Bone stress injuries causing exercise-induced knee pain

Background: No comprehensive studies of bone stress injuries in the knee based on magnetic resonance imaging findings have been published. Purpose: Assess the incidence, location, nature, and patterns of bone stress injuries in the knee in military conscripts with exercise-induced knee pain. Study Design: Case series; Level of evidence, 4. Methods: During a period of 70 months, 1330 patients with exercise-induced knee pain underwent magnetic resonance imaging of the knee. A total of 1577 knees were imaged; the images with bone stress injury findings were retrospectively reevaluated with respect to location and type of injury. The person-based incidence of bone stress injuries in the knee was calculated, based on the number of conscripts within the hospital's catchment area. Results: Of the 1330 patients, 88 (7%) met the inclusion criteria, and 141 bone stress injuries were found in the 110 knees imaged. The incidence of bone stress injuries was 103 per 100 000 person-years. Of the patients, 25% had bilateral bone stress injuries; 28% had 2 solitary bone stress injuries in the same knee simultaneously, all situated in the femoral condyle and tibial plateau. The most common anatomical location for a bone stress injury was the medial tibial plateau (31 %), which was also the most typical location for a more advanced injury. After the commencement of military service, a bone stress injury in the medial tibial plateau caused knee pain earlier than did a bone stress injury elsewhere in the knee (P = .014). Conclusion: The incidence of bone stress injuries in the knee with exercise-induced knee pain is relatively high in conscripts. Multiple and bilateral injuries can occur. For accurate diagnosis and to ensure appropriate treatment, magnetic resonance imaging is recommended as a routine imaging method when a physical activity can be regularly associated with the onset of symptoms.