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1. Elbow and Proximal Radioulnar Joints These joints are described together as they have a common capsule and synovial cavity.
1. Note the intimate relationships of the brachialis and triceps muscles to the anterior and posterior parts of the elbow joint respectively, and the supinator to the proximal radioulnar joint. Remove these muscles and then remove the flexor and extensor muscles from their epicondylar origins. Take care so as not to damage the capsule of the elbow joint and the anular ligament; the latter surrounds the head of the radius and is attached to the margins of the radial notch of the ulna.
2. Define the ulnar collateral ligament of the elbow joint. This is composed of three distinct bands: anterior, posterior and oblique. The anterior band passes between the medial epicondyle of the humerus and the coronoid process of the ulna; the posterior band passes between the medial epicondyle and the olecranon process of the ulna; and the oblique band passes between the coronoid and olecranon processes.
3. Define the triangular shaped radial collateral ligament of the elbow joint which extends fanwise from the lateral epicondyle to the anular ligament.
4. Observe that the anterior and posterior parts of the capsule of the elbow joint are weak. Make a transverse cut through the anterior part of the joint capsule and examine the articular surfaces.
5. Note that the anular ligament of the proximal radioulnar joint is somewhat funnel-shaped, being wider superiorly. The ligament passes around the head of the radius and is attached to the anterior and posterior margins of the radial notch of the ulna. Cut through the anular ligament on its lateral aspect and verify its shape. This joint is part of the elbow joint.
Interosseous Membrane
Next examine the interosseous membrane which forms a bond between the radius and ulna. Remove the muscles, nerves and vessels in order to see the interosseous membrane.
3. Distal Radioulnar and Wrist Joints These two joints are considered together because the inferior radioulnar joint cannot be studied without cutting through the capsule of the wrist joint.
1. Review the flexor and extensor tendons related to the wrist joint.
2. Define the capsule of the wrist joint and observe the palmar radiocarpal and palmar ulnocarpal ligaments; the dorsal radiocarpal and dorsal ulnocarpal ligaments; and the radial and ulnar collateral ligaments.
3. Cut through the dorsal part of the capsule of the wrist joint and expose the articular surfaces. Look at the triangular articular disc, whose apex is attached to the root of the styloid process of the ulna and its base to the lower margin of the ulnar notch of the radius.
4. Intercarpal, Midcarpal, Carpometacarpal, Metacarpophalangeal and Interphalangeal Joints
1. Remove the muscles related to these joints and note the palmar, dorsal and intersseous ligaments at the intercarpal joints. Open the midcarpal joint from the dorsal aspect and examine the articular surfaces.
2. Carpometacarpal joint of the thumb. Examine the loose capsule. Open the capsule posteriorly and examine the shape of the articular surfaces. What movements are possible at this joint?
3. Next examine the strong palmar and collateral ligaments of the metacarpophalangeal joints. Note that the deep transverse metacarpal ligaments connect the medial four palmar ligaments.
4. The interphalangeal joints. Note the strong palmar and collateral ligaments.
Summary
The elbow joint is a hinge joint in which movements of flexion and extension take place. To facilitate these movements, the anterior and posterior parts of the capsule are thin. However, the collateral ligaments are strong to provide stability to the joint. The axis of movement is not entirely transverse and consequently the forearm tends to deviate outwards to produce the so-called carrying angle when the forearm is fully extended in the supine position. This angle disappears during pronation of the forearm and during flexion of the elbow. The radioulnar joints. The movements occurring at these joints are pronation and supination. The axis for these movements passes through the centre of the head of the radius and the root of the styloid process of the ulna. Pronation and supination are most effective when the elbow is semiflexed. In this position the elbow joint is most stable. The wrist joint is an ellipsoid joint in which the articular surface of the carpus extends more on to the dorsal than the palmar aspect. This explains why extension of the wrist is more than flexion. However, it should be noted that movement of the wrist joint involves simultaneous movements at the midcarpal joint. In flexion of the wrist, there is more movement taking place at the midcarpal joint than at the wrist joint. Furthermore, the range of adduction at the wrist is more than abduction. The carpometacarpal joint of the thumb is a saddle joint between the trapezium and the first metacarpal bone. Abduction and adduction occur at right angles to the plane of the palm, while flexion and extension take place in a plane parallel to the palm. In addition, rotation also occurs at this joint. Opposition of the thumb is the movement whereby the palmar surface of the thumb is brought into apposition with the palmar surfaces of the other digits.
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