Posterior Compartment of the Arm
Posterior compartment of arm contains triceps brachii and anconeus innervated by the radial nerve.
The posterior compartment of the arm (extensor compartment) contains muscles primarily responsible for extension of the elbow joint. It is bounded by the brachial fascia and separated from the anterior compartment by the medial and lateral intermuscular septa. The radial nerve and profunda brachii artery run within this compartment.
Boundaries
Structure | Description |
---|---|
Anterior | Humerus and intermuscular septa |
Posterior | Brachial fascia and skin |
Medial & Lateral | Intermuscular septa (medial and lateral) |
Muscles of the Posterior Compartment
Muscle | Origin | Insertion | Function | Innervation |
---|---|---|---|---|
Triceps brachii |
Long head: infraglenoid tubercle of scapula Lateral head: posterior surface of humerus (above radial groove) Medial head: posterior surface of humerus (below radial groove) |
Olecranon process of ulna | Extension of elbow; long head also aids in shoulder extension and adduction | Radial nerve (C6–C8) |
Anconeus | Lateral epicondyle of humerus | Lateral surface of olecranon and posterior ulna | Assists triceps in elbow extension; stabilizes elbow | Radial nerve (C7–T1) |
Contents
- Radial nerve: Innervates all posterior arm muscles; runs in the radial groove of the humerus
- Profunda brachii artery (deep brachial): Travels with the radial nerve in the radial groove
- Posterior cutaneous nerve of the arm and forearm: Branches of the radial nerve supplying skin
Function
- Elbow Extension: Triceps brachii is the main extensor of the elbow joint
- Shoulder Movement: Long head of triceps assists in shoulder adduction and extension
- Joint Stabilization: Anconeus stabilizes the elbow during forearm rotation
Blood Supply
- Profunda brachii artery: Main blood supply; branches into radial collateral arteries
Innervation
- Radial nerve: Sole motor nerve of the compartment (C6–C8)
Surface Anatomy
The triceps forms the large muscular mass on the back of the arm. Its tendon is prominent just above the olecranon. The anconeus is small and less visible but lies lateral to the olecranon during elbow extension.
Clinical Significance
- Radial Nerve Injury: Mid-shaft humeral fractures may injure the radial nerve in the radial groove, causing wrist drop and triceps weakness
- Compartment Syndrome: Rare but possible; may present with posterior swelling and loss of elbow extension
- Triceps Reflex: Deep tendon reflex tested over the olecranon; evaluates C7 spinal segment
Comparative Anatomy
In quadrupeds, the triceps muscle is also well-developed due to weight-bearing needs. In humans, while less load-bearing, it is adapted for precise, forceful extension required in tasks like pushing, throwing, or lifting.
Last updated on May 12, 2025