Study: Less hip range of motion is associated with a greater
A higher alpha angle has been proposed to correlate with lower hip range of motion. The aim of this Study were to: (1) assess the association between range of motion and alpha angle in patients with longstanding hip and groin pain; (2) examine if a cut-off value in range of motion variables could identify patients with an alpha angle above or below 60°.

72 participants were consecutively recruited after referral for hip- and groin-related pain. Passive hip range of motion was measured in flexion, internal rotation with 90° hip flexion, internal rotation in neutral hip position, external rotation with 90° hip flexion, and abduction. The alpha angle was calculated from a frog-leg lateral radiograph.

--Lower range of motion in internal rotation in flexion, external rotation, and abduction were associated with higher alpha angle.

--Internal rotation of 27° or less displayed good sensitivity (81%) and specificity (85%) to detect an alpha angle above 60°, while a cut-off of 41° in external rotation and 27° in abduction showed a sensitivity of 72% and specificity of 50% and 60%, respectively.

In a group of persons with chronic hip and groin pain, reduced internal rotation in flexion, external rotation, and abduction are linked to a higher alpha angle. A cut-off of 27° in internal rotation offers strong sensitivity and specificity for identifying people with an alpha angle greater than or equal to 60°, and could be used in the clinical situation to identify patients who need more imaging or are unlikely to have cam morphology.