Robert T Sullivan and William E. Garrett
DEFINITION
Stretch-induced proximal hamstring injury is common among athletes.
These injuries represent a continuum including strain at the musculotendinous junction (MTJ), partial tear of the tendon, or complete avulsion of the hamstring muscle complex from the ischial tuberosity.1,9
ANATOMY
The hamstring muscle group consists of three muscles: the biceps femoris (long and short heads); the semitendinosus; and the semimembranosus. All three muscles, except for the short head of the biceps femoris, originate from the ischial tuberosity of the pelvis.
The biceps femoris and semitendinosus have a common origin.
The hamstrings are biarticular muscles bridging the hip and knee.
The proximal tendons of the biceps femoris and semimembranosus have been shown to extend for about 62% and 73%, respectively, of their muscle bellies.9,11
The sciatic nerve lies immediately lateral to the hamstring origin.
PATHOGENESIS
Eccentric activation while under stretch, as seen in a flexed hip and extended knee when the hamstrings attempt to decelerate the leg during knee extension in high-speed sportsrelated activity, is thought to be the principal mechanism of injury.2,21
An additional, but rare, mechanism for hamstring injury is extreme stretch with an uncertain amount of muscle activation. This may occur in situations such as waterskiing or when the knee is extended and there is sudden hip flexion.1,9,11,18
NATURAL HISTORY
The natural history of these injuries varies considerably, with a more proximal injury resulting in a longer time for recovery to pre-injury status and a greater likelihood of surgical intervention due to the persistent and significant disability associated with hamstring avulsion.1
Partial or complete hamstring avulsions should not be confused with strain at the musculotendinous junction. Avulsions can be extremely disabling and, unlike strain at the musculotendinous junction, may warrant surgical intervention. Avulsions cause symptoms of weakness and loss of muscle control, especially during fast-paced running.
Fortunately, most proximal hamstring injuries are strains at the musculotendinous junction that are best managed nonoperatively. Strains most often occur in the biceps femoris, and the most common location is near the muscle–tendon junction. Recovery time has been correlated directly with the percentage of muscle involved by measuring the cross-sectional area or the longitudinal length of abnormal muscle signal on MRI.1,5,13,20
Injuries involving over 50% of the cross-sectional area result in a recovery period longer than 6 weeks, whereas normal imaging findings result in a recovery period of approximately 1 week.13
The greatest risk factor for injury to the hamstring muscle complex is a history of previous injury to the same place.16,21 Peterson17 reported the recurrence rate for hamstring injury to be 12% to 31%. Whether the reinjury is attributed to insufficient rehabilitation and early return to sport or the persistence of pre-existing risk factors, the treating physician must have the ability to assess the degree of injury, a knowledge of the reparative process of healing muscle, and an understanding of the rehabilitative and preventive measures for hamstring injury.
PATIENT HISTORY AND PHYSICAL FINDINGS
Proximal hamstring injury typically results in sudden onset of pain in the posterior proximal thigh during athletic competition or training.
Severe injury, such as an avulsion, may present with a visible deformity, swelling, ecchymosis, and a palpable defect. Focal tenderness to palpation and pain on provocation with resisted knee flexion are consistent findings.
With the patient lying prone and the hamstrings activated, palpation of proximal hamstring origin is undertaken.
A palpable defect implies proximal avulsion.
Pain without a defect suggests partial avulsion.
Obvious increase in apparent hamstring flexibility of the injured extremity implies proximal avulsion.
The current classification of muscle injuries identifies mild, moderate, and severe injuries, based on the degree of clinical impairment.
Mild muscle injury is minimal to no loss of strength, whereas moderate injury is a clear loss of strength.
Severe injury is the complete absence of muscle function. In severe injury, neurogenic symptoms may be present secondary to direct compression or a traction neuritis on the adjacent sciatic nerve.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Plain radiographs are useful in evaluating for a bony avulsion.
