Hamstring Strains: Expediting Return to Play
Thomas M. Best, MD, PhD; William E. Garrett Jr, MD, PhDTHE PHYSICIAN AND SPORTSMEDICINE - VOL 24 - NO. 8 - AUGUST 96
In Brief: Strains to the hamstring muscle group are prevalent and, unfortunately, often recurrent, with prolonged rehabilitation and persistent disability. Most hamstring injuries are of a single muscle near the muscle-tendon junction. Rarely, the hamstring muscle group may avulse from the ischial tuberosity. The diagnosis can usually be made by history and physical exam, but MRI can be used to help pinpoint the extent and location of the injury. Initial treatment typically consists of rest, ice, compression, elevation, and pain relief. There is no consensus on optimal rehabilitation, but functional exercises with stretching and strengthening have been emphasized.
Hamstring strains are among the most common injuries in sports, and they often frustrate physician and athlete alike with a long recovery and high rate of recurrence. But by diagnosing the extent of the injury accurately and taking appropriate therapeutic steps, clinicians can improve the odds.
Case 1: Acute Hamstring Injury
A 34-year-old male recreational bicyclist and tennis player felt a painful "pop" in his left posterior thigh while playing tennis but continued to play despite pain. Over the next few days, he experienced mild pain in his midposterior thigh when playing tennis. Ten days after the initial injury, he experienced a similar "pop" with his hip flexed and knee extended, but the pain was worse. He was unable to continue play and had difficulty sleeping that night because of pain.
On physical exam the next day, the patient walked with a limp. He had a subcutaneous ecchymosis and palpable tenderness over the left semimembranosus muscle 4 cm distal to the ischial tuberosity. When he performed an isometric contraction with knee flexion, his hamstring muscles were felt to be in continuity. He had full range of motion of both hips. When he touched his fingertips to his ankles while standing, he had moderate tenderness at the left hamstring origin. Strength and sensation were intact except for 4-/5 strength in the left hamstrings. Straight-leg raise was 90° on the right and 75° on the left. Knee and ankle jerk reflexes were symmetric.
The patient was diagnosed as having an acute left hamstring strain and started on a physical therapy program of passive stretching and isometric strengthening. He maintained aerobic conditioning initially with swimming pool and stationary bicycle activities as tolerated. Ice and electrical stimulation were used before and after workouts. Nonsteroidal anti-inflammatory drugs (NSAIDs) were prescribed for pain control.
One week later the patient was walking without a limp and began concentric strengthening and more aggressive hamstring stretching. He began a jogging program when he was able to walk without hamstring discomfort for 20 to 30 minutes. He gradually advanced to sport-specific skills over the next 2 weeks and also started eccentric strengthening. He was discharged from physical therapy about 1 month after starting rehab and was advised that he could play tennis. The patient has not had further problems, although he notes that the muscle periodically is "a little stiff."
Case 2: Chronic Hamstring Pain
A 23-year-old professional football player was referred for persistent left hamstring pain of 4 months' duration. Four months prior to initial consultation he had injured the hamstring when diving for a loose ball and had felt a pop. He also noticed that he felt painful nervelike sensations down the lateral aspect of his leg. Six weeks after the initial injury he was subjectively better, although he still had a large ecchymosis in the midbelly of his hamstring with occasional pain radiating from the popliteal fossa into the foot. Magnetic resonance imaging (MRI) showed significant changes within the belly of the muscle. Two weeks later, the patient was able to jog lightly but could not sprint and had not returned to play. One month later, repeat MRI was obtained by another consulting physician and showed no interval change. Electromyography (EMG) studies were normal.
On presentation to our clinic 2 months later (4 months after the initial injury), physical exam revealed a well-muscled individual with a normal gait. He had no appreciable quadriceps atrophy. An obvious asymmetry of the hamstring muscles was visible with distal retraction of the muscle belly, and a defect was palpated immediately distal to the ischial tuberosity on the left side. When the patient attempted to contract the muscle, the hamstrings could be felt retracting at the mid and distal thigh. It was easy to feel the ischial tuberosity on the patient's left side, in contrast to the uninjured leg, where the hamstring origin prevented palpation of this bony landmark.
