Changes in Bone Microarchitecture and Estimated Bone Strength Over 12 Months After Tibial Stress Fracture Diagnosis: Implications for Return to Sport

Abstract

Stress fractures (SF), common injuries among athletes, have been reported in up to 20% of track and field athletes. Typically, after a period of unloading and gradual return to weight-bearing activities, athletes return to unrestricted participation in their given sport 12-14 weeks after SF diagnosis. However, the time course of the recovery of mechanical competence of the bone is not well characterized, and reinjury rates are high. PURPOSE: To determine changes in bone microarchitecture and estimated bone strength over 12 months following tibial SF diagnosis. METHODS: We enrolled 30 women, ages 18-35, with a tibial SF (grade 2 or higher) for this prospective observational study. Participants completed a baseline visit within 3 weeks of SF diagnosis. At baseline, 6, 12, 24, and 52 weeks following SF diagnosis, we collected high-resolution peripheral quantitative computed tomography (HR-pQCT) scans of the ultradistal tibia (4% of tibia length), background and lifestyle questionnaires, and a physical activity assessment. RESULTS: Over the initial 12 weeks, total volumetric bone mineral density (vBMD) declined by 1.2% (p=0.001), trabecular vBMD by 1.2% (p=0.006), cortical thickness by -1.0% (p=0.007), and bone volume/total volume by 1.2% (p=0.008). At 24 weeks, mean values for all bone parameters were nearing baseline values, and by 52 weeks, mean values had surpassed baseline values. A similar trend was seen in estimated bone strength, though changes did not reach statistical significance. Of the 30 participants, 7 incurred a subsequent SF during the course of the 12 month-follow up and 2 incurred ≥2 subsequent SFs. CONCLUSION: Persisting decrements in bone microarchitecture and estimated bone strength suggest bone mechanical integrity does not return to baseline for 3-6 months after tibial SF diagnosis. This, coupled with the high rate of recurrent SFs, suggests more conservative return to sport guidelines may be in order. The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the U.S. Army or of the U.S. Department of Defense. This abstract has been approved for public release with unlimited distribution.