Practice Essentials
Hamstring injuries are common problems that may result in significant loss of on-field time for many athletes because these injuries tend to heal slowly. Once injury occurs, the patient is at high risk for recurrence without proper rest and rehabilitation. [1]
The hamstring muscles are 3 muscles in the posterior thigh: the semitendinosus, semimembranosus, and biceps femoris. The semitendinosus originates at the ischial tuberosity and inserts at the pes anserine; the semimembranosus originates at the ischial tuberosity and inserts at the posterior medial tibia. The biceps femoris has a long head that originates at the ischial tuberosity and a short head at the posterolateral femur and inserts into the head of the fibula. These muscles serve as knee flexors and hip extensors. See the image below.
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.
At heel strike of the gait cycle, the hamstrings actually contribute to knee extension through closed chain kinetics. During the gait cycle, the biceps femoris contracts eccentrically in terminal swing, which is important in the pathology of the injury, as discussed later. [2, 3, 4, 5]
Signs and symptoms of hamstring strain
In addition to pain in the posterior thigh, the physical examination may reveal any of the following signs or symptoms:
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Tenderness over the site of injury
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Ecchymosis
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Palpable mass
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Pain with passive extension of the knee and the hip flexed at 90°, as compared with the noninjured side
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Pain with resisted knee flexion, which activates the muscle
Workup in hamstring strain
Hamstring strain is diagnosed primarily by physical examination and history. However, radiographs can rule out an avulsion injury from the ischial tuberosity or other fractures.
Ultrasonographic studies may aid the physician when confirming the diagnosis of hamstring strain, but they do not always indicate definitive results.
When a confirmation or grading of a hamstring strain is necessary, magnetic resonance imaging (MRI) is the most sensitive test used, but it should be employed sparingly because of the cost and patient discomfort. [4]
For higher-level athletes, isokinetic muscle-strength testing may quantify muscle weaknesses or imbalances that may lead to a chronic injury or recurrence. [6]
Management of hamstring strain
Physical therapy (PT) is the mainstay of treatment. [7] Management during the various phases of injury includes the following:
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Acute phase - During the acute phase (1-5 d), most of the treatment is geared toward decreasing the inflammation and maintaining range of motion
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Subacute phase - The goal of treatment in this stage (5 d to 3 wk) is to begin some active range of motion and start strengthening.
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Remodeling phase - In this phase (1-6 wk), prone isotonic hamstring exercises are added to therapy; once concentric strengthening is tolerated at a normal level, the patient may begin eccentric strengthening
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Functional stage - During this stage (2 wk to 3 mo), when the patient can ambulate for 20-30 minutes at a fast speed without pain or stiffness, short periods of jogging can be added to the fast walking; when the patient can perform a 15- to 30-minute jog, then short periods of sprinting may be added to the jog; eventually, more sport-specific exercises may be added; during the later stages of therapy, plyometric exercises may be used to increase speed and power during training
The need for surgical intervention is extremely rare after a hamstring injury. Surgery is recommended only in the case of complete rupture of the proximal or distal attachment of the myotendinous complex into the bone. [8]
Epidemiology
Frequency
Hamstring strain is a fairly common injury in physically active individuals. In a prospective study of 61 male track-and-field athletes, Tokutake et al reported that 30% of them suffered hamstring strain in association with high-speed running, with the incidence of such strains being 2.88 per 1000 practices or competitions. [9]
Mortality/Morbidity
No mortality is associated with hamstring strain; however, morbidity is common, due to pain and reinjury if proper rehabilitation does not occur before the patient returns to preinjury activity levels. [10, 11]
Age
While hamstring injuries can occur in people of any age, incidence increases with age.
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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.
