Semitendinosus

Original Editor - Evan Thomas

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Description

Semitendinosus is one of the three muscles that make up the hamstrings muscle group, and it is located at the posterior and medial aspect of the thigh. The semitendinosus is so named due to it having a long tendon of insertion.

The muscle is fusiform and ends a little below the middle of the thigh in a long round tendon which lies along the medial side of the popliteal fossa; it then curves around the medial condyle of the tibia and passes over the medial collateral ligament of the knee-joint, from which it is separated by a bursa, and is inserted into the upper part of the medial surface of the body of the tibia, nearly as far forward as its anterior crest.

The semitendinosus is more superficial than the semimembranosus (with which it shares very close insertion and attachment points). However, because the semimembranosus is wider and flatter than the semitendinosus, it is still possible to palpate the semimembranosus directly.

The Semitendinosus muscle is highlighted in red

At its insertion it gives off from its lower border a prolongation to the deep fascia of the leg and lies behind the tendon of the sartorius, and below that of the gracilis, to which it is united. These three tendons form the Pes Anserinus, thus named due to the appearance resembling a webbed “goose’s foot”.

Anatomy

Origin

It arises, by a common tendon origin with the long head of the biceps femoris, from from the lower medial facet of the lateral section of the ischial tuberosity. The semitendinosus muscle mainly originates from the medial surface of the tendon of the long head of the biceps femoris, and also originates from the ischial tuberosity with a thin tendon and a muscular part.

Insertion

The semitendinosus tendon inserts at the upper part of the medial surface of the tibia, behind the attachment of sartorius and infero-anterior to the attachment of gracilis.

Nerve Supply

Tibial portion of the sciatic nerve (L5, S1, 2).

Artery

Branches from the internal iliac, popliteal, and profunda femoris arteries.

Function

1. Extension of the thigh at the hip

• Agonists: gluteus maximus, semimembranosus, biceps femoris (long head), and adductor magnus (posterior part)
• Antagonists: psoas major and iliacus

The semitendinosus is also a weak medial rotator of the hip.

2. Flexion of the leg at the knee

• Agonists: biceps femoris (long head), biceps femoris (short head), and semimembranosus
• Antagonists: vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris

Gracilis, sartorius, popliteus, gastrocnemius, and plantaris assist with flexion of the knee.

3. Internal rotation of the knee when the knee is flexed

• Agonists: popliteus and semimembranosus
• Antagonist: biceps femoris (long head) and biceps femoris (short head)

Sartorius and gracilis assist with internal rotation of knee.

Clinical Relevance

A grafted semitendinosus tendon (sometimes combined with gracilis tendon) may be used to replace an unrepairable cruciate or collateral ligament, a service that was previously provided by a graft from the patellar ligament. While either donor site may be used, the hamstring choice provides less post-operative consequences to kneeling.

Muscle Injuries

Injuries to the semitendinosus muscle can range from mild strains to more severe tears. These types of injuries can occur as a result of sudden movements, overstretching, or overuse of the muscle. Some common causes of semitendinosus muscle injuries include:

1. Sports activities: Participating in sports that involve running, jumping, or sudden changes in direction can put a strain on the hamstring muscles, including the semitendinosus.
2. Muscle imbalances: If the muscles in the leg are not properly balanced, it can lead to overuse or strain on certain muscles, including the semitendinosus.
3. Poor technique: Using improper form or technique during exercise or physical activity can put excessive strain on the hamstring muscles and lead to injury.
4. Previous injuries: If you have previously injured your hamstring muscles, you may be more susceptible to future injuries, including those to the semitendinosus.

Symptoms

1. Pain or discomfort in the back of the thigh or knee
2. Swelling or bruising in the affected area
3. Limited range of motion in the leg or difficulty walking
4. Muscle weakness or stiffness
5. Muscle spasms or cramping.

Assessment

Physical examination is an important part of assessing the semitendinosus muscle. During the examination, the healthcare provider may evaluate the following:

• Strength: The strength of the semitendinosus muscle can be assessed through manual muscle testing. The patient may be asked to flex the knee against resistance while lying on their stomach. The healthcare provider can then evaluate the strength of the muscle.
• Flexibility: The flexibility of the semitendinosus muscle can be assessed through range of motion testing. The healthcare provider may ask the patient to bend their knee while lying on their back and assess the range of motion.
• Tenderness: The healthcare provider may palpate the semitendinosus muscle to assess for any pain or tenderness in the area.

Functional Tests

Functional tests can assess the ability of the semitendinosus muscle to perform specific movements and activities. The following tests may be used:

• Single-leg hop test: This test assesses the ability of the semitendinosus muscle to generate power during jumping and landing. The patient may be asked to hop on one leg and then land on the same leg, while the healthcare provider evaluates the movement.
• Nordic hamstring curl test: This test assesses the eccentric strength of the hamstrings, including the semitendinosus muscle. The patient is asked to perform a slow, controlled curl while keeping their body straight.

Treatment

Treatment for a semitendinosus muscle injury typically involves rest, ice, compression, and elevation (RICE) in the initial stages to help reduce swelling and pain. Your doctor may also recommend over-the-counter pain medications or anti-inflammatory medications to help manage pain and inflammation.

Physical therapy may be recommended to help restore range of motion and strength in the affected muscle. This may include exercises to stretch and strengthen the hamstring muscles, as well as other muscles in the leg that may have been affected.

In more severe cases, surgery may be necessary to repair a torn or ruptured semitendinosus muscle. Your doctor will be able to determine the best course of treatment based on the severity of your injury and your individual needs.