Despite an aggressive 4-month rehabilitation program of eccentric strengthening and stretching, isokinetic testing showed a 50% strength reduction in the left hamstring. The clinical diagnosis at this time was complete avulsion of the hamstring muscle complex from the ischial tuberosity. An MRI confirmed this injury and showed significant distal retraction of the muscle complex into the midthigh (figure 1).
Treatment options at this point included continued rehabilitation or surgical exploration of the avulsed hamstring. Findings at surgery included a complete avulsion of the hamstring complex with a retracted and scarred distal muscle belly. A delayed primary repair was performed with a fractional release of the muscle belly distally. He was back training for football 6 months later but still had symptoms. Other injuries prevented his return to football.
Hamstring Anatomy and Function
The hamstrings consist of three muscles that run from the hip to the knee and assist with hip extension and knee flexion: the semitendinosus, the semimembranosus, and the biceps femoris (figure 2). The semimembranosus muscle forms the bulk of the mass of the muscle group. Both the semimembranosus and semitendinosus are innervated by the tibial portion of the sciatic nerve. The biceps femoris has a dual innervation: The long head is supplied by the tibial part of the sciatic, and the short head is supplied by the common peroneal part of the sciatic. As with other frequently injured muscles, the hamstrings span two joints and are therefore subject to stretching at more than one point.
During walking and running, the hamstrings probably function primarily to decelerate the extending knee prior to foot strike and to assist with hip extension after foot strike (1). In the first half of the swing phase of the running cycle, the hip rapidly flexes. Knee flexion is passive during this period and results from the rapid forward acceleration of the thigh during hip flexion. Midway through the swing phase, however, while hip flexion continues, the knee begins to rapidly extend. During the latter part of the swing phase of gait, or float phase of running, the hamstring muscles decelerate the forward swing of the tibia, thus opposing the activity of the quadriceps.
Efforts have been made to correlate EMG data and time of maximum muscle activity with time of injury during the gait cycle (2). On the basis of conflicting results, it appears that there is probably a complex, poorly understood neuromuscular coordination pattern that may help explain why the hamstrings are injured.
Possible Risk Factors
Hamstring injuries are common in sports that require bursts of speed or rapid acceleration, such as soccer, track and field, football, and rugby. Improper warm-up, fatigue, previous injury, strength imbalance, and poor flexibility have been correlated with injury, but evidence showing a cause-and-effect relationship is sparse. These ideas have largely been based on results from small patient samples. For example, Burkett (3) correctly predicted 4 of 6 hamstring muscle injuries in professional football players based on strength imbalances between the quadriceps and hamstrings. In each of the injured players, hamstring strength was less than 60% of quadriceps strength. Furthermore, hamstring injuries were more likely to occur if the isometric strength of the right and left knee flexors differed by more than 10%. Despite these data, we are unaware of a published study that identifies athletes at risk because of strength imbalance and attempts to correct the imbalance to determine if this reduces the risk for injury.
Dorman (4) reported on 140 hamstring injuries and found that they usually occurred either quite early or in the latter stages of practices or matches and concluded that improper warm-up and fatigue are risk factors for injury.
What appears clear from the literature is the tendency for hamstring injuries to recur. Ekstrand and Gillquist (5) prospectively studied male Swedish soccer players and found hamstrings to be the muscle group most often injured. Perhaps more important, they noted that minor injuries doubled the risk of having a more severe injury within 2 months. Others (6) have noted a recurrence rate of 25% for hamstring injuries in intercollegiate football players. Despite such observations, it is not well understood why these injuries tend to recur so frequently.
History and Physical Findings
Hamstring strains can usually be diagnosed from history and physical exam findings. The patient will often describe pain in the posterior thigh, particularly during and following activities during which the hamstring is eccentrically activated, like running. On physical examination, tenderness and swelling can exist at the location of the injury, which is most often the muscle-tendon junction.
A careful physical exam can also usually help in detecting an avulsion of the hamstring complex from its bony origin. The patient often has a palpable defect extending from the retracted muscle belly proximally to the ischium.
When Imaging Is Warranted
Imaging studies, including x-rays, are probably not routinely warranted when evaluating hamstring strains. The clinician must always keep in mind, however, the high incidence of bony avulsions in children with open epiphyseal plates and rule this out by x-ray if indicated.
