Pulled hamstring

Hamstring injuries

Hamstrings are a group of muscles of the posterior thigh which cross both the hip and knee joints and are involved in thigh extension and knee flexion

• hamstring muscle group comprises three separate muscles: semitendinosus, semimembranosus and biceps femoris
  
  
• hamstring injury is defined by the anatomical site within the muscle that is affected, and injury must be present in one or more of the component muscles
  
  
• hamstring injuries are commonly classified as grades one, two and three, where severity increases with the grade of injury
  
  
• diagnosis is based on patient history, including the cause of injury and clinical findings of local pain and loss of function, demonstrated by palpation, range of motion and muscle testing
  
  
• magnetic resonance imaging (MRI) can provide further information on the extent of injury

The hamstring muscles are three separate muscles which work together to flex the knee and extend the hip. The muscles are semimembranosus, semitendinosus and biceps femoris.

It is important to note that the frequency and severity of injury may differ in adolescents from that in skeletally mature people. Injuries occur in patterns unique to the skeletally immature adolescent, reflecting their developing bones and supporting ligamentous structures (1).

• musculotendinous injuries usually occur as a result of either direct or indirect trauma
  • direct trauma such as from a blow results in muscle contusion (bruising)
  • indirect trauma can occur as a result of alteration in the intensity or synergy of contraction, resulting in a single powerful muscle contraction
    • indirect trauma can also result from an overstretch of the musculotendinous unit leading to a strain, tear or avulsion
  • hamstring muscles are most vulnerable to injury during the rapid change from eccentric to concentric function, such as where the leg decelerates to strike the ground during running (2)
    • concentric function is where a muscle actively shortens in order to produce movement. For example, concentric action of the quadriceps, the muscle at the front of the thigh, straightens the knee to produce a kicking action
    • eccentric function is where a muscle generates active tension as it lengthens, braking a movement. For example, the hamstrings, situated at the back of the thigh, would function eccentrically to brake the kicking action.)

It is generally claimed that strain injuries most often occur near the musculotendinous junction

Hamstring injuries are commonplace in many mainstream sports and occupations involving physical activity.

Click here for video about mechanism of hamstring injury

Reference:

• 1) Frank JB, Jarit GJ. Bravman JT, Rosen JE. Lower extremity injuries in the skeletally immature athlete. Journal of the American Academy of Orthopaedic Surgeons 2007;15(6):356-66.
• 2) Verrall GM, Slavotinek JP, Barnes PG. The effect of sports specific training on reducing the incidence of hamstring injuries in professional Australian Rules football players. British Journal of Sports Medicine 2005;39(6):363-8.
• 3)Garrett WE Jr. Muscle strain injuries. American Journal of Sports Medicine 1996;24(6 Suppl):S2-8l

Additional contributions: Dr Ralph Mitchell BSc (hons) MBChB (August 2011)