Radiographic knee osteoarthritis is associated with higher lumbar spine bone mineral density but not reduced vertebral fracture prevalence: a retrospective cross-sectional study in older Asian women.

BACKGROUND

The relationship between knee osteoarthritis (OA), bone mineral density (BMD), and vertebral fractures remains controversial. Degenerative changes associated with OA may artifactually elevate lumbar spine BMD measured by dual-energy X-ray absorptiometry (DXA), potentially obscuring true skeletal fragility. We examined the association of radiographic knee OA with site-specific BMD and vertebral fracture prevalence in older Asian women.

METHODS

This retrospective cross-sectional study included 2,036 postmenopausal women who underwent knee radiography, lumbar spine and hip DXA, and lateral thoracolumbar radiography (T4-L4) during health examinations at a single center. Radiographic knee OA was defined as Kellgren-Lawrence grade ≥ 2. Lumbar spine and hip BMD T-scores were recorded. Vertebral fractures were assessed using a semi-quantitative radiographic approach. Logistic regression analyses were performed to evaluate associations between knee OA and prevalent vertebral fractures, adjusting for age and body mass index (BMI).

RESULTS

Radiographic knee OA was present in 27.0% of participants. Women with OA were older and had higher BMI. Lumbar spine T-scores were significantly higher in women with OA, whereas hip T-scores were not independently associated with OA after adjustment. Vertebral fractures were more prevalent in women with OA in crude analyses (41.5% vs. 30.7%), but this association was fully attenuated after adjustment for age and BMI (adjusted OR 0.95, 95% CI 0.76-1.20).

CONCLUSIONS

In this cross-sectional sample of older Asian women, radiographic knee OA was associated with higher lumbar spine BMD but not with lower vertebral fracture prevalence after accounting for age and BMI. Elevated spine BMD in OA may reflect degenerative artifact rather than enhanced skeletal strength. In patients with knee OA, hip BMD and clinical fracture history may provide more reliable indicators of skeletal fragility than lumbar spine BMD alone.