Abstract
Some military personnel are having Femoral Acetabular Impingement (FAI) surgery. The use of the alpha angle (AA) to help assess the diagnosis is common. Currently there are no standardised values available across a asymptomatic pre-arthritic population.
Retrospective analysis of 200 consecutive individuals (400 hip joints) with ages 20 to 50, who had a CT performed between 1 Apr 2011 and 29 Nov 2011 due to abdominal pathology. The AA of Notzli was measured on the axial view.
The mean AA value was 53.5 (95%CI 1.30) for Right hips and 53.4 (95% CI 1.31) for the left. In age 20–30 Right 52.6 (95%CI 3.5) the Left 52.0 (95%CI 2.9), 31–40 Right 53.9 (95%CI 2.5) Left 53.4 (95%CI 3.1), 41–50 Right 53.8 (95% CI 1.9) Left 53.2 (95% CI 1.8). Mean male Right 52.9 (95% CI 1.5) Left 53.2 (95%CI 1.9) Female Right 52.5 (95% CI 1.5) Left 49.9 (95% CI 1.6). 144/400 (37%) of patients had angle >55 degrees.
Previous literature suggests an AA >55 degrees is diagnostic of FAI, we suggest that the AA is highly variable across age and sex and that >1/3rd of asymptomatic patients will have an AA that was previously regarded as abnormal.
