Hamstring Injury 

Updated: May 22, 2018
Author: Herman Brad Ruiz, MD; Chief Editor: Craig C Young, MD 

Overview

Practice Essentials

This article focuses on injuries to the hamstring muscles. The word "hamstrings" was derived from the fact that it is these muscles by which a butcher would hang a slaughtered pig.

The hamstrings are a group of muscles (ie, semimembranosus, semitendinosus, biceps femoris) located on the back of the upper leg.[1, 2] The hamstrings are a common source of injury and chronic pain in athletes. Injuries to the hamstring muscles primarily occur proximally and laterally, and they usually involve the biceps femoris. The severity of injury to the hamstring muscles is classified according to the following grades:

  • Grade 1 is a mild strain, with few muscle fibers being torn.

  • Grade 2 is a moderate strain, with a definite loss in strength.

  • Grade 3 is a complete tear of the hamstrings.

Hamstring injuries almost always occur at the proximal myotendinous junction. In the biceps femoris, this junction extends over most of its entire length. Injury usually does not occur within the tendon itself unless there is preexisting pathology.

Bony avulsion at the ischial origin may occur as well, but this is usually associated with sudden, large-force, hip-flexion injuries.[3] Avulsions are commonly seen in individuals who have been involved in waterskiing accidents in which the knee is extended and the hip is suddenly flexed as the skier falls forward.[4]

One study involving 47 football players with hamstring injuries reported an average of 14 days of convalescence before return to play.

For patient education resources, see the Sports Injury Center, Sprains and Strains Center, and Foot, Ankle, Knee, and Hip Center, as well as Muscle Strain and Ruptured Tendon.

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Epidemiology

Frequency

United States

As a percentage of lower-extremity injuries, hamstring injuries peak at 33% in persons aged 16-25 years, and they most often occur in sports in which the hamstrings can be stretched eccentrically at high speed.[5, 6, 7, 8, 9, 10] Prime examples of such sporting activities include sprinting, track and field, and other running contact sports, such as football and soccer. Recreational sports such as waterskiing, in which the knee is fully extended during injury, are also common causes of hamstring injuries.[4] One study analyzed data from the National Football League’s Injury Surveillance System and found that a high percentage of hamstring injuries occur in the preseason. Over the 10-year study period, 1716 hamstring strains were noted, with slightly more than 50% occurring during the preseason. Players on the special teams units as well as wide receivers and defensive secondary were found to have an elevated risk for injury.[11]

International

An Australian study involving 1614 individuals with hamstring injuries revealed that such injuries compose 54% of the injuries in rugby, 10% of the injuries in soccer, 14% of the injuries in track, and less than 2% of the injuries in tennis, squash, ballet, and gymnastics.

A 13-year longitudinal analysis by Ekstrand et al that included 36 European Football clubs and 1614 hamstring injuries reported that training-related hamstring injury rates increased by 4.0% per year since 2001 while match-related injury rates have remained stable.[12]

Functional Anatomy

The hamstrings are composed of 3 muscles, as follows:

  • Biceps femoris muscle (long head and short head)

  • Semimembranosus muscle

  • Semitendinosus muscle

Origins and insertions

All of the muscles of the hamstrings originate on the ischial tuberosity. The second head of the biceps femoris (ie, short head) originates medial to the linea aspera on the distal posterior femur.

The short head of the biceps femoris crosses only one joint to insert with the long head of the biceps femoris onto the fibular head and lateral tibial condyle.

The other hamstring muscles cross 2 joints to reach their insertions. The semitendinosus muscle forms the pes anserinus with the sartorius and gracilis tendons to insert on the medial tibial metaphysis. The semimembranosus muscle interweaves with the fibers of the semitendinosus to eventually insert onto the posteromedial tibial condyle.

Innervations

The short head of the biceps femoris muscle is also unique in that it is innervated by the peroneal portion of the sciatic nerve, whereas the long head of the biceps femoris, semimembranosus, and semitendinosus are innervated by the tibial portion of the sciatic nerve.

Sport-Specific Biomechanics

In track and field events in which the hamstring is eccentrically contracted, the risk of a hamstring injury can be high. Contact sports such as football can result in contusions of the hamstring muscle.[13, 14] The contusion is superficial when the muscle is contracted on impact, and it is deep when the muscle is relaxed on impact. Waterskiing accidents have an association with proximal, bony avulsions because the individual's knee is extended when the hip undergoes a violent, forceful flexion as he/she falls forward.

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Presentation

History

See the list below:

  • The onset of pain and/or weakness is usually sudden and may occur during an explosive movement, such as sprinting.

  • Patients may report hearing an audible pop at the time of injury.

  • Onset of posterior thigh pain is often near the beginning or near the end of the sport activity. This is consistent with the belief that fatigue and lack of warm-up are factors that may lead to muscle injury.

