Standing anterior pelvic tilt is correlated with the proximal femur shape of individuals with cam morphology.

Abstract

Spinopelvic morphology and alignment have been theorized to play a role in causing femoroacetabular impingement syndrome symptoms in individuals with cam morphology. However, prior studies have used hip morphological and alignment measurements that are interdependent, limiting understanding of form-function relationships. Statistical shape modeling and biplane videoradiography were used for accurate, 3D assessment of femur and pelvis morphology and in vivo standing hip and pelvis orientation among individuals with and without cam morphology and impingement symptoms. Group differences in standing posture and shape were assessed, along with correlations between shape and posture. Patients stood with less anterior pelvic tilt and greater hip extension than asymptomatic individuals without cam morphology. A more patient-like proximal femur shape was correlated with less anterior pelvic tilt. Asymptomatic individuals with cam morphology showed no standing posture differences but had a unique pelvic shape featuring an internally rotated ilium. Further, femur and pelvis anatomical features, primarily describing changes at hip-crossing muscle attachment sites and the sacroiliac region, showed significant associations with hip and pelvis orientation in the sagittal and frontal planes. Patients with symptomatic impingement due to cam morphology may preemptively adopt less anterior pelvic tilt to enable functional hip range of motion. The associations between shape and standing posture may identify patients best suited for treatment involving pelvic posture modification. Results support further investigation of hip crossing muscle characteristics and spinopelvic alignment during dynamic activities to strengthen understanding of the underlying mechanisms responsible for symptoms in patients with femoroacetabular impingement syndrome.