Fascia of the forearm and hand

The fascia of the forearm (fascia antebrachii) is thickened in the proximal part, reinforced with fibrous fibers, and thin distally, loosely connected to the deeper muscles and their tendons. On the back of the forearm, the fascia is thick, firmly fused with the posterior edge of the ulna. In the proximal part of the forearm, the muscles of the superficial layer begin from the fascia. In the anterior part of the forearm, 3 grooves are distinguished on the fascia: radial, median and ulnar. The radial groove (sulcus radialis) is limited by the brachioradialis muscle laterally and the radial flexor carpi radialis medially. The radial artery, two veins of the same name and the superficial branch of the radial nerve pass through it. The median groove (sulcus medianus) is located between the radial flexor of the wrist and the superficial flexor of the fingers. It contains the ulnar artery with two adjacent veins of the same name and the ulnar nerve. The ulnar groove (sulcus ulnaris) is bounded laterally by the superficial flexor of the fingers and medially by the ulnar flexor of the wrist. The median nerve and the accompanying ulnar artery pass through the depths of the median groove.

From the forearm fascia, two intermuscular septa extend deep into the forearm - anterior and posterior, attaching to the radius and dividing the subfascial space into 3 fascial beds: anterior, posterior and lateral. The anterior radial intermuscular septum runs along the radial groove of the forearm, and the posterior septum runs along the lateral edge of the brachioradialis muscle.

The anterior fascial compartment is bounded laterally by the anterior radial intermuscular septum and medially by the fascia of the forearm, which is fused with the posterior edge of the ulna. The anterior wall of this compartment is the fascia of the forearm, and the posterior wall is the anterior surface of the ulna and radius and the interosseous membrane. The anterior fascial compartment is divided into superficial and deep sections by the deep plate of the fascia of the forearm. This plate is located between the superficial and deep flexors of the fingers.

The lateral fascial compartment is located between the anterior radial intermuscular septum on the medial side, the posterior radial intermuscular septum at the back, and the fascia of the forearm on the lateral side.

The posterior fascial compartment is laterally limited by the posterior radial intermuscular septum. The medial border of this compartment is the fascia of the forearm, which is attached to the posterior edge of the ulna. The anterior wall of the posterior fascial compartment is the posterior surface of the radius and ulna and the interosseous membrane, and the posterior wall is the fascia of the forearm.

Each fascial compartment of the forearm contains muscles, as well as nerves and blood vessels. The anterior fascial compartment is the widest, with 8 muscles arranged in 4 layers. The superficial layer contains 4 muscles: the pronator teres, the flexor carpi radialis, the flexor carpi ulnaris, and the palmaris longus. The second layer contains the superficial flexor of the fingers; the third layer contains the flexor digitorum profundus and the flexor pollicis longus. The fourth layer contains one muscle, the pronator quadratus, which occupies a place in the distal part of the forearm. In the depth of the anterior fascial compartment, between the flexor digitorum profundus and the flexor pollicis longus, is the Pirogov space, filled with loose cellular tissue. Under the muscles, directly on the interosseous membrane of the forearm, lies the vascular-nerve bundle, formed by the anterior interosseous artery, veins and nerve.

In the lateral fascial compartment there are only 3 muscles: the brachioradialis muscle lies more superficially, and underneath it are the long and short extensors of the wrist.

The posterior fascial compartment contains 10 muscles that form two layers. The superficial layer contains 3 muscles: the radial extensor of the wrist, more lateral - the extensor of the little finger, and even more lateral - the extensor of the fingers (hand). The deep layer of the posterior fascial compartment contains 5 muscles: the supinator muscle (in the proximal part of the forearm), the long muscle that abducts the thumb (near the ulna), the short extensor of the thumb (near the radius), the long muscle that abducts the thumb (behind the radius and interosseous membrane), and the extensor of the index finger (near the ulna). Between the superficial and deep layers of muscles are the posterior cellular space of the forearm and the deep plate of the fascia of the forearm, which is thin in the proximal part and denser in the distal part. In the distal part, the deep plate fuses with the sagittally oriented septa under the extensor retinaculum, separating the tendons of the extensor muscles of the hand and fingers. The anterior and posterior cellular spaces of the forearm communicate with each other through openings in the interosseous membrane, where the interosseous vessels pass. In the depth of the posterior fascial bed, a vascular nerve bundle formed by the interosseous artery, veins, and deep branch of the radial nerve passes along the interosseous membrane.

