Flexor and Extensor Retinacula-Flexor Retinaculum-Extensor Retinaculum-Carpal Tunnel-Absent Palmaris Longus-Contents of the Anterior Fascial Compartment of the Forearm-

Flexor and Extensor Retinacula

The flexor and extensor retinacula are strong bands of deep fascia that hold the long flexor and extensor tendons in position at the wrist.

Flexor Retinaculum

The flexor retinaculum is a thickening of deep fascia that holds the long flexor tendons in position at the wrist. It stretches across the front of the wrist and converts the concave anterior surface of the hand into an osteofascial tunnel, the carpal tunnel, for the passage of the median nerve and the flexor tendons of the thumb and fingers.

It is attached medially to the pisiform bone and the hook of the hamate and laterally to the tubercle of the scaphoid and the trapezium bones. The attachment to the trapezium consists of superficial and deep parts and forms a synoviallined tunnel for passage of the tendon of the flexor carpi radialis.

The upper border of the retinaculum corresponds to the distal transverse skin crease in front of the wrist and is continuous with the deep fascia of the forearm. The lower border is attached to the palmar aponeurosis

Extensor Retinaculum

The extensor retinaculum is a thickening of deep fascia that stretches across the back of the wrist and holds the long extensor tendons in position. It converts the grooves on the posterior surface of the distal ends of the radius and ulna into six separate tunnels for the passage of the long extensor tendons. Each tunnel is lined with a synovial sheath, which extends above and below the retinaculum on the tendons. The tunnels are separated from one another by fibrous septa that pass from the deep surface of the retinaculum to the bones.

The retinaculum is attached medially to the pisiform bone and the hook of the hamate and laterally to the distal end of the radius.



The upper and lower borders of the retinaculum are continuous with the deep fascia of the forearm and hand, respectively.

Carpal Tunnel

The bones of the hand and the flexor retinaculum form the carpal tunnel. The median nerve lies in a restricted space between the tendons of the flexor digitorum superficialis and the flexor carpi radialis muscles.

Absent Palmaris Longus

The palmaris longus muscle may be absent on one or both sides of the forearm in about 10% of persons. Others show variation in form, such as centrally or distally placed muscle belly in the place of a proximal one. Because the muscle is relatively weak, its absence produces no disability.

Contents of the Anterior Fascial Compartment of the Forearm

■■ Muscles: A superficial group, consisting of the pronator teres, the flexor carpi radialis, the palmaris longus, and the flexor carpi ulnaris; an intermediate group consisting of the flexor digitorum superficialis; and a deep group consisting of the flexor pollicis longus, the flexor digitorum profundus, and the pronator quadratus

■■ Blood supply to the muscles: Ulnar and radial arteries

■■ Nerve supply to the muscles: All the muscles are supplied by the median nerve and its branches, except the flexor carpi ulnaris and the medial part of the flexor digitorum profundus, which are supplied by the ulnar nerve.

Injuries to the Bones of the Hand-Dislocation of the lunate bone-Fractures of the metacarpal bones-Bennett’s fracture-Compartment Syndrome of the Forearm--Volkmann’s Ischemic Contracture

Injuries to the Bones of the Hand

Fracture of the scaphoid bone is common in young adults; unless treated effectively, the fragments will not unite, and permanent weakness and pain of the wrist will result, with the subsequent development of osteoarthritis. The fracture line usually goes through the narrowest part of the bone, which, because of its location, is bathed in synovial fluid. The blood vessels to the scaphoid enter its proximal and distal ends, although the blood supply is occasionally confined to its distal end. If the latter occurs, a fracture deprives the proximal fragment of its arterial supply, and this fragment undergoes avascular necrosis.

Deep tenderness in the anatomic snuffbox after a fall on the outstretched hand in a young adult makes one suspicious of a fractured scaphoid.

Dislocation of the lunate bone
occasionally occurs in young adults who fall on the outstretched hand in a way that causes hyperextension of the wrist joint. Involvement of the median nerve is common.

Fractures of the metacarpal bones
 can occur as a result of direct violence, such as the clenched fist striking a hard object.

The fracture always angulates dorsally. The “boxer’s fracture” commonly produces an oblique fracture of the neck of the fifth and sometimes the fourth metacarpal bones. The distal fragment is commonly displaced proximally, thus shortening the finger posteriorly.

Bennett’s fracture
is a fracture of the base of the metacarpal of the thumb caused when violence is applied along the long axis of the thumb or the thumb is forcefully abducted. The fracture is oblique and enters the carpometacarpal joint of the thumb, causing joint instability.

Fractures of the phalanges are common and usually follow direct injury.

