What is it?
The hamstring is composed of 3 major muscles which together perform hip extension and knee flexion. These muscles can become strained from excessive load during an eccentric contraction or from extreme stretch.
Hamstring strains are classified from grade 1 to grade 3 based upon the amount of tissue damage. A grade 1 is a strain without significant tearing while a grade 2 indicates a partial muscle tear. A grade 3 represents a complete muscle or tendon rupture.
The hamstring muscles are the most commonly strained muscle in the lower extremity of elite athletes. Injury to the hamstring is also the most prevalent source of disability in professional football players. Sports that involve sprinting and jumping, predispose athletes to eccentrically strain injuries whereas participants in activities like dancing are more prone to stretch-type injuries.
The majority of sports related hamstring injuries tend to occur during competition, especially because the athlete is more vulnerable as they tire. As muscle fatigue is a contributing factor, a combination of several other factors increases the risk of hamstring strain, including insufficient warm-up, a history of prior injury, and hamstring inflexibility or weakness.
Additional known biomechanical risk factors include hypertonicity (excessive tension) in the quadriceps or iliopsoas, poor control of the lumbopelvic muscles, and poor running mechanics. Injuries are thought to occur when the number of risk factors reaches a high volume.
The majority of hamstring injuries occur abruptly during activity, accompanied by a tearing feeling and significant pain. In only 9% of cases do symptoms start more gradually. Symptoms of hamstring strains vary from mild to debilitating pain, based upon the site and amount of tissue damage. The most common presenting symptoms include pain in the lower buttock and posterior thigh when straightening the leg.
Clinical evaluation may demonstrate bruising, which begins at the site of injury and slowly gravitates inferiorly (down the leg). Palpation will reveal local tenderness, swelling, and hypertonicity. Range of motion screens may produce pain upon passive hip flexion and knee extension, such as a straight leg raise. Motion palpation may reveal deficits in sacroiliac or lumbar mobility.
The diagnosis of hamstring strain should be based upon an accurate history and physical evaluation. Radiographs are generally unnecessary unless there is a suspicion of bony pathology. Advanced imaging of the hamstring, including an MRI or ultrasound, is reserved for more severe injuries in order to help determine whether surgical intervention will be necessary.
The management of hamstring injuries is challenging for both clinicians and patients, as healing is often delayed with persistent symptoms and re-injury rates between 12-31%. The average recovering period ranges from one to three weeks and is based upon the severity and location of the injury. Injuries that result from slow speed stretching generally take longer to heal.
Recurrent injuries often take twice as long to heal as the initial injury. Athletes who do not adequately rehabilitate their injury and return to sport prematurely are at a greater risk of re-injury and diminished performance.
The rehabilitation of hamstring injuries can be divided into three phases.
The focus of phase I is reduction of pain and swelling immediately after an injury. Clinicians should educate and initiate PEACE and LOVE to start the healing process. The use of compression bandage may help to limit intramuscular swelling. A short period of immobilization, including the use of crutches, may be necessary for more severe strains. Clinicians give out light range of motion exercises, including knee flexion and extension. Excessive stretching of the injured tissue should be avoided initially and range of motion may be defined by the onset of pain. Manipulation may be utilized to resolve joint restrictions in the lumbar spine, sacroiliac joints, and/or lower extremities.
Progression to phase II begins when the patient can walk without pain and can tolerate a moderate degree of resisted knee flexion. The goal of phase II is to improve flexibility, strength, and biomechanical function of the hamstring and related lumbopelvic tissues. Athletes should gradually increase running to 50% of their maximum and avoid sprinting. Cross training with stationary biking or swimming may be incorporated.
Rehabilitation programs that incorporate core stabilization and progressive agility drills have been shown to decrease re-injury rates when compared to more traditional isolated stretching and strengthening programs. Soft tissue manipulation and myofascial release techniques, including IASTM, may be implemented for the hamstring and associated hip musculature.
Progression to phase III begins when the patient is able to perform pain free resisted knee flexion and can run at 50% speed without pain. The goal of phase III is to return the patient to activity through sports-specific drills and trunk stabilization. During the final phase, patients will gradually increase from jogging to full sprinting.
Athletes should not be returned to unrestricted sporting activities until they have achieved full range of motion, adequate strength back in the hamstring, and pain-free sports specific function. Return to competition before restoration of pain-free, sport-specific function will likely result in recurrent or more severe injury. Athletes should be counseled on proper warm up and cool down as they return to activity.