In primates, including humans, the elbow joint is the synovial hinge joint between the humerus in the upper arm and the radius and ulna in the forearm which allows the hand to be moved towards and away from the body. The superior radioulnar joint shares joint capsule with the elbow joint but plays no functional role at the elbow. The elbow region includes prominent landmarks such as the olecranon (the bony prominence at the very tip of the elbow), the elbow pit, and the lateral and medial epicondyles. The name for the elbow in Latin is cubitus, and so the word cubital is used in some elbow related terms, as in cubital nodes for example.
The elbow joint and the superior radioulnar joint are enclosed by a single fibrous capsule. The capsule is strengthened by ligaments at the sides but relatively weak in front and behind.
On the anterior side the capsule consists mainly of longitudinal fibres. However, some bundles among these fibers run obliquely, thicken and strengthen the capsule, and are referred to as the capsular ligament. Deep fibres of the brachialis muscle insert anteriorly into the capsule and act to pull it and the underlying membrane during flexion in order to prevent them from being pinched.
On the posterior side the capsule is thin and mainly composed of transverse fibres. 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.