Background Femoroacetabular impingement (FAI) describes a painful, abnormal (bony) contact between the femoral neck and acetabulum, which, if left untreated, contributes to early osteoarthritis (OA) of the hip. Despite its flat learning curve and long operation times, hip arthroscopy has been used increasingly often in recent years in the surgery of femoroacetabular impingement. The mini-open technique (MOT) offers a possible alternative that addresses the abnormal morphological prominence and allows minimally invasive clearance of hip motion. There is still a lack of information on the influence of the greater degree of soft tissue intrusion inherent to the mini-open approach. Therefore we decided to evaluate the medium-term outcome of the mini-open technique and to compare the results to those of the arthroscopic technique reported in the literature. Patients, Material und Methods 99 patients (105 hips, 40 women, 59 men) underwent mini-open surgical treatment for FAI between 2005 and 2012 and were followed-up for an average of 40.5 months. The evaluation focused on the pre- and postoperative pain intensity (NRS: numeric rating scale), the clinical and functional outcomes such as ROM (range of motion), HOS (Hip Outcome Score) and mHHS (modified Harris Hip Score), changes in athletic behaviour and the satisfaction of the patients. Radiological analysis (α-angle, anterior head-neck-offset (HNO), head-neck-offset ratio, ossification, grade of OA) was performed using preoperative, immediate postoperative as well as follow-up radiographs. Finally our results were compared to those reported for the arthroscopic technique in the literature. Results The average pain level decreased from 6.5 ± 2.3 to 2.3 ± 2.6 (p < 0.001). 80 % (84) confirmed a mean postoperative pain-free period of 29.5 months (2-103 months), and 52.4 % (55) were still almost pain-free by the time of the final follow-up. The mHHS increased from 68.2 ± 13.5 to 85.2 ± 18.2 (p < 0.001). The HOS-ADL (ADL: activities of daily life) was 82.2 % ± 19.7 and the HOS-sport was 69.7 % ± 27.9 at the final follow-up. At the time of the last follow-up, 93 % of the preoperatively active patients (n = 84) returned to athletic activities (n = 78). In a comparison of athletic behaviour, significantly fewer patients were performing high-impact and more patients were performing low-impact sports after surgery. Flexion (113°±16 to 117°±16) and internal rotation (12°±8 to 25°±12) improved significantly. α-angle reduction from 62°±11 to 42°± 9 (p < 0.01) was observed. The HNO increased from 3.8 mm ± 3.2 to 10.7 mm ± 3.2. In 17.6 % of the cases, progression of OA was noticed. Patients with initial OA Kellgren ≥ 2 showed significantly worse outcome than those without OA. Conclusion MOT is a safe and effective alternative for treating FAI. It leads to recovery of pain-free hip function in short- and medium-term follow-up and allows a return to practicing sports in most cases. Patients with preoperative OA ≥ 2 seem to experience insufficient gains from MO surgery, so surgeons should be reluctant to apply the technique under these circumstances.
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