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Hamstring Strain

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Hamstring Strain
Kara D. Cox
Basics
Description
Hamstring strain is a common injury in athletes that can be painful and disabling. The musculotendinous unit (biceps femoris, semitendinosus, and semimembranosus) can be injured at multiple sites, including the proximal bony attachment, the musculotendinous junction, the central muscle belly, and the distal tendon. The injury occurs due to an excessive load during an eccentric contraction, such as with running or jumping. Treating hamstring strain can be frustrating due to slow healing, persistent symptoms, and high recurrence rates.
Epidemiology
Hamstring strains are among the most common injuries in running, jumping, and kicking sports, particularly those that involve sprinting. The biceps femoris is the most commonly injured muscle, and strain most commonly occurs at the muscle-tendon junction.
Prevalence
  • Prevalence rates vary due to differing definitions and underreporting:
    • Prevalence rates vary from 8–25% (1).
    • Single-season prevalence has been reported to be as high as 50% (1).
  • Reinjury is common and is reported at rates of 12–31% (2).
Risk Factors
  • Nonmodifiable risk factors:
    • Increased age: Athletes between 23 and 25 yrs were between 1.3 and 3.9 times more likely to suffer strains, and in increasing age groups, the risk was shown to increase by 30% annually (1)[A].
    • Black racial background: Studies suggest that this is not specific to any one nationality, but to all athletes of black racial background (1)[A].
    • Higher levels of competition: Hamstring strain was infrequently reported in amateur sport, but prevalence was significantly greater (p <.01) in higher levels of competition (1)[A].
  • Modifiable risk factors:
    • Previous history of hamstring strain injury: Previously injured athletes were 2–6 times more likely to suffer subsequent strains (1)[A].
    • Strength imbalances, including 10% difference between right to left hamstring or low hamstring to quadriceps ratio (H:Q ratio) have been quoted as risk factors, but have not been shown to be significant predictors of future injury (1,3)[C]
    • Poor flexibility: Inflexible hip flexors is a significant risk factor, and increased quadriceps flexibility is inversely related to hamstring strain incidence; however, hamstring flexibility does not demonstrate significant association (1)[C]
    • A proposed multifactorial model for hamstring injury includes poor flexibility, strength imbalances, inadequate warm-up, and muscle fatigue (1,2,3,4)[C]
General Prevention
  • Balanced strength of hamstrings from side to side and of hamstrings to quadriceps
  • Eccentric strengthening programs
  • Flexible hamstrings and, just as important, flexible hip flexors and quadriceps
  • Proper warm-up
  • Proper recovery following hamstring injury and avoidance of premature return to play
Etiology
  • Muscle injuries can be as simple as a muscle cramp or as complicated as a complete rupture, and in between are the muscle strains.
  • Strains are classified by severity of muscle fiber injury (2,4):
    • Mild strain (1st degree): Stretch type injury with few muscle fibers injured, causing only minor swelling/pain and minimal loss of strength/motion
    • Moderate strain (2nd degree): Partial tear with strength loss and functional limitations due to more extensive muscle injury
    • Severe strain (3rd degree): Extensive or complete tear across whole muscle with disabling loss of muscle function
  • The healing process in muscle injury includes initial muscle fiber injury with immediate hemorrhage followed by inflammatory cell introduction to the damaged tissue, production of connective scar tissue, and regeneration of damaged muscle fibers.
  • The hamstring musculotendinous unit (biceps femoris, semitendinosus, and semimembranosus) is susceptible to injury for many reasons (5):
    • The hamstrings cross 2 joints, which can be moving in opposing directions.
    • The short head of the biceps femoris has a long, inconstant origin along the femur.
    • The hamstrings (specifically the biceps) have dual innervation, which causes forceful, uncoordinated contractions (the hamstrings, including the long head of the biceps, are innervated by the tibial branch of the sciatic nerve, with the exception being the short head of the biceps, which alone is innervated by the peroneal branch of the sciatic nerve).
    • During the gait cycle, the hamstrings have differing activity (the semimembranosus has increased eccentric activity to slow hip flexion during the swing phase, while the biceps are most active during take-off).
  • The usual mechanism of injury occurs in the later part of the swing phase as the hamstrings rapidly change from eccentrically working to decelerate knee extension to concentrically becoming an extensor of the hip (2).