  • Patients may only have a sense of apprehension due to a feeling of inadequate leg control as a result of the injury.

  • Patients may report pain with sitting or while walking uphill or ascending stairs.

  • Swelling and ecchymosis may accompany more severe injuries.

Physical

See the list below:

  • Physical findings are absent in many hamstring injuries.

  • The patient often has pain with active knee flexion against resistance. The procedure is performed with the hip in a neutral position and the knee in an extended starting position.

    • With the patient in a prone position and the affected extremity's knee flexed at 90 º, palpate from the ischial muscle origins to their insertions. This minimizes patient pain, which can limit detecting muscle defects.

    • Next, with the patient in the supine position and the hips flexed to 90 º, the maximum tolerable active and passive knee extension angle should be noted and compared to the contralateral leg. This allows the physician to assess the severity of the injury and to monitor future rehabilitation progress.

  • In severe cases, swelling and ecchymosis may be present.

  • With a complete hamstring rupture, the muscle may contract into a ball, with an accompanying strength deficit.

Causes

See the list below:

  • The major predisposing factors are lack of warm-up, poor flexibility, fatigue, and a hamstring-to-quadriceps ratio less than 50%.

  • A previous hamstring injury is the most recognized risk factor for injury. A study of elite track and field athletes with acute, first-time, unilateral hamstring muscle strains found that low-grade hamstring muscle injuries may lead to a higher risk of reinjury than high-grade injuries.[15, 16, 17]

  • Poor running style, especially overstriding, predisposes some runners to hamstring injuries. Overstriding stretches the hamstring and places it in a position of active insufficiency.

  • Dyssynergia secondary to dual innervation of the hamstring muscles may also be a factor that contributes to hamstring injuries.

  • Rapid growth seen during adolescence sometimes leads to tight hip flexors with a resultant anterior hip tilt. This can cause a natural predisposition to hamstring injuries for this age group.

 

DDx

 

Workup

Laboratory Studies

See the list below:

  • Laboratory studies are typically not needed to make the diagnosis of hamstring injury. Most often, a diagnosis can be made with the history and physical examination alone.

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Imaging Studies

See the list below:

  • In most cases, imaging studies have no role in the workup of hamstring injuries.

    • Radiographs of the pelvis can be negative even though the patient may have a bony avulsion. However, radiographs may reveal calcifications that may be present in patients with chronic hamstring pain.

    • Ultrasound or magnetic resonance imaging (MRI) studies 2-3 days postinjury may be recommended to rule out total muscular rupture or an intramuscular hematoma if significant weakness is still present.

    • An MRI is often ordered to help clinicians prepare for possible surgery if radiographs reveal a gross deformity.

Procedures

Past treatment options for acute hamstring injuries included intramuscular corticosteroids; however, given the evidence of delayed healing in acute muscle injury as well as muscle atrophy, this treatment could have detrimental effects over the long term.

In a retrospective study of the use of intramuscular corticosteroid injection for hamstring injuries in professional football players, Levine et al found that players with a partial hamstring tear had no ill effects of the corticosteroid injection in terms of functional outcome[10] ; however, the follow-up time frame was not clearly defined. Although this study does not address the issue of the physiologic effects of corticosteroids in muscle injury, it does offer some initial clinical outcomes for this procedure in athletes.[10]

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Treatment

Acute Phase

Rehabilitation Program

Physical Therapy

Treatment of hamstring injuries varies according to the severity of the injury. Patients with minor strains may progress quickly to strengthening exercises, whereas those with full-thickness ruptures require surgery. Up to 1 week after a minor injury, the focus of therapy is to limit pain, inflammation, and swelling. Rest, ice, compression, and elevation (RICE) are recommended. Elastic thigh bandages can be useful for compression. Icing for 20 minutes, 4 times per day, provides pain relief.

Most patients may begin active range of motion (AROM) exercises within their pain tolerance after 1-2 days. Individuals with more serious injuries benefit from immobilization in knee extension for 1-5 days to prevent contracture formation and further damage. Crutches enable ambulation while resting the injured leg.

After several days, most patients may begin pain-free submaximal isometrics, pool therapies, and upper-body exercises. Isometric exercises are performed at various knee angles in increments of 20°. Patients hold the contraction for 5-15 seconds, and perform 3 sets at each angle.

Medical Issues/Complications

If patients return to their usual activities too soon, delayed healing or reinjury may result. In more serious injuries, compartment syndrome can result from an extending hematoma. The most common symptom of compartment syndrome is increasing pain.

Surgical Intervention

Surgery is rarely performed for large hematomas; on the other hand, it is performed in more than 50% of cases of muscle belly tears, with consideration given to the patient's activity demands. However, surgery is generally indicated for bony avulsions only.

Consultations

In cases of severe hamstring injuries, consultation with a sports medicine specialist or an orthopedic surgeon may be indicated. Physiatrists may be consulted to oversee rehabilitative therapies and to help prevent further injuries.

