Bone Geometry, Strength, and Muscle Size in Runners with a History of Stress Fracture

School of Kinesiology, Laboratory of Musculoskeletal Health, University of Minnesota, Minneapolis, MN 55455, USA.
Medicine and science in sports and exercise (Impact Factor: 3.98). 11/2009; 41(12):2145-50. DOI: 10.1249/MSS.0b013e3181a9e772
Source: PubMed


Our primary aim was to explore differences in estimates of tibial bone strength, in female runners with and without a history of stress fractures. Our secondary aim was to explore differences in bone geometry, volumetric density, and muscle size that may explain bone strength outcomes.
A total of 39 competitive distance runners aged 18-35 yr, with (SFX, n = 19) or without (NSFX, n = 20) a history of stress fracture were recruited for this cross-sectional study. Peripheral quantitative computed tomography (XCT 3000; Orthometrix, White Plains, NY) was used to assess volumetric bone mineral density (vBMD, mg x mm(-3)), bone area (ToA, mm(2)), and estimated compressive bone strength (bone strength index (BSI) = ToA x total volumetric density (ToD(2))) at the distal tibia (4%). Total (ToA, mm(2)) and cortical (CoA, mm(2)) bone area, cortical vBMD, and estimated bending strength (strength-strain index (SSIp), mm(3)) were measured at the 15%, 25%, 33%, 45%, 50%, and 66% sites. Muscle cross-sectional area (MCSA) was measured at the 50% and 66% sites.
Participants in the SFX group had significantly smaller (7%-8%) CoA at the 45%, 50%, and 66% sites (P <or= 0.05 for all), significantly lower SSIp (9%-10%) at the 50% and 66% sites, and smaller MCSA (7%-8%) at the 66% site. The remaining bone parameters including vBMD were not significantly different between groups. After adjusting for MCSA, there were no differences between groups for any measured bone outcomes.
These findings suggest that cortical bone strength, cortical area, and MCSA are all lower in runners with a history of stress fracture. However, the lower strength was appropriate for the smaller muscle size, suggesting that interventions to reduce stress fracture risk might be aimed at improving muscle size and strength.

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    • "According to Crossley et al. and Franklyn et al., the cross sectional area (CSA) of the tibial cortex is less in male athletes with a history of tibial stress injury than uninjured male athletes (Crossley et al., 1999; Franklyn et al., 2008). Popp et al. and Schnackenburg et al. reported similar findings in female runners (Popp et al., 2009; Schnackenburg et al., 2011). Franklyn et al. also indicated geometric measures related to bone strength, specifically the second moment of area and section modulus in "
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    • "However, a meta-analysis study has shown that there is an association between low bone density and fractures, in children.19 Several studies have reported that fractures occurring during youth might be associated with a reduction in bone gain during puberty, and it might be associated with subsequent low-peak bone mass,20 genetic factors,21 and physical inactivity, and muscle, loss secondary to fractures.22 It is likely that the greater bone strength (mainly determined by bone mass) is, the lower is the incidence of fractures during practice. "
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    • "Studies have focused on muscle and kinetic parameters and their possible relationships with the incidence of tibia stress fractures in groups with a recent history of injury, rather than examining the pre-fracture period. Moreover, most studies have given priority to long-distance runners (1,8,11,12) and have made no comparisons with other sports that also result in fractures. Therefore, studying the muscle and kinetic characterization of vertical ground reaction forces among triathlon athletes and long-distance runners, and comparing them with non-athletic individuals who are not subjected to high training loads, is important for developing possible strategies to prevent overuse injuries in these two sports. "
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