Upper limb fascial compartments

Upper limb fascial compartments

Upper limb fascial compartments

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Upper Limb Fascia - The Body's Tupperware

  • Axillary Fascia: Forms the axilla floor, blending with pectoral and brachial fascia.
  • Brachial Fascia (Arm): A deep fascial sleeve creating two compartments via intermuscular septa:
    • Anterior: Flexors (Biceps, Brachialis, Coracobrachialis).
    • Posterior: Extensors (Triceps).
  • Antebrachial Fascia (Forearm): Encases forearm muscles; continuous with brachial fascia.

Compartment Syndrome: A surgical emergency common in the forearm due to its tight fascial boundaries, risking neurovascular compromise from swelling.

Axial cross-section of arm showing fascial compartments

Arm Compartments - Flex vs. Extend

Cross-section of arm showing fascial compartments

  • Anterior (Flexor) Compartment

    • Muscles: Biceps brachii, Brachialis, Coracobrachialis.
    • 📌 Mnemonic: Buy Big Cars.
    • Innervation: Musculocutaneous nerve (C5-C7).
    • Artery: Brachial artery.
    • Function: Flexes elbow & supinates forearm.
  • Posterior (Extensor) Compartment

    • Muscles: Triceps brachii.
    • Innervation: Radial nerve (C5-T1).
    • Artery: Profunda brachii artery (deep brachial).
    • Function: Extends elbow.

Clinical Pearl: Mid-shaft humeral fractures risk injuring the radial nerve in the radial groove, leading to paralysis of extensors ("wrist drop").

Forearm Compartments - Grip & Go

Two primary fascial compartments separated by the interosseous membrane and lateral intermuscular septum.

FeatureAnterior (Flexor-Pronator)Posterior (Extensor-Supinator)
MusclesSuperficial & deep groups. Flexors of wrist/digits, pronators.Superficial & deep groups. Extensors of wrist/digits, supinator.
InnervationMedian & Ulnar NervesRadial Nerve (deep branch)
ArteryUlnar & Radial ArteriesPosterior Interosseous Artery
FunctionWrist flexion, finger flexion, pronation.Wrist extension, finger extension, supination.
-   Superficial: Pronator Teres, Flexor Carpi Radialis, Palmaris Longus, Flexor Carpi Ulnaris.
-   📌 Mnemonic: **P**ass **F**ail **P**ass **F**ail (from lateral to medial).
-   Intermediate: Flexor Digitorum Superficialis.
-   Deep: Flexor Digitorum Profundus, Flexor Pollicis Longus, Pronator Quadratus.

Compartment Syndrome: The earliest and most common sign is pain disproportionate to injury, especially with passive stretch of the digits. Paresthesia is a later sign. Pulselessness is a very late finding.

Hand & Clinical Spaces - Danger Zones

Hand Fascial Spaces & Synovial Sheaths

  • Key Spaces & Infection Routes:

    • Thenar Space: Lateral aspect; infections from index finger.
    • Midpalmar Space: Central; infections from middle/ring fingers.
    • Space of Parona: Deep wrist space; potential for proximal spread to forearm.
  • Infectious Tenosynovitis:

    • 📌 Kanavel's Signs (FLEX):
      • Finger held in slight flexion.
      • Length of tendon sheath is tender.
      • Enlarged finger (fusiform swelling).
      • Xtension (passive) causes pain.

Horseshoe Abscess: Infection can spread from the little finger (ulnar bursa) to the thumb (radial bursa) via the communicating Space of Parona.

High‑Yield Points - ⚡ Biggest Takeaways

  • Fascial compartments of the upper limb separate anterior (flexor) and posterior (extensor) muscle groups.
  • Compartment syndrome, a surgical emergency, results from increased intracompartmental pressure, leading to ischemia.
  • Arm: The anterior compartment is innervated by the musculocutaneous nerve; the posterior by the radial nerve.
  • Forearm: The anterior compartment is primarily supplied by the median nerve; the posterior by the radial nerve.
  • Severe forearm compartment syndrome can cause Volkmann's ischemic contracture, a permanent flexion deformity.

Practice Questions: Upper limb fascial compartments

Test your understanding with these related questions

A patient presents with difficulty extending their wrist following trauma to the posterior forearm. Which of the following muscles would be most affected by injury to the posterior interosseous nerve?

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Flashcards: Upper limb fascial compartments

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The organization of the femoral region from lateral to medial is the _____

TAP TO REVEAL ANSWER

The organization of the femoral region from lateral to medial is the _____

nerve-artery-vein-lymphatics (NAVeL)

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