Post-operative Alpha Angle Not Associated with Outcomes 5 Years following Hip Arthroscopy for FAI

Abstract

The alpha angle is currently the most used parameter for defining cam type femoroacetabular impingement(FAI). The purpose of this study was to determine if post-operative alpha angle is a predictor of patient outcomes 5 years following hip arthroscopy for FAI. Our hypothesis was that post-operative alpha angle(AA) would not influence clinical outcomes in patients with FAI. 230 patients had primary hip arthroscopy for FAI. Average age was 38(range 18 to 69). All patients had preoperative and post-operative alpha angles recorded. At 5 years following arthroscopy, all patients completed a questionnaire that included the modified Harris Hip score(MHHS), WOMAC, HOS ADL, HOS Sport, SF12 and patient satisfaction. This study was IRB approved. Patients were grouped based on their postoperative AA: <55°(n=158) and >55°(n=56) The average preoperative AA was 73°(range 50° to 105°) and the postoperative AA was 48°(range 30° to 100°). The post-operative AA did not correlate with any outcome measure. The average preoperative alpha angle in the <55° group was 72° and in >55° group the average was 76°(p=0.024). At average follow-up of 5.5 years(range 5 to 7) there were no significant differences in outcomes between groups. The average mHHS was 52(±8) in the <55° and 53(±6) in the >55° group; WOMAC was 10(±11) in the <55° and 8(±10) in the >55° group; HOS ADL was 90(±13) in the <55° and 92(±11) in the >55° group; HOS Sport was 78(±25) in the <55° and 82(±21) in the >55° group. Median patient satisfaction was 9(range 1 to 10) in both groups. There were no significant difference between any outcome score based on correction to 55° at 5 years. While alpha angle has been shown to be an excellent preoperative diagnostic tool, the postoperative angle does not correlate with midterm outcomes or the development of osteoarthritis.