Site-specific variance in radius and tibia bone strength as determined by muscle size and body mass.

PURPOSE: To investigate the predictive ability of muscle cross-sectional area (MCSA) and body mass on bone mineral content, compressive bone strength index (BSIc), and the polar stress-strain index (SSIp) of the forearms and lower legs of middle-aged adults.
METHODS: A total of 53 healthy adults (37 male, 16 female; mean age 50.4; SD 2.1 y) were scanned with peripheral quantitative computed tomography (pQCT) to measure radius and tibia total and cortical bone mineral content, BSIc, SSIp, and forearm and lower-leg MCSA (BSIc: 4% distal; SSIp and MCSA at 65% and 66% radius and tibia shaft sites, respectively). Multiple regression models adjusted for sex and height were used to assess the relative variance in radius or tibia bone outcomes predicted by body mass and/or forearm or lower-leg MCSA.
RESULTS: Forearm MCSA independently predicted total bone-mineral content, BSIc, and SSIp in radius (r partial=0.59, 0.56, 0.42). Body mass was a negative predictor of radius BSIc (r partial=-0.32) and did not predict other radius outcomes when both body mass and MCSA were forced in the models. In the lower leg shaft, MCSA, and body mass predicted bone content and strength similarly when independently added to the models with sex and height.
CONCLUSIONS: Forearm MCSA was a dominant predictor of radius bone content and estimated strength. In the tibia, both body mass and lower-leg MCSA contributed to predicting bone content and estimated strength.