Clinical History: A 29 year-old professional football player was injured while trying to make a catch. (1a) Sagittal T2-weighted, (1b) fat-suppressed axial proton density-weighted, and (1c) fat-suppressed coronal proton density-weighted images are provided. What are the findings? What is your diagnosis?
Grade II tear of the biceps femoris muscle (hamstring tear).
Hamstring tears are among the most commonly encountered injuries in athletes. Because of the tendency for hamstring tears to heal slowly and to recur, these injuries are a significant cause of lost playing time. The diagnosis of hamstring injury is usually suspected clinically, but because the hamstrings span two joints, tears can occur at multiple levels. MRI readily identifies the location and severity of the injury. In conjunction with the physical findings, this information helps guide a more comprehensive and effective rehabilitation program.
Anatomy and Function
The hamstrings are comprised of the semimembranosus, semitendinosus, and the biceps femoris muscles. The biceps femoris and semitendinosus arise from a common tendon along the posteromedial aspect of the ischial tuberosity. The muscle belly of the semitendinosus is the most cepahalad muscle of the hamstring complex. The biceps femoris also has a second ‘short” head that arises from the approximate mid-shaft level of the femur, at the lateral aspect of the linea aspera. The semimembranosus arises from the posterolateral aspect of the ischial tuberosity, anterior to the common origin of the biceps femoris and semitendinosus, and has the longest proximal tendon segment (5a-9a). The main distal attachment of the biceps femoris tendon is at the fibular head. The semimembranosus tendon attaches to the posteromedial tibia in several locations, with the primary insertion occurring along the posterior aspect of the tibial epiphysis. The semitendinosus continues to the anteromedial aspect of the proximal tibia, joining the gracilis and sartorius to insert as the pes anserine complex. The hamstrings act to flex the knee and extend the hip. Their primary function appears to be deceleration of the extended knee prior to foot strike and to assist hip extension after foot strike.
Injury Mechanism and Physical Examination
With the exception of the short head of the biceps femoris, the hamstrings span two joints, increasing their susceptibility to injury. Hamstring musculotendinous strains and tears typically occur during running, as excessive strain forces occur during eccentric contraction of the hamstrings. This type of injury is seen in sports such as football, track, and soccer that require rapid acceleration while running. The same mechanism of injury may also cause an avulsion injury. Avulsions of bone or tendon can also be the result of severe stretching of the hamstrings due to forceful hip flexion with the knee in extension. Waterskiing and ice skating are sports that may lead to this type of injury.1
The typical presentation of a hamstring strain or tear is the acute onset of pain during rapid acceleration or stretching. An audible pop often accompanies the injury. In more severe injuries, ecchymoses and swelling may be visible, and a palpable defect may be felt. Pain is elicited with passive extension of the knee with the hip flexed to 90 degrees and also with resisted knee flexion. Because of the proximity of the sciatic nerve, temporary sciatica or even a sciatic neuropathy may be encountered. The athlete’s functional impairment can range from minor discomfort and tightness to a complete loss of strength.
MRI reliably depicts the location and extent of hamstring injuries. Fluid sensitive sequences such as Proton-density and T2-weighted fat-suppressed sequences or STIR sequences depict tendon tears and avulsions as fluid-signal filled defects at the site of disruption. Adjacent hemorrhage and edema are readily apparent. The multiplanar capabilities of MRI enable a detailed depiction of the muscles or tendons involved.
Avulsions at the bone-tendon interface may occur with or without fracture avulsions from the ischial tuberosity. Bony avulsions are most common in adolescents with incomplete fusion of the ischial tuberosity apophysis (10a,11a). These injuries are typically treated conservatively if there is less than 2 cm distraction at the fracture. Because cortical avulsions can be difficult to discern on MRI, plain films are important in the detection of this pattern of injury.
Tendon avulsions without bony avulsions are felt to represent an indication for surgical repair in the competitive athlete (K,L). Avulsion injuries most commonly involve the entire proximal hamstring complex, but can occasionally be limited to either the semimembranosus or common biceps femoris-semitendinosus tendon.
Because of the close proximity of the sciatic nerve to the proximal hamstring complex, injuries resulting in large hematomas (12a,13a) or excessive callus and displaced bone (14a,15a) may lead to sciatic compression and neuropathy.
The tendons of the hamstrings essentially span the full length of the muscles, and musculotendinous injuries can occur at any level along the muscle tendon interface. Proximal injuries (above the level of the short biceps femoris) appear to be slightly more common. The biceps femoris muscle is the most commonly injured hamstring component, either as an isolated injury or as the primary component of a multiple muscle injury. Multiple hamstring muscle injuries are more common than the isolated form.2
MRI is useful in grading the extent of disruption in muscular strain injuries. Grade I injuries are considered a mild injury with limited muscle fiber disruption. On MRI the injured muscle demonstrates a mild feathery pattern of intramuscular edema confined to the muscle (16a). Grade II injuries are more severe, representing partial tears at the musculotendinous junction without retraction, and may be accompanied by hematoma at the site of the tear. Extension of hemorrhage and edema beyond the muscle margin may be present and suggests a more extensive injury with disruption of the muscle sheath (2a,3a,4a). Grade III injuries represent a complete disruption of the musculotendinous junction. Retraction and laxity of the musculotendinous elements are seen. MRI is helpful in determining the extent of retraction in these injuries, an important feature for surgical planning.
The treatment options for hamstring injury depend on the location and severity of the injury. Tendon avulsions are an indication for surgical repair. Minimally displaced bony avulsions are treated conservatively, allowing 6-12 weeks for healing. For most musculotendinous strain injuries, a conservative approach to treatment will allow healing and full functional recovery. Certain findings on MRI are associated with a longer recuperation time. These include a greater than 50% cross-sectional muscle involvement, injury to the biceps femoris, and injuries that involve a long length of muscle fibers.3,4 Grade III musculotendinous ruptures often require surgery.
Focused preventative conditioning and strengthening are important in preventing both initial injuries and recurrence. During rehabilitation, factors that are felt to contribute to hamstring injury should be addressed, including poor flexibility, quadriceps-hamstring imbalance, and poor running mechanics.
Hamstring injuries are a quite common athletic injury. Though the diagnosis of hamstring injury is usually clinically suspected, the ability of MRI to accurately depict the location and extent of injury can greatly influence treatment and rehabilitation plans in these patients.
1 Bencardino JT and Mellado JM. Hamstring Injuries of the Hip In: Magnetic Resonance Imaging Clinics of North America. Rosenberg ZS ed. Magn Reson Imaging Clin N Am 13(2005);677-690.
2 De Smet AA, Best TM. MRI imaging of the distribution and location of acute hamstring injuries in athletes. AJR 2000;174:393-9.
3 Slavotinek JP, Verral GM, Fon GT. Hamstring injury in athletes: using MR imaging measurements to compare extent of muscle injury with amount of time lost from competition. AJR 2002;179:1621-8.
4 Connell DA, Schneider-Kolsky ME, Hoving JL, et al. Longitudinal study comparing sonographic and MRI assessments of acute and healing hamstring injuries. AJR 2004;183:975-84.