Hamstring Injuries

Introduction

Hamstring injuries are common in athletic populations and can affect athletes at all levels of competition. Several studies have shown that the rates of muscle strain in high school football (12% to 24%) and collegiate football (18.9% to 22.2%) are fairly high. In one study, injury surveillance conducted by the National Football League identified 1716 hamstring strains among all players, with a range of 132 to 210 injuries per year, which accounts for an overall injury rate of 0.77 per 1000 athlete-exposures and a reinjury rate of 16.5%. Hamstring injuries accounted for nearly one-fifth of all injuries sustained by elite track and field athletes, with males at twice the risk compared with their female counterparts. One literature review identified previous hamstring injury as the greatest risk factor for reinjury, with age and male sex also increasing injury risk. The injured muscle may have an altered compliance or deformation pattern, predisposing it to reduced tensility or higher muscle strain. Although some studies suggest that contact activities are the cause of hamstring injuries, most studies have shown that more than 90% of injuries occur without contact, with the classic injury being sustained by a water skier who gets pulled up by the boat, resulting in abrupt knee extension and hip flexion.

The hamstring complex consists of the short and long heads of the biceps femoris, semitendinosus, and semimembranosus. The semitendinosus, semimembranosus, and long head of the biceps are biarticular and are innervated by the tibial portion of the sciatic nerve. The short head of the biceps is monarticular and innervated by the common peroneal nerve. These muscles work together to extend the hip, flex the knee, and externally rotate the hip and knee; they have significant overlap at the myotendinous junction.

The proximal hamstring complex has a strong bony attachment on the ischial tuberosity ( Fig. 86.1 ). The ischial footprint is composed of the common proximal tendon of the semitendinosus and the long head of the biceps femoris as well as a distinct semimembranosus footprint. The semimembranosus passes anteriorly to the conjoined semitendinosus/biceps femoris tendon to its origin on the lateral ischium (see Fig. 86.1 ).

Biomechanically the hamstrings are subjected to high tensile load, given their extensive eccentric role. Hip and knee flexion during the initial swing phase requires simultaneous eccentric and concentric activity of the hamstrings. During terminal swing, the hamstrings continue to play a dual role of preventing knee hyperextension while opposing hip flexion. The hamstrings work synergistically with the gluteal muscles to stabilize, decelerate, and propel the hip. During the propulsion phase, the medial hamstrings assist in decelerating hip external rotation, which maintains the gluteus maximus at an ideal length to act as an accelerator (along with the hamstrings) of the femur in the sagittal plane. The hamstrings along with the rectus abdominis are also decelerators of pelvic anterior tilt throughout stance. Given these functional relationships, it is conceivable that hamstring strain or rupture has its source in the inhibition and weakness of its closest synergists, the gluteal and abdominal muscles; these muscle groups have become targets for injury prevention and rehabilitation.

Hamstring injuries most commonly occur proximally, as one study of 275 soccer players has demonstrated. In this study of hamstring strains, purely tendinous injuries (7.9% of all hamstring strains) were relatively rare, with the proximal myotendinous junction, muscle belly, and distal myotendinous junction (36.1%, 32%, and 17.7%, respectively) implicated more frequently. The long head of the biceps femoris was most commonly (56.5%) implicated, whereas injuries to the short head of biceps femoris occurred only 5.6% of the time.

Hamstring injuries occur on a continuum that can range from musculotendinous strains to avulsion injuries. A strain is a partial or complete disruption of the musculotendinous unit. A complete tear or avulsion, in contrast, is a discontinuity of the unit. Distal avulsion injuries are quite rare and not discussed in this chapter. Most hamstring strains do not require surgical intervention and resolve with a variety of modalities and rest. Differentiating the complete and partial tears from the muscle strain subgroup is of importance, as patients with complete or partial tears can experience more substantial disability.

History

The history of an acute injury classically involves a traumatic event with forced hip flexion and the knee in extension, as observed in water skiing, although studies have suggested that most injuries occur during high-speed running or moments of rapid change of pace.

Commonly athletes with proximal hamstring tendon tears describe an acute popping or tearing sensation with associated function-limiting pain. Although pain is typically the chief complaint, the patient may also complain of a sense of instability or gait incoordination. Occasionally patients who present with hamstring tears may report altered sensation or pain in a dermatomal distribution much like that seen in radiculopathy. This may be explained by acute nerve traction, the caustic effect of blood on the nerve, or compression from the associated hematoma. The patient may complain of a previous similar injury in the same leg, given the high risk of recurrence.

