Association between bone mineral density and knee osteoarthritis in Koreans: the Fourth and Fifth Korea National Health and Nutrition Examination Surveys

Objective: The objective of the study was to investigate the association of hip and lumbar spine (LS) bone mineral density (BMD) with the presence and severity of radiographic knee osteoarthritis (OA), including both men and women over 50 years of age, while adjusting for potential confounders.

Design: Cross-sectional data from 5793 community-dwelling subjects (2491 men and 3302 women) aged ≥ 50 years in the Korea National Health and Nutrition Examination Surveys (KNHANES) were analyzed. BMDs for femoral neck (FN), total hip (TH), and LS were measured using dual-energy X-ray absorptiometry. Radiographic changes relating to OA were assessed using the Kellgren-Lawrence (KL) grading scale. The mean BMD, according to the presence of knee OA (KL grade ≥ 2) and the KL grades, were analyzed using the general linear models (GLM) adjusted for anthropometric and biochemical confounders.

Results: Adjusted FN and LS BMD were significantly higher in subjects with knee OA (P = 0.036 and P = 0.001, respectively). Within the subjects with knee OA (KL grades 2, 3 and 4), adjusted FN and TH BMD decreased as the KL grades increased, while the adjusted LS BMD was not different. Among the subjects with KL grades of 0, 1 and 2, FN, TH and LS BMD increased as the KL grades increased. These inverted U-shaped associations between adjusted FN and TH BMD and KL grades were presented in both men and women. The proportion of osteoporosis (OP) was as high as 39.5% among subjects with KL grade 4.

Conclusion: There is an inverse relationship between OP and the presence of knee OA, but there is a non-linear and site-specific association between OP and the severity of knee OA. The relationship between the two diseases has to take into account potential covariates.