Proximal Hamstring Syndrome

Anatomy

The term hamstrings refers to a group of muscles in the back of the thigh that perform the same function—bending the knee and, to a lesser extent, extending the hip. The hamstrings are usually considered to include three muscles: (1) the semitendinosus, (2) the semimembranosus, and (3) the biceps femoris. Two other muscles—the sartorius and gracilis—are also technically considered hamstrings because their actions include bending the knee. They have a different action at the hip joint, however, and they are much weaker than the three primary hamstring muscles.

The ischial tuberosity is the bony part of the pelvis that you sit on. The semitendinosus and biceps femoris share a common origin on the pelvis at the ischial tuberosity. In other words, the two muscles begin as a single tendon (a ropelike connection of muscle to bone). They then split into two separate muscles as they progress down the back of the thigh. The semitendinosus travels to the inner (medial) aspect of the tibia (leg bone), while the biceps femoris travels to the outer (lateral) aspect of the tibia and fibula. The semimem-branosus runs deep to the semitendinosus from its origin on the ischial tuberosity to its multiple insertions at the back of the knee. The sciatic nerve is the nerve that innervates the muscles of the lower leg. The sciatic nerve exits the pelvis and passes [Page 1163]just lateral to the origin of the semitendinosus and biceps femoris muscles. The nerve then passes beneath the biceps femoris muscle as it runs to its connection at the back of the knee. The gluteus maximus is the large buttock muscle that covers the upper part of all these structures. The hamstrings emerge from under the gluteus maximus about 3 inches (in.; 1 in. = 2.54 centimeters) below the ischial tuberosity.

Etiology

Proximal hamstring syndrome most commonly occurs in high-level athletes, especially sprinters and hurdlers. It is relatively rare, and there are few published reports describing its symptoms. Proximal hamstring syndrome is thought to be associated with prior hamstring strains. A strain occurs when a muscle overstretches, which tears some of the muscle fibers. These strains can range from minor injuries to complete ruptures of the entire muscle. As the muscle attempts to repair the strain, it can form thick, fibrous bands of scar tissue.

Hamstring strains in particular are extremely common sports-related injuries at all levels of participation. The most commonly injured muscle is the biceps femoris, and the most common location of injury is the upper junction between the muscle and the single tendon. This location is exactly where the sciatic nerve dives underneath the biceps femoris muscle to travel down the rest of the posterior thigh. It is thought that scarring in this area from prior hamstring strain injuries can entrap and compress the sciatic nerve. This leads to pain in the buttock area and can cause referred pain to other sites innervated by the sciatic nerve.

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