Bone mineral density and risk of incident and progressive radiographic knee osteoarthritis in women: the Framingham Study

Objective. To examine the relations of bone mineral density (BMD) and chang e in BMD to risk of incident and progressive radiographic knee osteoarthrit is COA) in a longitudinal cohort study. Methods. Female participants aged 63 to 91 years (mean age 71) in the Frami ngham Study received anteroposterior weight bearing knee radiographs at bie nnial examinations 18 (1983-85) and 22 (1992-93). Knee radiographs were giv en scores for global severity of OA (Kellgren-Lawrence scale: range 0 to 4) add for the presence of osteophytes and joint space narrowing (range 0 to 3). Femoral neck BMD was assessed using dual photon absorptiometry at exami nation 20 and dual x-ray absorptiometry at examination 22. We examined the relations of BMD at examination 20 and its change between examination 20 an d examination 22 to incident and progressive knee OA, as well as to worseni ng of individual radiographic features adjusting for age, body mass index, and other potential confounding factors. Results. In total, 473 women (ages 63 to 91 yrs) had complete assessments. Over 8 years of Followup, risk of incident radiographic knee OA increased f rom 5.6% among women in the lowest age-specific quartile of BMD to 14.2, 10 .3, and 11.8% among women in the 2nd, 3rd, and highest; quartiles, respecti vely, Multivariate adjusted OR of incident OA for each increase quartile of BMD were 1.0, 2.5, 2.0, and 2.3, respectively (p for trend = 0.222). This was mainly reflected in an increased risk of osteophyte: development. Howev er, risk of progressive OA decreased from 34.4 to 22,0, 20.3, and 18.9% as BMD increased. Compared to those in the lowest quartile of BMD, adjusted OR for progressive disease were 0.3, 0.2, and 0.1 among women in the 2nd, 3rd , and highest quartiles (p for trend < 0.001), respectively, mainly due to its effect on lowering the risk of joint space lass. Compared to those who lost BMD > 0.04 g/cm(2) over the followup period, women who gained BMD were at increased risk of incident but at a significantly decreased risk of pro gressive knee OA. BMD change was not associated with osteophyte development , but gain in BMD lowered the risk of joint space loss. Conclusion. High BMD and BMD gain decreased the risk of progression of radi ographic knee OA, but may be associated with an increased risk of incident knee Ok The protective effect was mainly through its influence on reducing the risk of joint space loss. Our results offer insights into how bone may affect the course of the most common joint disease, and thus may have poten tial therapeutic implications.