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

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

N.S. Riedstra, F. Boel, M.M. Van Buuren, 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, affecting at least 500 million people worldwide. Partly due to a lack of knowledge on its aetiology, OA currently cannot be cured. Hip morphology has been marked as an important risk factor for the development of hip OA, in particular acetabular dysplasia (AD). The under-coverage of the acetabulum relative to the femoral head in individuals with AD leads to increased joint load which may result in premature cartilage damage and ultimately cause hip OA. Attempts to relate AD to the development of hip OA from single cohort studies have yielded conflicting results as these studies may be underpowered to study this association. This study’s aim was to determine the relation between AD at baseline and the risk of radiographic hip OA within 8 years follow-up, using 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). 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 Wiberg center edge angle (WCEA) is a measurement of coverage of the femoral head by the acetabulum. The WCEA 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 weight bearing acetabulum (the sourcil), see Figure 1. From the outline of the hip shape, the WCEA was calculated automatically. The threshold used for AD is a WCEA ≤ 25°. We excluded all hips with a lateral center edge angle (LCEA) ≥ 40° in order to exclude hips with pincer morphology, which is a hip shape that may also be associated with the development of hip OA. Development of radiographic hip OA was defined by K&L grade ≥2, Croft score ≥2, OA score =2 or total hip replacement (THR), depending on available scores per cohort. The associations between baseline AD 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 pincer morphology, we included 13902 hips. Of the included hips 3731 hips (27%) had acetabular dysplasia. Within a maximum of 8 years (mean 6.1 ±1.7) follow-up, 547 hips (4%) developed radiographic hip OA. AD was significantly associated with hip OA with an OR of 1.24 (95% CI 1.021-1.495).


The odds of developing radiographic hip OA within 8 years in a population with an average age of 62.2 and an average BMI of 27.2 for hips with AD is 1.24 times higher than in hips without AD. The large and heterogeneous sample size allowed for a robust estimate of this effect. Future studies within the World COACH consortium will elucidate whether this is an overall effect or if specific high-risk subgroups, for instance the younger individuals, are responsible for the association found.