Tibial Density and Trabecular Microarchitecture in Army Recruit Stress Fracture Cases and Matched Uninjured Controls

Abstract

Stress fractures are common overuse injuries experienced by military recruits during initial training. Lower cross sectional area of the tibia in stress fracture cases compared with uninjured controls supports an important role of bone structure in injury predisposition. With the advent of high resolution techniques, other determinants of bone strength can now be evaluated in the development of stress fracture injury. PURPOSE: To investigate differences in bone density and trabecular (Tb) microarchitecture at the distal tibia using in vivo high-resolution peripheral quantitative computed tomography (HR-pQCT) between stress fractured and uninjured British Army infantry recruits. METHODS: 324 British Army infantry recruits were followed through 26 weeks of infantry training. Twenty-one recruits were diagnosed with a stress fracture injury of the lower limb (22 ± 3 years, 73.3 ± 8.3 kg, 1.78 ± 0.06 m, 593 ± 68 s 1.5 km run time), and matched to 21 non-injured controls (22 ± 3 years, 74.2 ± 10.0 kg, 1.77 ± 0.06 kg, 588 ± 58s 1.5 km run time) in the same training platoon. Groups were matched for age, height, body mass and aerobic fitness (1.5 km run time). Scans at the distal tibia of the dominant leg were performed on all volunteers using HR-pQCT (Xtreme CT, Scanco Medical, Switzerland) in week one of training. RESULTS: No significant differences were observed in bone density or Tb microarchitecture between stress fracture cases and uninjured controls (P > 0.05). A subgroup of seven cases suffering stress fractures to the tibia had higher Tb bone density (245 ± 32 vs 209 ± 28 mg HA/cm3, P = 0.042), higher sub-endocortical Tb density (320 ± 21 vs 282 ± 32 mg HA/cm3, P = 0.047) and higher Tb volume to tissue volume ratio (0.204 ± 0.027 vs 0.174 ± 0.023, P = 0.042) than uninjured controls. CONCLUSION: Young healthy men suffering stress fracture in training do not differ in their bone structure or Tb microarchitecture at the distal tibia from uninjured matched counterparts. Our understanding of bone microarchitecture in the development of stress fractures is limited by the utility of high resolution techniques to distal sites. Future studies should explore phenotypic characteristics in stress fracture cases at specific sites of injury, which typically develop at the distal third of the tibia in military recruits. Supported by UK MoD (Army).