Stress fractures have been described in baseball pitchers, a tennis player, a javelin thrower, a body-builder, weight lifters, a softball player, and a cricket player [39-49]. Humeral stress fractures in throwing athletes such as baseball pitchers most commonly are spiral fractures that involve the middle and distal third of the humerus [40,43-46]. These fractures predominate in two main age groups: adolescent Little League pitchers and healthy middle-aged pitchers [44-46], although, Polu and colleagues  reported a nondisplaced fracture in a collegiate pitcher. The most likely explanation for stress fractures in the adolescent age group is a high level of activity, which places a high degree of stress on immature bone, aggravated by growth spurts and inadequate muscular development [4,47]. The authors in one study believe that in the middle-aged pitchers, the most probable reason for these fractures was muscle fatigue caused by a prolonged layoff from pitching and a lack of a preseason conditioning and a regular exercise program . The axial loads applied to the humerus generated by the biceps and triceps muscles during pitching serve as stress protection against torsional forces placed on the humerus . Therefore, when these muscles are fatigued by overuse and lack of conditioning, more torsional stress is placed on the humerus, predisposing it to stress fracture.
These athletes present with either an acute onset of pain or a "pop" sound after a period of prodromal throwing arm pain or with an insidious onset of increasing arm pain if the fracture is incomplete or nondisplaced [40,43-46]. Plain radiographs most commonly reveal the fracture, especially if it is complete and displaced (Fig. 1). In incomplete fractures, plain radiographs may reveal only subtle cortical hypertrophy . In these cases, radionuclide imaging or MRI may be needed to aid in the diagnosis. MRI will show a linear zone of decreased signal intensity within the cortex or medullary cavity or both on Tl-weighted scans and increased signal in the medullary cavity on T2-weighted images. MRI also can help in determining the stage of the injury, with more recent injuries having increased signal on the T2-weighted views.
Treatment is determined by many factors, including the age of the patient and degree of fracture displacement. Adolescent patients and those with non-displaced fractures often can be treated nonsurgically with a cuff and collar for 1 week, followed by a fracture brace until the fracture heals clinically and radiographically. Patients with displaced fractures often require open reduction and internal fixation. Preventive measures include a well-structured preseason strengthening and conditioning program.
The stress fractures seen in the weight lifters were transverse and involved the proximal humeral shaft [41,42]. Both patients complained of proximal arm and anterior shoulder pain, which occurred during bench press exercises for a period of time before presentation. One patient presented with a transversely oriented radiolucency in the proximal humerus, suggestive of cortical lysis with surrounding periosteal reaction, whereas the other patient presented with a transverse fracture of the proximal diaphysis with greater than 50% displacement. The former patient was treated with cessation of weight lifting for 8 weeks, followed by a gradually progressive supervised training program. The latter patient was treated with surgical fixation with an intramedullary nail. In terms of the mechanism of injury, these fractures were transverse in nature, suggesting a bending force rather than a rotational force, and occurred anatomically between the insertions of the pectoralis major and deltoid muscles. During bench pressing, the humerus is exposed to mechanical forces generated by the supporting musculature of the shoulder girdle and the weight being lifted . The muscles are able to dynamically redistribute these forces across the bone, allowing the bone to endure more stress and load. However, with muscle fatigue, the "stress shielding" effect of the muscles is diminished, which predisposes the bone to fracture.
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Since World War II, there has been a tremendous change in the makeup and direction of kid baseball, as it is called. Adults, showing an unprecedented interest in the activity, have initiated and developed programs in thousands of towns across the United States programs that providebr wholesome recreation for millions of youngsters and are often a source of pride and joy to the community in which they exist.