Three-Dimensional Modelling and Squat Depth to Examine Geometric Hip Joint Parameters of Cam Femoroacetabular Impingement

Abstract

Many patients with a cam deformity, quantified by the alpha angle, do not demonstrate symptoms of mechanical impingement of the hip. We included additional geometric hip joint parameters along with a maximal squat depth analysis to distinguish patients with cam femoroacetabular impingement (FAI). Twenty participants were recruited and classified as either symptomatic FAI, asymptomatic FAI, or a healthy control, based on the presence of a cam deformity and symptoms. Hip joint models were segmented from subject-specific CT data and then the femoral neck-shaft angle, anterior femoral head-neck offset, and acetabular version, in addition to conventional alpha angle parameters, were measured. Maximal squat depth kinematics was collected from each participant. The symptomatic FAI group had smaller femoral neck-shaft angles and could not squat as low. A discriminant function analysis determined that femoral neck-shaft angle and radial alpha angle were significantly the most suitable parameters to classify participants with their respective subgroups (p<0.0001; p=0.003). The femoral neck-shaft angle and squat depth were the significant parameters to distinguish FAI participants (p<0.0001). Femoral neck-shaft angle and squat depth parameters can be considered as additional classifiers for FAI, in addition to the conventional alpha angles, and can perhaps explain why some patients exhibit symptoms.