MRI is the imaging of choice to confirm the existence of a muscle injury or avulson, particularly when a discrepancy exists between the examiner's findings and the patient's symptoms.
In separate investigations Connell, Kouloris, Askling, and Slavotinek correlated rehabilitation time to the percentage of muscle involved by measuring the cross-sectional area or the longitudinal length of abnormal muscle signal on MRI.
Kouloris stated injuries involving greater than 50% of the cross-sectional area resulted in a greater than 6 week recovery period, whereas normal imaging resulted in a recovery period of approximately 1 week.1,5,13,20
Schneider-Kolsky et al19 questioned the ability of MRI to predict rehabilitation time for minor and moderate injury. Despite a limitation of variable methods of rehabilitation, they concluded MRI to be useful in predicting the duration of convalescence for moderate and severe injury. Conversely, they determined clinical assessment to be slightly better than MRI for minor injury.
Verall reported on a subset of patients with a clear clinical diagnosis of hamstring strain, but an MRI negative for muscle injury. Like Schneider-Kolsky's findings, Verall reported patients with hamstring muscle strain injuries demonstrable by MRI had a poorer prognosis than those whose posterior thigh injury was not MRI-positive. Askling also demonstrated a correlation between the location of injury by MRI and time to recovery. He found longer recovery times for injuries in close proximity to the hamstring origin. In other words, the more cranial the injury the longer the recovery time. Interestingly, the prediction of recovery time was equally good using the point of highest pain on palpation, established within 3 weeks of the injury.
MRI is most useful in the setting of moderate or severe injury to predict recovery time based on injury location or percentage of involved muscle or to detect an avulsion imperceptible on physical exam due to a massive hematoma or swelling (FIG 1).
DIFFERENTIAL DIAGNOSIS
Referred lower back pain (discogenic, arthropathy, etc.)
Radiculopathy (HNP, spinal stenosis)
Sciatica
Tumor
Piriformis syndrome
Apophysitis
Pelvic stress fracture
NONOPERATIVE MANAGEMENT
The vast majority of proximal hamstring injuries involve strain at the musculotendinous junction and are managed with nonoperative measures focusing on restoration of flexibility and muscle strength.8,10
Treatment of a proximal hamstring injury is predicated on the grade or severity of the injury and an understanding of the balanced progression of muscle regeneration and scar formation.10
Proximal hamstring strains are typically treated with a few days of rest based on the grade of injury followed by early active and passive mobilization within the limits of pain.
Ice and compression are useful adjuncts to diminish bleeding and inflammation as large hematomas may adversely influence scar formation.
Sport specific training usually starts approximately 2 weeks post injury.
If there is no improvement by 3 to 4 weeks, an MRI should be obtained.
Once athletes return to their sports, they should continue an in-season strengthening and stretching program, as prevention of reinjury is critical due to the high rate of recurrence.2,6,17,21,22
FIG 1 • A,B. Hamstring strain reveals increased T2 signal along the entire length of the left hamstrings, particularly along the musculotendinous junction, involving the biceps femoris and to a lesser degree the semitendinosus and semimembranosus. C. Surgical exposure reveals complete avulsion of the proximal tendon from the ischial tuberosity. (C: Courtesy of Gary Fetzer, MD, and Brad Nelson, MD, Minneapolis.)
SURGICAL MANAGEMENT
Unlike proximal hamstring strains, treatment of hamstring avulsion may necessitate surgical repair, particularly in the high demand athlete or in individuals with complete rupture of the proximal hamstring complex. Complete avulsion has been rarely reported, as most avulsion injuries are partial and involve the biceps femoris.
Several authors have reported on acute and delayed surgical intervention for partial and complete proximal hamstring avulsions with satisfactory outcomes.3,4,7,12,14,15 Late diagnosis and delayed intervention are believed to lead to an inferior result. Most arguments for surgical intervention are derived from Sallay's initial report on the poor outcome from nonoperative management in five waterskiers with complete avulsions who were unable to run or return to sporting activity. Sallay also reported on a prolonged recovery time and diminished function in seven individuals with partial avulsions.
