Stress fractures pose growing threat to teenage athletes

Ever greater competitive pressures on our sports stars of the future risk jeopardizing their health, but imaging is playing an increasingly important role in the early and accurate detection of potential musculoskeletal problems.

Young athletes are vulnerable to stress fractures due to fatigue or insufficiency, said Dr. Shaheen Noorani, a radiologist at the Nuffield Orthopaedic Centre in Oxford, U.K., in an education exhibit at RSNA 2008. Over 90% of stress fractures occur in the lower limbs.

Plain radiographs may be normal in the majority of early cases, so other examinations are often necessary. MRI is the gold standard for detecting and delineating stress fractures and has superseded scintigraphy. CT may be useful in specific circumstances, such as detecting the nidus in osteoid osteoma and confirming pars defects. Ultrasound may fortuitously pick up cortical breaks and periosteal reactions, but is not a first-line investigation, Noorani said.

Stress fractures occur due to abnormal repetitive stress on normal bone. Their frequency is increasing as a result of growing demands on young athletes. About 9% occur in children less than 15 years of age, around 32% occur in athletes between 16 and 19 years, and 59% occur in those aged 20 or over.

Fatigue stress fractures, on the other hand, occur in normal healthy bone due to abnormal muscular stress or unusual forces. Insufficiency stress fractures occur under normal physiological conditions in unhealthy bone that is mineral-deficient or abnormal.

For the pathogenesis, there are three main hypotheses, Noorani said.

The first is Wolff's Law, in which the remodelling process is inundated with an unusual intensity of mechanical stresses, resulting in a stress fracture. The second theory is that during repetitive exercise, the muscles tire, leading to different movements and strain patterns and causing excessive tension focused on specific areas of bone not usually subject to these forces. The third hypothesis is that repetitive forces cause an increase in muscle action, which results in disproportionate forces at the site of the muscle origin or insertion.