The forearm represents a crucial segment of the upper limb, connecting the elbow to the wrist. This part of the arm facilitates many daily activities, from lifting objects to intricate hand movements. Understanding its underlying skeletal structure helps in appreciating its functional versatility. The bones provide the framework for strength and dexterity, enabling a wide range of motions.
The Radius and Ulna
The forearm contains two long bones, the radius and the ulna, which extend from the elbow to the wrist. These parallel bones provide the framework that supports the hand and enables its wide range of motions. Their shapes and articulations are fundamental to forearm function.
The radius is positioned on the lateral side of the forearm, aligning with the thumb. It broadens at its distal end, near the wrist, where it forms an articulation surface for the carpal bones of the hand. Its proximal end features a disc-shaped head, which articulates with the humerus and the ulna, contributing to forearm rotation.
The ulna is located on the medial side of the forearm, corresponding to the pinky finger. This bone is longer than the radius and more robust at its proximal end, forming the main component of the elbow joint. The olecranon process, a bony projection of the ulna, forms the pointed part of the elbow. The ulna’s distal end is smaller and articulates with the radius, providing stability for the wrist.
Forearm Movement
The arrangement of the radius and ulna, along with their articulations at the elbow and wrist, allows for the forearm’s range of motion. While the elbow functions as a hinge joint, enabling flexion and extension, the relationship between these two forearm bones facilitates rotational movements.
The radius and ulna are connected along their shafts by an interosseous membrane, which distributes forces and maintains their relative positions. The joints at their ends—the proximal and distal radioulnar joints—enable the rotation of the forearm.
The two rotational movements are pronation and supination. During pronation, the palm rotates to face downwards or posteriorly. This action occurs as the radius crosses over the ulna, with its distal end rotating medially around the fixed ulna. Supination involves the rotation of the palm to face upwards or anteriorly. In this movement, the radius uncrosses from the ulna, returning to its parallel position. This interaction allows for actions like turning a doorknob.
Common Forearm Bone Injuries
Given their exposed position and mechanical roles, the radius and ulna are susceptible to injuries, with fractures being common. These bones can break individually or simultaneously, depending on the mechanism of injury.
A common injury is a distal radius fracture, often resulting from a fall onto an outstretched hand. This type of fracture occurs near the wrist, due to the radius’s wider distal end and its role in supporting body weight during such falls. An isolated ulnar shaft fracture, sometimes called a “nightstick fracture,” can occur from a direct blow to the forearm.
Combined fractures of both the radius and ulna are possible, often indicating a higher energy trauma. Examples include Monteggia fractures, an ulnar fracture with dislocation of the radial head, and Galeazzi fractures, a radial fracture with dislocation of the distal ulna. Such injuries require prompt medical evaluation and management for proper healing and restoration of forearm function.