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The olecranon is situated at the proximal end of the ulna, one of the two bones in the forearm. [1] When the hand faces forward the olecranon faces towards the back (posteriorly). It is bent forward at the summit so as to present a prominent lip which is received into the olecranon fossa of the humerus during extension of the forearm. [2] [3]
Osborne's ligament, also Osborne's band, Osborne's fascia, Osborne's arcade, arcuate ligament of Osborne, or the cubital tunnel retinaculum, refers to either the connective tissue which spans the humeral and ulnar heads of the flexor carpi ulnaris (FCU) or another distinct tissue located between the olecranon process of the ulna and the medial epicondyle of the humerus.
Close to the elbow, the ulna has a bony process, the olecranon process, a hook-like structure that fits into the olecranon fossa of the humerus. This prevents hyperextension and forms a hinge joint with the trochlea of the humerus. There is also a radial notch for the head of the radius, and the ulnar tuberosity to which muscles attach.
A few of these fibres stretch across the olecranon fossa without attaching to it and form a transverse band with a free upper border. On the ulnar side, the capsule reaches down to the posterior part of the annular ligament. The posterior capsule is attached to the triceps tendon which prevents the capsule from being pinched during extension. [8]
The styloid process of the ulna projects from the medial and back part of the ulna. It descends a little lower than the head. The head is separated from the styloid process by a depression for the attachment of the apex of the triangular articular disk, and behind, by a shallow groove for the tendon of the extensor carpi ulnaris muscle.
On a person's distal forearm, just before the wrist, there are either two or three tendons. The tendon of the flexor carpi ulnaris is the most medial (closest to the little finger) of these. The most lateral one is the tendon of flexor carpi radialis muscle, and the middle one, not always present, is the tendon of palmaris longus.
Schematic diagram of the medial side of the elbow showing the ulnar nerve passing through the cubital tunnel. Chronic compression of the ulnar nerve in the cubital tunnel is known as cubital tunnel syndrome. [4] There are several sites of possible compression, traction or friction of the ulnar nerve as it courses behind the elbow. [5]
Beneath the neck of the radius, on the medial side, is an eminence, the radial tuberosity; its surface is divided into: . a posterior, rough portion, for the insertion of the tendon of the biceps brachii.