To examine the possible inverse relationship between osteoporosis and osteoarthritis (OA) by evaluating the association between bone mineral density (BMD) and knee OA in the Framingham Study cohort.
Of the 1,154 Framingham Study cohort subjects in whom BMD measurements were obtained at biennial examination 20, 932 (81%) had had knee OA assessed during the Framingham Knee OA Study 4 years earlier. BMD of the proximal femur and radius was measured by densitometry. Knee OA was assessed from a weight-bearing anteroposterior radiography and graded on a scale of 0 (no OA) to 4 (severe OA). Osteophytes and joint space narrowing were also evaluated separately. Linear regression was used to test the association of BMD with knee OA, with osteophytes, and with joint space narrowing, after adjustment for age, body mass index, and mean number of cigarettes smoked per day.
The subjects included 572 women and 360 men with an age range of 63-91 years (mean 71 years). Of these, 351 had no OA, 269 had grade 1 OA, 170 had grade 2 OA, 93 had grade 3 OA, and 49 had grade 4 OA. Mean femoral BMD at the 3 proximal femur sites was 5-9% higher in men and women with either grade 1, grade 2, or grade 3 knee OA, compared with those with no knee OA (P < 0.0001). Mean femoral BMD in those with grade 4 OA was not higher than in those with no OA. Radius BMD was not associated with knee OA in subjects of either sex. Women with osteophytes had higher BMD compared with women with no osteophytes. Mean BMD did not differ across levels of joint space narrowing.
We conclude that, among women, femoral BMD is higher in those with osteophytosis of the knee, and BMD is not necessarily associated with joint space narrowing.