What is the ulna?
The ulna is a long bone that lies parallel and close to the radius (radius) and is connected to it by a strong membrane of tight connective tissue. There are three parts to the ulna: the shaft (corpus) and an upper (proximal) and lower (distal) end.
The shaft of the ulna is about the same thickness as that of the radius. It is triangular in cross-section, but becomes rounded toward the bottom (toward the wrist). At the upper end, the ulna is much stronger than at the lower end because the joint connection from the humerus to the forearm is primarily through the ulna. The joint connection between the forearm and the hand, on the other hand, occurs primarily via the radius, which is why the ulna is less strong here.
The posterior surface of the elbow bump (olecranon) lies directly under the skin and is protected by a bursa (bursa olecrani). The upper surface is the insertion for the three-headed arm muscle (triceps brachii), the only extensor muscle of the forearm. Below the coronoid process, the arm flexor (brachialis) attaches.
The shaft of the ulna serves as the attachment for the deep finger flexor (flexor digitorum profundus) in the upper and middle regions, which flexes the 2nd to 5th fingers in the middle, base and end joints. In the lower quarter originates the inward square rotator (pronator quadratus), which rotates the palm downward. Two other muscles besides the deep finger flexor attach to the posterior edge of the ulna: the ulnar hand flexor (flexor carpi ulnaris), which flexes the wrist and pulls it outward, and the ulnar hand extensor (extensor carpi ulnaris), which pulls the hand upward and outward with the back of the hand.
The articular head (caput ulnae) at the lower (distal) end of the ulna ends in the styloid process, which is connected to the wrist by a cartilaginous articular disc (discus articularis or triangularis) and bears ligamentous connections.
What is the function of the ulna?
The function of the ulna is to connect the humerus to the wrist – along with the radius, which is closely connected by a membrane. The multitude of muscles that attach to the ulna allow for flexion in the elbow, wrist, and fingers, inward and outward rotation of the palm, extension and flexion of the hand, and outward splaying of the hand.
Where is the ulna located?
The ulna is one of the two long bones that connect the lower end of the upper arm to the carpal bones, and thus to the hand.
What problems can the ulna cause?
The ulna can fracture in any section, for example at the olecranon (olecranon fracture).
In an ulna plus variant, the ulna is longer than the radius due to injury or congenital, and shorter in an ulna minus variant.
The bursa at the proximal end of the ulna (bursa olecrani) can become inflamed, either as a result of an open injury or continuous mechanical stress (desk work).
