Back of Thigh

Topic Overview

Back of Thigh — Introduction

• The back of the thigh extends from the gluteal fold above to the popliteal fossa below.

• It is mainly composed of the hamstring muscles covered by fascia and skin.

• The sciatic nerve and branches of the profunda femoris artery traverse this region.

Muscles and Nerves

• The muscles on the back of thigh are the hamstring muscles — semimembranosus, semitendinosus, biceps femoris (long head), and the ischial part of adductor magnus

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• Common features:

  • Origin from ischial tuberosity.

  • Insertion into bones of the leg.

  • Supplied by the tibial part of the sciatic nerve.

  • Act as hip extensors and knee flexors.

Muscles of the Back of Thigh

1. Semitendinosus

   • Origin: Inferomedial impression of ischial tuberosity (common with biceps femoris).

   • Insertion: Upper medial surface of tibia (part of pes anserinus).

   • Action: Extends hip, flexes knee, and medially rotates leg.

   • Nerve: Tibial part of sciatic nerve.

2. Semimembranosus

   • Origin: Superolateral impression of ischial tuberosity.

   • Insertion: Posterior surface of medial condyle of tibia; forms oblique popliteal ligament.

   • Action: Extends thigh and flexes knee.

   • Nerve: Tibial part of sciatic nerve.

3. Biceps Femoris

   • Long head: From ischial tuberosity.

   • Short head: From linea aspera and lateral supracondylar ridge.

   • Insertion: Head of fibula.

   • Action: Flexes knee; long head extends thigh.

   • Nerve: Long head by tibial part, short head by common peroneal part of sciatic nerve.

4. Ischial Head of Adductor Magnus

   • Origin: Ischial tuberosity.

   • Insertion: Adductor tubercle of femur.

   • Action: Extends thigh.

   • Nerve: Tibial part of sciatic nerve.

Dissection Guide

• Make a vertical incision along posterior thigh.

• Reflect the skin and fascia to expose hamstrings.

• Identify sciatic nerve and trace its branches to muscles.

• Separate hamstrings to reveal ischial part of adductor magnus.

• Observe profunda femoris artery and its perforating branches crossing through the muscles

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Clinical Anatomy

• Hamstring Injury (Tear or Avulsion): Common in athletes during sudden acceleration; causes posterior thigh pain and bruising.

• Hamstring Contracture: Shortened hamstrings limit forward bending (cannot touch toes).

• Semimembranosus Bursitis: Inflammation of bursa under semimembranosus; may present as swelling in upper popliteal region.

• “Sleeping Foot” Phenomenon: Prolonged sitting compresses the sciatic nerve between the femur and seat edge, causing temporary numbness

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Sciatic Nerve

• Largest nerve in the body; continuation of sacral plexus (L4–S3).

• Course:

  • Enters gluteal region via greater sciatic foramen below piriformis.

  • Descends deep to gluteus maximus and lies on adductor magnus.

  • Divides at upper angle of popliteal fossa into tibial and common peroneal nerves.

• Relations:

  • Posteriorly covered by gluteus maximus and hamstrings.

  • Anteriorly related to adductor magnus.

• Branches:

  • Muscular: To semitendinosus, semimembranosus, biceps femoris, and ischial head of adductor magnus.

  • Articular: To hip joint.

Clinical Anatomy of Sciatic Nerve

• Sciatica: Pain radiating along posterior thigh and leg due to nerve compression (herniated lumbar disc).

• Intragluteal Injection Safety: Inject in upper outer quadrant of buttock to avoid sciatic nerve injury.

• Sciatic Nerve Injury:

  • Paralysis of hamstrings, leg flexors, and all muscles below knee.

  • Loss of sensation below knee (except medial side).

  • Foot hangs as foot drop.

• Piriformis Syndrome: Compression of the nerve by the piriformis muscle, causing buttock pain radiating down the thigh.

Arteries of the Back of the Thigh

• The main arterial supply of the back of the thigh is through the perforating branches of the profunda femoris artery (deep artery of the thigh).

• Additional small contributions come from the medial and lateral circumflex femoral arteries (branches of profunda femoris).

• These arteries create rich anastomoses ensuring collateral circulation between the internal iliac, femoral, and popliteal systems.

Perforating Branches of Profunda Femoris

• Number: Four perforating arteries.

• Course:
  Each artery arises on the front of the thigh, passes through the adductor longus, adductor brevis, and adductor magnus, then winds around the back of the femur to reach the hamstrings.

• Distribution:

  • Muscular branches → Hamstrings and adductor magnus.

  • Cutaneous and anastomotic branches → Posterior thigh skin and arterial networks.

  • Second perforating artery gives the nutrient artery to femur.

• Termination:
  The fourth perforating artery is the terminal branch of the profunda femoris.

Anastomoses on the Back of the Thigh

Two main longitudinal arterial chains are found posteriorly:

1. Superficial Chain:

   • Lies on or within the adductor magnus.

2. Deep Chain:

   • Lies close to the linea aspera of the femur.

Sources of Anastomosis:

• Internal iliac branches: Gluteal arteries.

• Femoral system: Medial and lateral circumflex femoral arteries.

• Popliteal artery (via its muscular branches).

Important Sites of Communication:

1. Gluteal arteries ↔ Circumflex femoral arteries.

2. Circumflex femoral arteries ↔ First perforating artery → forms the cruciate anastomosis.

3. Perforating arteries ↔ Each other → ensure longitudinal continuity.

4. Fourth perforating artery ↔ Muscular branches of popliteal artery.

5. Companion artery of sciatic nerve ↔ Perforating arteries → forms a small anastomotic link on the nerve’s surface.

Functional Significance:
These anastomotic networks act as collateral channels maintaining blood flow to the lower limb when the external iliac or femoral arteries are obstructed.