Bones of the Arm and Forearm

The bones of the arm and forearm form the skeletal structure that extends from the shoulder to the wrist. This includes the humerus in the arm, and the radius and ulna in the forearm. These bones provide support, facilitate movement, and serve as attachment sites for muscles involved in locomotion and fine motor control.

Structure

The upper limb bones from shoulder to wrist include:

• Humerus: The single long bone of the arm, extending from the shoulder to the elbow.
• Radius: One of the two long bones of the forearm, located on the lateral (thumb) side when in anatomical position.
• Ulna: The other forearm bone, located on the medial (pinky) side in anatomical position.

Humerus

• Head: Articulates with the glenoid cavity of the scapula to form the shoulder joint.
• Anatomical neck: Separates the head from the tubercles.
• Greater and lesser tubercles: Serve as attachment points for rotator cuff muscles.
• Shaft: Long cylindrical portion containing the deltoid tuberosity.
• Distal end: Includes the trochlea and capitulum (articulates with ulna and radius), medial and lateral epicondyles, and the olecranon fossa.

Radius

• Head: Disc-shaped; articulates with the capitulum of the humerus and the radial notch of the ulna.
• Neck: Narrow region below the head.
• Radial tuberosity: Insertion site of the biceps brachii.
• Shaft: Gradually widens distally.
• Distal end: Contains the ulnar notch (for the ulna), styloid process, and articulates with the carpal bones.

Ulna

• Olecranon: Prominent posterior projection forming the tip of the elbow.
• Trochlear notch: Articulates with the trochlea of the humerus.
• Coronoid process: Anterior projection below the trochlear notch.
• Radial notch: Lateral depression that articulates with the head of the radius.
• Shaft: Tapers toward the distal end.
• Distal end: Includes the head and styloid process, which articulate with the radius and carpal bones.

Location

The arm and forearm bones are located between the shoulder and the wrist:

Function

• Support and framework: Provide structure to the upper limb and support the soft tissues of the arm and forearm.
• Movement: Facilitate various movements including flexion, extension, supination, and pronation of the forearm and elbow.
• Joint articulation: Form the elbow joint (humeroulnar and humeroradial) and the superior and inferior radioulnar joints for forearm rotation.
• Muscle attachment: Numerous muscles (e.g., biceps brachii, triceps brachii, brachialis, pronator teres) attach to these bones to produce motion.

Development

The humerus ossifies from one primary center (shaft) and several secondary centers (head, tubercles, capitulum, trochlea, and epicondyles). Fusion typically completes by late adolescence (ages 17–20).

The radius and ulna each develop from one primary shaft center and two secondary centers—at the proximal and distal epiphyses. Ossification starts around the 8th fetal week, with complete fusion occurring in the late teens.

Clinical Significance

• Humeral fractures: May occur at the surgical neck, mid-shaft, or distal end; radial nerve injury is a risk with mid-shaft fractures.
• Forearm fractures: Both bones may break together in falls; common fracture types include Colles' (distal radius) and Monteggia (proximal ulna with radial head dislocation).
• Elbow dislocations: Typically posterior; may be associated with fractures of the coronoid or radial head.
• Osteomyelitis: Bone infection, more common in children affecting long bones such as the humerus.
• Growth plate injuries: In children, damage to epiphyseal plates can impair bone growth and joint function.