The Thigh

Contents:

• Introduction
• Muscle groups
  • quadriceps
  • adductors
  • hamstrings
• Strap muscles

Introduction

The thigh is the region between the hip and the knee.

Anteriorly it meets the abdomen at the inguinal region. Laterally and posteriorly it meets the gluteal region (hip and buttock). Below the knee the thigh meets the leg.

The leg extends from the knee to the ankle.

Muscle groups

There are three main muscle groups of the thigh: the quadriceps; the adductors; and the hamstrings. The thigh is seen here in transverse section.

Quadriceps

As its name suggests the quadriceps is composed of four muscles which unite as single tendon. The muscles are: vastus medialis vastus lateralis vastus intermedius rectus femoris

Rectus femoris arises from the ilium of the hip bone but the three vasti arise from the front and sides of the shaft of the femur. They encircle the complete shaft except for the small area at the back of the femur (the linea aspera) which is used for the attachment of other muscle groups such as the adductors.

The four muscles unite to form a common tendon of the quadriceps which is inserted into the patella (or kneecap). The patella ligament then continues to insert into the tibial tuberosity below the knee joint. This may be simplified to think of the quadriceps muscles as attaching to the tibial tuberosity by a tendon which embraces the patella. Bones within tendons are called sesamoid bones and they serve to keep tendons clear of joints and improve mechanical efficiency. The patella is the biggest example.

The quadriceps muscles extend the knee joint and move the leg forwards. The nerve supply to these muscles is from the femoral nerve (L2,3,4). The patellar tendon is the tendon which is used to elicit the quadriceps stretch reflex ("knee-jerk"). When the the tendon is struck sharply the stretch imposed on the muscle spindles in the quadriceps result in a reflex contraction (via a monosynaptic loop) extending the leg.

Adductors

The adductors of the thigh: pectineus adductor longus adductor brevis adductor magnus (+ gracilis which is considered later) All arise from the hip bone and all insert into the back of the femur - especially into the linea aspera.

The adductor muscles arise from a horseshoe of attachments on the hip bone.

These run from the junction between the ilium and pubis via the body of the pubis right round to the ischial tuberosity.

1. that the muscles form layers in the thigh with those muscles from the upper part of the horseshoe lying anterior to those arising from the lower part of the horseshoe. There are in fact three layers.
2. that the adductor group has an opportunistic nerve supply - due chiefly to the close proximity of several lower limb nerves. The bulk of muscles are supplied by the obturator nerve but pectineus is supplied by the femoral nerve and adductor magnus has a dual supply, the rear part via the sciatic nerve.

The anterior layer of adductors consists of pectineus adductor longus These muscles form much of the floor of the femoral triangle.

The middle layer of adductors consists only of adductor brevis. The anterior branch of the obturator nerve (L2,3,4) lies between adductor brevis and the anterior layer.

The third layer consists solely of the muscle adductor magnus.

As well as being attached to the linea aspera at the back of the femur it has strong attachments to the adductor tubercle. The tibial collateral ligament of the knee joint may represent an original downward continuation of this tendon.

At its lower end there is a hiatus in adductor magnus which permits the femoral artery to pass back into the popliteal fossa.

The posterior division of the obturator nerve lies between adductor magnus and adductor brevis (The muscle of the middle layer).

Hamstrings

The hamstrings group consists of three muscles:

• semimembranosus
• semitendinosus
• biceps femoris

All three arise from the ischial tuberosity and biceps ("two heads") has a second origin from the linea aspera.

These muscles insert below the knee; biceps into the head of the fibula and semimembranosus and semitendinosus into the tibia.

1. flex the knee, pulling the leg backwards
2. extend the hip joint to pull the trunk backwards from a stooping position
3. support the pelvis on the femur

The two strap muscles of the thigh

There are two long strap muscles in the thigh:

• sartorius
• gracilis

Sartorius arises from the canterior superior iliac spine and crosses the thigh diagonally to insert into the tibia (supply: femoral nerve).

gracilis arises chiefly from the pubis of the hip bone and descends vertically to insert into the tibia (supply: obturator nerve).

Sartorius flexes both the hip and the knee joints and laterally rotates the thigh resulting in a "cross-legged" position (sartor = a tailor).

gracilis helps to flex the knee and adduct the thigh.

Related Tutorials:

• The hip joint
• The knee joint
• femoral triangle
• Venous and lymphatic drainage

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