There is some interest in the surgical treatment of partial avulsions, but there are few studies proving poor results in nonoperatively managed partial avulsions.14
Preoperative Planning
Plain radiographs of the pelvis are obtained to evaluate for a bony avulsion.
MRI is obtained to confirm a partial or complete avulsion and to assess the degeree of hamstring retraction.
A neurovascular exam of the affected extremity is documented.
EMG may be considered to evaluate a persistent, perceived neurologic deficit.
Positioning
The patient is placed in the prone position over chest rolls.
The operative extremity is draped free to allow for hip and knee flexion and extension.
Approach
In acute cases with minimal hamstring retraction, we use a tranverse incison within the gluteal crease.
A longitudinal incision starting from the ischial tuberosity, over the posterior thigh, is used in chronic cases requiring significant mobilization or fractional lengthening of the hamstrings or sciatic neurolysis. A longitudinal incision is also employed in acute cases with significant retraction (FIG 2).
FIG 2 • A longitudinal incision starting from the ischial tuberosity, over the posterior thigh, is used in chronic cases requiring significant mobilization or fractional lengthening of the hamstrings or sciatic neurolysis. A longitudinal incision is also employed in acute cases with significant retraction. (Courtesy of Gary Fetzer, MD, and Brad Nelson, MD, Minneapolis, MN.)
TECHNIQUES
REPAIR OF HAMSTRING COMPLETE AVULSION
The posterior femoral cutaneous nerve and its proximal branches are identified running deep to fascia down the back of the thigh obliquely crossing the long head of the biceps femoris.
Branches of the posterior femoral cutaneous nerve are the inferior cluneals and perineals.
The inferior clunial nerves, three or four in number, turn upward around the lower border of the gluteus maximus.
The perineal branches are distributed to the skin at the upper and medial side of the thigh.
The inferior border of the gluteus maximus muscle is mobilized by dividing the posterior fascia and retracting the muscle superiorly in order to expose the ischial tuberosity and avulsed tendon stumps.
Starting distally from normal anatomy, the sciatic nerve is identified lateral to the ischium.
If required, a careful sciatic neurolysis is performed in chronic cases.
Care is taken to identify and protect the branches to the semimembranosus.
The avulsed tendon stumps are identified and tagged with a grasping suture using a no. 2 high strength suture (TECH FIG 1A).
Mobilization of the tendon stumps and proximal musculature is carefully performed in order to minimize tension on the repair and limit the amount of knee flexion, if any, required to aproximate the tendons to their origin on the lateral aspect of the ischial tuberosity. In chronic cases, a distal hamstring lengthening may be necessary.
If there is an adequate residual, proximal tendon stump, a direct repair is performed. Otherwise the repair is performed using suture anchors after clearing the soft tissue from the anatomic footprint on the ischial tuberosity (TECH FIG 1B).
If a tendon cannot be mobilized to its anatomic origin on the ischium other authors have reported tenodesing the tendon to the adjacent myotendinous complex.
The fascia and overlying skin are then approximated in separate layers.
TECH FIG 1 • A. The repair is performed using suture anchors after clearing the soft tissue from the anatomic footprint on the ischial tuberosity. B. Final suture passage is completed, demonstrating reapproximation of the avulsed tendon to the ischial tuberosity. (Courtesy of Gary Fetzer, MD, and Brad Nelson, MD, Minneapolis.)
POSTOPERATIVE CARE
The knee is held in the minimal amount of flexion to limit tension on the repair for approximatley 3 to 4 weeks.
Range of motion is initiated thereafter in order to obtain a normal gait by 6 weeks post surgery.
A progressive strengthening regimen is initiated after 6 weeks with a return to sports related activity no earlier than 3 months after surgery.
