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 10% of all pelvis avulsion fractures in the skeletally immature 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 most often occur during sudden takeoff phase of running proximal hamstring avulsions occurs as a result of hip flexion and knee extension eccentric contraction of hamstring at the end of swing phase when muscle fibers are at maximal elongation. Pathobiology satellite cell plays a role in muscle healing following muscle injury Anatomy Hamstrings 4 muscles semimembranosus semitendinosus biceps femoris long head short head origin all originate on ischial tuberosity except short head short head originates from linea aspera on femur conjoint tendon attaches more medially biceps femoris attachment more proximal than semitendinosus semimembranosus has most lateral attachment 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 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 proximal avulsions Physical exam inspection ecchymosis in posterior thigh most common seen in proximal avulsions or high grade myotendinous tears palpation may have palpable mass in middle 1/3 of posterior thigh (myotendinous rupture) tenderness to palpation ischial tuberosity myotendinous junction distal tendinous insertions gait "stiff-legged" gait (avoiding knee and hip flexion) motion increased popliteal angle flexing hip to 90 degrees with knee flexed to 90 degrees, and then slowly extending knee knee angle where posterior thigh pain is felt is compared to uninjured leg motor weak hamstring strength while prone, knee flexion strength measured with knee at 90 degrees flexion compared to contralateral side 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 Puranen-Orava Test heel is placed on an elevated surface and patient reaches for toes sensitivity 0.76, specificity 0.82 bent-knee stretch test with patient supine, hip and knee are maximally flexed and knee is slowly passively extended sensitivity 0.84, specificity 0.87 modified bent-knee stretch test with patient supine, hip and knee are maximally flexed and then the knee is rapidly fully extended sensitivity 0.89, specificity 0.91 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 most hamstring injuries all single tendon tears 2 tendon tears with < 2 cm retraction rupture at myotendinous junction less active patients and those with significant medical comorbidities outcomes take up to 6 weeks to heal only return when strength is 90% of contralateral side to avoid further injury PRP injection indications acute hamstring strains in high level athletes outcomes some low level studies have shown earlier return to play by 3-5 days in NFL players Operative tendon repair indications proximal avulsion ruptures partial avulsion that has failed nonoperative management for 6 months (persistent symptoms) 2 tendons with at least > 2 cm retraction in young, active patients 3 tendon tears outcomes 80% return to preinjury level/sports at 6 months high level of complications with surgery, up to 23% in some studies higher complication rate with repair of chronic cases compared to acute (< 6 weeks) ORIF indications bony avulsions with > 2 cm displacement chronic symptomatic bony avulsions outcomes union rates vary across studies 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 athlete kneels while heels are held on ground by an assistant; the athlete than leans forward until he is prone and then returns to original upright position shown to reduce injuries by 50-70% in some studies isolated targeting of specific hamstring muscles long head of the biceps femoris and semimembranosus are more active during hip extension semitendinosus and short head of biceps femoris more active during knee flexion 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 can be extended distally in "T" configuration for large retracted tear hamstring fascia typically intact vertical fascial incision will often lead to encountering a hematoma or fluid collection 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 avoid burr to decreased risk to sciatic nerve repair to the ischial tuberosity with the use of multiple suture anchors (4-6 suture anchors) with the knee flexed allograft bridge may be needed in severely chronic cases when hamstrings are not able to be re-approximated to tuberosity Achilles allograft has shown comparable results to acute repairs in small studies. post-operative protocol patients typically made partial weight bearing for 4-6 weeks with knee flexed to 40 degrees knee brace or hip brace can be used ORIF approach as above technique direct reduction followed by fixation with multiple partially or fully threaded screws with washers can supplement with suture anchors and/or interference screws Complications Recurrence incidence most common complication 12-31% of patients sustain repeat injury 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