Introduction: When subjected to strain or strain rates are higher than usual, the bone remodels to repair microdamage and to strengthen itself. During the initial resorption phase of remodeling, the bone is transitorily weakened and microdamage can accumulate leading to stress fracture.

Methods: To determine whether short –term suppression of bone turnover using bisphosphonates can prevent the initial loss of bone during the remodeling response to high bone strain and strain rates and potentially prevent stress fractures, we conducted a randomized, double blind, placebo-controlled trial of 324 new infantry recruits known to be at high risk for stress fracture. Recruits were given a loading dose of 30 mg of residronate or placebo daily for 10 doses during the first two weeks of basic training and then a once a week maintenance dose for following 12 weeks. Recruits were monitored by biweekly orthopedic examinations during 15 weeks of basic training for stress fractures. Bone scans for suspected tibial and femoral stress fractures and radiographs for suspected metatarsal stress fractures were used to verify stress fracture occurrence.

Results: By the intension to treat analysis and per protocol analysis, there was no statistically significant difference in the tibial, femoral, metatarsal, or total stress fracture incidence between the treatment group and the placebo.

Discussion: We conclude that prophylactic treatment with residronate in a training population at high risk for stress fracture using a maintenance dosage for the treatment of osteoporosis does not lower stress fracture risk.

Mechanical loading during physical activity produces strains within bones. It is thought that these forces provide the stimulus for the adaptation of bone. Tibial strains and rates of strain were measured in vivo in six subjects during running, stationary bicycling, leg presses and stepping and were compared with those of walking, an activity which has been found to have only a minimal effect on bone mass.

Running had a statistically significant higher principal tension, compression and shear strain and strain rates than walking. Stationary bicycling had significantly lower tension and shear strains than walking. If bone strains and/or strain rates higher than walking are needed for tibial bone strengthening, then running is an effective strengthening exercise for tibial bone.

We have shown that stress fractures can be induced in the tibial diaphysis of an animal model by the repeated application of non-traumatic impulsive loads. The right hind limbs of 31 rabbits were loaded for three to nine weeks and changes in the bone were monitored by radiography and bone scintigraphy. The presence of stress fractures was confirmed histologically in some cases. Most animals sustained a stress fracture within six weeks and there was a positive correspondence between scintigraphic change and radiological evidence. Microscopic damage was evident at the sites of positive bone scans. The progression, location, and time of onset of stress fractures in this animal model were similar to those in clinical reports, making the model a useful one for the study of the aetiology of stress fractures.