Imaging of Acute Hamstring Muscle Strain Injuries
Acute athletic hamstring muscle strain injuries are common and a cause of significant time off sport. An understanding of the anatomy of the hamstring muscle-tendon units is a prerequisite for interpreting the spectrum of structural abnormalities on imaging. The site of injury may range from proximal tendon, proximal myotendinous junction, with or without tendon injury, muscle, myofascial junction, distal myotendinous junction to distal tendon. Imaging findings in muscle injury range from intrafascicular and interfascicular muscle edema, blurring of fascicular margins, distortion of pennation angle, localized muscle fascicle discontinuity through to more extensive multi-fascicular discontinuity. Imaging findings in tendon injury include tendon edema, redundancy, zipper-like morphology, and partial-complete tendon discontinuity. Imaging findings in fascial injury include poor definition of fascial margins with perifascial edema through to a fascial defect. Published grading systems are presented, and their so far limited utility in predicting return to play is reviewed.