The radius is one of two long bones in the forearm, extending from the elbow to the wrist on the thumb side. It plays a role in various arm and wrist movements, acting as a structural component that enables the hand to perform a wide range of actions.
Anatomy and Location
The radius is a long bone with a wider end near the wrist and a smaller, disc-shaped head near the elbow. It is located on the lateral side of the forearm, parallel to the ulna. At its proximal (upper) end, the radial head articulates with the capitulum of the humerus (upper arm bone) to form part of the elbow joint. It also articulates with the radial notch of the ulna, forming the proximal radioulnar joint.
Moving distally, the shaft of the radius is slightly curved and triangular in cross-section. The distal (lower) end is broad and forms the main articulation with the carpal bones of the wrist. Its concave surface articulates with the scaphoid and lunate bones. The distal end also features an ulnar notch, which articulates with the head of the ulna, forming the distal radioulnar joint. This intricate arrangement of articulations allows for coordinated movement between the radius, ulna, humerus, and wrist bones.
Role in Forearm and Wrist Movement
The radius bone is central to forearm and wrist movements. Its unique structure allows it to rotate around the ulna, facilitating pronation and supination. Pronation turns the palm downward, while supination turns the palm upward. These rotational movements occur at the proximal and distal radioulnar joints, where the radial head pivots within the annular ligament and the distal radius crosses over the ulna.
Beyond rotation, the radius also contributes to wrist mobility. It articulates directly with carpal bones, enabling movements like flexion (bending the wrist forward), extension (bending the wrist backward), and radial and ulnar deviation (moving the hand side to side). The radius also supports the attachment of various muscles and ligaments that contribute to forearm and hand strength and flexibility.
Common Injuries and Conditions
The radius is frequently affected by injuries, particularly fractures. Fractures of the distal radius, occurring near the wrist, are among the most common bone fractures in the arm. These injuries often result from a fall onto an outstretched hand, a common mechanism in various accidents and sports. The severity of a distal radius fracture can vary, ranging from simple cracks to more complex breaks involving the joint surface.
One prevalent type is the Colles’ fracture, characterized by an upward (dorsal) displacement of the broken bone fragment. This fracture often creates a “dinner fork” deformity in the wrist. Another common injury is a radial head fracture, which occurs at the elbow end of the radius. These fractures are also caused by falling onto an outstretched hand, with the impact traveling up the forearm to the elbow. While less common than fractures, other conditions affecting the radius can include dislocations or degenerative changes in the joints it forms.