The Piriformis Muscle

Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

LATERAL ROTATORS OF THE HIP

There are six short external rotators of the hip:

• Piriformis

• Superior gemellus

• Obturator internus

• Inferior gemellus

• Obturator externus

• Quadratus femoris

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ORIGIN

• Arises from:

  • The anterior surface of the lateral process of the sacrum

  • The capsule of the sacroiliac joint

  • The gluteal surface of the ilium near the margin of the greater sciatic notch

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INSERTION

• Inserts into the superior border of the greater trochanter of the femur

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RELATIONS (POSTERIOR)

Structures related posteriorly to the piriformis muscle include:

• Sciatic nerve (normally passes inferior to the muscle)

• Superior gluteal artery

• Superior gluteal nerve

• Nerve to piriformis (nerve roots L5, S1, S2)

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ACTIONS

• Lateral rotation of the hip

• Abduction of the hip when the hip is flexed

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ANATOMICAL VARIATIONS OF THE SCIATIC NERVE

• The sciatic nerve is composed of:

  • Tibial division

  • Common peroneal division

• These divisions are usually bound together but may separate in relation to the piriformis muscle.

Variations in Relationship

• Sciatic nerve passes beneath an undivided piriformis muscle (most common).

• Piriformis muscle is divided, with the common peroneal division passing between the two heads.

• Common peroneal division passes over the piriformis, while the tibial division passes beneath.

• Entire sciatic nerve passes through a divided piriformis muscle.

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CLINICAL SIGNIFICANCE

Piriformis Fossa

• The piriformis fossa is the proximal entry point for most intramedullary femoral nail insertions.

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PIRIFORMIS SYNDROME

Definition

• A condition in which the sciatic nerve is compressed by the piriformis muscle or associated fibrous bands.

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Diagnosis

• Requires a high index of clinical suspicion

• Based primarily on:

  • Patient history

  • Physical examination

• Electromyography and bone scan are generally not helpful

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Symptoms

• May follow blunt trauma to the buttock

• Localized buttock pain

• Pain aggravated by:

  • Sitting

  • Driving

  • Bicycling

  • Running, especially in young individuals

• Tenderness in the region of the sciatic notch

• Radicular pain and paresthesia are uncommon

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Clinical Signs

• Deep palpation over the greater sciatic notch reproduces pain

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Provocative Test

Lasègue Maneuver

• Hip flexed to 90 degrees with knee extension

• Reproduction of pain indicates compression of the sciatic nerve

• Compression may be due to:

  • Piriformis muscle

  • Fibrous bands

  • Vascular anomalies

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Imaging

Magnetic Resonance Imaging Findings

• Enlarged piriformis muscle

• Vascular anomalies

• Compression or displacement of the sciatic nerve

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TREATMENT

Conservative Management

• Aquatic therapy

• Physiotherapy

• Nonsteroidal anti-inflammatory medications

• Local injections

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Surgical Management

• Reserved as a last resort

• Involves:

  • Surgical release of the piriformis muscle

  • Decompression of the sciatic nerve

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KEY POINTS

• The piriformis muscle is a critical anatomical landmark in the deep gluteal region.

• Variations in sciatic nerve anatomy explain differing clinical presentations.

• Most cases of piriformis syndrome respond to conservative treatment.

• Accurate anatomical knowledge is essential during hip surgery and intramedullary nailing.