I. Description: [1,3,5]
A hamstring strain is a frequent injury within the posterior compartment of the thigh; it is a common sport-related injury that mostly occurs in athletic activities that have high demands on sprinting such as rugby, football, soccer, and track-and-field. The hamstring strain is a relatively wide classification of a condition that can range from a few torn muscle fibers or a partial muscle tear to a more severe, complete tear of the tendon or muscle fibers. Hamstring strain rehabilitation is challenging due to slow healing times, persistent symptoms, and the hamstring's high re-injury rate.
The hamstring is conjointly recognized as three muscles: biceps femoris, semitendinosus, and semimembranosus which are located in the posterior compartment of the thigh. The biceps femoris muscle consists of two heads, a long head and short head. The long head originates on the ischial tuberosity in the inferiomedial aspect of the upper area, whereas the short head originates on the lateral lip of the linea aspera on the shaft of the femur. Both heads of the biceps femoris come together to form a tendon that inserts at the head of the fibula. The semitendinosus originates medially alongside the long head of the biceps femoris muscle and inserts at the medial surface of proximal tibia. The semimembranosus muscle originates superolaterally on the ischial tuberosity and inserts on the medial tibial condyle which lies deep to the semitendinosus muscle. The hamstring muscles collectively function to flex the leg at the knee joint and extend the thigh at hip joint. The biceps femoris muscle also acts as a lateral rotator of the thigh at the hip joint and laterally rotates the leg at the knee joint, whereas both the semitendinosus and semimembranosus muscles act as medial rotators of the thigh at the hip joint and medially rotate the leg at the knee joint. The hamstrings are innervated by the tibial division L5, S1,S2 of the sciatic nerve
(Image source: http://orthoinfo.aaos.org/figures/A00408F01R.jpg)
The severity of injury including the extent of pain, weakness, decreased motion, and the level of damage to the muscle and tendon fibers of the hamstring can be classified according to the following grades:
- Grade 1 or first-degree strain (mild): Minimal damage and tearing of the muscle or tendon fibers. Mild pain during the time of injury and minimal functional loss.
- Grade 2 or second-degree strain (moderate): A more severe muscle tearing without complete disruption of the muscle or tendon fibers. Pain is typically felt during activity.
- Grade 3 or third-degree strain (severe): A complete tear or rupture of the muscle or tendon fibers with a palpable defect noted.
IV. Incidence/ Prevalence:[1,5]
Hamstring strain is a very common occurrence in sports-related injuries due to the prevalence of high speed running, sprinting, rapid acceleration-deceleration, and kicking and dancing. Hamstring strain is likely to see more occurrences in sports such as rugby, track-and-field, football, and soccer due to their common exercise of the risk factors previously stated. The re-injury rate of hamstring strain is nearly one-third after returning to the sport in the first year and is a leading cause of absence in these sports. Incidence of hamstring strain increases with age.
According to Heiderscheit et al, common signs and symptoms of a hamstring strain injury are as follows:
- Age: Increased risk for older athletes and young athletes who are still growing
- Prior history of hamstring strain
- Insufficient or incomplete rehabilitation for a prior strain may increase chance of re-injury soon after
- Muscle overload: Including sudden load or insufficient muscle warm-up
- Poor flexibility of hamstring and/or quadriceps
- Strength imbalance between hamstring and quadriceps
- Muscle fatigue
- Poor running mechanics and/or gait
VII. Diagnostic Tests:[4,5,9,12]
Radiographs are generally of little help in diagnosing hamstring strains except for ruling out an avulsion fracture from the ischial tuberosity. Ultrasonography and magnetic resonance imaging may be used to diagnose hamstring strains. In the acute stage, ultrasongraphic studies showed as equally sensitive as MRI in diagnosing the existence of hamstring strain, but in the healing phase, MRI was better able to show a more detail examination of injuries to deep portions of the muscles and previous hamstring injury. Also, MRI’s increased sensitivity in showing edema provides for more accurate size measurement. Magnetic resonance imaging can be used as further assessment of prognosis. A positive MRI generally indicates a poorer prognosis than a negative MRI. An MRI can help determine the recovery time and time of absence from sport.
Image sources: http://radiographics.rsna.org/content/25/3/571/F18.small.gif , http://radiographics.rsna.org/content/25/3/571/F12.small.gif , http://radiographics.rsna.org/content/25/3/571/F14.small.gif
- Palpation: Posterior thigh is palpated in order to locate the specific region of maximum pain and possible palpable defect at site of injury. The closer the maximum pain site is to the ischial tuberosity, the longer the recovery period is expected to be.
- Strength: Substantial decrease in strength and existence of pain with manual muscle testing with hip extension and knee flexion indicates a positive test for hamstring strain. Bilateral comparison is suggested.
- Range of motion: Substantial decrease in hamstring flexibility and existence of pain with passive straight leg raise and active knee extension test indicates a positive test for hamstring strain. Bilateral comparison is suggested.
- Slump test: To rule out adverse neural tension. Positive slump test indicates more proximal contribution suggesting sciatic nerve or lumbar spine involvement.
Hip extension manual muscle test with knee positioned at 0 degree of flexion
Image source: http://at.uwa.edu/mmt/HipExt.jpg
Hip extension manual muscle test with knee positioned at 90 degrees of flexion
Passive straight leg raise test
Active knee extension tests
IX. Conservative Treatment:[5,13]
Grade I and Grade II hamstring strain can be treated conservatively in three phases of rehabilitation. The primary objective for the rehabilitation program is to return the individual to their previous level of activity with the smallest risk of re-injury. The primary goal of phase one is to reduce pain and edema, and to protect scar formation. In this phase, the athlete should stay away from excessive stretching of the injured hamstring and ice should be applied two to three times per day. Phase one therapeutic exercises begin with low-intensity, painless exercises involving the entire lower extremity and lumbopelvic region. The primary goal of phase two is to increase intensity of range of motion exercises and begin eccentric movement of the hamstring. In this phase, the athlete should avoid end range lengthening if weakness continues, and ice should be applied after exercises. The objective of phase three is to get the athlete ready for functional return to their previous level of participation in the sport. In this phase, functional sport-specific movements, full unrestricted range of motion and speeds of eccentric hamstring strengthening at end range of motion and trunk stabilization and postural control are incorporated.
X. Surgery & post-op treatment:
Surgery is rarely utilized but is considered for complete hamstring avulsion where the tendon has pulled entirely away from the bone. In addition, surgery may also be considered for a complete tear within the muscle. To repair a hamstring avulsion, the hamstring tendon is reattached, suture anchors are placed in the bone by large stitches or staples, and scar tissue is removed. To repair a complete tear within the muscle, stitches are used to sew the muscle back together. Post-operative treatment includes the use of a crutch to avoid weight bearing of the leg and a brace to protect and keep the hamstring in a position of comfort. Physical therapy treatment usually includes: gentle stretches for flexibility and range of motion, gait training exercises, suggested therapeutic exercises including quad sets, ankle pumps, abdominal isometrics, and strengthening of hamstrings.
XI. Additional Web Based Resources: