Femoroacetabular impingement (FAI) is a pathologic condition of the hip joint that leads to hip pain and osteoarthrosis (OA), especially in the young and active patient population. It is characterized by an early pathologic contact during hip motion between osseous malformation of the femoral neck and acetabular rim. The goal of the surgical dislocation of the hip is to prevent the development of OA by correcting these malformations. We investigated the clinical and radiographic outcome, the survivorship, and factors predicting poor outcome at 5-year followup.

We retrospectively evaluated 101 hips in 78 patients that underwent surgical hip dislocation at a mean age of 32 ± 8.4 (range, 15 – 52) years. The mean followup was 5.7 ± 1.0 (0.9 – 7.1) years. The series included pincer type impingement in 5 hips (5%), cam type in 9 hips (9%), and mixed type of FAI in 87 hips (87%). Pre-operatively, the patients presented with a mean Merle d’Aubigné score of 14.3 ± 3.3 (8 – 17) and a mean osteoarthrosis score according to Tönnis of 0.13 ± 0.34 (0 – 1). At followup, the clinical results were graded using the Merle d’Aubigné score and the radiographic results using the Tönnis score. Failure was defined as a conversion to a total hip arthroplasty (THA), a Merle d’Aubigné score of less than 15 or a progression of osteoarthrosis with a Tönnis score ≥2 at last followup. Demographic, clinical, radiographic, and surgical factors were tested for predictive factors for poor outcome using the Cox regression.

At followup the mean Merle d’Aubigné score was 17.2 ± 1.2 (12 – 18) and the mean Tönnis score was 0.19 ± 0.47 (0 – 2). Failures (13 hips, 13%) included 6 hips (6%) with a progression of osteoarthrosis, 5 hips (5%) hips that converted to a THA, and 2 (2%) hips presenting with a Merle d’Aubigné score of less than 15. This resulted in a cumulative survivor ship at 5 years of 97.0 ± 3.3 % (95%-confidence interval, 93.6 – 100%). Factors predicting poor outcome were a preoperative Tönnis score of 1, a cartilage tear in the Arthro-MRI, and increased age or BMI at operation.

Surgical hip dislocation has the potential to prevent the progression of osteoarthrosis and to decrease hip pain in patients with FAI. The optimal patient is young, with a decreased BMI and no sign of degeneration in the conventional radiograph or Arthro-MRI.

Pelvic tilt is a characteristic feature of the individual patients’ posture. Large differences in pelvic tilt are well known among individuals, over time or related to activity. To our knowledge, it is unknown how patients with developmental dysplasia of the hip (DDH) behave in terms of pelvic tilt. One can assume that patients with a dysplastic acetabulum might compensate for their acetabular under coverage by functionally increasing pelvic tilt. Theoretically, this effect should be reversible when an acetabular redirection osteotomy is performed. We therefore hypothesized that pelvic tilt decreases after periacetabular osteotomy.

Sixty-three consecutive patients (67 hips) with documented PAO at our institution were analyzed. 39 patients (40 hips) were excluded because of indications than other DDH (e.g. acetabular retroversion), incomplete radiographic documentation or insufficient follow-up leaving us 24 patients (27 hips) for evaluation. Preoperative, intraoperative (under general anesthesia), and at least 1 year postoperative anteroposterior radiographs were analysed. All x-rays were done in a standardized manner. Two distances were measured: the vertical/horizontal distance between the mid point of the sacrococcygeal joint and the symphysis. The change of these distances allows exact determination of the pelvic tilt.

A significant decrease for pelvic tilt was found between the preoperative x-ray and the one after at least one year. Pelvic tilt did not change significantly between the pre- and the intraoperative x-ray, and between the intra- and follow-up x-ray.

Our findings support the hypothesis that patients with DDH try to compensate for their insufficient acetabular coverage by increasing the tilt of their pelvis. After PAO, i.e. after iatrogenically increasing acetabular coverage, the patients’ pelvis significantly turns back in to less lordosis.