Der Einfluss des alpha-Winkels und der Vollständigkeit der Cam-Resektion auf das Outcome nach einer Hüftarthroskopie

The treatment of femoroacetabular impingement (FAI) with hip arthroscopy has steadily gained popularity in recent years. An anatomical imbalance in the area of the femoral head-neck transition and the acetabulum can lead to the development of such an FAI. In the present study, clinical and radiological parameters are used to determine the extent of cam resection necessary to achieve the best possible clinical outcome for patients. In particular, the change in the alpha angle was assessed. The study included patients who were diagnosed with FAI between 2006 and 2014 and treated surgically with hip arthroscopy. Out of 529 patients, 234 showed an isolated cam impingement and 190 patients showed a so-called mixed form. A mixed form is a deformity of the femoral and acetabular components of the joint. The clinical and radiological results were collected by means of a questionnaire catalogue and the evaluation of the radiographs taken. The questionnaire included the WOMAC score, the VAS for pain, the SF 36 questionnaire, the Harris hip score and the hip outcome score. In addition, intra- and postoperative complications and patient satisfaction were recorded. Complete data sets were collected from 484 patients (91.4 %). The average follow-up was 42.5 months and the patients were 47.8 years old on average. 83 study participants (17.7 %) underwent surgery again. Statistically significant postoperative clinical improvements were achieved in all scores. The median postoperative alpha angle was 46.8°. Regression analysis demonstrated that particularly high preoperative alpha angles were associated with a new operation. In contrast, the postoperative alpha angles had no influence on the outcome "reoperation". Also in the data of the subgroup analysis, which included only patients with pure cam deformities, no significant influence regarding the completeness of a cam resection on the outcome of the scores could be recorded. The investigation of the changes of the preoperative to the postoperative alpha angles showed that the large resection dimensions (over 30°) as well as small changes, which however assume high preoperative alpha angles, are associated with an increased risk of a renewed operation. On the one hand, the data of the present work highlight the high value of the alpha angle as a diagnostic tool for predictive analysis of the preoperative situation. On the other hand, they could possibly indicate that the definition of a threshold value for the alpha angle is inappropriate for the assessment of the postoperative clinical situation. These results show the importance of adequate patient selection. Especially in patients with changes of the hip joint that are associated with arthrosis, low preoperative clinical scores and high preoperative alpha angles, a particularly careful indication for surgery should be provided.