Commonly Associated Conditions
  • Apophyseal injury, such as traction apophysitis (found in children when the ischial apophysis appears at ages 13–15 and up to ages 20–25 when it fuses with the pelvis) (5)
  • Complete tendon rupture, with or without avulsion fracture (found mostly in adults, more commonly proximal at the ischium vs distal, which is rare) (5)
  • Development of myositis ossificans
Diagnosis
Most hamstring strain injuries occur in an acute setting with sudden onset of posterior thigh pain that often limits participation. Typical hamstring strain injury can be diagnosed based on thorough history and physical exam.
History
  • Hamstring strain is most commonly seen in kicking or speed athletes (2,3,4)[C].
  • In cases of avulsion injury other activities are reported, such as water skiing, dance, weight lifting, and ice skating (2,3,4)[C].
  • Often the athlete can relay information about fatigue or improper warm-up (3)[C].
  • Acute or chronic:
    • Some hamstring strain injuries are more chronic in nature with recurring “tightness” or muscle “pull” complaints (3)[C].
    • Treatment protocol is different for acute injury vs chronic as well as for initial injury vs recurrent injury (3,4)[C].
  • Mechanism: Increased risk of avulsion if there is extreme hip flexion with the knee in full extension (3)[C]
  • Severity: Discontinuation of activity, inability to ambulate following the injury, or describing an audible pop at the time of injury can point toward a more severe strain or an avulsion injury (3)[C].
Physical Exam
  • Position patient prone, knee in flexion, and palpate entire muscle from origin to insertion (3)[C]:
    • Biceps femoris is most commonly injured.
  • Examine the patient with the muscles relaxed and also with mild tension (3)[C].
  • Inspect for swelling, induration, tenderness, and/or ecchymosis (3)[C].
  • An abnormality can be difficult to palpate even with more diffuse injury (3)[C].
  • Active range of motion, strength, flexibility, and neurovascular testing of bilateral lower extremities (3)[C]
  • Note severity of injury using maximal tolerance of passive straight leg raise/knee extension (3)[C].
Diagnostic Tests & Interpretation
Imaging
  • Further examination beyond the physical exam is not typically necessary, but if needed, radiographs, MRI, and sonography have been found useful (2).
  • Radiographs: Anteroposterior pelvis can be helpful acutely if an avulsion is suspected or chronically to look for development of myositis ossificans (3,4).
  • US and MRI can help determine more accurate location and extent of injury (4,5):
    • US is as useful as MRI for acute hamstring injury and has added benefit of low cost.
    • MRI images of an acute injury appears as high signal in or around the muscle on T2-weighted images.

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Pathological Findings
  • Remodeling phase of muscle includes muscle regeneration and fibrous scar formation (3).
  • Chronic tendinopathy can develop if the healing process forms a disorganized scar.
Differential Diagnosis
In addition to the associated injuries listed above, consider these in the differential diagnosis:
  • Direct hamstring injury, including muscle laceration or contusion (common direct mechanism for injury as opposed to indirect sprain mechanism) (2)
  • Posterior lateral corner knee injury (rare, can have associated distal hamstring injury) (3)
  • Pelvic or proximal femoral stress fracture
  • Piriformis syndrome, gluteus medius injury, adductor strain
  • Pain radiating from the lumbar back, sacroiliac joint, or hip
Treatment
  • The treatment protocol is different for acute vs chronic injury as well as for initial vs recurrent injury (4)[C].
  • The protocol must be individualized for the patient based on sport-specific needs, risk factors, and location of the injury (4)[C].
  • Acute:
    • Goals: Control pain, swelling, hemorrhage, and muscle fiber adhesion; work toward restoration of normal active range of motion and gait (may require crutches early) (3,4)[C]
    • Treatment:
      • 24–72 hr: Rest, ice, compress, elevate, early immobilization in extension, passive gentle range of motion (2,3,4)[C]
      • NSAIDs: Standard NSAID precautions apply:
        • Begin after acute injury and continue for a limited time (3–7 days) (3,4)[C].
        • May be beneficial to delay treatment for 2–4 days to allow for the normal inflammatory response needed for healing (2)[C]
        • Limit prostaglandin-mediated inflammation, allowing for earlier/more effective rehab
        • When used early in muscle injury, NSAIDs have been shown to decrease pain/strength loss and improve recovery, though limited studies in hamstring injuries (4)[C]
        • There are concerns for delay of muscle regeneration and functional losses related to the use of NSAIDs (4)[C].
      • Corticosteroids not routinely recommended (4)[C]:
        • There is controversy about injection after acute muscle injury.
