ELBOW JOINT
1. This hinge joint is formed by the trochlea
and the capitulum of the humerus, and the trochlear notch of the ulna and the
head of the radius.
2. It is an extremely stable joint because the
humeral and ulnar surfaces interlock, and the capsule is very strong.
3. Extracapsular structures consist of
anterior, posterior, medial and lateral strengthening ligaments, which
contribute to joint stability.
MUSCLES AND MOVEMENTS
Because of the
structure of the elbow joint, the only two movements it allows are flexion and
extension. The biceps is the main flexor of the forearm, aided by the
brachialis; the triceps extends it.
PROXIMAL AND DISTAL
RADIOULNAR JOINTS
1. The proximal radioulnar joint is a pivot
joint formed by the rim of the head of the radius rotating in the radial notch
of the ulna, and is in the same capsule as the elbow joint.
2. The annular ligament is a strong
extracapsular ligament that encircles the head of the radius and keeps it in
contact with the radial notch of the ulna.
3. The distal radioulnar joint is a pivot
joint between the distal end of the radius and the head of the ulna.
4. Note, in addition, the presence of a
fibrous membrane linking the bones along their shafts; this interosseous
membrane is an example of the fibrous joint and prevents separation of the
bones when force is applied at either end, i.e. at the wrist or elbow.
MUSCLES AND MOVEMENTS
The forearm may be
pronated (turned palm down) or supinated (turned palm up). Pronation is caused
by the action of the pronator teres and
supination by the supinaotr and biceps muscles .
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