Forearm
Region of the upper limb between elbow and wrist.
The forearm is the anatomical region of the upper limb situated between the elbow joint and the wrist. In precise anatomical terminology, the term "forearm" is used to distinguish this lower segment from the "arm," which technically refers only to the upper arm, though common usage often applies "arm" to the entire limb. This region is homologous to the crus, the part of the leg between the knee and ankle. The skeletal framework of the forearm consists of two long bones: the radius, located on the lateral (thumb) side, and the ulna, on the medial side. These bones articulate with each other at both the proximal and distal radioulnar joints and are connected along their length by the interosseous membrane. Proximally, the head of the radius meets the capitulum of the humerus and the radial notch of the ulna at the elbow, while the trochlear notch of the ulna articulates with the trochlea of the humerus. Distally, the radius articulates with the scaphoid and lunate bones of the wrist, and the ulna also contributes to the wrist joint. The forearm is enveloped by skin, with the anterior surface typically being less hairy than the posterior. Its musculature is extensive, including flexors and extensors of the wrist and digits, a flexor of the elbow (the brachioradialis), and muscles for pronation and supination of the hand. These muscles are organized into two fascial compartments: the anterior compartment, which houses the flexors (more massive as they work against gravity) and is primarily supplied by the median nerve, and the posterior compartment, containing the extensors and supplied by the radial nerve. The ulnar nerve also runs the length of the forearm. Blood supply comes from the radial and ulnar arteries and their branches, which typically course along the anterior aspect of the bones. The main superficial veins—the cephalic, median antebrachial, and basilic veins—are accessible for venipuncture, though the cubital fossa is often preferred. Functionally, the forearm allows flexion and extension at the elbow, as well as pronation and supination of the hand.
- Bones
- Radius and ulna
- Joints
- Proximal and distal radioulnar joints, elbow joint, wrist joint
- Nerves
- Median, radial, and ulnar nerves
- Arteries
- Radial and ulnar arteries
- Veins
- Cephalic, median antebrachial, and basilic veins
- Compartments
- Anterior (flexors) and posterior (extensors)
Lore & Background
The forearm is the region of the upper limb situated between the elbow and the wrist. It is homologous to the crus, the portion of the leg between the knee and ankle. The forearm contains two long bones: the radius on the lateral side and the ulna on the medial side. These bones form the proximal and distal radioulnar joints and are connected along their length by the interosseous membrane. The forearm is covered by skin, with the anterior surface typically less hairy than the posterior surface. Within the forearm, two fascial compartments are present. The posterior compartment houses the extensor muscles of the hand, supplied by the radial nerve. The anterior compartment contains the flexor muscles, which are more massive than the extensors as they function against gravity; this compartment is mainly supplied by the median nerve, while the ulnar nerve also runs the length of the forearm. Muscles of the forearm include flexors and extensors of the wrist and digits, a flexor of the elbow (brachioradialis), and pronators and supinators that turn the hand palm-down or palm-up. Blood supply comes from the radial and ulnar arteries and their branches, which typically run along the anterior faces of the radius and ulna. The main superficial veins are the cephalic, median antebrachial, and basilic veins. The forearm can be flexed and extended at the elbow, and pronated and supinated through movement at the elbow and the distal radioulnar joint.
Reader's Guide
The forearm is significant as a distinct anatomical region, distinguished from the arm (upper arm) in technical anatomy. Its two bones, radius and ulna, form the radioulnar joints and articulate with the humerus and wrist. The forearm's muscles are organized into anterior flexor and posterior extensor compartments, supplied by the median and radial nerves respectively, with the ulnar nerve also running its length. The radial and ulnar arteries supply blood, and superficial veins like the cephalic and basilic are used for venipuncture, though the cubital fossa is preferred. Fractures may involve the ulna, radius, or both; torus fractures in children are better treated with splinting than casting. Hereditary multiple exostoses can cause forearm deformities due to growth disturbance of the epiphyses.
Did You Know?
- The forearm contains two long bones: the radius on the lateral side and the ulna on the medial side.
- The anterior surface of the forearm is usually less hairy than the posterior surface.
- The flexor muscles of the forearm are more massive than the extensors because they work against gravity.
- The main superficial veins of the forearm are the cephalic, median antebrachial, and basilic veins.
Frequently Asked Questions
What bones make up the forearm?
The forearm is built around two long bones: the radius on the thumb side and the ulna on the pinky side. Together they span the segment of the upper limb between the elbow and the wrist.
How is the forearm divided into compartments?
Fascial sheets split the forearm into an anterior compartment that houses the wrist and finger flexors and a posterior compartment containing the extensors. This separation keeps the two opposing muscle groups organized and allows them to work independently.
Which nerves run through the forearm?
Three major nerves — the median, radial, and ulnar — travel through the forearm to supply its muscles and skin. Each follows a distinct path, producing the region's characteristic pattern of sensation and motor control.
What joints does the forearm participate in?
The forearm connects to the rest of the limb via the elbow joint proximally and the wrist joint distally. It also forms proximal and distal radioulnar joints that permit the rotation needed for pronation and supination.
What is the vascular supply of the forearm?
The radial and ulnar arteries carry arterial blood through the forearm and anastomose to form the palmar arches near the wrist. Venous return is handled primarily by the cephalic, median antebrachial, and basilic veins.
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