Healing of Stress Fracture in an Animal Model

This project aimed to develop effective ways to prevent or treat stress fractures. The authors investigated the role of an exercise program in the prevention of stress fractures using the ulna axial compression loading model. Loading was applied on right ulnas using a 2-Hz haversine waveform with a peak force of 17 H for 360 cycles/day, 3 days per week for 5 consecutive weeks. Exercise loading improved the structural properties of the ulna, especially the minimum second moment of the area, which increased about 2-fold. However, the exercise program also increased fatigue resistance by 100-fold. The authors also studied the individual and combined roles of anti-inflammatory agents (cyclooxygenase-2 inhibitor, celebrex) and low-intensity pulsed ultrasound (LIPUS) in the treatment of stress fractures. The data indicate that LIPUS has a beneficial effect and celebrex has a detrimental effect on stress fracture repair. While neither LIPUS nor celebrex influenced bone resorption, both had significant effects on intracortical bone formation. These effects were opposing, and indicate that LIPUS may be used to facilitate stress fracture repair, whereas celebrex may delay tissue-level repair of stress fractures. There were no interactions between LIPUS and celebrex, indicating that the beneficial LIPUS effect was not mediated by a COX-2 pathway. The findings have implications for the clinical utility of these interventions in the management of stress fractures.