Models for the pathogenesis of stress fractures in athletes.

Abstract

It would seem that the development of a stress fracture results from unsuccessful adaptation of bone to a change in its mechanical environment caused by repetitive loading. It involves the physiological processes of microdamage production and remodelling. Whether the initiating factor is microdamage production or activation of remodelling through direct effects of strain is unclear. The remodelling process involves both the removal of bone which has become fatigue damaged or is extraneous to the requirements of the new loading environment, and the addition of new bone in an manner that is best suited to withstand the new mechanical strain. Normally this process is well modulated and does not cause symptoms. If the amount of bone removed is not sufficient to unduly weaken bone structure and the addition of new bone occurs sufficiently rapidly to correct any weakness before failure occurs or to repair microdamage, the process will successfully lead to a bone with appropriate material strength and geometry to withstand the new strain environment. However, if there is imbalance between bone removal and replacement, together with accumulation of microdamage, signs and symptoms of a stress fracture may result. Any factors which influence bone load, bone strength, or remodelling have the potential to result in a stress fracture. Attention should be paid to the identification of these factors in an attempt to prevent this overuse injury in athletes.

Effect of rest from running on overuse injuries in Army basic training

“…This might occur sometime during the second to fourth week after onset of intensive physical conditioning. Scully and Besterman, 19 referring to theories of stress fatigue fractures 13,18,20 and extrapolating from the data of Johnson et al, 21 proposed that a period of rest during training, specifically the third week, be incorporated to allow for bone repair prior to new cycles of bone stress. A number of military studies have found maximum stress fracture rates during the first 3 weeks of military training, although there is some disagreement.…”

Experimental validation of finite element predicted bone strain in the human metatarsal

“…There are two hypotheses relating the role of bone repair to the pathophysiology of stress fractures: the primary microdamage hypothesis, and the primary remodeling hypothesis (28). According to the primary microdamage hypothesis, the rate of microdamage accumulation exceeds the rate of bone repair.…”

“…Skeletal muscle may contribute to both the risk and prevention of stress fractures, depending on the site of injury (28). Some investigators believe that muscles produce large strains in bone, especially at the muscle attachment points (29).…”

“…According to the primary microdamage hypothesis, the rate of microdamage accumulation exceeds the rate of bone repair. This could be caused by an abrupt change in duration, frequency, or intensity of training programs (14) or if the rate of bone formation is impaired (28).…”

“…This accelerated bone remodeling may be caused by genetics, increased stimuli for remodeling, systemic or reproductive hormones, or dietary intake (28,137). As bone resorption precedes formation during the repair response, the bone becomes temporarily weaker as bone is resorbed and resorption cavities are formed, making the bone more porous (138,139).…”