In the anterior and posterior areas of the wrist, the forearm fascia reaches a considerable thickness, forming tendon retainers on the palmar and dorsal sides, which fix them, preventing the tendons from shifting when the muscles that go from the forearm to the hand and fingers contract. The retainers create the most favorable conditions for the manifestation of muscle strength.

The flexor retinaculum, or transverse carpal ligament (retinaculum flexorum, s.lig. carpi transversum-BNA), is thrown over the carpal groove in the form of a bridge, attaching to the pisiform and hamate bones medially, to the scaphoid and trapezium bones laterally. Due to the retinaculum between it and the carpal bones, covered with deep ligaments, the groove turns into a carpal canal (canalis carpi). In this canal pass 8 tendons of the superficial and deep flexors of the fingers, the median nerve and the tendon of the long flexor of the thumb. The tendons of the flexors of the fingers are located in the common synovial sheath of the flexors of the fingers (vagina synovialis communis musculorum flexorum). The tendon of the flexor pollicis longus is located in its own synovial sheath of the same name (vagina synovialis tendinis miisculi flexor pollicis longi). Both synovial sheaths extend 2-2.5 cm proximal to the flexor retinaculum.

In the distal direction, the synovial sheath of the tendon of the long flexor of the thumb ends at the level of the base of its distal phalanx. The common synovial sheath of the flexors of the fingers ends blindly in the middle of the palm, and on the ulnar side it continues along the course of the tendons of the superficial and deep flexors. going to the V finger and reaching the base of its distal (nail) phalanx. The synovial sheaths of the tendons of the I, II, III and IV fingers are isolated from the common synovial sheath and from each other. They go from the level of the metacarpophalangeal joints to the base of the distal (nail) phalanges of the II-IV fingers. At the level from the distal part of the metacarpal bones to the level of the metacarpophalangeal joints, the flexor tendons of the II-IV fingers, devoid of synovial sheaths, pass under the palmar aponeurosis in loose fibrous connective tissue.

The dense fibrous connective tissue that forms the flexor retinaculum is stratified in its medial and lateral parts. This creates two canals: the radial and ulnar canals of the wrist. The radial canal of the wrist (canalis carpi radialis) contains the tendon of the radial flexor of the wrist, surrounded by a synovial sheath (vagina tendinis musculi flexoris carpi radialis), which extends 1-2 cm above the flexor retinaculum. The ulnar canal of the wrist (canalis carpi ulnaris) contains the ulnar nerve, and the ulnar artery and veins lie outside of it.

On the back of the wrist is the extensor retinaculum (retinaculum extensorum), which is a thickening of the fascia at the level of the wrist joint. This thickening connects the anterior edge of the distal end of the radius on the lateral side and the styloid process of the ulna, as well as the ulnar collateral ligament of the wrist - on the medial side. The space under the extensor retinaculum is divided by connective tissue septa extending from the retinaculum into 6 canals, in which the tendons of the extensors of the hand and fingers pass, surrounded by synovial sheaths. The first (lateral) canal contains the tendons of the long muscle that abducts the thumb and the short extensor of the thumb. The second channel contains the tendons of the long and short radial extensors of the wrist, the third channel contains the tendon of the long extensor of the thumb, the fourth channel contains the tendons of the extensors of the fingers and index finger, as well as the posterior interosseous nerve of the forearm, the fifth channel contains the tendon of the extensor of the little finger, and the sixth (medial) channel contains the tendon of the ulnar extensor of the carpi ulnaris. The synovial sheaths of the tendons of the extensor muscles protrude from under the extensor retinaculum 2-3 cm above the level of the styloid process of the radius.

