Individuals with high bone mass have an increased prevalence of radiographic knee osteoarthritis

We previously reported an association between high bone mass (HBM) and a bone-forming phenotype of radiographic hip osteoarthritis (OA). As knee and hip OA have distinct risk factors, in this study we aimed to determine (i) whether HBM is also associated with knee OA, and (ii) whether the HBM knee OA phenotype demonstrates a similar pattern of radiographic features to that observed at the hip. HBM cases (defined by DXA BMD Z-scores) from the UK-based HBM study were compared with unaffected family controls and general population controls from the Chingford and Hertfordshire cohort studies. A single blinded observer graded AP weight-bearing knee radiographs for features of OA (Kellgren-Lawrence score, osteophytes, joint space narrowing (JSN), sclerosis) using an atlas. Analyses used logistic regression, adjusting a priori for age and gender, and additionally for BMI as a potential mediator of the HBM-OA association, using Stata v12. 609 HBM knees in 311 cases (mean age 60.8years, 74% female) and 1937 control knees in 991 controls (63.4years, 81% female) were analysed. The prevalence of radiographic knee OA, defined as Kellgren-Lawrence grade≥2, was increased in cases (31.5% vs. 20.9%), with age and gender adjusted OR [95% CI] 2.38 [1.81, 3.14], p<0.001. The association between HBM and osteophytosis was stronger than that for JSN, both before and after adjustment for BMI which attenuated the ORs for knee OA and osteophytes in cases vs. controls by approximately 50%. Our findings support a positive association between HBM and knee OA. This association was strongest for osteophytes, suggesting HBM confers a general predisposition to a subtype of OA characterised by increased bone formation.