Hamstring Strain

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.

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.

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.[1, 2, 3]

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.[4]

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.[5, 6]

Age

While hamstring injuries can occur in people of any age, incidence increases with age.

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

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

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.

Hamstring strain is diagnosed primarily by physical examination and history. Lab studies are not of significant assistance in making the diagnosis.

The diagnosis is typically clinical, but some imaging studies may helpful if the clinical picture is unclear.[11]

Radiographs can rule out an avulsion injury from the ischial tuberosity or other fractures, but they generally are not otherwise of significant help.

Ultrasonographic studies may aid the physician when confirming the diagnosis of hamstring strain, but they do not always indicate definitive results. The quality of the study is related to the expertise of the technician and the cooperation of the patient.

When a confirmation or grading of a hamstring strain is necessary, magnetic resonance imaging (MRI) is the most sensitive test used when considering the diagnosis of hamstring strain, but it should be used sparingly because of the cost and patient discomfort.[3] Some data suggest that MRI is helpful when attempting to predict return in a high-performance athlete in combination with supporting clinical evidence. Studies have shown that more than 6 weeks' delay before return to sport has been reported with the following:

• Complete transection
• Involvement of 50% of cross-sectional muscle
• Ganglionlike fluid collections
• Hemorrhagelike signal
• Distal myotendinous tears
• Deep muscle tears

For higher-level athletes, isokinetic muscle-strength testing may quantify muscle weaknesses or imbalances that may lead to a chronic injury or recurrence.[12]

Physical Therapy

The key to successful recovery from a hamstring strain is recognition of the injury and of the severity of the stain. Physical therapy (PT) is the mainstay of treatment.[13] The program depends on the severity of the injury and on the time that has elapsed since the injury. Very few scientific data are available to determine specific rehabilitation and treatment protocols for hamstring injuries. The program below is just a guide and should be tailored to individual patient needs.

Acute phase

During the acute phase (1-5 d), most of the treatment is geared toward decreasing the inflammation and maintaining range of motion. As for most strains, PRICE (ie, protection, rest, ice, compression, elevation) is the initial treatment. When the pain has decreased, the therapist may begin painless gentle passive range of motion and active-assistive range of motion. The patient also may benefit from a cane or crutches to aid in ambulation to keep active. Even if a patient with a first-degree injury is feeling better after a few days and wants to return to participating in his or her sport, it is usually recommended that he or she complete a rehabilitation program to avoid chronic injury. Muscle strengthening, balance, and stretching should be emphasized to the patient as a prevention of recurrence.[14, 15]

Subacute phase

The subacute phase (5 d to 3 wk) is when the inflammation of the injury appears to be lessening. The goal of treatment in this stage is to begin some active range of motion and start strengthening. Aquatic therapy is helpful in encouraging activity with decreased weight bearing. Pain-free submaximal isometric exercises also are encouraged. A transcutaneous electrical nerve stimulation unit may be used to provide some pain relief at this time. Ice is also helpful to decrease pain and inflammation. The patient also should resume cardiovascular training, which may include swimming with a pull buoy between the legs, and upper extremity exercises.

Remodeling phase[3]

The remodeling phase (1-6 wk) is when the patient is able to perform isometric exercises at 100% effort without pain. Prone isotonic hamstring exercises are now added to the transcutaneous electrical nerve stimulation unit and ice. Begin unilaterally with ankle weights, using low weight and a high number of repetitions. Slowly increase the weight as tolerated as long as the patient's pain is not increased afterwards. Importantly, do not increase the weight too rapidly because this could lead to a chronic injury.

Once concentric strengthening is tolerated at a normal level, the patient may begin eccentric strengthening. Because this exercise puts the most strain on the muscle, supervised exercising and slow progression of weight is recommended. In the prone position, the patient performs a unilateral contraction to 90° of knee flexion and then slowly lowers the weight. If the patient experiences pain or stiffness, then decrease the weight to a more tolerable amount. When the affected leg is within 10% of the unaffected leg, then the patient may advance to a more aggressive therapy program. Continued stretching of the hamstring is essential and should occur prior to exercise. Moist heat prior to exercise may provide improved results. A posterior pelvic tilt may help eliminate lumbar compensation.

Functional stage

The functional stage is 2 weeks to 6 months. At this point, the patient should have a normal gait pattern and can begin fast walking. 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. Have the patient continue with the hamstring strengthening and stretching throughout this stage.

During the later stages of therapy, plyometric exercises may be used to increase speed and power during training. These exercises consist of muscle stretching followed by concentric contraction, allowing for a stronger contraction because of muscle facilitation and decreased inhibition. Low-level exercises may be used initially (eg, jumping rope), followed by higher-level exercises as tolerated (eg, side jumping over a low object, jumping onto and off a box). Because the higher level exercises are associated with a higher rate of injury, they should be performed with supervision.

Return to play

This can occur anywhere between 3 weeks and 6 months. Isometric strength testing and flexibility testing may be performed prior to returning to play to ensure that no subtle deficits are present that may lead to chronic injury.[16] The clinician must impress upon the patient the importance of stretching and warm-up prior to activities to prevent reinjury. Less than 5 weeks are required before return to play for patients with (1) superficial muscle injury or (2) muscle injury that involves a small cross-section of muscle. In patients whose injury was due to poor biomechanics, care should be taken to correct the underlying cause. The patient should be supervised during stretching and exercise in order to assess poor technique and correct it.

In a study of 59 Australian footballers who had incurred a hamstring strain, Warren et al found evidence that 2 factors—the amount of time it took a player to walk without pain and whether or not the player had suffered a previous hamstring injury—could be used to help predict the length of time needed for the athletes to return to competition and how likely it was that the injury would again recur.[17] According to the study, players who needed more than 1 day to walk without pain were more likely to require more than 3 weeks of convalescence before they could again compete.

