Hamstring Injury

Hamstring muscles comprise the three major muscles of the posterior aspect of the thigh. These include the semimembranous as the medial most, long and short heads of the biceps femoris as the lateral most, and semitendinosus in between. These groups of muscles are clinically significant as they are highly susceptible to injury, especially in the athletes. The semimembranosus and long head of the biceps femoris have a common origin on the posterolateral aspect of the ischial tuberosity while semitendinosus has an origin on the anterolateral part of the ischial tuberosity. The short head of biceps has origin medial to the linea aspera on the distal aspect of the posterior part of the femur. Both the long and short head of biceps femoris go on to insert over the head of the fibula while semimembranosus inserts over the medial condyle of the tibia. Semitendinosus inserts onto the pes anserine region on the medial part of the tibia. All the hamstring muscles traverse two joints (hip and knee) from origin to insertion except the short head of biceps femoris, which only traverses knee joint from its origin to insertion. The main function of the hamstring muscles is flexion at the knee joint and extension at the hip joint. Biceps femoris also helps in the external rotation of the hip while semimembranosus and semitendinosus help in the internal rotation of the hip joint. Hamstring injuries mostly occur while players are running or sprinting. These groups of muscles are particularly susceptible to injury due to their anatomic arrangement. Also, their mechanism of action over two joints (knee and hip) that occur together with opposing effects on the hamstring length makes them vulnerable to injury. Also, their key role in deceleration while walking, running, and making acute changes in direction at high speed, makes them more prone to getting injured. Hamstrings bear the major strain during the phase of motion when they transition from decelerating the extension of the knee to extending the hip joint. During this rapid transition of functional biomechanics of these muscles, they are most vulnerable to injury.Besides this, dual nerve supply of two heads of biceps femoris leading to asynchronous stimulation as well as an anatomical variance of attachment of its two heads makes it more commonly injured hamstring. Grade 1: Mild pain or swelling, non-appreciable tissue disruption, no or minimal loss of function. Grade 2: Identifiable partial disruption of tissue with moderate pain and swelling, leading to loss of function. Grade 3: Complete disruption or tear of the musculotendinous unit with severe pain and swelling and lack of function.