Scintigraphic uptake of 99mTc at non-painful sites in athletes with stress fractures. The concept of bone strain.

Stress fractures are commonly found in athletes attending sports medicine clinics for diagnosis of lower limb pain. Plain radiographs are less reliable than the 99mTc bone scan for diagnosing stress fractures because of their low sensitivity. While the heightened sensitivity of the bone scan is advantageous as a diagnostic aid, the uptake of 99mTc at non-painful sites occurs frequently in the athlete. Although the clinical significance has not been determined, asymptomatic uptake may indicate bone remodelling as part of a continuum of adaptation to physical stress. It is not known whether athletes who have uptake of 99mTc in asymptomatic areas represent a separate population from those who do not. This study retrospectively reviewed the medical charts and bone scan reports of 320 athletes diagnosed as having stress fractures, to determine the frequency of asymptomatic focal uptake at sites other than the site of pain. This group was compared with the group who had no asymptomatic uptake on a number of demographic variables and physical findings. Asymptomatic focal uptake was found in 37.5% of athletes with the average number of sites being 1.8 per person. No significant differences between groups with focal asymptomatic uptake and groups with no asymptomatic uptake were found when compared for age, height, weight, mileage in runners, times to diagnosis and recovery, frequency of tenderness, swelling, trauma history, varus alignment, and x-ray abnormalities. It is concluded that asymptomatic uptake of 99mTc occurs frequently in athletes with stress fractures and there are no significant clinical differences between the group with asymptomatic uptake and the group without. It is suggested that symptomatic uptake of 99mTc represents the remodelling response of bone to physical stress.