The elbow is a hinge joint. This means that the operation principle of a door hinge is based on this naturally-occurring example. The elbow allows the arm to bend at the halfway point in a bi-directional arc encompassing about 150 degrees. The way in which the elbow is able to perform this function is due to the ligaments, which are incredibly strong, slightly stretchy bands of collagen fibres that join bone to bone. The range of motion of the forearm is limited by the ligaments, so that the joint does not come apart by accident. Here is an overview of those ligaments found in the elbow joint.
-Medial Collateral Ligament
The Medial Collateral Ligament (MCL) is composed of the anterior oblique ligament, the posterior oblique ligament and the small transverse ligament. The MCL begins behind the elbow and runs round the inside of the joint, controlling the range of movement from 30 - 120 degrees when the joint is flexed. The anterior oblique offers primary stabilisation from 20-120 degrees and the posterior oblique offers secondary stabilisation from 30 degrees. The transverse ligament is a small, weak connective structure which does not contribute much to the stability of the joint. The MCL is also partly responsible for connecting the humerus to the ulna.
-Lateral Collateral Ligament
The Lateral Collateral Ligament (LCL) extends from the back of the humerus around the outside of the joint and onto the ulna. This is the other ligament responsible for attaching the ulna to the humerus. It blends with the annular ligament as well, adding stability. The LCL is also responsible for limiting the range of movement of the elbow joint so that dislocation does not occur.
The Annular Ligament is a short, circular ligament which wraps round the base of the radial head and fixes it into place in the pocket formed at the end of the humerus. The annular ligament sits beneath the LCL.
There are other structures which also contribute to the stabilisation of the elbow joint, such as muscles and tendons, but this overview gives a a general description of the primary ligamentous structures which are found in the joint itself. For further information the sources below should be used, in addition to sound medical training by a recognised institution.