The relationship of bone density and fracture to incident and progressive radiographic osteoarthritis of the knee: The Chingford study

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Abstract
Investigators performing cross-sectional studies have reported small increases in bone mineral density (BMD) in subjects with osteoarthritis (OA). This study was undertaken to examine the association of bone mass with incident and progressive disease and to determine whether prior fractures influence the development of OA. Eight hundred thirty women had repeat knee radiographs 48 months from baseline. All radiographs were graded on the presence or absence of osteophytes and joint space narrowing (JSN). Incident knee OA was defined as new disease in the 715 women without knee OA at baseline. Progression was a change of at least one grade in the 115 women with baseline knee OA. All women underwent bone densitometry of the lumbar spine and hip. Rates of subsequent incident OA were compared between fracture groups. The 95 women with incident knee osteophytes had significantly higher baseline spine BMD (1.01 gm/cm2 versus 0.95 gm/cm2, or 6.3%; P = 0.002) and significantly higher hip BMD (0.79 gm/cm2 versus 0.76 gm/cm2, or 3.9%; P = 0.02) than those without incident disease. For the 33 women whose osteophytes progressed, no difference was seen compared with nonprogressors in spine BMD, but hip BMD was modestly reduced (-2.5%). The 81 women who had incident JSN had nonsignificantly higher baseline spine BMD (3.0%), while no difference was seen for the 30 women whose JSN had progressed. For hip BMD, a nonsignificant increase was seen in those with incident JSN (1.3%), and a nonsignificant reduction was seen in those whose JSN progressed (-2.7%). One hundred forty-five women sustained peripheral fractures, mainly in the distal forearm (27.6%) and vertebrae (28.3%). Women with a peripheral fracture had a reduced risk of subsequently developing incident knee OA (odds ratio [OR] 0.30, 95% confidence interval [95% CI] 0.11-0.84). Although numbers were smaller, nonsignificant reductions in rates of incident OA were seen for those with distal forearm (OR 0.40, 95% CI 0.11-1.49) and vertebral (OR 0.20, 95% CI 0.07-1.61) fractures. These results confirm that for women who develop incident knee OA, defined by osteophytes, BMD is higher and of a magnitude similar to that shown in cross-sectional studies. Low BMD at the hip appears weakly related to progression. Women with previous fractures have less chance of developing OA, independent of BMD status. Although the mechanism for this action is unclear, these results suggest a possible common role of bone turnover and repair in the early manifestations of OA.