OUTCOMES
Klingele13 reported on suture anchor fixation in 11 individuals (average age 41.5 years) with complete proximal avulsion injuries. There were 7 acute and 4 chronic (>4 weeks) injuries treated with a 78% return to sport by 6 months and a 91% satisfaction after a minimum 2 year follow-up. Varying degrees of hamstring mobilization and fractional lengthening were performed in the chronic cases. However, for patients who underwent repair of chronic injuries the average hamstring muscle strength was 89% of the uninjured extremity by cybex testing at an average 34-month follow-up.
Chakravarthy performed either direct or suture anchor repair in 4 patients, 1 acute and 3 chronic, with all patients obtaining normal strength and near-normal flexibility at an average 15 months of follow-up.4Three of these four patients returned to their preinjury level of sport.
Cross performed repairs on 9 patients (average age 34 years) with chronic, complete avulsions at an average of 36 months post injury.7 These patients were held at 90 degrees of knee flexion for 8 weeks after surgery with full knee range of motion obtained by 14 weeks in all cases. At an average 4 year follow-up, hamstring strength was 60% of the unaffected side with 7 of 9 patients having returned to a lower level of sports.
Brucker performed surgical repair in 8 complete avulsions, 6 acute and 2 chronic, also immobilizing the operative extremity at 90 degrees of knee flexion for 6 weeks post surgery.3 Full range of motion was obtained in all patients by 16 weeks. At 33 months follow-up all patients were satisfied and 7 had returned to sports. The minimum time to return to sports was 6 to 8 months with 2 individuals delayed more than 24 months. Objective measures revealed no difference in hamstring flexibility relative to the contralateral extremity. Cybex dynanometer testing revealed an average peak torque of the operated hamstring muscles of 88.8% compared to the opposite limb.
Orava described surgical intervention in 8 patients, 5 acute and 3 chronic, with complete or incomplete proximal avulsions using suture anchors, drill holes, or tenodesis of the avulsed hamstring to an adjacent and intact hamstring.15 Hip and knee flexion were avoided for 1 month with full weight bearing initiated at 1 month. All 5 acutes exhibited normal strength and full range of motion at 5.7 year follow-up. However, those patients surgically treated 3 or more months from their injury had inferior outcomes.
Lempainen recently described surgical repair of 48 MRI confirmed partial proximal hamstring avulsions or tendon tears in athletes who failed to respond to nonsurgical measures.14 Fortythree of these injuries were operated on more than 4 weeks from the time of injury with an average delay of 13 months. No immobilization was performed and full weight bearing was initiated at 2 weeks after repair. Eighty-eight percent of these patients reported good or excellent results and 87% returned to their preinjury level of sport at a mean follow-up of 36 months. However, this population predominantly consisted of patients who had failed conservative treatment. There are no reports on the number of patients successfully managed with nonoperative measures for partial avulsions.
Despite variable technique, degree of chronicity, and heterogeneous patient populations, these reports indicate repair of acute and chronic complete or partial proximal hamstring avulsion can improve patient outcomes. Early surgical intervention for complete tears is preferred in order to limit hamstring retraction and muscle atrophy and to obtain a better functional outcome. Whether or not surgical treatment should be considered in the acute setting for partial injuries remains unclear. The delay in return to sport and the persistent functional impairment associated with partial avulsions as reported by Sallay and Lempainen suggests further study is warranted regarding the indications and timing of surgical intervention in this population.
COMPLICATIONS
Surgical repair of proximal hamstring avulsions have resulted in satisfactory outcomes; however, several authors have reported on several patients with persistent pain and/or spasm associated with strenuous exercise.
Brucker reported on a loss of fixation for a single suture anchor from the ischial tuberosity. The anchor was removed in a second surgical procedure due to pain in a sitting position.
Others have reported on perisitent sciatica mandating a neurolysis to address postoperative scarring.
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