History
Hamstring strain is a noncontact injury and usually occurs with either acute or insidious onset. Strain injuries frequently are seen in athletes who run, jump, and kick. Avulsion injuries are seen in patients who participate in water-skiing, dancing, weight lifting, and ice-skating. [7, 8, 9] The avulsion injury usually follows a burst of speed, and the patient may report a popping or tearing sensation. The most commonly affected muscle area in the hamstring complex is the short head of the biceps femoris, [3] possibly because of its innervation.
The aforementioned study by Tokutake et al found that in athletes who engage in high-speed track-and-field running, the likelihood of recurrence of hamstring strain is significantly greater than that of first-time occurrence. [4]
As with most strain injuries, hamstring injury can occur at the following 4 places:
-
Origin of the muscle
-
Musculotendinous junction
-
Muscle belly
-
Insertion of the muscle
Injury is most likely to occur while the musculotendinous junction undergoes maximum strain during eccentric contraction of the hamstrings.
The American Medical Association (AMA) has described the following 3 grades of severity of hamstring injuries:
-
First-degree strain - The result of stretching of the musculotendinous unit; involves tearing of only a few muscle or tendon fibers
-
Second-degree injury - Refers to a more severe muscle tear without complete disruption of the musculotendinous unit
-
Third-degree injury - Refers to a complete tear of the musculotendinous unit
Physical
In addition to pain in the posterior thigh, the physical examination may reveal any of the following signs or symptoms:
-
Tenderness over the site of injury
-
Ecchymosis
-
Palpable mass
A palpable defect may be felt with severe strains, but swelling and the deep location of the muscle may obscure this finding in the acute stage.
Palpate the muscle for a defect with the patient in a prone position and the knee flexed to 90°. This position relaxes the muscle and decreases cramping and pain. Palpate while maintaining slight tension on the muscle.
-
Pain with passive extension of the knee and the hip flexed at 90°, as compared with the noninjured side, which stretches the muscle
-
Pain with resisted knee flexion, which activates the muscle
Causes
Many different causative factors can contribute to hamstring injuries. The most significant causes include the following [10] :
-
Inadequate flexibility of the hamstrings can result in injury. This may be related to the patient having no or a poor stretching routine.
-
Inadequate strength or endurance of the hamstrings with either a side-to-side weakness or an imbalance between the hamstrings and the knee extensors can lead to injury.
-
Muscle fatigue can lead to dyssynergia of muscle contraction.
-
Insufficient warm-up time may be involved.
-
Poor running technique may play a role.
-
Return to activity before complete healing has occurred can lead to recurrence.
-
Normal sagittal alignment permits the knee to lock in full extension, aided by powerful quadriceps and an intact extensor mechanism. The ground reaction force passes anterior to the "center of rotation" of the knee, while the posterior cruciate ligament, posterior capsule, hamstrings, and gastrocnemius provide a tension band effect.
