Usefulness of cortical thickness ratio of the third metacarpal bone for prediction of major osteoporotic fractures.

Objective: Patients with rheumatoid arthritis (RA) are at high risk for osteoporotic fractures. We developed an index called the third metacarpal cortical thickness ratio (CTR), which reflects bone mineral density (BMD) in RA patients. A longitudinal study was conducted to verify the usefulness of CTR during the follow-up period.

Methods: Patients with RA who underwent dual energy X-ray absorptiometry (DXA) and hand X-ray simultaneously were monitored for disease activity and activities of daily living at 3-month intervals, and BMD and CTR were measured at 1-year intervals. Mean CTR during follow-up was tested for correlation with mean BMD at both the lumbar spine (LS) and femoral neck (FN) during follow-up. Correlations were examined, including other variants potentially correlated with BMD. The risk ratio of accidental major osteoporotic fractures (MOF) in the variance including CTR and BMD was evaluated.

Results: A total of 300 patients, 40 men and 260 women, were enrolled. Mean follow-up length was 49.6 months. CTR was significantly associated with BMD in FN using a multivariate model of linear regression analysis (p < 0.0001), whereas CTR was significantly associated with BMD in LS using only a univariate model (p < 0.01). The only variant with a significantly higher risk ratio for incident MOF was the presence of prevalent MOF. CTR and BMD did not show a significantly higher risk ratio using Cox regression analysis.

Conclusion: CTR correlated significantly with BMD even during follow-up, especially in FN. However, CTR and BMD were not risk factors for major MOF.