The ulnar is one of the two bones of the forearm. Proximally it forms a hinge joint with the humerus and distally it forms a gliding synovial joint with the triangular fibroclartilagenous complex. Several muscles of the anterior and posterior compartments of the forearm originate from the ulna, as well as part of brachialis.
The name ulnar comes from the Latin word for arm. The bone articulates proximally with the trochlea of the humerus at the humeroulnar joint, which is a hinge joint with a high degree of congruence. The word trochlea comes from the Latin word for pulley, and denotes the long curved shape of the trochlea and the trochlear notch of the ulna. The olecranon process lies at the posterior aspect of the olecranon (the triceps brachii insert here, and the supinator muscle attaches to its lateral surface). The olecranon process limits extension when it fits into the olecranon fossa of the ulna. Extension is also limited by the tautness of the ligaments surrounding the joint. The ulnar head of the pronator teres originates from the coronoid process of the ulna, as does flexor digitorum superficialis, flexor digitorum profundus. The abductor pollicis longus, extensor pollicis longus and extensor indicis all originate in part from the dorsal shaft of the ulna. A key point to remember is that flexion and extension occur at the humeroulnar joint.
shaft of the ulna is slightly concave in its shape, with the base of the bone
lying proximally, and forming the proximal radioulnar joint via the circular
annular ligament (extends from the neck of the radius to the radial notch), and
the quadrangular quadrate ligament providing inferior support to the joint.
Distally the head of the ulna articulates with the triangular fibrocartilaginous
complex at the wrist (TFCC). The TFCC articulates with the triquetrum, and also
anchors the distal surface of the ulna to the distal surface of the radius. The
ulnar styloid process is where the triangular pad of fibrocartilage (part of
the TFCC) inserts. The ulnocarpal ligaments (ulnolunate and ulnotriquetral)
also arise from the ulnar styloid process. The medial border of the radius is
attached to the lateral border of the ulna along its length by the syndesmotic
joint formed by the interosseus membrane.
Monteggia Fracture- This is a fracture of the ulnar shaft with dislocation of the radial head from the proximal radioulnar joint.
The ulnar is one of the two bones of the forearm. It forms a hinge joint with the humerus and a gliding synovial joint with the TFCC. The bone gives rise to a wide range of muscles.