Prevalence of CAM deformity and its influence on therapy success in patients with osteonecrosis of the femoral head.

Osteonecrosis of the femoral head (ONFH) and CAM-type femoroacetabular impingement (FAI) present two different pathologies of the hip joint. The aim of this study is to describe the prevalence of CAM-FAI in a collective of ONFH hips and to evaluate its influence on ONFH therapy outcome. A cohort of 86 ONFH hips with a mean follow-up of 46.7 months (±20.5) after advanced core decompression (ACD) was evaluated regarding CAM deformity by measuring the alpha angle (α) and head-neck offset. The influence of CAM-type FAI was investigated using the Kaplan-Meier estimator and the Cox regression model. The mean α was 60.4° (±13.8) with 41 hips (47.7%) being ≥60°. The mean head-neck offset was 4.5 mm (±3.2), with 78 hips (90.7%) being ≤9 mm. Survival analysis indicated noticeably better ACD results for α < 60° versus α ≥ 60° (p = 0.07). Treatment failure within the first 2 years was statistically estimated as 27.7% for α < 60° versus 40.7% for α ≥ 60°: The hazard ratio for α ≥ 60° was 1.94. Head-neck offset-dependent survival showed better, though not significant, results for offset >9 mm (p = 0.38, hazard ratio 1.89 for offsets ≤9 mm). The prevalence of CAM-type deformity is greatly increased in patients with concomitant ONFH. There is a strong indication that CAM-type FAI has a negative influence on ONFH therapy outcome. The risk that ONFH treatment will fail seems to be twice as high for α ≥ 60° as for α < 60°. We recommend cotreatment of pathological head-neck offset in patients with ONFH.