Muscles - Thigh (Posterior Compartment)

Question 1

What are the different hamstring muscles?

Answer 1

1) Biceps femoris
2) Semitendinosus
3) Semimembranosus

Question 2

What is the general function of these muscles?

Answer 2

Extend of the hip joint

Flex at the knee joint

Note: The hamstring portion of the adductor magnus (medial compartment) has a similar function.

Question 3

Which nerve innervates the muscles of the posterior compartment?

Answer 3

Sciatic nerve (L4-S3)

Question 4

Biceps femoris

Answer 4

Like the biceps brachii, it has two muscle heads - long and short head.

It is the most lateral muscle of the posterior compartment. The common tendon can be palpated laterally at the posterior knee.

Origin (long head) - ischial tuberosity

Origin (short head) - linea aspera

Insertion - head of the fibula

Innervation (long head) - tibial part of the sciatic nerve

Innervation (short head) - common fibular part of the sciatic nerve

Action - flexion at the knee, extension and the hip, laterally rotates the hip and knee.

Question 5

Semitendinosus

Answer 5

Largely tendinous muscle. Located medially to the biceps femoris and covers the majority of the semimembranosus.

Origin - ischial tuberosity

Insertion - medial surface of tibia

Innervation - tibial part of the sciatic nerve

Action - flexion at the knee. Extension at the hip. medially rotates leg and hip.

Question 6

Semimebranosus

Answer 6

Flattened and broad. Located beneath the semitendinosus.

Origin - ischial tuberosity (more superior than the other hamstring muscles).

Insertion - medial tibial condyle

Innervation - tibial part of the sciatic nerve

Action - flexion of the knee. Extension at the hip. Medially rotate the knee and leg.

Question 7

Clinical relevance - hamstring strain

Answer 7

Excessive stretch or tearing of hamstring muscles.

Often seen in running and kicking sports.

Damage to muscle fibres is likely to damage surrouding blood vessels - resulting in a haematoma (a collection of blood). The haematoma is contained by the overlying fascia lata.

Treatment - RICE

Question 8

Clinical relevance - avulsion fracture of the ischial tuberosity

Answer 8

Avulsion fracture occurs when a fragment of a bone breaks away from the main body of bone.

In this case, hamstring tendon ‘tears off’ a piece of the ischial tuberosity.

Such an injury occurs in sports that required rapid contraction and relaxation of the muscles, such as sprinting and football.