Differences in anatomical parameters between the affected and unaffected hip in patients with bilateral cam-type deformities.

BACKGROUND

It is still unclear why many individuals with bilateral cam deformities demonstrate only unilateral symptoms of femoroacetabular impingement, thus symptoms may be attributed to additional anatomical parameters. The purpose was to examine patients with bilateral cam deformities, with unilateral symptoms, and compare anatomical hip joint parameters between their affected (symptomatic) hip and their contralateral, unaffected (asymptomatic) hip.

METHODS

Twenty participants (n=20) with unilateral symptoms, but bilateral cam deformities, underwent CT imaging to measure their affected and unaffected hip's: axial and radial alpha angles, femoral head-neck offset, femoral neck-shaft angle, medial proximal femoral angle, femoral torsion, acetabular version, center-edge angle; and a physical examination (hip flexion, straight-leg raise, internal rotation, external rotation) to ascertain clinical signs.

FINDINGS

The affected hips demonstrated limited motions during physical examination, compared with unaffected hips (effect size=0.550 to 0.955). The affected hips had significantly lower femoral neck-shaft angles (mean 125° (SD 3)) and lower medial proximal femoral angles (mean 79° (SD 4)), compared with the unaffected hips (mean 127° (SD 3), P=0.001, effect size=0.922; and mean 81° (SD 4), P=0.011, effect size=0.632; respectively). There were no differences in cam deformity parameters (axial and radial alpha angles, femoral head-neck offset), femoral torsion, acetabular version, and center-edge angle, between affected and unaffected hips.

INTERPRETATION

A decreased femoral neck-shaft angle or medial proximal femoral angle can be implemented as a diagnostic predictor, to determine which hip may be at a greater risk of developing early symptoms.