SQUATTING MECHANICS FOLLOWING AN OSTEOCHONDROPLASTY FOR IDIOPATHIC FEMOROACETABULAR IMPINGEMENT

Background: Femoroacetabular impingement (FAI) is primarily due to the repetitive motion of aberrant bone in provocative positions such as hip flexion and internal rotation (IR). The purpose of this study is to evaluate the kinematic changes that occur in the hip during a squat prior to and following an osteochondroplasty for idiopathic FAI. Methods: Subjects were prospectively enrolled when scheduled to undergo hip preservation surgery for primary CAM hip impingement by one of 3 surgeons. Prior to the procedure, subjects were evaluated in the movement science lab while performing a standardized bilateral limb gravity squat. Kinematic data of the trunk, pelvis and lower limbs were analyzed during the descent phase of the squat. Statistical comparison of the operative and non-operative hips was performed prior to and at a minimum of one year following surgery. Results: Twenty-seven hips with a mean age of 16.3 years (12.4 – 19.9 years, 8 males) underwent an osteochondroplasty (8 arthroscopic, 19 surgical hip dislocation) resulting in a decrease in the alpha angle (60.8° versus 46.8°, p<0.001) and a significant improvement in HOOS and UCLA scores. When combining the entire cohort, no statistical difference was seen in side to side nor pre-operative to post-operative kinematic or kinetic data. Asymmetry was seen in the transverse plane hip rotation with 6/27 subjects demonstrating an average reduction of 9.4° in ROM on the affected side and a decrease in both peak IR and external rotation (ER) (average decrease 4.7°). Following osteochondroplasty, asymmetry resolved in 4/6 patients. Also, 16/27 subjects demonstrated asymmetry in rotation at 40° of hip flexion during the squat (11 more ER, 5 more IR) in which 37.5% had resolution of the asymmetry following an osteochondroplasty. Conclusion: Asymmetry in squatting mechanics in patients with FAI is not consistent with all subjects. Those with asymmetry in rotation at 40° of hip flexion during the squat or reduction in overall hip rotation may see a resolution in asymmetry following an osteochondroplasty. Dynamic impingement may present as asymmetry during different positions of hip flexion in a squat.