Hamstring Anatomy

Hamstrings and Sciatic Nerve Damage

The muscles in the posterior compartment of the thigh are collectively known as the hamstrings. Consisting of the biceps femoris, semitendinosus and semimembranosus, these prominent tendons form medially and laterally at the back of the knee. Working as a group, the hamstrings extend the hip and flex the knee, all while being innervated by the sciatic nerve (L4-S3).

The Muscles of the Posterior Compartment of the Thigh

• Biceps Femoris:
• Attachments: The long head originates from the ischial tuberosity of the pelvis, while the short head originates from the linea aspera on the posterior surface of the femur. Together, the heads form a tendon, which inserts into the head of the fibula.
• Actions: The primary action of the biceps femoris is flexion at the knee. It also extends the thigh at the hip and laterally rotates at the hip and knee.
• Innervation: The long head is innervated by the tibial part of the sciatic nerve, while the short head is innervated by the common fibular part.
• Semitendinosus:
• Attachments: Originates from the ischial tuberosity of the pelvis and attaches to the medial surface of the tibia.
• Actions: Flexion of the leg at the knee joint, extension of the thigh at the hip, medially rotating the thigh at the hip joint and the leg at the knee joint.
• Innervation: Tibial part of the sciatic nerve.
• Semimembranosus:
• Attachments: Originates from the ischial tuberosity (more superiorly than the origin of the semitendinosus and biceps femoris). Attaches to the medial tibial condyle.
• Actions: Flexion of the leg at the knee joint, extension of the thigh at the hip, medially rotating the thigh at the hip joint and the leg at the knee joint.
• Innervation: Tibial part of the sciatic nerve.

Clinical Relevance of Hamstring Avulsion Fracture of the Ischial Tuberosity

An avulsion fracture occurs when a fragment of bone attached to a ligament or tendon is pulled away from the main mass of the bone. This type of injury is often accompanied by a sudden pain in the posterior thigh, followed by an inability to walk due to sciatic nerve damage. This type of nerve damage is possible because the sciatic nerve lies in close proximity and could be compressed by a displaced fragment of bone.

Treatment for avulsion fractures of the ischial tuberosity may consist of a combination of conservative and surgical methods. Conservative approaches include rest, pain control, and physical therapy, while surgical methods may consist of open reduction and internal fixation. Open reduction requires setting the fracture in the correct position and then fixing it in place with metalwork.

Treatment of Ischial Tuberosity Avulsion Fractures

The posterior compartment of the thigh contains three muscles: the biceps femoris, semitendinosus, and semimembranosus, which are all innervated by the sciatic nerve. Each of these muscles has its proximal attachment on the ischial tuberosity, with the biceps femoris having its distal attachment on the lateral aspect of the head of the fibula and the other two muscles attaching to the medial aspect of the tibia. The actions of the hamstrings muscles include extension of the hip, flexion of the knee, and lateral and medial rotation at the hip and knee joints.

An ischial tuberosity avulsion fracture is a common injury of the hamstrings muscles and occurs when forceful extension is met with resistance. It is important to recognize this type of injury and provide the appropriate treatment in order to prevent long-term complications.

Treatment of an ischial tuberosity avulsion fracture can be conservative or surgical. Conservative treatment consists of rest, pain control, and physiotherapy, whereas surgical treatment may involve an open reduction and internal fixation of the fracture. Open reduction and internal fixation is a procedure where the fractured bone is reset into the correct position and then secured in place with metalwork.

When an ischial tuberosity avulsion fracture is suspected, patients should be referred to a medical professional who can provide an accurate diagnosis and the appropriate treatment. Depending on the severity of the injury, conservative treatment or surgical intervention may be necessary in order to ensure a full recovery and to prevent long-term complications. Regardless of the chosen treatment, it is important to follow the recommended instructions and to adhere to the prescribed rehabilitation program in order to ensure that the patient is able to return to their normal activities as quickly and safely as possible.