title: Bone strength estimates relative to vertical ground reaction force discriminates women runners with stress fracture history.
abstract: 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.
  
  
  
  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, mm3and 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.
  
  
  
  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).
  
  
  
  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.
authors.affiliation: School of Kinesiology, Laboratory of Musculoskeletal Health, University of Minnesota, 1900 University Ave SE, Minneapolis, MN 55455, USA. Electronic address: kpopp@mgh.harvard.edu.
authors.forename: Kristin L
authors.initials: KL
authors.lastname: Popp
authors.affiliation: The Orthopedic Specialty Hospital, 5848 S Fashion Blvd, Murray, UT 84107, USA.
authors.forename: William
authors.initials: W
authors.lastname: McDermott
authors.affiliation: United States Army Research Institute of Environmental Medicine, 10 General Greene Ave, Natick, MA 01760, USA.
authors.forename: Julie M
authors.initials: JM
authors.lastname: Hughes
authors.affiliation: The Orthopedic Specialty Hospital, 5848 S Fashion Blvd, Murray, UT 84107, USA.
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Baxter
authors.affiliation: Department of Family Medicine and Community Health, University of Minnesota, 420 Delaware St. SE. MMC381, Minneapolis, MN 55455, USA.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Stovitz
authors.affiliation: School of Kinesiology, Laboratory of Musculoskeletal Health, University of Minnesota, 1900 University Ave SE, Minneapolis, MN 55455, USA.
authors.forename: Moira A
authors.initials: MA
authors.lastname: Petit
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001842:Bone and Bones / Q000473:pathology* / Q000503:physiopathology*; D016022:Case-Control Studies; D003710:Demography; D005260:Female; D015775:Fractures, Stress / Q000473:pathology* / Q000503:physiopathology*; D006801:Humans; D012420:Running / Q000502:physiology*; D013977:Tibia / Q000473:pathology / Q000503:physiopathology
keywords: Cortical area; Female; Peripheral quantitative computed tomography (pQCT); Running mechanics; Volumetric bone mineral density (vBMD)