The elbow is specific elbow with rheumatoid arthritis humans and other primates. The elbow joint has three different portions surrounded by a common joint capsule.
In any position of flexion or extension, the radius, carrying the hand with it, can be rotated in it. The groove running across the trochlea is, in most people, vertical on the anterior side but spirals off on the posterior side. This results in the forearm being aligned to the upper arm during flexion, but forming an angle to the upper arm during extension — an angle known as the carrying angle. 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. 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. Distally, it is prolonged down to the neck of the radius and the superior radioulnar joint. Several synovial folds project into the recesses of the joint.