Recently, computed tomography (CT) has been used to accurately define the anatomy of injuries, which may aide in choosing between surgical and conservative measures (7,8). CT scanning of acute hamstring injuries has shown that the site of injury in running athletes is most often the muscle-tendon junction of the long head of the biceps femoris. Images taken 1 to 2 days after injury show areas of hypodensity consistent with inflammation and edema (high-density images suggest hemorrhage). Follow-up scans on patients with chronic injury often show calcifications at the muscle-tendon junction where the injury occurred, but their significance is unknown.
On T2-weighted MRI images, acute lesions appear as increased signal densities because of the increase of free water in traumatized muscle tissue (8,9) Acute hemorrhage is difficult to detect by MRI; the hemoglobin must become methemoglobin before it shows up.
MRI has shown some promise in predicting recovery following hamstring injuries. In a retrospective study (9) of 14 professional athletes, recovery was delayed in those who had complete muscle transection or had greater than a 50% cross-sectional muscle involvement. We use two possible indications for MRI: a suspected total proximal avulsion of the hamstring muscle complex from the ischial tuberosity, and a suspected complete muscle transection. In both cases, surgical referral may be warranted.
Conservative Treatment vs Surgical Care
As is true of most strains in general, the vast majority of injuries to the hamstrings can be managed without surgery. Initial treatment typically consists of rest, ice, compression, elevation, and pain relief. Compression of the affected area with elastic wrap may help reduce swelling. For pain relief, NSAIDs or acetaminophen can be used for 7 to 10 days. However, no optimal treatment regimen has been developed based on carefully designed clinical trials.
There is likewise no consensus on optimal rehabilitation following initial treatment, but functional rehabilitation that includes stretching and strengthening has been emphasized. A complete rehab program should also address the cardiovascular demands of the patient's sport.
One exception to the general preference for nonsurgical treatment may be avulsion of the hamstring complex at or near the proximal bone-tendon junction. This lesion often leads to chronic pain and functional deficits. Sallay et al (10) reported that it took 12 patients an average of 7 weeks to walk without a limp after sustaining an avulsion-type injury while water skiing. Three of the 12 patients went on to surgery because of persistent functional limitations and chronic pain. Complete rupture of the hamstring muscles may also require surgical repair (10,11).
Based on these small anecdotal patient samples, we believe that surgical referral may be indicated in individuals with total avulsion of the hamstring complex from the ischial tuberosity. The exact timing of surgery is debatable given the infrequent reporting of this injury. Prospective, randomized studies would need to be done to provide clear guidelines and indications for surgical referral. It is our opinion that acute primary repair is preferable so that the risk of scar formation and loss of function is minimized.
Most clinicians prescribe warm-up and stretching to help reduce the incidence and severity of muscle strains. The evidence supporting these ideas is sketchy at best and largely based on retrospective studies. For example, following hamstring injury, the affected extremity and muscle group are significantly less flexible than the uninjured side, but there are no differences in isokinetic strength (12) Jonhagen et al (13) found decreased flexibility and lower eccentric hamstring torques in runners who sustained a hamstring strain when compared with uninjured subjects matched for age and speed.
It may well be that stretching and warm-up do more to improve performance than to prevent injury. A recent study (12) showed that hamstring stretching and increased flexibility were effective for improving hamstring muscle performance as measured by peak torque values. The role of stretching and warm-up in injury prevention needs to be better understood so that optimal strategies can be developed.
Emphasizing Nonoperative Steps
Hamstring strains continue to be a challenging and often frustrating problem for professionals who care for athletes. The often long convalescence and high recurrence suggest the need for a better understanding of the mechanism and pathophysiology of these injuries. Fortunately, most patients can be treated nonoperatively. Surgical consultation is probably required for patients with hamstring avulsion from the ischial tuberosity and distal muscle retraction, scarring, and functional limitation. The role of stretching, strengthening, and warm-up in injury prevention is unclear at this time.
Dr Best is an assistant professor of family medicine and orthopedic surgery at the University of Wisconsin in Madison and an associate editor of Medicine and Science in Sports and Exercise. Dr Garrett is a professor of orthopedic surgery at Duke University in Durham, North Carolina, and an editorial board member of The Physician and Sportsmedicine. Address correspondence to Thomas M. Best, MD, PhD, Research Park, 621 Science Dr, Madison, WI 53711; e-mail to [email protected].
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