In Vivo Hip Morphology and Kinematics in Elite Baseball Pitchers.

PURPOSE: To compare passive and real-time active hip range of motion (ROM) in asymptomatic collegiate pitchers, to investigate whether differences in hip morphology and ROM exist between lead and trail hips, and to relate active hip ROM during the pitch to hip morphology and femoroacetabular impingement.

METHODS: Eleven collegiate baseball pitchers participated in kinematic testing that involved throwing 4 fastball pitches while wearing a full-body inertial-based motion-capture system. Passive flexion and rotation of each hip were measured using a goniometer. Nine pitchers also underwent a computed tomography (CT) pelvic scan, from which subject-specific computer models for each hip were created. Morphologic measurements were calculated from the models, and the models were tested for impingement during simulated pitching.

RESULTS: Hip flexion was the only passive ROM measurement showing a significant difference between the lead and trail hips (mean difference [MD], 4°; P = .027). During the pitching motion, within-individual differences were discovered between the lead and trail hips for flexion (MD, 34°; P < .0001), extension (MD, 26°; P < .0001), abduction (MD, 8°; P = .026), adduction (MD, 6°; P = .008), external rotation (MD, 20°; P = .001), and total arc of rotation (MD, 13°; P = .001). There were no significant differences in morphologic measures between the lead and trail hips. Dynamic CT modeling did not lead to bony impingement in any subject.

CONCLUSIONS: Asymptomatic collegiate pitchers approach their extremes of passive hip rotation when executing a fastball pitch. No differences were found in passive hip ROM or morphology other than a small difference in passive hip flexion. Dynamic CT modeling did not show femoroacetabular impingement during the pitching motion.

CLINICAL RELEVANCE: Hip dysmorphology or poor pitching mechanics may lead to a high risk of bony impingement because pitchers have little reserve hip motion during the fastball pitch.