SUMMARY Hamstring injuries most commonly occur at the myotendinous junction in running athletes as a result of sudden hip flexion and knee extension. Diagnosis can be made clinically with ecchymosis in the posterior thigh, tenderness over the hamstring muscles and avoidance of knee extension. Diagnosis can be confirmed with MRI. Treatment is generally conservative with rest, ice, and protected weightbearing. Multiple tendon involvement or bony avulsion may require operative management. Epidemiology Incidence make up 30% of new lower extremity injuries in athletes annual increase of 4% noted in soccer players over last ~15 years Demographics most commonly seen in rapid acceleration sports soccer, track and field, and football Anatomic location myotendinous junction is the most common site of rupture in adults often occurs during sprinting avulsion of ischial tuberosity less common seen in skeletally immature login to view 1 more bullet seen in water skiers Risk factors previous hamstring injury (increases risk of reinjury by factor of 6) previous injury leads to formation of weakened scar tissue lowering threshold to recurrent injury inadequate warm-up strength imbalance (hamstring to quadriceps ratio < 0.6) hamstring strength difference with contralateral leg (> 10-15%) reduced hip extension leg-length differences (shorter leg has tighter hamstrings) Etiology Pathophysiology Mechanism of injury intramuscular and musculotendinous injuries login to view 1 more bullet proximal hamstring avulsions login to view 2 more bullets Pathobiology satellite cell plays a role in muscle healing following muscle injury Anatomy Hamstrings 4 muscles semimembranosus semitendinosus biceps femoris login to view 2 more bullets origin all originate on ischial tuberosity except short head login to view 4 more bullets insertion semimembranosus inserts on posterior aspect of medial tibial condyle semitendinosus inserts on superomedial tibial shaft within the pes anserine biceps femoris long head inserts on fibular head biceps femoris short head has many insertions (fibular head, biceps femoris long head, lateral knee capsule) innervation tibial branch of sciatic nerve: semimembranosus, semitendinosus, long head of biceps femoris common peroneal branch of sciatic nerve: short head of biceps femoris blood supply inferior gluteal artery and profunda femoral artery other hamstring origin on ischial tuberosity is ~6 cm proximal to inferior border of overlying gluteus maximus sciatic nerve is 1.2 cm from lateral bony aspect of hamstring origin pudendal nerve is 2-3cm superior-medial to the ischial tuberosity Biomechanics cross and act upon 2 joints: the hip and knee except short head which only crosses the knee joint Classification Hamstring Tear MRI Classification Grade 1 T2 hyperintense signal about a tendon or muscle without fiber disruption Grade 2 T2 hyperintense signal around and within a tendon/muscle with fiber disruption less than half the tendon/muscle width Grade 3 Tendon/muscle fiber disruption greater than half its tendon/muscle width Presentation History sudden pain in the posterior thigh during running, kicking or jumping activity occasionally a "pop" felt Symptoms common symptoms posterior thigh pain hamstring tightness pain with sitting login to view 1 more bullet Physical exam inspection ecchymosis in posterior thigh login to view 1 more bullet palpation may have palpable mass in middle 1/3 of posterior thigh (myotendinous rupture) tenderness to palpation login to view 3 more bullets gait "stiff-legged" gait (avoiding knee and hip flexion) motion increased popliteal angle login to view 2 more bullets motor weak hamstring strength login to view 2 more bullets neurovascular may have peroneal nerve weakness (foot drop etc.) provocative tests the following tests are positive for hamstring tendinopathy or strain if the patient feels pain login to view 9 more bullets Imaging Radiographs recommended views AP pelvis, AP and lateral femur findings may show bony avulsion off of ischial tuberosity MRI indications evaluation of the insertion site and quantify number of involved tendons and degree of tendon retraction evaluate the sciatic nerve location (in chronic cases) findings may show avulsion off ischial tuberosity tendinopathy will be seen as increased signal intensity in T1-weighted images partial tears will have increased signal intensity on T2-weighted images Diagnosis Clinical and MRI diagnosis confirmed by history, physical exam, and MRI Treatment Nonoperative rest, ice, NSAIDS, protected weightbearing for 4 weeks followed by stretching and strengthening indications login to view 5 more bullets outcomes login to view 2 more bullets PRP injection indications login to view 1 more bullet outcomes login to view 1 more bullet Operative tendon repair indications login to view 4 more bullets outcomes login to view 3 more bullets ORIF indications login to view 2 more bullets outcomes login to view 1 more bullet Techniques rest, ice, NSAIDS, protected weightbearing for 4 weeks followed by stretching and strengthening modalities that have shown benefit massage, ultrasound, electrical stimulation protected weightbearing most studies state 4 weeks, but should be extended if patient still significantly symptomatic stretching and strengthening as symptoms resolve, abdominal, hip and quadriceps should be added to hamstring strengthening program to prevent reinjury hamstrings should be strengthened to correct any hamstring-quadriceps strength imbalance injury prevention Nordic hamstring exercise login to view 2 more bullets isolated targeting of specific hamstring muscles login to view 2 more bullets PRP injection recommendation is to administer within 24-48 hours of acute injury ultrasound-guided injection recommended tendon repair positioning prone with leg free so knee can be flexed to relieve hamstring tension. approach transverse incision over gluteal crease login to view 1 more bullet hamstring fascia typically intact login to view 1 more bullet sciatic nerve runs on average 1.2 cm lateral to the most lateral aspect of ischial tuberosity technique ischium insertion site should be scraped with a periosteal elevator or curette to improve healing environment login to view 1 more bullet repair to the ischial tuberosity with the use of multiple suture anchors (4-6 suture anchors) with the knee flexed login to view 2 more bullets post-operative protocol patients typically made partial weight bearing for 4-6 weeks with knee flexed to 40 degrees login to view 1 more bullet ORIF approach as above technique direct reduction followed by fixation with multiple partially or fully threaded screws with washers login to view 1 more bullet Complications Recurrence incidence most common complication login to view 1 more bullet risk factors hamstring weakness hamstring-quad imbalance premature return to activity Peroneal nerve injury risk factors distal non-insertional hamstring injuries treatment usually self-resolving Sciatic nerve injury incidence 8% of surgical cases risk factors chronic cases with scarring of the nerve to the hamstring treatment nerve exploration Hamstring syndrome localized posterior buttock and ischial tuberosity pain secondary to nonoperatively treated hamstring avulsion injuries treatment surgical release and sciatic nerve decompression Ischial tuberosity nonunion risk factors bony avulsion fractures > 2 cm treated nonoperatively treatment ORIF +/- bone graft Prognosis Can be very unpredictable injuries with variable return to sport Overall 84% of patients recover pre-injury strength and 89% recover pre-injury endurance Poor prognostic variables severely retracted tears chronic tears with scarring to sciatic nerve