Can the Alpha Angle Assessment of Cam Impingement Predict Acetabular Cartilage Delamination?

Background Substantial acetabular cartilage damage is commonly present in patients suffering from femoral acetabular impingement (FAI). A better understanding of which patient is at risk of developing substantial cartilage damage is critical for establishing appropriate treatment guidelines. Questions/Purposes We asked: (1) Does the cam deformity severity in FAI as assessed by alpha angle predict acetabular cartilage delamination? And (2) what are the clinical and radiographic findings in patients with acetabular cartilage delamination? Methods One hundred sixty-seven patients (129 males, 38 females) with a mean age of 38 years (range, 17-59 years) underwent joint preservation surgery for cam-type FAI. All data were collected prospectively. We assessed center-edge angle and Tonnis grade on AP radiographs and alpha angle on specialized lateral radiographs. Acetabular cartilage damage was assessed intraoperatively using the classification of Beck et al., with Type 3 and greater qualifying as delamination. Results For all hips, mean alpha angle was 65.5 degrees (range, 41 degrees-90 degrees), and mean center-edge angle was 33.3 degrees (range, 21 degrees-52.5 degrees). Patients with an alpha angle of 65 degrees or greater had an odds ratio (OR) of 4.00 (95% CI, 1.26-12.71) of having Type 3 or greater damage. Increased age (OR, 1.04; 95% CI, 1.01-1.07) and male sex (OR, 2.24; 95% CI, 1.09-4.62) were associated with Type 3 or greater damage, while this was the opposite for acetabular coverage as assessed by center-edge angle (OR, 0.94; 95% CI, 0.89-0.99). Conclusions Patients with cam-type FAI and an alpha angle of 65 degrees or more are at increased risk of substantial cartilage damage while increasing acetabular coverage appears to have a protective effect.