Pincer Morphology Is A Risk Factor For Developing Radiographic Hip Osteoarthritis; Data From The World Coach Consortium

Pincer Morphology Is A Risk Factor For Developing Radiographic Hip Osteoarthritis; Data From The World Coach Consortium

N.S. Riedstra, M.M. Van Buuren, F. Boel, H. Ahedi, V. Arbabi, N. Arden, S.M. Bierma-Zeinstra, C.G. Boer, F.M. Cicuttini, T.F. Cootes, D.T. Felson, W.P. Gielis, S. Kluzek, N.E. Lane, C. Lindner, J. Lynch, J. van Meurs, A.E. Nelson, M.C. Nevitt, E.H. Oei, J. Runhaar, T.D. Spector, J. Tang, H.H. Weinans, R. Agricola



Osteoarthritis (OA) is the most prevalent joint disease with an estimated prevalence of 8% in the general population. Hip morphology has been marked as an important risk factor for the development of hip OA. One of the types thought to increase the risk of hip OA is pincer morphology, which is an overcoverage of the femoral head by the acetabulum. The overcoverage may result in the femoral neck impinging against the acetabulum during motion and possibly creating intra-articular damage over time. However, attempts to relate pincer morphology to the development of hip OA have yielded conflicting results. We studied the relationship between pincer morphology at baseline and the risk of developing radiographic hip OA within 8 years follow-up, using individual participant data from the Worldwide Collaboration on OsteoArthritis prediCtion for the Hip (World COACH).


The World COACH consortium was established to collect and harmonize all available individual participant data from prospective cohort studies (n=9) that have sequential pelvic or hip imaging available. For the current study, we included the 6 cohorts that had baseline pelvic radiographs and radiographic OA scores available within a maximum of 8 years. Standardized anteroposterior (AP) pelvic and/or hip radiographs were taken at baseline and at a follow-up visit between 4-8 years in each included cohort. Scores for radiographic OA were already available for each cohort, either by Kellgren & Lawrence grade (K&L), (modified) Croft grade, or an adaptation. For this analysis we harmonized these scores into “definitely no OA” (any score 0), “doubtful OA” (any score 1), or “definite OA” (any score ≥2 or total hip replacement (THR)). We only included hips without OA (any score 0) at baseline. An automatic Bonefinder® search model was used to annotate all baseline radiographs, outlining the bony shape per hip. The lateral center edge angle (LCEA) is a measurement for coverage of the femoral head by the acetabulum. The LCEA is formed by a vertical line perpendicular to the horizontal reference line and a line from the center of the femoral head to the most lateral point of the acetabulum (Figure 1). From the outline of the hip shape, the LCEA was calculated automatically. The threshold used for pincer morphology is a LCEA ≥ 45°. We excluded all hips with a LCEA ≤ 25° in order to exclude hips with acetabular dysplasia as this is a hip shape that may also be related to hip OA. Development of radiographic hip OA was defined as a K&L grade ≥2, Croft score ≥2, OA score =2 or THR, depending on available scores per cohort. The associations between baseline pincer morphology and development of radiographic hip OA were estimated using a logistic regression model with generalized mixed effects with 3 levels: hip side (left/right), individual and cohort. The results are expressed as odds ratios (OR) and were adjusted for baseline age, sex, and BMI.


The six cohorts included yielded radiographic hip OA data on 51,363 hips (Table 1). We excluded 5,004 hips with definite OA and 18,250 hips with doubtful OA or missing OA scores at baseline. This left 28,109 hips without OA at baseline. After exclusion of hips with other missing data, insufficient quality radiographs or acetabular dysplasia, we included 16655 hips. At baseline 759 hips (5%) had pincer morphology. Within a maximum of 8 years (mean 6.1 ± 1.7) follow-up, 683 hips (4.6%) developed radiographic hip OA. Pincer morphology was significantly associated with radiographic hip OA with an aOR of 1.59 (95% CI 1.156-2.195).


In hips without radiographic OA at baseline, the odds of developing hip OA within 8 years are 1.59 times higher in hips with pincer morphology than in hips without pincer morphology. The large and heterogeneous sample size allowed a robust estimate of this effect. Further studies within the World COACH consortium will elucidate whether this is an overall effect or if specific high-risk subgroups are responsible for the association found.