JOINTS OF SHOULDER REGION

AND BACK OF FOREARM AND HAND

Examine the joints of the shoulder girdle:

1. The sternoclavicular joint: Detach the tendinous sternal head of the sternocleidomastoid muscle. Note the capsule. Detach the subclavius from its costal origin. Look for the important costoclavicular ligament that extends from the inferior surface of the medial end of the clavicle to the first rib and costal cartilage. This is an accessory ligament of the joint. It prevents excessive forward and backward movement and also upward displacement of the medial end of the clavicle. Cut downwards through the upper part of the capsule close to the sternum and carefully pull the clavicle laterally to see the articular disc. Note that the disc is attached to the upper part of the medial end of the clavicle above, to the first costal cartilage below, and anteriorly and posteriorly to the capsule.

2. Now continue to work on the free upper limb.

3. The acromioclavicular joint: Note this joint and its capsule. Look for the coracoclavicular ligament stretching between the inferior surface of the clavicle and the superior surface of the coracoid process. This ligament is an accessory ligament. Observe the coracoacromial ligament extending from the horizontal part of the coracoid process to the apex of the acromion process.

4. The shoulder joint: Define the capsule and note the tendons of the rotator cuff which are fused to it. Cut the subscapularis medial to its insertion, reflect the two parts and identify the subscapular bursa deep to the subscapularis tendon and note that it communicates with the shoulder joint. Detach the short head of biceps and coracobrachialis from their origin on the coracoid process. Identify the tendon of the long head of the biceps lying deep to the transverse humeral ligament which stretches across the upper part of the intertubercular groove. Note that the coracohumeral ligament extends from the root of the coracoid process (above the supraglenoid tubercle) towards the greater tubercle of the humerus. This strengthens the upper part of the capsule. Observe the laxity of the capsule of the joint and note its attachment to the anatomical neck of the humerus except inferiorly where it passes down for 1cm on to the shaft of the bone. This is the weakest and least protected part of the capsule. Carefully cut the remaining rotator cuff muscles around the shoulder joint.

(a)Make a vertical incision through the posterior part of the capsule and rotate the head of the humerus medially. Try to view the glenohumeral ligaments passing from the anterior margin of the glenoid cavity towards the anatomical neck of the humerus. Now cut through the anterior part of the capsule and identify the origin of the long head of the biceps from the supraglenoid tubercle of the scapula. Note the difference in the size of the humeral and scapular articular surfaces.

(b) Identify the labrum glenoidale attached to the margins of the glenoid cavity.

BACK OF FOREARM AND HAND

1. Now make the following incisions on the posterior aspect of the forearm and hand:

(a)a median incision from the middle of the forearm down to the root of the middle finger;

(b) a transverse incision across the wrist;

(c) a curved incision at the level of the heads of the metacarpal bones; and

(d) a longitudinal incision along the middle of each digit to the nail bed; Reflect the skin flaps.

2. Clean the dorsal venous arch which lies over the posterior aspect of the metacarpal region and note the commencement of the basilic and cephalic veins from the ulnar and radial sides of the arch respectively.

3. Note that the dorsal branch of the ulnar nerve pierces the deep fascia above the wrist on the medial side of the forearm. This nerve supplies the medial one and a half digits. The superficial branch of the radial nerve supplies the remaining digits. It can be seen in the lower lateral part of the forearm.

4. Define the extensor retinaculum which is attached to the lower end of the radius laterally and the pisiform and triquetral medially. It retains the tendons in their position. Remove the deep fascia and open the extensor retinaculum with a scalpel.

5. Define the three marginal muscles of the forearm:

(a)brachioradialis arising from the upper part of the lateral supracondylar ridge of the humerus and gaining insertion into the lower lateral end of the radius;

(b) extensor carpi radialis longus passing from the lower part of the lateral supracondylar ridge to the base of the second metacarpal bone;

(c) extensor carpi radialis brevis extending from the lateral epicondyle of the humerus to the base of the third metacarpal. Note, once again, the nerve supply from the trunk of the radial nerve to the first two muscles and to the extensor carpi radialis brevis from the deep branch of the radial nerve which you will see later.

6. Now examine the three superficial extensors:

(a)extensor digitorum;

(b) extensor digiti minimi; and

(c) extensor carpi ulnaris.

