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, the National Football League surveillance system 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%. One literature review identified previous hamstring injury as the greatest risk factor for reinjury. The injured muscle may have an altered compliance or deformation pattern, predisposing it to less tissue motion or higher muscle strain. Age was also found to be an independent risk factor for hamstring injury. 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.
The thigh contains a large cross-sectional area of muscles with three main muscle groups: hamstrings, quadriceps, and adductors. The hamstring complex consists 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 is innervated by the common peroneal nerve. These muscles work together to extend the hip, flex the knee, and externally rotate the hip and knee. The myotendinous junctions of the hamstrings have significant overlap.
The proximal hamstring complex has a strong bony attachment on the ischial tuberosity ( Fig. 88-1 ). Their footprint on the ischium is composed of the semitendinosus and the long head of biceps femoris beginning as a common proximal tendon and footprint, and there is a distinct semimembranosus footprint. The semimembranosus footprint is medial (and anterior) to the crescent-shaped footprint of the common insertion of the semitendinosus and long head of the biceps femoris (see Fig. 88-1 ).
Biomechanically, the hamstrings are subjected to high tensile load given their extensive eccentric role. During initial swing, the knee and hip are flexing, which requires simultaneous eccentric and concentric activity of the hamstrings. During the last portion of swing, the hamstrings continue to play a dual role of controlling knee extension while extending the hip. 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, also are 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.
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. In one study, 12.3% of 170 cases of hamstring injuries were tendon tears; the majority (90.5%) were muscle belly injuries. Most hamstring strains do not require surgical intervention and resolve with a variety of modalities and rest. The most important point in evaluating these patients is to differentiate the complete or partial tears from the muscle strain subgroup, because patients with complete or partial tears can experience more substantial disabilities.
History
The history of an acute injury usually involves a traumatic event with forced hip flexion and the knee in extension, as is classically observed in waterskiing. However, the injury can result from a wide variety of sporting activities that require rapid acceleration and deceleration.
Proximal hamstring injuries can be categorized as complete tendinous avulsions, partial tendinous avulsions, apophyseal avulsions, and degenerative (tendinosis) avulsions. Degenerative tears of the hamstring origin are more insidious in onset and are commonly seen as an overuse injury in middle- and long-distance runners. The mechanism of injury in these patients is presumably repetitive irritation of the medial aspect of the hamstring tendon (typically along the lateral aspect of the tuberosity, where the bursa resides), ultimately causing an attritional tear of the tendon.
Commonly, athletes with proximal hamstring tendon tears typically describe a popping or tearing sensation with associated pain and bruising over the posterior hip. They may also have weakness with active knee flexion, a sensation of instability, or difficulty controlling their legs. Occasionally, patients who present with either acute or chronic tears may report a pins-and-needles sensation in sciatic nerve distribution, much like sciatica. This sensation may be due to acute compression of a hematoma in the proximity of the sciatic nerve or chronic scarring and tethering of the tendon to the nerve.
Symptoms of ischial bursitis include buttock or hip pain and localized tenderness overlying the ischial tuberosity. Additional symptoms of chronic ischial bursitis may include tingling into the buttock that spreads down the leg, presumably from local inflammation and swelling in the area of the sciatic nerve. The symptoms usually worsen while sitting. Clinically, the persons most affected tend to sit with the painful buttock elevated off their seat.
Physical Examination
The examination is typically performed with the patient in the prone position. Maintaining the knee in a slightly flexed position will limit muscle spasms and make the examination more comfortable for persons with acute ruptures. Inspection and palpation of the posterior thigh may reveal muscle spasm. Ecchymosis may only be observed if the fascial covering is also disrupted. Palpation of the entire posterior thigh is very important to localize the injury. Persons with acute injuries typically have focal tenderness and swelling. However, with delayed presentation, patients are more likely to have diffuse swelling and tenderness. Persons with low-grade strains typically have limited swelling and tenderness, whereas in persons with a more severe strain, a palpable defect may be appreciated.
An examination technique has been described in which the patient is positioned prone and asked to actively apply tension to his or her hamstring tendon. The degree of tension is then compared with the passive tendon tension while sitting. Decreased tension compared with the normal side suggests a proximal tendon rupture. In a cohort of 25 patients with complete tears, the examiner was able to identify all patients with tendon tears (100% sensitivity); however, specificity was not measured because the examination was not applied to healthy subjects.
The most critical aspect of the examination is to have a high degree of suspicion for a tear. In less acute situations in which the tear is several days old, it is possible that even a large defect may not be palpable clinically as a result of the overlying hematoma. It is especially critical to assess these patients with imaging studies to delineate the type of tear that is present.
Imaging
If a high level of suspicion exists for a proximal hamstring injury, both routine and advanced imaging is performed. Plain radiographs of the pelvis and a lateral radiograph of the affected hip are obtained to rule out any apophyseal avulsions, particularly to the ischial tuberosity in adolescent athletes ( Fig. 88-2 ). If a fracture is identified, a computed tomography scan may assist in assessing the displacement and fracture configuration for surgical planning.
