Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

Featured on Channel NewsAsia

Hamstring Strain

Basics
Description
  • The hamstrings are long muscles in the posterior thigh that extend from the ischial tuberosity behind the hip, down to the knee.
  • A hamstring strain is a stretch-induced muscle injury.
  • Tears result from the hamstring muscle suddenly changing from a stabilizing flexor to an extensor.
  • It usually is caused by quick starts with sudden hamstring contraction.
  • Strain classification:
    • Mild: Muscle spasm only, with no evidence of tear, with minimal discomfort and with only minimal loss of strength
    • Moderate: Muscle fiber tear that results in a loss of strength and pain
    • Severe: A tear across the entire muscle or tendon
General Prevention
  • Stretching the hamstrings while muscles are fatigued
  • Anaerobic interval training
  • Sport-specific training drills
Epidemiology
  • Common in athletes, especially those who sprint or jump
  • 12% of the injuries in professional football players
  • 34% of injuries have a later recurrence.
Risk Factors
  • Age
  • Low muscular strength
  • Previous hamstring injury
  • Tight hamstrings
Pathophysiology
  • The hamstring muscles are the biceps femoris, the semitendinosus, and the semimembranosus muscles.
    • All 3 arise from the ischial tuberosity and extend in the posterior aspect of the thigh and cross the knee.
    • The biceps femoris also has a short head that inserts into the femur.
    • The hamstring muscles contract eccentrically to absorb kinetic energy during gait.
    • Muscle strain most commonly occurs at the proximal musculotendinous junction of the biceps femoris.
  • Children and adolescents may avulse the bone at the hamstring origin, resulting in an ischial fracture.
  • Adults may avulse the tendon.
Etiology
  • Predisposing factors:
    • Poor flexibility
    • Inadequate warm-up
    • Fatigue
    • Dehydration
    • Deficiency in the reciprocal actions of opposing muscle groups
    • Strength imbalance between the quadriceps and hamstring muscles
  • Movements that commonly result in strain:
    • Flexing the leading hip during a hurdle
    • Sprinting out of the start-up blocks
    • Charging by a football lineman
    • Take-off by a jumper
    • Water-skiing falls
Associated Conditions
  • Back strain
  • Groin strain
Diagnosis
Signs and Symptoms
History
  • The patient has a sudden onset of pain and tenderness in the posterior thigh.
  • 10% of patients have an insidious onset of pain.
  • With more severe strains, a pop may be felt, with an immediate loss of function.
Physical Exam
  • Look for tenderness and swelling in the posterior thigh over one of the hamstring muscles.
  • Bruising or hematoma may be visible in the posterior thigh.
  • Look for pain on resisted knee flexion or hip extension.
Tests
Pathological Findings
This symptom complex may represent a partial or a complete tear of one of the hamstring muscles (biceps, semitendinosus, or semimembranosus).
 
Imaging
  • Imaging usually is not indicated if the diagnosis is straightforward.
  • Radiography:
    • Radiographs of the pelvis may show an ischial avulsion in a young athlete.
    • Radiographs of the knee may show a fibular avulsion if the symptoms are in this area.
    • Plain radiographs of the femur may be helpful if a fracture is suspected.
  • MRI:
    • Can differentiate a stress fracture from a hamstring strain.
    • Can show the location and extent of the muscle tear.
      • Bone scintigraphy can differentiate a stress fracture from a hamstring strain.
Differential Diagnosis
  • Acute fracture
  • Stress fracture
  • Muscle contusion
Treatment
General Measures
  • Acute (1st week after injury):
    • RICE protocol
    • Early gentle motion
  • Subacute (up to 3 weeks):
    • After inflammation resolves, concentric strength exercises should begin with cross-training.
  • Remodeling phase (2-6 weeks):
    • More aggressive stretching
    • Eccentric strengthening
    • Progressive agility and trunk stabilization exercises
  • Functional stage (up to 6 months):
    • Gentle return to running and sports activities when the patient is pain free
  • Competitive phase:
    • Focus on prevention, strengthening, and stretching
Activity
Rest, return to activity gradually as tolerated
 
Special Therapy
Physical Therapy
  • Ice massage and ultrasound are advised after swelling is controlled.
  • Exercise in water may help ROM.
  • The patient may begin active ROM followed by knee curls and extensions once soreness is resolved.
Medication
First Line
  • NSAIDs: Ibuprofen, Naprosyn, COX-2 inhibitors:
    • Not shown to improve outcome, but help symptoms
Second Line
Acetaminophen for analgesia
 
Surgery
  • Surgery is not indicated for musculotendinous junction injuries.
  • Ischial avulsion fractures:
    • >2 cm displacement: May be considered for internal fixation
    • >2 cm displacement can lead to a symptomatic nonunion.
  • Tendinous avulsions may be considered for operative repair.
Follow-up
Disposition
Issues for Referral
Evidence of complete tendinous avulsion or rupture should lead to referral to an orthopaedic sports-medicine specialist.
 
Prognosis
  • Mild strains heal in a few days to a week.
  • Moderate strains heal in 1-3 weeks.
  • Severe strains involving avulsion fractures at the ischial tuberosity or fibular head may take a month or more to heal.
Complications
  • Patients with a hamstring strain are at high risk for recurrent strain.
  • Patients with ischial avulsion fractures with substantial displacement are at risk for chronic symptomatic nonunion.
Patient Monitoring
Patients with hamstring strain must continue an active program of stretching and strengthening to prevent additional injury.
 
Miscellaneous
Codes
ICD9-CM
843.8, 843.9 Sprain or strain of hip and thigh
 
Patient Teaching
  • Explain the importance of hamstring stretch before activity.
  • Explain the importance of maintaining strength in these muscles as well as the quadriceps.
Activity
Patients are prone to reinjury.
 
Prevention
  • Stretching, strengthening
  • Hydration
  • Proper training
  • Team-wide prevention with stretching and strengthening, especially in high-risk sports
FAQ
Q: Ice or heat?
A: Neither is shown to decrease time to return to sport. Ice is recommended after activity and in the early days after injury. Heat is recommended before activity to help loosen muscles.
 
Q: Who is most prone to hamstring strains?
A: Patients with a history of previous strains who are involved in sports are most susceptible. These patients must actively follow a program of stretching and strengthening to prevent reinjury.

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