Muscle injury: the role of imaging in prognostic assignment and monitoring of muscle repair.

Muscle injury is common among athletes, and imaging is increasingly being used to confirm injury, to assess its location, extent, and severity, and on occasion to make inferences regarding prognosis and timing of return to sports. Ultrasound and magnetic resonance imaging (MRI) are accurate for diagnosis of acute injuries, but measurements of the extent of injury (cross-sectional area and longitudinal extent of muscle injury adjacent to the musculotendinous junction) have also been shown to correlate with athlete prognosis and recovery time. Specifically, normal MRI studies shortly after injury are associated with rapid (1- to 2-week) recovery and low risk of recurrent injury. Abnormal muscle cross-sectional area >55% is associated with a convalescence interval of >6 weeks, but larger measurements are not clearly associated with higher recurrence risk. The clinical value of follow-up imaging before return to competition is not established, but residual muscle abnormality is often present at this time.