More commonly, no fractures are identified and magnetic resonance imaging (MRI) is used to assess the proximal hamstring insertion on the ischial tuberosity. A number of different combinations of injury can thus occur at this tendon insertion. A complete rupture of all three tendons is common and most easily identified on an MRI scan, with accurate measurement of the amount of retraction possible ( Fig. 88-3 ). All three MRI planes (coronal, sagittal, and axial) should be used to define the tear pattern. A commonly associated finding with an acute complete hamstring avulsion is a large posterior thigh hematoma.
Partial hamstring origin tears are somewhat more difficult to diagnose, particularly in the case of two-tendon tears, which commonly have an associated musculotendinous junction injury to the third “intact” tendon. Unfortunately, retraction of the two tendons more than 2 cm typically renders the intact tendon functionally impaired and is clinically comparable to a complete rupture. Despite this diagnostic difficulty, MRI is very helpful in distinguishing complete versus partial tears. As such, one or two tendon injuries can be identified, and this distinction often determines a patient’s need for surgical repair. In addition, partial insertional tears without any significant retraction can be seen on MRI as a “sickle sign” ( Fig. 88-4 ). These tears are typically partial avulsion of the common biceps and semitendinosus origin.
Another imaging modality that can be used in the assessment of proximal hamstring injuries is ultrasound. Although ultrasound can be extremely user specific, it can also be highly accurate to evaluate partial tears and insertional tendinosis. Its potential for bedside use as a dynamic test may lead to the detection of more subtle injuries, particularly in the athletic population. Currently, however, ultrasound is still less sensitive than MRI, and it does not supplant this modality. In one study, 170 cases of hamstring muscle strains were evaluated with MRI and ultrasound. In 21 patients with complete tears, 100% of the tears were identified with MRI, whereas 58% were identified with ultrasound. With use of ultrasound, large hematomas can produce mixed echogenic patterns, which can make visualization of retracted tendons difficult ( Fig. 88-5 ).
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 imaging. 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 must be performed in an open fashion at this time. The first indication for surgery is an acute hamstring avulsion 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 discernable tear and conservative treatment has failed, including at least 6 weeks of physical therapy and two ultrasound-guided ischial injections.
Treatment
Nonoperative
Nonoperative treatment of proximal hamstring injuries is most commonly recommended in the setting of low-grade partial tears and insertional tendinosis. Initial treatment consists of active rest, use of oral nonsteroidal antiinflammatory medications, and a physical therapy program, which consists of a gentle hamstring stretching and strengthening program. As the initial symptoms resolve, core, hip, and quadriceps exercises can be added in association with a more aggressive hamstring injury prevention program. Full return to sports and activities is allowed when the patient is asymptomatic. If progress does not occur with this program, an ultrasound-guided corticosteroid injection may be used and has been shown to provide initial relief in up to 50% of patients at 1 month. Patients who experience failure of nonoperative treatment of partial tears may benefit from surgical debridement and repair, similar to patients with other commonly seen partial tendon tears (i.e., the patella, quadriceps, and biceps). As will be described, newer and less invasive endoscopic techniques are perfectly suited for this problem.
Nonoperative treatment of complete ruptures of the proximal hamstring is less frequently recommended because surgical repair has resulted in the successful return of patients to a high level of function. One study identified a group of water skiers with hamstring avulsion injuries that initially were treated nonoperatively. Persistent cramping or pulling with vigorous activity was experienced by 83% of the patients. Seven patients returned to sports activities but at a lower level, and five patients were only able to perform limited activities. Upon Cybex testing, these patients had a hamstring and quadriceps deficit of 61% and 23%, respectively. Two patients ultimately underwent delayed surgical repairs.
Surgical Treatment
Endoscopic
To date, no reports of endoscopic management of these injuries have been published. After gaining experience in the open management of these injuries, I have developed an endoscopic technique that allows a safe approach to the area of damage in most tears, including acute disruptions. It is expected that the benefits of a more direct approach—without elevating the gluteus maximus and with the use of endoscopic magnification to protect the sciatic nerve—will improve the management of these injuries and reduce the morbidities associated with the open approach.
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. The posterior aspect of the hip is then sterilized, ensuring that the leg and thigh are free so that the leg and hip can be repositioned intraoperatively ( Fig. 88-6 ).
Two portals are then created, 2 cm medial and 2 cm lateral to the palpable ischial tuberosity ( Fig. 88-7 ). 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 switching stick serves to palpate the prominence of the tuberosity and identify the medial and lateral borders of the ischium. 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. The lateral aspect is then exposed with the use of a switching stick as a soft tissue dissector. With the lateral aspect identified, the dissection continues anteriorly and laterally toward the known area of the sciatic nerve ( Fig. 88-8 ). 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. In cases of acute disruptions in which some scarring is taking place, significant bands are often encountered ( Fig. 88-9 ).