In the distal direction, the synovial sheaths continue to the middle of the metacarpal bones. The synovial sheath of the tendons of the extensor of the fingers and index finger (vagina synovialis tendinum musculorum digitorum et extensoris indicis) is the widest. The synovial sheath of the tendon of the ulnar extensor of the wrist (vagina synovialis tendinis musculi extensoris carpi ulnaris) is located on the posterior surface of the distal epiphysis of the ulna, the synovial sheath of the tendon of the extensor of the little finger is on the posterior surface of the radio-ulnar joint. All other synovial sheaths of the extensor tendons are located on the posterior surface of the diotal epiphysis of the radius.

On the palm of the hand, under the skin, there is a palmar aponeurosis (aponeurosis palmaris), which is a continuation in this place of the tendon of the long palmaris muscle, reinforced by longitudinal and transverse tendinous fibers of the superficial fascia of the palm. The apex of the palmar aponeurosis connects with the distal edge of the flexor retinaculum and with the tendon of the long palmaris muscle, and the base is directed towards the fingers. At the level of the metacarpophalangeal joints, the palmar aponeurosis divides into 4 strands directed towards the fingers and participating in the formation of fibrous sheaths of the fingers of the hand (vaginae fibrosa digitorum manus) for the tendons of the superficial and deep flexors of the II-IV fingers. On the palmar surface of the finger sheaths, transverse fiber bundles are clearly visible - the annular part of the fibrous sheaths and oblique fibers crossing with similar fibers on the other side - the cruciform part of the fibrous sheath. The fibrous canals contain tendons of the superficial and deep flexors of the fingers surrounded by synovial sheaths.

Connective tissue bundles of the palmar aponeurosis and fibrous sheaths of the fingers are woven into the skin, causing grooves to form on the surface of the skin of the palm of the hand and fingers. In the medial and lateral directions from the palmar aponeurosis, the superficial fascia covers the muscles of the elevation of the thumb and little finger (thenar and hypothenar). The superficial fascia forms 3 interfascial cellular spaces on the palm thanks to two fascial septa extending from the palmar aponeurosis to the III-V metacarpal bones. The muscles of the elevation of the thumb lie in the external interfascial space located between the synovial sheath of the tendon of the long flexor of the thumb, the III metacarpal bone and the fascial septum leading to it.

The middle interfascial cellular space is bounded on the sides by the two fascial septa mentioned above. It has two sections: superficial and deep. The superficial section contains the tendons of the superficial and deep flexors of the fingers, as well as the superficial palmar (arterial) arch. The common palmar digital arteries branch off from this arch, dividing into the proper palmar digital arteries at the level of the metacarpophalangeal joints. Branches of the median and ulnar nerves pass under the superficial palmar arch. The deep section of the middle interfascial cellular space is located under the flexor tendons, between them and the deep plate of the palmar fascia. The deep palmar arterial arch lies here, from which 4 palmar metacarpal arteries branch off. The deep section of the cellular space communicates through the carpal canal with the Pirogov cellular space, located on the anterior side of the forearm. Along the vermiform and other deep muscles, this cellular space communicates with the cellular tissue of the back of the III, IV and V fingers of the hand.

The third, medial, interfascial cellular space is limited on the lateral side by the medial fascial septum and the proper fascia, which is also attached to the 5th metacarpal bone. The muscles of the eminence of the 5th finger are located in this space. The poorly developed deep plate of the palmar fascia of the hand (interosseous palmar fascia) covers the interosseous muscles, separating them from the flexor tendons of the fingers. The proximal part of the deep plate of the palmar fascia passes onto the palmar surface of the carpal bones. On the sides of the interosseous spaces, this plate fuses with the periosteum of the metacarpal bones and with the deep transverse metacarpal ligaments. In the area of the thenar and hypothenar, a thinner fascia forms fascial beds for the corresponding muscles.

The dorsal fascia of the hand (fascia dorsalis manus) consists of two plates - superficial and deep. The superficial plate, poorly expressed, is located above the tendons of the extensors of the fingers. On the back of the fingers, this plate fuses with the tendons of their extensors. The more developed deep plate of the dorsal fascia of the hand covers the dorsal interosseous muscles and is attached to the periosteum of the dorsal surface of the metacarpal bones. At the level of the bases of the proximal phalanges of the fingers, the deep plate connects with the palmar fascia.

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