Radioulnar Joints
The Radioulnar Joints are proximal and distal articulations permitting forearm pronation and supination.
The radioulnar joints are a set of two synovial joints - the proximal (superior) radioulnar joint and the distal (inferior) radioulnar joint - located at either end of the radius and ulna. These joints enable rotation of the forearm, allowing the hand to turn palm up (supination) or palm down (pronation). A fibrous interosseous membrane between the shafts of the two bones also contributes to force transmission and stability.
Structure
Proximal Radioulnar Joint
Type: Synovial pivot joint
Location: Near the elbow; between the radial head and radial notch of the ulna
Joint surfaces:
Annular ligament: Encircles the head of the radius, holding it against the ulna and allowing rotation within the ring.
Distal Radioulnar Joint
Type: Synovial pivot joint
Location: Near the wrist; between the ulnar notch of the radius and the head of the ulna
Joint surfaces:
Ulnar notch of the radius (concave)
Head of the ulna (rounded)
Articular disc (triangular fibrocartilage complex): Stabilizes the joint and separates it from the wrist joint.
Interosseous Membrane
Dense fibrous sheet connecting the shafts of the radius and ulna
Provides additional stability and a surface for muscle attachment
Transmits forces from the hand (through the radius) to the ulna and humerus
Location
The radioulnar joints span the length of the forearm:
Joint Location Articulating Structures Proximal Radioulnar Joint Elbow region Radial head and ulna (radial notch) Distal Radioulnar Joint Wrist region Ulnar head and radius (ulnar notch)
Function
Forearm rotation: The radioulnar joints allow supination (palm up) and pronation (palm down) by rotating the radius around the ulna.
Force transmission: The interosseous membrane transmits axial forces from the distal radius to the ulna and humerus.
Stability: Ligaments and the interosseous membrane stabilize the radius and ulna during motion.
Development
The proximal and distal radioulnar joints form during fetal development as the radius and ulna differentiate. Ossification centers for the radius and ulna appear around the eighth week of gestation, and the joints become functional by birth. The interosseous membrane develops in tandem with limb musculature during embryogenesis.
Clinical Significance
Radial head subluxation (nursemaid’s elbow): Common in young children; radial head slips out of the annular ligament due to a sudden pull on the extended arm.
Distal radioulnar joint dislocation: May occur in trauma or associated with fractures of the forearm.
Triangular fibrocartilage complex (TFCC) injuries: A common cause of ulnar-sided wrist pain; affects stability of the distal radioulnar joint.
Fractures involving the radius or ulna: May disrupt rotation or alignment of the forearm; common examples include Monteggia and Galeazzi fractures.
Degenerative changes: Osteoarthritis or inflammatory arthritis can affect the distal joint, limiting rotation and causing pain.