        • Consider within 72 hr if severe injury and palpable defect (4)[C]
        • Concerns include delayed healing, tendon rupture (several case series), and infection (4)[C]
        • 1 retrospective study showed favorable results with no complications and limited time lost with quick return to play (1,4)[C].
  • Subacute/rehab (day 3 up to 6 wks)
    • Goals: Control pain and swelling, promote muscle fiber alignment, strength, and repair; restore flexibility and muscle imbalances; begin muscle conditioning and advance over time while maintaining cardiovascular fitness (3,4)[C]
    • Treatment:
      • Pain-free passive range of motion, then pain-free active range of motion (3)[C]
      • Maintain cardiovascular conditioning with pool activities or stationary bike (3,4)[C].
      • Therapeutic modalities may assist in rehab (3,4):
      • Electric stimulation can decrease pain and swelling.
      • Moist heat or US can warm muscle.
      • Deep friction massage or myofascial release can resolve adhesions and stimulate repair.
      • Proceed with flexibility and strength restoration in a slow progression (4)[C]:
        • Back off intensity if painful (2,4)[C]
        • Stretch all lower extremity musculature, with focus on quads and hip flexors.
        • Strengthen the gluteals and correct thigh muscle imbalances.
        • Progress hamstring strengthening from early concentric to more advanced eccentric conditioning (2,4)[C].
  • Functional (2 wks up to 6 mos)
    • Goals: Perform functional rehab in a progressive fashion to minimize reinjury (1,2,3,4)[C]
    • Treatment:
      • Functional rehabilitation programs that incorporate sport-specific drills should be used in combination with traditional interventions (1)[B].
      • Walk to jog to run to sprint, then sport-specific drills
  • Return to play:
    • Goals: Safe and timely return to play with best possible functionality
    • Treatment:
      • May return when able to perform pain-free sport-specific activity, has normal flexibility, and normal strength (often measured as within 10% of uninjured leg) (4)[C]
      • Maintain strength and flexibility (2,3,4)[C]
Additional Treatment
Additional Therapies
Newer therapies aimed at the treatment of tendinopathy may play a role in treatment of hamstring strain injury, especially in chronic and recurrent hamstring strain injury. These therapies include US-guided needle tenotomy, prolotherapy, autologous blood, or platelet-rich plasma injections.
Surgery/Other Procedures
Surgical referral should be considered to prevent poor outcome in complete soft tissue ruptures or bony avulsions that are >2 cm displaced (2,3,4,5)[C].
Ongoing Care
Follow-Up Recommendations
  • Recovery time after hamstring strain injury can be as short as 3 wks and as long as 6 mos, depending on the severity and chronicity of the injury.
  • Although reinjury is common, proper functional rehab and appropriate return to play can minimize the risk.
  • Maintenance and prevention protocols should focus on the modifiable risk factors outlined above.
References
1. Prior M, Guerin M, Grimmer K. An evidence based approach to hamstring strain injury: a systematic review of the literature. Sports Health: A Multidisciplinary Approach. 2009;1:154–164.
2. Petersen J, Hölmich P. Evidence based prevention of hamstring injuries in sport. Br J Sports Med. 2005;39:319–323.
3. Clanton TO, Coupe KJ. Hamstring strains in athletes: diagnosis and treatment. J Am Acad Orthop Surg. 1998;6:237–248.
4. Drezner JA. Practical management: hamstring muscle injuries. Clin J Sport Med. 2003;13:48–52.
5. Mann G, Shabat S, Friedman A, et al. Hamstring injuries. Orthopedics. 2007;30:536–540; quiz 541–542.
Additional Reading
Evidence-based material is lacking for interventions for prevention and treatment of hamstring strain injury (1).
Further high-quality prospective studies with large samples from broad populations investigating risk factors and management are needed to provide better framework to target interventions for hamstring injury (1)[A].
Davis KW. Imaging of the hamstrings. Semin Musculoskelet Radiol. 2008;12:28–41.
Lempainen L, Sarimo J, Mattila K, et al. Proximal hamstring tendinopathy: results of surgical management and histopathologic findings. Am J Sports Med. 2009.
Codes
ICD9
  • 843.8 Sprain of other specified sites of hip and thigh
  • 843.9 Sprain of unspecified site of hip and thigh
Clinical Pearls
  • Previous history of hamstring injury is a significant risk factor for hamstring strain injury.
  • Functional rehab programs with sport-specific drills along with traditional interventions can be used for both prevention and treatment of hamstring strain injury.


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