Compartment Syndrome of the Forearm

The forearm is enclosed in a sheath of deep fascia, which is attached to the periosteum of the posterior subcutaneous border of the ulna. This fascial sheath, together with the interosseous membrane and fibrous intermuscular septa, divides the forearm into several compartments, each having its own muscles, nerves, and blood supply. There is very little room within each compartment, and any edema can cause secondary vascular compression of the blood vessels; the veins are first affected, and later the arteries.

Soft tissue injury is a common cause, and early diagnosis is critical. Early signs include altered skin sensation (caused by ischemia of the sensory nerves passing through the compartment),

pain disproportionate to any injury (caused by pressure on nerves within the compartment), pain on passive stretching of muscles that pass through the compartment (caused by muscle ischemia), tenderness of the skin over the compartment (a late sign caused by edema), and absence of capillary refill in the nail beds (caused by pressure on the arteries within the compartment). Once the diagnosis is made, the deep fascia must be incised surgically to decompress the affected compartment. A delay of as little as4 hours can cause irreversible damage to the muscles.

Volkmann’s Ischemic Contracture

Volkmann’s ischemic contracture is a contracture of the muscles of the forearm that commonly follows fractures of the distal end of the humerus or fractures of the radius and ulna. In this syndrome, a localized segment of the brachial artery goes into spasm, reducing the arterial flow to the flexor and the extensor muscles so that they undergo ischemic necrosis. The flexor muscles are larger than the extensor muscles, and they are therefore the ones mainly affected. The muscles are replaced by fibrous tissue, which contracts, producing the deformity. The arterial spasm is usually caused by an overtight cast, but in some cases the fracture itself may be responsible. The deformity can be explained only by understanding the anatomy of the region.

Three types of deformity exist:

■■ The long flexor muscles of the carpus and fingers are more contracted than the extensor muscles, and the wrist joint is flexed; the fingers are extended. If the wrist joint is extended passively, the fingers become flexed.

■■ The long extensor muscles to the fingers, which are inserted into the extensor expansion that is attached to the proximal phalanx, are greatly contracted; the metacarpophalangeal joints and the wrist joint are extended, and the interphalangeal joints of the fingers are flexed.

■■ Both the flexor and extensor muscles of the forearm are contracted. The wrist joint is flexed, the metacarpophalangeal joints are extended, and the interphalangeal joints are flexed.

Fascial Compartments of the Upper Arm-Contents of the Anterior Fascial Compartment of the Upper Arm-Muscles of the Anterior Fascial Compartment-Lymphangitis-Lymphadenitis-Biceps Brachii and Osteoarthritis of the Shoulder Joint-

Fascial Compartments of the Upper Arm

The upper arm is enclosed in a sheath of deep fascia. Two fascial septa, one on the medial side and one on the lateral side, extend from this sheath and are attached to the medial and lateral supracondylar ridges of the humerus, respectively. By this means, the upper arm is divided into an anterior and a posterior fascial compartment, each having its muscles, nerves, and arteries.

Contents of the Anterior Fascial Compartment of the Upper Arm

■■ Muscles: Biceps brachii, coracobrachialis, and brachialis

■■ Blood supply: Brachial artery

■■ Nerve supply to the muscles: Musculocutaneous nerve

■■ Structures passing through the compartment: Musculocutaneous, median, and ulnar nerves; brachial artery and basilic vein. The radial nerve is present in the lower part of the compartment.

Muscles of the Anterior Fascial Compartment

The muscles of the anterior fascial compartment ,Note that the biceps brachii is a powerful supinator, and this action is made use of in twisting the corkscrew into the cork or driving the screw into wood with a screwdriver. The biceps also is a powerful flexor of the elbow joint and a weak flexor of the shoulder joint.

 

Lymphangitis

Infection of the lymph vessels (lymphangitis) of the arm is common. Red streaks along the course of the lymph vessels are characteristic of the condition. The lymph vessels from the thumb and index finger and the lateral part of the hand follow the cephalic vein to the infraclavicular group of axillary nodes; those from the middle, ring, and little fingers and from the medial part of the hand follow the basilic vein to the supratrochlear node, which lies in the superficial fascia just above the medial epicondyle of the humerus, and thence to the lateral group of axillary nodes.

Lymphadenitis

Once the infection reaches the lymph nodes, they become enlarged and tender, a condition known as lymphadenitis.

Most of the lymph vessels from the fingers and palm pass to the dorsum of the hand before passing up into the forearm. This explains the frequency of inflammatory edema, or even abscess formation, which may occur on the dorsum of the hand after infection of the fingers or palm.

Biceps Brachii and Osteoarthritis of the Shoulder Joint

The tendon of the long head of biceps is attached to the supraglenoid tubercle within the shoulder joint. Advanced osteoarthritic changes in the joint can lead to erosion and fraying of the tendon by osteophytic outgrowths, and rupture of the tendon can occur.