Physical Examination

The examination is typically performed with the patient in the prone position. Maintaining the knee in a slightly flexed position will make the examination more comfortable for individuals with more severe injuries. Inspection and palpation of the posterior thigh may reveal fasciculations or muscle spasm. Ecchymosis may be observed if the fascial covering is also disrupted. Palpation of the entire posterior thigh is important to localize the injury. Palpation should be performed systematically, starting at the broad insertion along the ischial tuberosity. Identification of a more proximal injury is important, as studies have shown a prolonged recovery course for injuries occurring more proximally, especially within the tendon. Given the biarticular nature of the hamstring complex, it is important to examine the strength of both knee flexion and hip extension as well as range of motion (ROM). The authors suggest evaluating knee flexion in both relative extension (15 to 30 degrees flexion) and flexion at 90 degrees as well as hip extension with the knee fully extended and again at 90 degrees of knee flexion while the patient is prone. Eccentric testing of the hamstrings via resisted extension of the knee from 90 to 15 degrees may elicit pain with milder injuries. Careful note should be taken of side-to-side strength differences. Similarly, a decrement in painless ROM may be used to identify a more chronic hamstring injury, and several examination maneuvers have been described to assess for tendinopathic functional changes. Our preferred test for proximal tendinopathy pain is a supine single-leg plank.

During examination, one must have a high index of suspicion for a tear. In less acute situations where the tear is several days old, it is possible that even a large defect may not be palpable clinically owing to the overlying hematoma. It is especially critical to assess these patients with imaging studies to delineate the type of tear that is present and to guide management.

Imaging

No initial imaging is indicated for hamstring injuries involving no loss of strength and minimal to moderate pain, especially if discomfort is isolated to the muscle belly. If pain is more severe and located proximally, plain radiographs including an anteroposterior view of the pelvis and lateral image of the affected hip are warranted to rule out and characterize an avulsion injury. If a fracture is identified, computed tomography (CT) or magnetic resonance imaging (MRI) may assist in assessing the displacement and fracture configuration for possible surgical planning. Special consideration should be given to obtaining radiographs in the younger patient at risk for apophyseal injuries ( Fig. 86.2 ).

MRI and ultrasound are the imaging modalities of choice to evaluate nonavulsion injuries resulting in weakness, gait abnormalities, or severe pain or in lesser injuries involving elite athletes. MRI has been shown to be more accurate in evaluating tears, especially to deeper tissues or in patients with recurrent tears, as scar tissue can be more easily mistaken for acute injury with ultrasound. However, studies have not examined this in recent years, as ultrasonographic image resolution has greatly improved. MRI findings, particularly the Peetrons classification and size of muscular edema, have been shown to be predictive of return to play (RTP) following grade 1 and 2 injuries. Data support the use of MRI as the preferred tool for the evaluation of tendon retraction in the case of a complete tear as well, making it particularly helpful in surgical planning ( Fig. 86.3 ). Incomplete tears without retraction often reveal a “sickle sign,” as demonstrated by a curvilinear signal on T2-weighted images ( Fig. 86.4 ). One must be cautious in considering advanced imaging, as partial hamstring tears have been detected in up to 15% of asymptomatic patients.

Ultrasound is useful as a point-of-care examination tool; it allows for dynamic imaging and comparison to the contralateral limb; it is also far less expensive than MRI. Recent advances in technology have allowed for the development of portable units with resolution allowing for their use as sideline tools, and there are no considerations for patient mass, implanted devices, or claustrophobia. Ultrasound is highly user-dependent and not available universally. Moreover, the evaluation of pathology can be hindered by the presence of large hematomas, as is often common in hamstring tears ( Fig. 86.5 ). Despite this, ultrasound has been shown to be highly accurate in the evaluation of partial tears and insertional tendinosis.

Decision-Making Principles

Whether the surgical procedure is performed with an open approach or endoscopically, the indications are the same. The only certain indication for the open procedure is a large retracted tear with chronic atrophy as noted on MRI. In these cases, the procedure would more than likely require extensive mobilization and probably the use of a graft for reconstruction of the avulsed segment, which would have to be performed in an open fashion at this time, usually with a longitudinal incision. The first indication for surgery is an acute hamstring avulsion of at least two out of the three tendons in an active patient with greater than 2 cm of retraction. Some patients have a clinically evident partial hamstring avulsion involving the biceps/semitendinosus tendon, with refractory ischial pain and the inability to return to high-level sports. Finally, patients are also candidates for surgical intervention when they have a history of refractory ischial bursitis and no discernible tear and conservative treatment has failed, including at least 12 weeks of physical therapy and potentially ultrasound-guided ischial injections with corticosteroids and/or biologics.

Treatment Options

Surgical Treatment

Open

Open techniques are still the standard of care and are most often described in the literature. The indications for surgical treatment of proximal hamstring ruptures include all acute complete three-tendon tears and two-tendon tears with retraction of 2 cm or more. Acute surgical repair initially is not indicated for patients with a one- or two-tendon tear with less than 2 cm of retraction; they are treated surgically if nonoperative treatment is not successful. In addition, less active patients or patients who are unable to comply with the postoperative rehabilitation protocol should be managed nonoperatively. Patients with complete or partial tears for whom conservative management fails may be candidates for delayed repair.

A transverse incision in the gluteal crease inferior to the ischial tuberosity is used. The tendon should be placed on the lateral aspect of the ischial tuberosity and should lie down flat to allow optimal bone healing as well as to prevent prominence ( Fig. 86.6 ).

