Sex differences in parameters of bone strength in new recruits: beyond bone density

Rachel K Evans, Charles Negus, Amanda J Antczak, Ran Yanovich, Eran Israeli, Daniel S Moran
Medicine and Science in Sports and Exercise 2008, 40 (11): S645-53

BACKGROUND: Stress fracture (SF) injuries in new recruits have long been attributed to low bone mineral density (BMD). Low areal BMD assessed using two-dimensional dual-energy x-ray absorptiometry imaging, however, reflects structural density and is affected by smaller measures of bone geometry. Recent studies support a relationship between bone size and SF and indicate that slender bones are more susceptible to damage under identical loading conditions. Peripheral quantitative computed tomography (pQCT) is a three-dimensional imaging tool that provides measures of tissue density and geometry parameters of the tibia, a common site of SF.

PURPOSE: To evaluate sex differences in parameters of volumetric BMD (vBMD), geometry, and strength of the tibia in new recruits using a novel pQCT image analysis procedure.

METHODS: pQCT images were obtained from 128 healthy men and women (20 male, 108 female, aged 18-21 yr) entering a 4-month gender-integrated combat training program in the Israeli Defense Forces. Tibial scans taken at sites 4% (trabecular bone), 38%, and 66% (cortical bone) from the distal end plate were analyzed using MATLAB to assess whole-bone and regional parameters. Measures included vBMD, geometry (diameter, area, cortical thickness, and canal radius), and strength (moments of inertia and bone strength and slenderness indices).

RESULTS: With the exception of normalized canal radius, which did not differ between sexes, all measures of bone geometry (P < 0.0001) and strength (P < 0.0001 to P = 0.07) were greater in men. Women exhibited 2.7% to 3.0% greater cortical vBMD than men, whereas trabecular vBMD was 8.4% lower in women (P < 0.001). These differences remained significant after adjusting for body size.

CONCLUSION: Sex differences in bone geometry and mineralization of the tibia may contribute to a decreased ability to withstand the demands imposed by novel, repetitive exercise in untrained individuals entering recruit training.

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