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A radioulnar joint injury is an injury sustained by one of two articulations between the radius and ulna bones in the human forearm, either the proximal radioulnar joint beneath the elbow or the distal radioulnar joint above the wrist. The types of injury incurred may range from dislocations or fractures of the bones in the joint to damage to the ligaments surrounding the joint. Symptoms of an injury to this area may include pain at the site and upon rotation of the forearm, swelling, tenderness, stiffness, and a complete inability to move the injured joint.
At the proximal radioulnar joint, where the parallel radius and ulna meet at their topmost parts, the articulating surfaces are the head of the radius bone along its medial or inner side and the radial notch of the ulna, an oblong depression near the top of the bone just below the elbow. This joint comprises a cylindrical bone — in this case the head of the radius — rotating within a ring of ligament attached to the ulna known as the annular ligament. Like a ring on a finger, the annular ligament encircles the head of the radius and allows it to rotate back and forth alongside the ulna.
At the lower articulation of the radius and ulna, the distal radioulnar joint, the adjoining surfaces are the opposite of those on the proximal joint: the cylindrical head of the ulna meets with the ulnar notch on the bottom of the radius. In this case, the two are held together not by a ring-shaped ligament but by the volar and dorsal radioulnar ligaments, horizontal ligaments that connect the anterior and posterior aspects of the bones, respectively. This structure allows the entire radius to rotate past the ulna during forearm rotation.
Because these two joints make rotation of the forearm possible, radioulnar joint injury may occur during rotational arm movements, particularly ligament damage. Frequent, repetitive rotation of the forearm — either pronation, as in turning the hand palm-down, or supination, as in turning the hand palm-up — can lead to ligament strain or even gradual tears from overuse. This can be seen in athletes like tennis players or in workers whose job requires frequent pronation and supination of the forearm, as in turning a dial. Symptoms of ligament damage in either joint will most likely include inflammatory pain, swelling, and stiffness upon movement.
More severe injuries include dislocation, in which one or both bones separates from the joint, or fractures, in which one or both bones breaks away from the joint. These types of injuries are most likely to occur upon impact or other sudden force. An example can be seen at the distal joint, as in rotating the hand palm-down to catch oneself during a fall and dislocating or fracturing one of the bones. Most commonly, the head of the ulna is damaged, an injury known as a dorsal subluxation. Symptoms of this injury include pain above the wrist, a prominent head of the ulna projecting from the pinky-finger side of the arm, and an inability to supinated the forearm, or turn the hand palm-up.
Another example of a radioulnar joint injury involving a dislocation, this one seen at the proximal joint, is known as a radial head subluxation or nursemaid’s elbow. Again, this is more often sustained when the forearm is pronated, and it involves the dislocation of the head of the radius from the annular ligament that is often caused by an abrupt yanking of the arm. This injury tends to be seen in small children, as by a stronger adult, and symptoms include pain that presents low in the forearm away from the injury site, slight swelling, and the inability to supinate the forearm, or turn the hand palm-up.