Background
Hamstring injuries are common problems that may result in significant loss of on-field time for many athletes because these injuries tend to heal slowly. Once injury occurs, the patient is at high risk for recurrence without proper rest and rehabilitation.
The hamstring muscles are 3 muscles in the posterior thigh: the semitendinosus, semimembranosus, and biceps femoris. The semitendinosus originates at the ischial tuberosity and inserts at the pes anserine; the semimembranosus originates at the ischial tuberosity and inserts at the posterior medial tibia. The biceps femoris has a long head that originates at the ischial tuberosity and a short head at the posterolateral femur and inserts into the head of the fibula. These muscles serve as knee flexors and hip extensors. See the image below.
Normal sagittal alignment permits the knee to lock in full extension, aided by powerful quadriceps and an intact extensor mechanism. The ground reaction force passes anterior to the "center of rotation" of the knee, while the posterior cruciate ligament, posterior capsule, hamstrings, and gastrocnemius provide a tension band effect.
At heel strike of the gait cycle, the hamstrings actually contribute to knee extension through closed chain kinetics. During the gait cycle, the biceps femoris contracts eccentrically in terminal swing, which is important in the pathology of the injury, as discussed later. [1, 2, 3]
Epidemiology
Frequency
Hamstring strain is a fairly common injury in physically active individuals. In a prospective study of 61 male track-and-field athletes, Tokutake et al reported that 30% of them suffered hamstring strain in association with high-speed running, with the incidence of such strains being 2.88 per 1000 practices or competitions. [4]
Mortality/Morbidity
No mortality is associated with hamstring strain; however, morbidity is common, due to pain and reinjury if proper rehabilitation does not occur before the patient returns to preinjury activity levels. [5, 6]
Age
While hamstring injuries can occur in people of any age, incidence increases with age.
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Normal sagittal alignment permits the knee to lock in full extension, aided by powerful quadriceps and an intact extensor mechanism. The ground reaction force passes anterior to the "center of rotation" of the knee, while the posterior cruciate ligament, posterior capsule, hamstrings, and gastrocnemius provide a tension band effect.
