Anatomical Description of the Forearm & Elbow

The forearm and elbow are complex structures that provide strength and flexibility, allowing for a wide range of movements. They are composed of bones, joints, muscles, ligaments, nerves, and blood vessels.

The structure of the forearm and elbow allows for a wide range of movements, including flexion, extension, pronation, and supination. However, this area can be prone to injury and conditions such as tennis elbow (lateral epicondylitis), golfer’s elbow (medial epicondylitis), and fractures.

Bones: The elbow is a complex hinge joint formed by the articulation of three bones:

  1. Humerus: The upper arm bone. Its lower end forms part of the elbow joint.
  2. Radius: One of the two bones in the forearm. It runs from the elbow to the thumb side of the wrist.
  3. Ulna: The other forearm bone. It runs from the elbow to the small finger side of the wrist. The olecranon process of the ulna can be felt as the ‘tip’ of the elbow.

Muscles: The muscles of the forearm are grouped into two compartments: the anterior (flexor/pronator) compartment and the posterior (extensor/supinator) compartment. These muscles control movements of the wrist and fingers, as well as pronation and supination of the forearm. The biceps brachii and triceps brachii muscles, located in the upper arm, are primarily responsible for elbow flexion and extension, respectively.

Several key muscles are associated with the elbow joint:

  1. Biceps brachii: Located in the upper arm, it’s primarily responsible for flexion of the elbow and supination of the forearm.
  2. Triceps brachii: This muscle, also in the upper arm, is the primary extensor of the elbow.
  3. Brachialis: Located beneath the biceps, it assists in elbow flexion.
  4. Brachioradialis: This forearm muscle assists in elbow flexion, especially when the forearm is in the mid (neutral) position between pronation and supination.

Ligaments: Ligaments are tough bands of tissue that connect bones to each other, providing stability to the joints. Key ligaments in the elbow include the ulnar collateral, radial collateral, and annular ligaments.

The primary ligaments of the elbow include:

  • Ulnar Collateral Ligament (UCL): This ligament is located on the inner side of the elbow and connects the humerus to the ulna. It provides stability to the elbow, particularly during throwing motions.
  • Radial Collateral Ligament (RCL): This ligament is located on the outer side of the elbow and connects the humerus to the radius. It provides stability to the elbow, particularly against varus forces (forces applied to the arm that try to bend it outward).
  • Annular Ligament: This ligament wraps around the head of the radius, allowing the radius to rotate during pronation and supination of the forearm while keeping it in contact with the ulna.

Tendons: Tendons connect muscles to bones, allowing for movement. The tendons of the forearm muscles attach at various points on the wrist and hand, allowing for precise movements.

  • Biceps Tendon: This tendon connects the biceps muscle to the radius. It allows the elbow to bend (flex) and the forearm to turn palm up (supinate).
  • Triceps Tendon: This tendon connects the triceps muscle to the ulna. It allows the elbow to straighten (extend).
  • Brachioradialis Tendon: This tendon connects the brachioradialis muscle, a muscle of the forearm, to the radius. It assists in elbow flexion and helps to pronate and supinate the forearm.
  • Flexor Tendons: These tendons connect the flexor muscles of the forearm to the bones of the hand. They allow for flexion of the wrist and fingers.
  • Extensor Tendons: These tendons connect the extensor muscles of the forearm to the bones of the hand. They allow for extension of the wrist and fingers.
  • Pronator Teres Tendon: This tendon connects the pronator teres muscle to the radius and ulna. It allows the forearm to rotate so the palm faces downward (pronation).
  • Supinator Tendon: This tendon connects the supinator muscle to the radius. It allows the forearm to rotate so the palm faces upward (supination).

Nerves: The main nerves in the forearm and elbow are the median, ulnar, and radial nerves, which are branches of the brachial plexus. These nerves control the muscles of the forearm and provide sensation to the skin.

Blood Supply: The main blood supply to the forearm and elbow comes from the brachial artery and its branches, the radial and ulnar arteries.

Fascial Compartments: The upper arm, which houses muscles that control elbow function, is not divided into separate compartments. However, the forearm, which contains muscles contributing to elbow function, is divided into anterior and posterior compartments by the interosseous membrane and the lateral and medial intermuscular septa.

Joint Anatomy: The elbow is a hinge joint that allows for flexion and extension. The radioulnar joints at the elbow and wrist allow for pronation and supination of the forearm (rotation of the hand and forearm so that the palm faces down or up). The elbow joint is actually three joints enclosed in a single synovial capsule:

  1. Humeroulnar joint: This is a hinge joint between the humerus and ulna that allows for flexion and extension.
  2. Humeroradial joint: Another hinge joint, between the humerus and radius, contributing to flexion and extension.
  3. Proximal radioulnar joint: This is a pivot joint that allows for rotation of the radius around the ulna, resulting in pronation and supination of the forearm.

Bursa Sacs: The primary bursa of the elbow is the olecranon bursa, located between the skin and the olecranon process of the ulna. It reduces friction over the elbow’s posterior tip.

Kinesiology: The primary movements of the elbow include:

  1. Flexion and extension: Movements of bending and straightening the arm, primarily facilitated by the biceps brachii (flexion) and triceps brachii (extension).
  2. Pronation and supination: Movements of turning the palm down and up, carried out by various muscles including the pronator teres and the supinator.