Pincer deformity does not lead to osteoarthritis of the hip whereas acetabular dysplasia does: acetabular coverage and development of osteoarthritis in a nationwide prospective cohort study (CHECK)

Objective: Determining the relation between acetabular coverage, especially overcoverage which may lead to pincer impingement, and development of osteoarthritis (OA) of the hip. Design: From a prospective cohort study of 1,002 individuals with symptoms of early OA (Cohort Hip and Cohort Knee, CHECK), 720 participants were included. Standardized anteroposterior pelvic radiographs and false profile lateral radiographs were obtained at baseline and 5 years follow-up. Acetabular undercoverage (mild dysplasia) and overcoverage (pincer deformity) were measured by a centre edge angle of <25° and >40° respectively in both radiographic views. The strength of association between those parameters at baseline and development of incident OA (Kellgren and Lawrence (K&L) grade >2 or total hip replacement), or joint space narrowing within 5 years was expressed in odds ratio (OR) adjusted for K&L grade, age, body mass index (BMI), and sex using generalized estimating equations. Results: At baseline, 76% of the included hips had no signs of radiographic OA (K&L = 0) whereas 24% had doubtful OA (K&L = 1). Within 5 years, 7.0% developed incident OA. Acetabular dysplasia was significantly associated with development of incident OA with ORs between 2.62 (95% confidence interval (CI) 1.44-4.77) and 5.45 (95% CI 2.40-12.34), dependent on the radiographic view. A pincer deformity was not associated with any outcome measure, except for a significantly protective effect on incident OA when a pincer deformity was present in both radiographic views OR 0.34 (95% CI 0.13-0.87). Conclusion: Acetabular dysplasia was significantly associated with development of OA. However, a pincer deformity was not associated with OA, and might even have a protective effect on its development, which questions the supposed detrimental effect of pincer impingement.

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