Stress fracture of the humerus in a collegiate baseball pitcher. A case report.

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As the number of young people participating in sports at the professional and amateur level grows, so does the incidence of stress fractures in the athletic population. 13 Stress fractures usually result from a sudden change in volume or intensity in the athlete's regimen. 5 Several theories have been proposed to explain stress fractures. One theory suggests that, over time, repetitive, nonviolent loads applied to bone overwhelm its ability to compensate. As a result, reabsorption exceeds formation and predisposes the weakened bone to a stress fracture. 1,5 A second theory considers that stress fractures occur when muscular fatigue leads to alterations in movement patterns, with a redistribution of force to the underlying bone. 5 In effect, the shock or energy absorption capabilities of muscle are overpowered, and the bone is subjected to abnormal forces and predisposed to development of a fracture. Devas 7 first described stress fractures in the athletic population in 1958. Since then, stress fractures have been documented in various athletic activities, most notably in the tibia or tarsus bones of runners. 16 In contrast, stress fractures of the upper extremity have not been as widely reported. Although upper extremity injuries account for 20% of all athletic injuries, 15 most are soft tissue injuries of the shoulder. 15,22 The number of reported humeral stress fractures is particularly low, and these fractures are usually not recognized until later in the course of injury, when a spiral fracture occurs secondary to muscular violence. 1,4,10,12,22 The patient who develops a humeral stress fracture usually experiences a period of arm fatigue and aching after cessation of the sporting activity. Gradually, the pain occurs during the activity itself and can be referred to the shoulder or elbow. Physical examination will reveal tenderness at the site of the stress fracture, but the range of motion of the elbow and shoulder are not affected. 7 Imaging modalities have played a valuable role in the diagnosis of stress fractures. Although plain radiographs are the first modality used in evaluation of bone injury, evidence of stress fracture on radiographs depends on the interval between injury and evaluation. It may take several weeks for stress fractures to become visible on plain radiographs. 6 Stress fractures usually appear as localized periosteal reaction, endosteal thickening, a radiolucent cortical line, or a combination of these three. 21 However, many patients with stress fractures do not have any radiographic findings. 6 Bone scan and MRI are both sensitive imaging tools in detecting occult fractures. Scintigraphy detects minimal changes in blood flow and metabolism occurring during the abnormal bone remodeling process and is usually positive within 12 to 15 days after the onset of symptoms. 5,17,20 Roub et al. 20 demonstrated that tibial stress fractures in young athletes could be detected on radionuclide imaging before changes were seen on plain radiographs.