Abstract
BackgroundKnee bone shape differs between men and women and the incidence of knee osteoarthritis (OA) is higher in women than in men. Therefore, the purpose of the present study was to determine whether the observed difference in the incidence of knee radiographic OA (ROA) between men and women is mediated by bone shape.MethodsWe randomly sampled 304 knees from the OAI with incident ROA (i.e., development of Kellgren/Lawrence grade ≥ 2 by month 48) and 304 knees without incident ROA. We characterized distal femur and proximal tibia shape on baseline radiographs using Statistical Shape Modeling. If a specific bone shape was associated with the risk of incident ROA, marginal structural models were generated to assess the mediation effect of that bone shape on the relation of sex and risk of incident knee ROA adjusting for baseline covariates.ResultsCase and control participants were similar by age, sex and race, but case knees were from higher body mass index (BMI) participants (29.4 vs. 27.0; p < 0.001). Women had 49% increased odds of incident knee ROA compared with men (adjusted odds ratio (OR) = 1.49, 95% Confidence Interval (C.I.): 1.04, 2.12). There was an inconsistent mediation effect for tibial mode 2 between sex and incident knee ROA, with an indirect effect OR of 0.96 (95% C.I.: 0.91–1.00) and a direct effect OR of 1.56 (95% C.I.: 1.08–2.27), suggesting a protective effect for this mode. Similar findings were also observed for the mediation effect of tibia mode 10 and femur mode 4. These shape modes primarily involved differences in the angular relation of the heads to the shafts of the femur and tibia.ConclusionsDistal femur and proximal tibia bone shapes partially and inconsistently mediated the relationship between sex and incident knee OA. Women had a higher risk of incident ROA, and specific bone shapes modestly protected them from even higher risk of ROA. The clinical significance of these findings warrant further investigation.
Highlights
Knee bone shape differs between men and women and the incidence of knee osteoarthritis (OA) is higher in women than in men
Recently investigators have used Statistical Shape Modeling (SSM) in both two and three dimensions and determined that specific shapes are associated with incident knee OA [13, 14]. Based on these new findings, the aims of this study were to determine whether knee bone shape is associated with risk of knee OA, and to what extent the difference in the incidence of knee radiographic OA (ROA) between men and women is mediated by bone shape
This study confirmed that bone shape in both the tibia and femur differ by sex and that knee bone shape is associated with incident knee ROA
Summary
Knee bone shape differs between men and women and the incidence of knee osteoarthritis (OA) is higher in women than in men. The purpose of the present study was to determine whether the observed difference in the incidence of knee radiographic OA (ROA) between men and women is mediated by bone shape. Women have a higher prevalence of OA, different patterns of OA in the knee, and an increased risk of total knee arthroplasty due to OA compared with men [2,3,4] and the explanation for these differences by sex are incompletely explained. Women have smaller cartilage volume in the knee and this appears to be independent of two known risk factors for knee OA, bone size and. Despite a significant body of research in the epidemiology of knee OA as noted above, comprehensive understanding of the factors that account for the difference in prevalence of knee OA by sex remain unclear
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