Endoscopic

Some surgeons have begun to utilize an arthroscopic approach. With this technique, the patient is placed in the prone position after induction of anesthesia, with all prominences and neurovascular structures protected. The table is flat (as opposed to the slightly flexed position of the table in the open repair procedure) to help maintain the space between the gluteal musculature and the ischium.

Two portals are then created, one each 2 cm medial and lateral to the palpable ischial tuberosity ( Fig. 86.7 ). The lateral portal is established first by using blunt dissection with a switching stick as the gluteus maximus muscle is penetrated and the submuscular plane is created. The medial portal is then established, taking care to palpate the medial aspect of the ischium. A 30-degree arthroscope is then inserted in the lateral portal and an electrocautery device is placed in the medial portal. The space between the ischium and the gluteus muscle is then developed, taking care to stay along the central and medial portions of the ischium to avoid any damage to the sciatic nerve. With the lateral aspect identified, the dissection continues anteriorly and laterally toward the known area of the sciatic nerve ( Fig. 86.8 ). Very careful and methodical release of any soft tissue bands is then undertaken in a proximal-to-distal direction to mobilize the nerve and protect it throughout the exposure and ultimate repair of the hamstring tendon.

Once the nerve has been identified and protected, attention is directed once again to the area of the tendinous avulsion. The tip of the ischium is identified through palpation with the instruments. The tendinous origin is then inspected to identify any obvious tearing. With acute tears the area is obvious and the tendon is often retracted distally. In these cases, a large hematoma is occasionally present and must be evacuated. It is especially important to protect the sciatic nerve during this portion of the procedure because it is sometimes obscured by the hematoma.

Once the area of pathology has been identified (in persons with incomplete tears), an endoscopic knife can be used to longitudinally split the tendon along its fibers. The hamstring is then undermined and the partial tearing is débrided with an oscillating shaver. The lateral wall of the ischium is cleared of devitalized tissue and a bleeding bed is established in preparation for the tendon repair.

An inferior portal may then be created approximately 4 cm distal to the tip of the ischium and equidistant from the medial and lateral portals. This portal is used for insertion of suture anchors as well as suture management. The principles are essentially the same as those used in arthroscopic rotator cuff repair. Once all of the sutures have been passed through the tissue of the avulsed hamstring, the sutures are tied and a solid repair of the tendon is completed.

Authors’ Preferred Technique

The authors’ preferred technique is to perform an outpatient open repair between 2 and 4 weeks postinjury in acute ruptures. With chronic full and partial ruptures that undergo surgical repair, there is no time constraint. Although primary repairs of acute ruptures can be successfully made up to 8 weeks postinjury, it is certainly easier to mobilize the tissue within 4 weeks of the injury. We like to pay close attention to their sciatic nerve examination, both preoperatively and postoperatively. We routinely decompress the sciatic nerve and perform a neurolysis in all cases to optimize the outcome for the nerve. We use a standard prone position with a table break at the patient's iliac crest, which will be flexed about 30 degrees to improve access at the gluteal crease ( Fig. 86.9 ). We place pillows and pads underneath the knee down to the foot, so the knee is in flexed position of about 30 degrees. We utilize a gluteal crease incision for cosmesis and keep this incision as short as safely possible and centered over the lateral aspect of the ischial tuberosity ( Fig. 86.10 ). We utilize a standard fascial layer approach, localize and protect the gluteal neurovascular structures, and then localize the sciatic nerve to perform a neurolysis and protect it throughout the remainder of the case ( Fig. 86.11 ). We then decompress any seroma and/or hematoma and decorticate the footprint of the ischial tuberosity with a rongeur and currete. We then utilize five 3-0 biocomposite, single-loaded SutureTak anchors (Arthrex) in a clustered pattern to fill the footprint. Once this is completed, we begin to suture the tendon after it has been débrided and prepared using a locking stitch and single-pass stitch in a mattress fashion from each anchor. Once all anchors have been sutured, we tie down beginning with the proximal footprint and bringing the knee into 45 degrees of flexion. A layered closure with Vicryl is performed of the hamstring and gluteal fascia; then Monocryl and Dermabond are used for the skin closure. Postoperatively we use a standard hinged postoperative knee brace locked at 30 degrees and make the patient non-weight-bearing for 6 weeks. Partial chronic tears that require surgery are performed in the same manner, and chronic retracted tears are repaired utilizing an Achilles allograft with a longitudinal incision ( Fig. 86.12 ). In the chronic technique, we will place a small bone block into the ischial tuberosity with a biocomposite interference screw and then add additional fixation around the bone block with suture anchors and soft-tissue fixation. We then attach the allograft to the native musculotendinous end of the hamstrings under tension and 90 degrees of knee flexion. Postoperatively, the knee is kept at 90 degrees for 6 weeks in the chronic repairs.

The postoperative protocol is similar for both arthroscopic and open techniques with similar expected outcomes. To date, there is no a study to our knowledge that compares outcomes for arthroscopic versus open techniques.