This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
In all joints there are two kinds of ligaments. One kind serves to retain the synovial fluid; it is a capsular ligament and is usually thin; the other kind is thick, firm, and strong, and is intended to bind the bones together and prevent their displacement and to limit movement. These two kinds of ligaments often blend together so that it is impossible to say where one begins and the other ends; at other places they are quite distinct. If an elbow-joint is distended with effusion (or wax) the distinction is readily seen. The capsule becomes distended in front and behind, while at the sides the ligaments remain closely applied to the bones; hence we learn that the anterior and posterior ligaments are capsular in their function while the lateral ligaments are retentive. These will be considered more in detail later.
While the superior radio-ulnar articulation is not considered a part of the elbow-joint proper, it is nevertheless so closely
Fig. 295. - The external lateral ligament of the elbow-joint, showing its shape. Its upper end is attached to the external condyle of the humerus: its lower ends are attached to the ulna. The circular fibres surrounding the head of the radius are called the orbicular ligament.
associated with it that it cannot be ignored. The head of the radius, in addition to its movements of flexion and extension on the humerus, possesses a motion of rotation. In order that it may rotate properly the ligaments are arranged in a peculiar manner. Its motion in respect to the ulna is a purely rotary one, so that it is bound to the ulna by a ligament which encircles its head, called the orbicular ligament. The bulk of the ligament encircles three-fourths of the head of the radius and is attached at its ends to the anterior and posterior edges of the lesser sigmoid cavity of the ulna. Its lower fibres are continuous below the lesser sigmoid cavity, forming a complete circle. The upper edge of this orbicular ligament blends with the anterior ligament in front, the posterior behind, and the external lateral at the side. We thus see that as the anterior and posterior ligaments are capsular in their function the radius is kept in place by the external lateral ligament, which branches below in the form of the letter Y to blend with the orbicular ligament. When we consider that these fibres are hardly inserted at all into the radius, but pass over it to the ulna, it is evident that this part of the joint is comparatively weak and not an excessive amount of force would be required to pull the head of the radius from beneath the orbicular ligament and so luxate it. The supinator (brevis) arises partly from the orbicular ligament and strengthens the joint somewhat.
The external lateral ligament is a strong band which is attached above to the lower portion of the lateral (external) condyle, blends with the orbicular ligament and is attached below to the ulna along the anterior and posterior edges of the lesser sigmoid cavity (Fig. 295).
The internal lateral ligament is a strong band attached above to the lower and anterior portion of the medial (internal) condyle, the groove beneath, and descends in the shape of a fan to insert into the inner edge of the coronoid process and olecranon (Fig. 296).
The anterior ligament is capsular in its nature and function, and is a broad, comparatively thin membrane which stretches between the lateral ligaments on the sides and is attached above to the upper edge of the coronoid fossa and below to the coronoid process and orbicular ligament. It sometimes possesses a few coarse fibres passing downward and outward, but it is mostly very thin, in places barely covering the lining membrane.
Fig. 296. - The internal lateral ligament of the elbow-joint, showing its fan-like shape.
The posterior ligament resembles the anterior. It blends on each side with the lateral ligaments and is attached above across the upper portion of the olecranon fossa and below to the olecranon and posterior portion of the orbicular ligament. It also has some cross fibres; but, especially at its upper attachment, it is very weak.