Athletes of all kinds can develop pain along the back of the thigh from a hamstring injury. But in this report, seven athletes with posterior thigh pain from an unusual hamstring injury tear are featured.

The hamstring muscle is divided into four parts: the semimembranosus, semitendinosis, biceps femoris, and gracilis. It is the isolated gracilis muscle injury that makes these seven athletes unusual. Posterior thigh strains affecting the biceps femoris are much more common. In fact, this is the first known report published on the topic of isolated gracilis muscle tears.

There wasn't just one sport that was associated with these injuries. Dancers, soccer players, tennis players, and even a tae kwon do enthusiast were injured. The mechanism of injury (how it happened) was similar for all seven.

Pulling the leg in toward the body (a movement called adduction) combined with full hip flexion and internal (inward) rotation was what did it. The knee of the injured leg was straight. Picture a ballet dancer doing a split with one leg bent. High speed moves like this apply enough tension to the muscle that it can no longer resist the force. The result is a tear at the muscle-tendon junction.

Symptoms of an isolated gracilis muscle tear were similar for all seven athletes. There was an initial sharp pain at the time of the movement that caused the tear. This was followed by uncomfortable pain that got worse over time. Six of the seven athletes developed a lump along the back of the thigh. This lump is where the torn tendon retracted (pulled back) toward the belly of the muscle.

The diagnosis was confirmed with ultrasound imaging that clearly showed the lesion. All seven athletes had a partial tear, labeled as a grade 2 injury.

How did things turn out for these athletes? Everyone recovered fully within six weeks with conservative (nonoperative) care. Full motion, strength, and function were reported by everyone. A recheck 12 months later revealed no further injuries (or reinjuries) of the hamstring muscle.

Could these injuries have been avoided? Can athletes prevent isolated gracilis muscle tears? These are important questions to have answered if you happen to be an athlete in training or someone helping with the training.

The answer may be found by determining why these particular athletes sustained this injury. Because the movements they made that caused the tear are commonly performed by many athletes not just dancers, soccer players, tennis players, and martial artists.

The key may be in the anatomy of the muscle -- something the athlete was born with. Of the four hamstring muscles, the gracilis is the thinnest. It is sandwiched between two other muscles, which may help protect it in most people.

It is described as a striplike muscle. It's a long muscle that crosses two joints (the hip and the knee), which can put it at a mechanical disadvantage. The tendon portion is also long: reaching up from its attachment at the knee half the distance to the hip.

Perhaps there is a difference in the shape, length, or tension in this muscle that puts some athletes at increased risk for injury. Or there may be something about the way it is positioned between the hamstrings and the hip adductors (muscles that move the leg toward the body) that make it vulnerable to tears with this movement. This study was not designed to look for those answers.

For now, it is clear that isolated gracilis hamstring muscle tears do occur. They can be very painful but recover within six weeks' time. Most athletes can continue to train during the recovery phase with some modifications in their training routine. Reinjury is not common.

Reference: Carles Pedret, MD, et al. Isolated Tears of the Gracilis Muscle. In The American Journal of Sports Medicine. May 2011. Vol. 39. No. 5. Pp. 1077-1080.