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12. 10. 2012.

Muscles flexing the wrist



Flexor carpi ulnaris
Flexor carpi radialis
Palmaris longus
Flexor digitorum superficialis
Flexor digitorum profundus
Flexor pollicis longus

Flexor carpi ulnaris

Flexor carpi ulnaris lies along the medial border of the forearm, being the most medial of the superficial flexor group. It arises from the humerus and ulna. The humeral head arises from the common flexor origin on the medial epicondyle of the humerus and the adjacent fascia. The ulnar head arises from the medial border of the olecranon and, by an aponeurotic attachment, from the upper two-thirds of the posterior border of the ulna. Between these two heads passes the ulnar nerve to gain the medial side of the flexor compartment of the forearm.
The muscle forms a long tendon about halfway down the forearm. This attaches to and invests the pisiform. The tendon is prolonged to reach the hook of the hamate and base of the fifth metacarpal by the pisohamate and pisometacarpal ligaments respectively. Occasionally, some fibres may be prolonged into abductor digiti minimi. Lateral to the tendon are the ulnar nerve and vessels.

Nerve supply

Flexor carpi ulnaris is supplied by several branches from the ulnar nerve, root value C7, 8. The skin overlying the muscle is supplied by roots C8 and T1.

Action

In conjunction with flexor carpi radialis, and to some extent palmaris longus, flexor carpi ulnaris is a flexor of the hand at the wrist. However, when working with extensor carpi ulnaris, it produces adduction or ulnar deviation of the hand at the wrist. However, when working with extensor carpi ulnaris, it produces adduction or ulnar deviation of the hand at the wrist. It also plays an important role in stabilizing the pisiform during abduction of the little finger, so that abductor digiti minimi has a firm base from which to work. As with flexor carpi radialis, flexor carpi ulnaris is an important synergist in extension of the fingers, preventing unwanted extension of the wrist.

Palpation

The tendon of flexor carpi ulnaris can easily be identified running proximally from the pisiform where it can be pinched between the thumb and index finger. In the upper medial part of the forearm, the muscle belly can be palpated when flexion of the wrist is performed against resistance.



Flexor carpi radialis

Flexor carpi radialis is a fusiform muscle and is the most lateral of the superficial flexor muscles in the lower half of the forearm. It arises from the medial epicondyle of the humerus via the common flexor tendon and the adjacent fascia. Halfway down the forearm, the muscle fibres condense to form a long tendon which passes beneath the flexor retinaculum, where it lies in its own lateral compartment within the carpal tunnel. Here the tendon is surrounded by its own synovial sheath as it grooves the trapezium. Distally the tendon inserts into the palmar surface of the bases of the second and third metacarpals. Its course in the forearm is oblique, running from medial to lateral and from above downwards. At the wrist, the tendon lies between the radial vessels laterally and median nerve medially.

Nerve supply

Flexor carpi radialis is supplied by the median nerve, root value C6, 7. The skin over the muscle is supplied by roots C6 and T1.

Action

Working with palmaris longus and flexor carpi ulnaris, flexor carpi radialis acts as a flexor of the wrist. Abduction or radial deviation of the wrist is produced by the combined action of flexor carpi radialis and extensors carpi radialis longus and brevis. Because of its oblique course in the forearm, flexor carpi radialis may aid pronation. It can also help to flex the elbow. It works in a similar way to flexor carpi ulnaris in preventing unwanted extension of the wrist when extending the fingers.

Palpation

When the wrist joint is flexed and abducted, the tendon of flexor carpi radialis can be palpated as the most lateral of the tendons on the anterior aspect of the wrist, at the level of the radial styloid process.

Palmaris longus

Palmaris longus is a small vestigial muscle, being absent in about 10% of the population. Lying centrally among the superficial flexor muscles of the forearm, palmaris longus arises from the front of the medial epicondyle of the humerus via the common flexor origin. The short muscle fibers soon form a long and slender tendon which passes distally to attach to the superficial surface of the flexor retinaculum and inserts into the apex of the palmar aponeurosis. At the wrist, the tendon lies on top of the median nerve.





Nerve supply

Palmaris longus is supplied by the median nerve, root value C8. The skin over the muscle is supplied by roots C7 and T1.

Action

Palmaris longus is a weak flexor of the wrist. However, because of its attachment to the palmar aponeurosis, it may have some slight action in flexing the metacarpophalangeal joints and it tightens the palmar fascia.

Palpation

The tendon of palmaris longus can be identified just proximal to the wrist, where it is the most central structure when flexion of the wrist is resisted. The tendon lies on the medial side of that of flexor carpi radialis.