A prospective study by Guillodo et al indicated that in patients who suffer hamstring injury, a visual analogue scale pain score of more than 6 and, for over 3 days, the occurrence of pain during everyday activities predicts a time to full recovery of more than 40 days. The study was conducted on 120 athletes, who were assessed by sports medicine specialists within 5 days of suffering an acute hamstring injury.[18]

A randomized, double-blind, parallel-group trial by Silder et al found that two different types of rehabilitation programs for acute hamstring injury—(a) progressive agility and trunk stabilization and (b) progressive running and eccentric strengthening—were each similarly effective to the other in terms of recovery. The study involved 25 patients who completed one of the two programs, with magnetic resonance imaging (MRI) and physical examinations performed prior to and after rehabilitation. Injury resolution was found to be nearly, but not totally, complete in all subjects at the time of return to sport.[19]

A study by Tyler et al found that in hamstring-strain injuries, reinjury after return to play is discouraged by a rehabilitation program that focuses on eccentric strength training with the hamstrings in a lengthened position. Among 50 athletes, 42 who were compliant with the program had sustained no reinjuries by an average of 24 months after returning to sport, while among eight noncompliant athletes, four suffered reinjury between 3 and 12 months following their return to sport. Moreover, full strength had been restored to the compliant athletes by the time they returned to sport, while significant hamstring weakness was experienced by the noncompliant athletes.[20]

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.[21]

The standard choice for medication is nonsteroidal anti-inflammatory drugs (NSAIDs). These medications not only provide analgesia but also can decrease some of the mediators of inflammation. When to administer NSAIDs to achieve the most beneficial effect is debated. One argument is to administer them immediately following injury to avoid side effects that may interfere with muscle remodeling and repair. The other argument is to delay use until 2-4 days after the injury, so they do not interfere with the chemotaxis required for the laying down of new muscle fibers. No consensus has been reached on which approach to timing yields the best outcome.

Class Summary

Have analgesic, anti-inflammatory, and antipyretic activities. Their mechanism of action is not known, but they may inhibit cyclo-oxygenase activity and prostaglandin synthesis. Other mechanisms may exist as well, such as inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation, and various cell-membrane functions.

Naproxen (Anaprox, Naprelan, Naprosyn)

Available in both a regular and delayed-release form.

Ibuprofen (Motrin, Ibuprin)

DOC for patients with mild to moderate pain. Inhibits inflammatory reactions and pain by decreasing prostaglandin synthesis.

Ketoprofen (Orudis, Actron)

For relief of mild to moderate pain and inflammation. Small doses initially are indicated in small and elderly patients and in those with renal or liver disease. Doses over 75 mg do not increase therapeutic effects. Administer high doses with caution and closely observe patient for response.

Class Summary

Cyclooxygenase 2 (COX-2) inhibitors have a lower incidence of GI bleeding as compared with other NSAIDs, although there is still a risk involved. They should be considered for use in patients with a history of GI bleed or those who have a high risk for a bleed.

Celecoxib (Celebrex)

Primarily inhibits COX-2. COX-2 is considered an inducible isoenzyme, induced by pain and inflammatory stimuli. Inhibition of COX-1 may contribute to NSAID GI toxicity. At therapeutic concentrations, COX-1 isoenzyme is not inhibited, thus incidence of GI toxicity, such as endoscopic peptic ulcers, bleeding ulcers, perforations, and obstructions, may be decreased when compared to nonselective NSAIDs. Seek lowest dose for each patient.

Neutralizes circulating myelin antibodies through anti-idiotypic antibodies; down-regulates pro-inflammatory cytokines, including INF-gamma; blocks Fc receptors on macrophages; suppresses inducer T and B cells and augments suppressor T cells; blocks complement cascade; promotes remyelination; may increase CSF IgG (10%).

Has a sulfonamide chain and is primarily dependent upon cytochrome P450 enzymes (a hepatic enzyme) for metabolism.

See the list below:

• See Physical Therapy section for a discussion of further outpatient care.

Prevention of reinjury is dependent upon successful completion of the rehabilitation program and preactivity warm-up and stretching, although there is limited evidence to prove this conclusion.

In a cluster-randomized controlled trial with 942 male soccer players, the authors explored the preventive effect of eccentric strengthening of the hamstring muscles using the Nordic hamstring exercise compared with no additional hamstring exercise. The results revealed 52 acute hamstring injuries in the control group compared with 15 injuries in the intervention group. The additional eccentric hamstring exercise not only decreased the rate of new injuries, but the overall and recurrent acute hamstring injury numbers were also lower compared with the control group.[22]

A study by Barbosa et al indicated that static hamstring stretching training used in isolation for performance improvement and prevention of hamstring strain injuries should be employed with caution owing to the possible negative impact of such exercises on knee flexor eccentric torque and—as demonstrated by reduced distance achieved on the triple-hop test—hamstring functional performance.[23]

See the list below:

• The prognosis usually is good for complete or near complete improvement in 6-18 weeks. Unfortunately, there are patients who develop chronic problems, possibly due to repeated stresses on the tendon that cause tendinosis. In this case, the tendon is not healing properly, and fibrotic changes take place in the tendon.

See the list below:

• Once the injury has healed and the rehabilitation program has been completed, emphasize the importance of proper warm-up and stretching before participation in vigorous physical activity.

• For excellent patient education resources, visit eMedicineHealth's First Aid and Injuries Center. Also, see eMedicineHealth's patient education articles Muscle Strain and Sprains and Strains.