OA, and increased weight/BMI represent relative contraindications. Excessive acetabular rim trimming with resulting insufficient femoral coverage leads to early deterioration of the joint.
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