Flexor digitorum superficialis

Flexor digitorum superficialis lies in the anterior compartment of the forearm deep to pronator teres, palmaris longus and flexors carpi radialis and ulnaris. It is superficial to flexor digitorum profundus and flexor pollicis longus. This large muscle has a long, linear origin but may be considered to arise by two heads. The medial or humeroulnar head arises from: the medial epicondyle via the common flexor tendon, the anterior part of the ulnar collateral ligament and the sublime tubercle at the upper medial part of the coronoid process of the ulna. The lateral or radial head arises from the upper two-thirds of the anterior border of the radius, which runs downwards and laterally from the radial tuberosity.
About halfway down the forearm, the muscle narrows to form four separate tendons which pass deep to the flexor retinaculum where they are arranged in two pairs to enter the hand. The superficial pair pass to the middle and ring fingers, while the deep pair pass to the index and little fingers. Within the carpal tunnel the tendons of superficialis are superficial to those of profundus, with which they share a common synovial sheath. In the palm, the tendons separate and pass towards their respective fingers, still lying superficial to the profundus tendons. At the level of the metacarpophalangeal joint, each superficialis tendon splits longitudinally into two parts. The two halves pass around the profundus tendon, twisting so that their outer surfaces unite to form a groove along which the tendon of flexor profundus passes. Prior to attaching to either side of the palmar surface of the base of the middle phalanx, the tendon splits again.
This peculiar arrangement of the superficialis tendons provides a tunnel which allows the profundus tendon to become superficial. The effect, as fat as superficialis is concerned, is to increase the lever arm of the tendon at the proximal interphalangeal joint, thereby enabling a powerful grip of the fingers to be exerted. As well as their main attachment to the middle phalanx, the tendons of superficialis also provide attachments for the vincula tendinium which convey blood vessels to the tendon. 



Nerve supply

Flexor digitorum superficialis is supplied by the median nerve, root value C7, 8, T1. The skin overlying the muscle and its tendons are supplied by roots C6, 7, 8 and T1.

Action

Flexor digitorum superficialis is primarily a flexor of the metacarpophalangeal and proximal interphalangeal joints. Because it crosses the wrist joint, it will also help flexion of the wrist if its action is continued.

Palpation

Contraction of flexor digitorum superficialis can be felt by applying deep pressure through the superficial flexor muscles in the upper part of the forearm whilst the fingers are flexed. The tendons can be palpated in a similar manner proximal to the flexor retinaculum. The muscle can be tested specifically by asking the subject to flex the proximal interphalangeal joint without flexing the distal interphalangeal joint.

Flexor digitorum profundus

Flexor digitorum profundus lies deep to superficialis on the medial side of the forearm. It arises from the medial side of the coronoid process of the ulna, the upper three-quarters of the anterior and medial surfaces of the ulna, and from the medial, middle-third of the anterior surface of the adjacent interosseus membrane. It also arises from the aponeurosis attaching flexor carpi ulnaris to the posterior border of the ulna.
The part of the muscle arising from the interosseus membrane forms a separate tendon about halfway down the forearm which passes to the index finger. The remaining tendons are not usually formed until just above the flexor retinaculum. The separate tendons, however, pass below the flexor retinaculum where they lie side-by-side, deep to those of superficialis, but within the same synovial sheath. In the palm, the four tendons pass to their respective fingers. At first, they travel deep to superficialis, but then pass superficially as they go through the tunnel formed by the superficialis tendon at the level of the metacarpophalangeal joint.
The tendon of profundus eventually inserts into the base of the palmar surface of the distal phalanx having passed through a fibro-osseous tunnel. Like the tendons of flexor digitorum superficialis, the profundus tendons are provided with vincula tendinium. 



Nerve supply

Flexor digitorum profundus has a dual nerve supply. The lateral part of the muscle, which gives off tendons to the index and middle fingers, is supplied by the anterior interosseus branch of the median nerve, root value C7, 8, T1. The medial part of the muscle, which gives off tendons to the ring and little fingers, is supplied by the ulnar nerve, root value C8, T1. The skin over the muscle is supplied by roots C7, 8, T1.

Action

The primary action of flexor digitorum profundus is flexion of the distal interphalangeal joint. However, because it crosses several other joints during its course, it also aids in flexion of the proximal interphalangeal, metacarpophalangeal and wrist joints.

Palpation

The muscular part of profundus can be palpated immediately medial to the posterior border of the ulna, where its concentration can be felt as the fingers are fully flexed from a position of extension.

Flexor pollicis longus

Flexor pollicis longus lies on the lateral side of flexor digitorum profundus. It arises from the anterior surface of the radius between the radial tuberosity above and pronator quadratus below, and the adjacent anterior surface of the interosseus membrane. Occasionally, the muscle also arises by a small slip from the medial border of the coronoid process of the ulna. The fibres pass almost to the wrist before a single tendon is formed.
The tendon of flexor pollicis longus passes below the flexor retinaculum, in its own synovial sheath, to insert into the palmar surface of the base of the distal phalanx of the thumb.

Nerve supply

Flexor pollicis longus is supplied by the anterior interosseus branch of the median nerve, root value C8, T1.

Action

Flexor pollicis longus is the only flexor of the interphalangeal joint of the thumb, and is thus vital for all gripping activities of the hand. It also flexes the metacarpophalangeal joint of the thumb and the wrist joint.

Palpation

When only the thumb is flexed, the contraction of flexor pollicis longus can be felt in the lower third of the forearm, immediately lateral to the superficial flexor tendons.



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