The elbow joint is a complex joint comprised of multiple articular surfaces within one articular capsule. The elbow joint can be subdivided into three distinct articular interfaces — the humero-ulnar joint, the humeroradial joint, and the proximal radioulnar joint. Two distinct pairs of movement occur as a result of the articulations within the elbow joint — the hinged movements of flexion and extension, which bend and straighten the elbow, and the rotational movements of pronation and supination, which roll the hand palm up and palm down. Unlike the shoulder joint, the elbow joint has strong extrinsic ligaments that limit movements and stabilize the articulating bones.
Elbow Joint is formed of three joints which are:
Ulno-humeral joint which is articulation between trochlea of the humerus with trochlear notch of the ulna.
Radio-capitular joint which is articulation between capitulum and radial head.
Proximal radio-ulnar joint between radial head and radial notch of the ulna,is a pivot-type synovial joint with articulation between the head of the radius and the radial notch of the ulna
Bones and Joints of the Elbow Joint
The elbow itself is essentially a hinge joint, meaning it bends and straightens like a hinge. The bones of the elbow are the humerus , the ulna and the radius.There is a second joint where the end of the radius meets the humerus. This joint is complicated because the radius has to rotate so that you can turn your hand palm up and palm down. At the same time, it has to slide against the end of the humerus as the elbow bends and straightens.The joint is even more complex because the radius has to slide against the ulna as it rotates the wrist as well. As a result, the end of the radius at the elbow is shaped like a smooth knob with a cup at the end to fit on the end of the humerus.Articular cartilage is the material that covers the ends of the bones of any joint. Articular cartilage can be up to one-quarter of an inch thick in the large, weight-bearing joints.Its function is to absorb shock and provide an extremely smooth surface to make motion easier.
Ligaments of The Elbow Joint
There are three main ligaments supporting the elbow joints:
Medial Collateral Ligament: Sometimes known as the Ulnar Collateral Ligament and consists of two triangular bands, anterior and posterior. Both sections arise from the Medial Epicondyle and pass over the inside of the elbow joint. The anterior portion then attaches to the front part of the top of the Ulna, known as the Coranoid process and the posterior part to the back of the Ulna, or Olecranon process.
Lateral Collateral Ligament: Sometimes known as the Radial Collateral Ligament and is a short, narrow band which passes from the base of the Lateral Epicondlye to the Annular Ligament.
Annular Ligament: This is a band of fibres which circle the head of the Radius, maintaining contact between the Radius and Humerus
Muscles of the Elbow Joint
There are a large number of muscles which cross the elbow joint to cause flexion/extension and supination/pronation. The following are the largest and most commonly injured:
Biceps Brachii: This muscle arises from the Coracoid process and Supragleniod tubercle (both parts of the shoulder blade) and travels down the arm, crosses the elbow joint and inserts on the Radius. Its action is to flex the elbow joint and supinate the forearm.
Triceps Brachii: Originates from the Scapula and back surface of the Humerus to cross the elbow and attach to the Olecranon process (posterior Ulna). This is the main extensor of the elbow.
Brachialis: This muscle is the strongest elbow flexor when the palm is pronated. It arises from the lower half of the front of the Humerus and inserts on the Coronoid process (front bony protusion) of the Ulna.
Brachioradialis: This muscle starts at the outer edge of the lower third of the Humerus, crosses the joint and inserts at the lower end of the Radius. Its job is to flex the elbow and aid pronation and supination.
Pronator Teres: This muscle is often involved in golfers elbow (Medial Epicondylitis) and its action is to aid flexion of the elbow and pronate the forearm. It originates just above the medial epicondyle and inserts on the outer surface of the Radius.
Extensor Carpi Radialis Brevis: Most often the muscle involved in tennis elbow (Lateral Epicondylitis), its action is to extend the wrist and aid extension of the elbow. It arises from the lateral epicondyle of the Humerus and inserts on the third Metacarpal of the hand.
Blood Supply of the Elbow Joint
The arteries supplying the joint are derived from the anastomosis between the profunda and the superior and inferior ulnar collateral branches of the brachial, with the anterior, posterior, and interosseous recurrent branches of the ulnar, and the recurrent branch of the radial. These vessels form a complete anastomotic network around the joint.The largest artery in the elbow is the brachial artery that travels across the front crease of the elbow. The brachial artery splits into two branches just below the elbow: the ulnar artery and the radial artery that continue into the hand. Damage to the brachial artery can be very serious because it is the only blood supply to the hand.
