MR imaging of the distribution and location of acute hamstring injuries inathletes

OBJECTIVE. Although hamstring injuries are common in athletes, the distribu tion and location of such injuries have not been well defined. We used MR i maging to determine the frequency of injury by muscle, involvement of one o r more muscles, and location of injuries within the musculotendinous unit. SUBJECTS AND METHODS. We performed MR imaging on 15 consecutive college ath letes with clinically diagnosed acute hamstring injuries. A hamstring injur y was diagnosed and located on MR imaging by identifying high signal intens ity within the muscle on T2-weighted images. RESULTS. We found that 10 athletes had injuries of a single muscle with six injuries of the biceps femoris, three of the semitendinosus, and one of th e semimembranosus. In an additional five athletes, we found primary injurie s of the biceps femoris and secondary injuries of the semitendinosus. The i njuries occurred in diverse locations within the muscles including five inj uries at the proximal musculotendinous junction, two at the distal musculot endinous junction, four within the proximal half of the muscle belly, and f our in the distal half. All eight intramuscular injuries were located at th e musculotendinous junction within the muscle. CONCLUSION. The biceps femoris is the most commonly injured hamstring muscl e and the semitendinosus is the second most commonly injured. Although hams tring injuries often involve one muscle injured proximally, multiple muscle s were involved in 33% of athletes (5/15) and the injuries were distal in 4 0% of athletes (6/15). All intramuscular injuries occurred at the musculote ndinous junction, either at the ends of the muscle or within the muscle bel ly.