Recovery Phase

Rehabilitation Program

Physical Therapy

Generally, treatment 1-6 weeks postinjury focuses on patient strengthening, improving range of motion (ROM), and flexibility.

Passive static stretching may begin at this stage. Moist heat may be used to warm up the muscle tissues before stretching and exercising. Electrical stimulation may be used in conjunction with ice for added pain relief.

Being pain free throughout the entire ROM is not required before strengthening exercises may be initiated. The patient may exercise, preferably with a therapist, to strengthen the muscle within the available pain-free ROM.

Next, the patient begins isotonic exercises with resistance, increasing the program gradually as tolerated. As healing continues, high-speed, low-resistance isokinetic exercises are started. Resistance is increased gradually, while exercise speed is decreased. Over time, the patient progresses from concentric to eccentric strengthening exercises. Before the athlete returns to play, sports-specific training maximizes recovery and minimizes the chances for additional injury.

Medical Issues/Complications

Reinjury and delayed healing result if the therapy is too aggressive or if activity limitations are not followed.

Maintenance Phase

Rehabilitation Program

Physical Therapy

From 1 month postinjury onward, the patient continues stretching and strengthening exercises to maintain flexibility and an adequate hamstring-to-quadriceps strength ratio.

 

Medication

Medication Summary

Although some inflammation may theoretically be desirable to facilitate clearing of necrotic tissue and to initiate healing, nonsteroidal anti-inflammatory drugs (NSAIDs) are usually started right away. However, NSAIDs are ideally used for only 3-7 days, given the evidence that their use may delay complete healing.

Acetaminophen or a narcotic may be administered in addition to an NSAID for most continuing pain. However, narcotics (eg, Vicodin) are usually reserved for those with serious injuries and extreme pain.

Some animal model studies show some evidence that anabolic steroids may aid in the healing of injured muscles. Animals that have been treated with anabolic steroids are able to generate greater forces through injured muscles than those that have not been treated with these agents. However, there is not enough evidence to recommend the use of anabolic steroids to promote faster healing.

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Nonsteroidal Anti-inflammatory Agents

Class Summary

NSAIDs have analgesic and antipyretic activities. The mechanism of action of these agents is not known, but NSAIDs may inhibit cyclooxygenase 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. Treatment of pain tends to be patient specific.

Naproxen (Aleve, Anaprox, Naprelan, Naprosyn)

Relieves mild to moderate pain. Inhibits inflammatory reactions and pain probably by decreasing the activity of the enzyme cyclooxygenase, which results in decreased prostaglandin synthesis.

Analgesics

Class Summary

Pain control is essential to quality patient care. Analgesics ensure patient comfort, promote pulmonary toilet, and have sedating properties, which are beneficial for patients who have sustained trauma or who have sustained injuries.

Acetaminophen (Feverall, Tempra, Tylenol)

DOC for pain in patients with documented hypersensitivity to aspirin or NSAIDs, in those diagnosed with upper GI disease, or in those taking oral anticoagulants.

Hydrocodone bitartrate and acetaminophen (Vicodin, Vicodin ES)

Drug combination indicated for moderate to severe pain.

 

Follow-up

Return to Play

A common threshold for return to play is when the strength of the injured hamstring has at least 90% of the strength of the unaffected hamstring and when the patient has full ROM. At least a 50-60% hamstring-to-quadriceps ratio is desired before allowing the athlete to return to play.

Strength testing is performed using isokinetic exercise equipment. In addition, it is also important to ensure the return of normal flexibility and endurance before the patient returns to play; reinjury is most often due to lack of both.

Therapy that incorporates sports-specific activities can help minimize the risk of reinjury.

Complications

Returning to play too early is a common factor leading to chronic hamstring pain and injury. Reinjury rates as high as 77% may be related to areas of calcification and inflammation in the hamstring after injury. Scar formation may impinge the sciatic nerve, resulting in hamstring syndrome.[18] Surgery has rarely been used to break up painful scar tissue.

Prevention

The implementation of proper warm-up and maintenance of flexibility and adequate strength are needed to prevent future injuries. The patient should be aware that as fatigue sets in, the risk of injury increases. With improved form and by emphasizing knee flexion during activities, the risk of further injuries is minimized.[2, 7, 8, 19, 20, 21]

Fifty Danish male professional and amateur soccer teams (942 players) were studied in a randomized controlled trial that compared a 10-week progressive eccentric training program followed by a weekly maintenance program. The overall results showed a significant reduction in hamstring injuries. The program was especially useful in prevention of recurrent injuries (number need to prevent 3), and to a lesser effect, the program was able to aid in the prevention of new injuries (number needed to treat 25).[22]

Prognosis

With minor activity limitations and proper rehabilitation, the prognosis is good for hamstring strains and even partial tears. Complete tears also heal but require a significantly longer and more intensive rehabilitation program.