Purpose To determine differences in bone geometry, estimates of bone strength, muscle size and bone strength relative to load, in women runners with and without a history of stress fracture. Methods We recruited 32 competitive distance runners aged 18–35, with (SFX, n = 16) or without (NSFX, n = 16) a history of stress fracture for this case-control study. Peripheral quantitative computed tomography (pQCT) was used to assess volumetric bone mineral density (vBMD, mg/mm3), total (ToA) and cortical (CtA) bone areas (mm2), and estimated compressive bone strength (bone strength index; BSI, mg/mm4) at the distal tibia. ToA, CtA, cortical vBMD, and estimated strength (section modulus; Zp, mm3 and strength strain index; SSIp, mm3) were measured at six cortical sites along the tibia. Mean active peak vertical (pkZ) ground reaction forces (GRFs), assessed from a fatigue run on an instrumented treadmill, were used in conjunction with pQCT measurements to estimate bone strength relative to load (mm2/N ∗ kg− 1) at all cortical sites. Results SSIp and Zp were 9–11% lower in the SFX group at mid-shaft of the tibia, while ToA and vBMD did not differ between groups at any measurement site. The SFX group had 11–17% lower bone strength relative to mean pkZ GRFs (p < 0.05). Conclusion These findings indicate that estimated bone strength at the mid-tibia and mean pkZ GRFs are lower in runners with a history of stress fracture. Bone strength relative to load is also lower in this same region suggesting that strength deficits in the middle 1/3 of the tibia and altered gait biomechanics may predispose an individual to stress fracture.
Bibliographical noteFunding Information:
This work is supported by the National Athletic Trainers Association [grant number CON000000012723 ].
The authors would like to acknowledge the National Athletic Trainers Association (NATA) for funding this study. This work was also supported by an appointment to the Postgraduate Research Participation Program at the U.S. Army Research Institute of Environmental Medicine administered by the Oak Ridge Institute for Science and Education through interagency agreement between the U.S. Department of Energy and U.S. Army Medical Research and Material Command (J.M.H.) We would like to thank the staff at The Orthopedic Specialty Hospital (TOSH) in Murry, UT for the use of their equipment, and contributions that allowed successful completion of the study. Thank you to Dr. Laurie Moyer-Mileur at the University of Utah, for the use of her pQCT machine. Thank you to Dr. Mary Bouxsein at Beth Israel Deaconess Medical Center for editorial and statistical guidance. Finally, we would like to thank the runners who participated in this study.
- Cortical area
- Peripheral quantitative computed tomography (pQCT)
- Running mechanics
- Volumetric bone mineral density (vBMD)