Nerve supply of the Elbow Joint
The nerves of the joint are a twig from the ulnar, as it passes between the medial condyle and the olecranon; a filament from the musculocutaneous, and two from the median.
Synovial Membrane of the Elbow Joint
The synovial membrane is very extensive. It extends from the margin of the articular surface of the humerus, and lines the coronoid, radial and olecranon fossæ on that bone; it is reflected over the deep surface of the capsule and forms a pouch between the radial notch, the deep surface of the annular ligament, and the circumference of the head of the radius. Projecting between the radius and ulna into the cavity is a crescentic fold of synovial membrane, suggesting the division of the joint into two; one the humeroradial, the other the humeroulnar.
Between the capsule and the synovial membrane are three masses of fat: the largest, over the olecranon fossa, is pressed into the fossa by the Triceps brachii during the flexion; the second, over the coronoid fossa, and the third, over the radial fossa, are pressed by the Brachialis into their respective fossæ during extension.
Movements of the Elbow Joint
The different movements possible at this joint include
Flexion (touch the shoulder with the finger tips of the same side)
Extension (straighten your upper limb)
Supination (palm facing upwards)
Pronation (palm facing downwards)
The elbow-joint comprises three different portions—viz., the joint between the ulna and humerus, that between the head of the radius and the humerus, and the proximal radioulnar articulation, described below. All these articular surfaces are enveloped by a common synovial membrane, and the movements of the whole joint should be studied together. The combination of the movements of flexion and extension of the forearm with those of pronation and supination of the hand, which is ensured by the two being performed at the same joint, is essential to the accuracy of the various minute movements of the hand.
The portion of the joint between the ulna and humerus is a simple hinge-joint, and allows of movements of flexion and extension only. Owing to the obliquity of the trochlea of the humerus, this movement does not take place in the antero-posterior plane of the body of the humerus. When the forearm is extended and supinated, the axes of the arm and forearm are not in the same line; the arm forms an obtuse angle with the forearm, the hand and forearm being directed lateral-ward. During flexion, however, the forearm and the hand tend to approach the middle line of the body, and thus enable the hand to be easily carried to the face. The accurate adaptation of the trochlea of the humerus, with its prominences and depressions, to the semilunar notch of the ulna, prevents any lateral movement. Flexion is produced by the action of the Biceps brachii and Brachialis, assisted by the Brachioradialis and the muscles arising from the medial condyle of the humerus; extension, by the Triceps brachii and Anconæus, assisted by the Extensors of the wrist, the Extensor digitorum communis, and the Extensor digiti quinti proprius.
The joint between the head of the radius and the capitulum of the humerus is an arthrodial joint. The bony surfaces would of themselves constitute an enarthrosis and allow of movement in all directions, were it not for the annular ligament, by which the head of the radius is bound to the radial notch of the ulna, and which prevents any separation of the two bones laterally. It is to the same ligament that the head of the radius owes its security from dislocation, which would otherwise tend to occur, from the shallowness of the cup-like surface on the head of the radius. In fact, but for this ligament, the tendon of the Biceps brachii would be liable to pull the head of the radius out of the joint.
The head of the radius is not in complete contact with the capitulum of the humerus in all positions of the joint. The capitulum occupies only the anterior and inferior surfaces of the lower end of the humerus, so that in complete extension a part of the radial head can be plainly felt projecting at the back of the articulation.
In full flexion the movement of the radial head is hampered by the compression of the surrounding soft parts, so that the freest rotatory movement of the radius on the humerus (pronation and supination) takes place in semiflexion, in which position the two articular surfaces are in most intimate contact. Flexion and extension of the elbow-joint are limited by the tension of the structures on the front and back of the joint; the limitation of flexion is also aided by the soft structures of the arm and forearm coming into contact.
In any position of flexion or extension, the radius, carrying the hand with it, can be rotated in the proximal radioulnar joint. The hand is directly articulated to the lower surface of the radius only, and the ulnar notch on the lower end of the radius travels around the lower end of the ulna. The latter bone is excluded from the wrist-joint by the articular disk. Thus, rotation of the head of the radius around an axis passing through the center of the radial head of the humerus imparts circular movement to the hand through a very considerable arc.
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