Hamstring Strains: Classification and Management

Abstract

The hamstring muscle complex (HMC) includes the semimembranosus, semitendinosus, and biceps femoris (BF) short and long heads, all of which act to extend the hip and flex the knee. 4,5 A primary function of the HMC is deceleration of the lower limb via eccentric contraction during running and kicking movements, placing the muscles under high strain while at high stretch. [2][3][4][5][6]8 Accordingly, most hamstring strain injuries (HSIs) are "sprint-type," occurring during high-speed running. They typically affect the proximal long head of the BF at the musculotendinous junction and/or intramuscular belly. [1][2][3][4]6,[8][9][10] "Stretch-type" HSIs may also occur with end-range hip flexion and knee extension, as might be seen in dancing and kicking, and typically involve the proximal semimembranosus tendon. 1,2,4,9,10 HSIs are commonly graded as follows: Grade I -microscopic tearing with minor swelling and discomfort and little to no loss of strength; Grade II -gross partial tear with clear weakness; Grade III -complete rupture with total loss of function. 2,[6][7][8] Grade III HSIs are often traumatic injuries, such as might occur during water-skiing when there is forceful hip flexion while the knee is in full extension. 2,5,6,9,10 Grade I and II HSIs can be treated nonoperatively with a 3-phase protocol. Phase I (~0-4 weeks) seeks to prevent scar formation while minimizing atrophy. It focuses on low-impact and isometric exercises with limits on range of motion and resistance. Phase II (~2-6 weeks) encourages gradual return to full range of motion (but not end-range lengthening) with an emphasis on submaximal eccentric strengthening, trunk stabilization, and agility. Phase III (~4-8+ weeks) incorporates sport-specific drills and further agility and trunk-stabilization exercises. Eccentric strengthening is advanced to maximal effort and range of motion, with return to sport when these can be achieved without pain. 2,10 Grade III HSIs may require open or endoscopic surgical repair, with a goal of returning to sport ~4 to 6 months postoperatively. 2,