Muscular System of the Elbow and Forearm

Posterior Elbow Mover (Extensor)

Triceps brachii serves as the primary antagonist to the elbow flexors. It is responsible for extending the forearm. This muscle is composed of three heads:

1. Long head: Originates from the infraglenoid tubercle of the scapula.
2. Lateral head: Originates from the posterior humerus.
3. Medial head: Originates from the posterior humerus.

All three heads converge to insert at the olecranon of the ulna.

Exam Tip: Remember that the Triceps brachii is the primary extensor. If a question asks for the muscle that moves the olecranon, think of the Triceps!

Forearm Flexors (Anterior Compartment)

The muscles of the anterior forearm are responsible for moving the wrist and the fingers. Most of these muscles share a common proximal attachment point: the medial epicondyle of the humerus.

Superficial Layer

The superficial layer consists of muscles that primarily act on the wrist:

• Flexor carpi radialis: Originates at the medial epicondyle and inserts on the metacarpals II–III; it functions to flex the wrist and abduct the hand.
• Palmaris longus: A narrow muscle that weakly assists in wrist flexion.
• Flexor carpi ulnaris: Originates at the medial epicondyle and functions to flex the wrist and adduct the hand.

Intermediate Layer

The intermediate layer is represented by a single, important muscle:

• Flexor digitorum superficialis: This muscle originates at the medial epicondyle. Its four tendons attach to the middle phalanges of fingers 2–5. It is responsible for flexing the wrist, the metacarpophalangeal (MP) joints, and the proximal interphalangeal (PIP) joints.

Forearm Extensors (Posterior Compartment)

The posterior compartment of the forearm is dedicated to extending the wrist and the digits. Unlike the flexors, these muscles generally utilize the lateral epicondyle of the humerus as their proximal attachment.

Superficial Layer

The superficial extensors include:

• Extensor carpi radialis longus: This muscle extends the wrist and assists in abducting the hand.
• Extensor digitorum: Originating at the lateral epicondyle and inserting at the distal phalanges of fingers 2–5, it extends the wrist, the MP joints, the PIP joints, and the distal interphalangeal (DIP) joints.
• Extensor carpi ulnaris: A muscle involved in the extension and adduction of the wrist.

Summary Table of Forearm Movements

To help synthesize this information, use the following table to distinguish between the compartments:

Clinical Correlation: Injuries to the epicondyles (like "Tennis Elbow" or "Golfer's Elbow") are often caused by repetitive strain to the muscles originating from the lateral or medial epicondyles, respectively.