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Updated: Nov 29 2023

Hamstring Injuries

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  • 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
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