Cam impingement causes osteoarthritis of the hip: a nationwide prospective cohort study (CHECK)

Objective To determine the association between cam impingement, which is hip incongruity by a non-spherical femoral head and development of osteoarthritis. Methods A nationwide prospective cohort study of 1002 early symptomatic osteoarthritis patients (CHECK), of which standardised anteroposterior pelvic radiographs were obtained at baseline and at 2 and 5 years follow-up. Asphericity of the femoral head was measured by the alpha angle. Clinically, decreased internal hip rotation (<= 20 degrees) is suggestive of cam impingement. The strength of association between those parameters at baseline and development of incident osteoarthritis (K&L grade 2) or end-stage osteoarthritis (K&L grades 3, 4, or total hip replacement) within 5 years was expressed in OR using generalised estimating equations. Results At baseline, 76% of the included hips had no radiographic signs of osteoarthritis and 24% doubtful osteoarthritis. Within 5 years, 2.76% developed end-stage osteoarthritis. A moderate (a angle >60 degrees) and severe (a angle >83 degrees) cam-type deformity resulted in adjusted OR of 3.67 (95% CI 1.68 to 8.01) and 9.66 (95% CI 4.72 to 19.78), respectively, for end-stage osteoarthritis. The combination of severe cam-type deformity and decreased internal rotation at baseline resulted in an even more pronounced adjusted OR, and in a positive predictive value of 52.6% for end-stage osteoarthritis. For incident osteoarthritis, only a moderate cam-type deformity was predictive OR = 2.42 (95% CI 1.15 to 5.06). Conclusions Individuals with both severe cam-type deformity and reduced internal rotation are strongly predisposed to fast progression to end-stage osteoarthritis. As cam impingement might be a modifiable risk factor, early recognition of this condition is important.