Imaging of Upper Extremity Stress Fractures in the Athlete

Mark W. Anderson, MD

Department of Radiology, Box 170, University of Virginia Health Sciences Center, 100 Lee Street, Charlottesville, VA 22908, USA

he incidence of stress fractures has been rising over the last several years in our increasingly active society. Although most of these injuries occur in the lower extremities, because of their weight-bearing function [1], they have also been reported to involve multiple sites in the upper extremities. Because of their relative infrequency, clinical diagnosis may be difficult, and diagnostic imaging studies can be exceedingly helpful in arriving at an accurate and timely diagnosis. The purpose of this article is to describe the most common sites of stress injuries in the upper extremity, their underlying pathophysiology, and their spectrum of imaging findings.

The skeleton is a dynamic organ that undergoes constant remodeling in response to applied stresses according to Wolfe's law (bone is formed and retained along the lines of stress within a bone). Cortical and trabecular microdamage occurs as a result of daily activities, and normally osteoclastic resorption of the damaged bone is followed by osteoblastic bone production, resulting in an equilibrium [2].

However, with new or increased physical activity, the degree of remodeling increases, and bone resorption outpaces bone production because there is usually a lag of several weeks before new, lamellar bone is laid down [3]. During this ''window of vulnerability,'' the imbalance between resorption and formation results in a localized weakening of the bone, and if the offending activity is not curtailed, the microdamage will begin to accumulate [3]. At this stage in the stress reaction, periosteal and endosteal new bone is produced in an attempt to buttress the temporarily weakened cortex [4]. Ultimately, if the activity is continued, further weakening of the bone will lead to mechanical failure and the development of a true, macroscopic fracture (stress fracture).

Stress fractures are classically divided into fatiguefractures (in which increased physical activity results in damage to normal bone) and insufficiency fractures (in

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