These three muscles have a common origin from the lateral epicondyle of the humerus. Trace the extensor digitorum into the hand where it splits into four tendons for the medial four digits. Note that the extensor digiti minimi fuses with the extensor digitorum tendon for the little finger. Next trace the extensor carpi ulnaris to its insertion into the base of the fifth metacarpal bone.

7. Divide the extensor digitorum, extensor digiti minimi and extensor carpi ulnaris midway between their origin and insertion to bring into view the deep group of five muscles. Study their attachments and follow them to their insertion. From above downwards, these are:

(a)the supinator, passing from the lateral epicondyle of the humerus and supinator crest of the ulna to the upper third of the radius. Note how the muscle winds round the posterior surface of the radius;

(b) abductor pollicis longus taking origin from the upper posterior surfaces of both radius and ulna, and gaining insertion into the base of the first metacarpal;

(c) extensor pollicis brevis arising from the posterior surface of the radius and inserting into the base of the proximal phalanx of the thumb; Observe that the tendons of the last two muscles run side by side on the lateral aspect of the wrist;

(d) extensor pollicis longus taking origin from the posterior surface of the ulna and gaining insertion into the base of the terminal phalanx of the thumb; note that the tendon passes medial to the dorsal tubercle of the radius on the posterior aspect of the distal end of the radius; and

(e) extensor indicis originating from the lower part of the posterior surface of the ulna and fusing with the extensor digitorum tendon for the index finger.

8. Trace the deep branch of the radial nerve through the supinator and note that it continues as the posterior interosseous nerve. In its lower part, the nerve accompanies the posterior interosseous artery. The posterior interosseous nerve supplies the superficial and deep extensor muscles.

9. Again trace the extensor tendons as they pass under the extensor retinaculum. Note that they lie in their separate osteofascial compartments. As they lie in these compartments, they are covered by synovial sheaths.

10. Identify once again the tendons of the extensor digitorum. Note that the tendons to the index and little fingers are joined by the tendons of the extensor indicis and extensor digiti minimi respectively. Observe that the tendons begin to expand towards the digits where they form the extensor expansions. These expansions also receive contributions from the lumbrical and interossei muscles in the hand. Trace the slips from the expansions to their insertions into the bases of the intermediate and distal phalanges.

1. Near the wrist find the radial artery passing backwards beneath the tendons of the abductor pollicis longus, extensor pollicis brevis and extensor pollicis longus to enter the palm from behind between the two heads of the first dorsal interosseous muscle in the first intermetacarpel space.

Summary

The sternoclavicular joint, though classified as a saddle joint, permits varying types of movements of the clavicle such as elevation, depression, forward and backward movements as well as rotation. The strength of this joint depends largely on the strength of the ligaments. In particular, the costoclavicular ligament and the interarticular disc check the upward displacement of the medial end of the clavicle. Consequently, dislocation of the medial end of the clavicle does not usually occur. The shoulder joint is a ball and socket joint in which mobility is greatly increased at the expense of stability. The strength of the joint depends chiefly on the rotator cuff muscles that are fused to the capsule of the joint. The joint is least protected inferiorly and consequently dislocations commonly occur here. The plane of the joint is set obliquely so that the arm is carried forwards and medially during flexion and backwards and laterally during extension. Abduction is initiated by the supraspinatus and further carried out by the deltoid. As abduction proceeds towards a vertical position, the humerus is rotated laterally. It must also be borne in mind that during movements of the shoulder joint, simultaneous movements occur at the sternoclavicular and acromioclavicular joints. Consequently, any restriction of movements of these joints will indirectly affect the movements of the shoulder joint. Moreover, movements of the shoulder joint are assisted by an excursion of the scapula on the thoracic wall. Therefore, any paralysis of muscles which moves the scapula will restrict the range of movement at the shoulder joint. Indeed, in abduction of the arm through a possible 180��, scapular rotation by itself contributes to about a third of the total movement. The muscles of the back of the forearm can be classified into superficial and deep groups. The superficial set comprises the brachioradialis, extensor carpi radialis longus and brevis which are situated laterally (marginal group) and the extensor digitorum, extensor digiti minimi and extensor carpi ulnaris which occupy the dorsal aspect of the forearm. The deep group is formed by the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus and the extensor indicis. All these muscles are supplied by the radial nerve or its branches. Consequently, in cases of injury to the radial nerve, the extensor muscles will be paralysed leading to a condition known as wrist drop.