The Hand
The cutaneous innervation of the hand
With regards to the cutaneous innervation of the hand, the ulnar nerve supplies the palmar and dorsal surface of the medial third of the hand, simultaneously with the palmar and dorsal aspects of the medial 1½ finger. The median nerve supplies the skin over the thenar eminence and the central part of the palm, the palmar surface of the lateral 3½ fingers and the dorsal surface of the distal 1/2 of the lateral 3½ fingers. The radial nerve supplies the skin of the lateral 2/3 of the dorsal surface of the hand and over the proximal phalanges of the lateral 3½ fingers. The radial nerve also supplies a small area of the skin on the palmar surface to the thenar eminence.
The palmaris brevis muscle
The skin of the palm, is considered to be thick skin, and has creases that increase the efficiency to grip. The superficial fascia of the palm contains the palmar cutaneous branch of the ulnar and median nerves, beside palmaris brevis that is used in cupping the palm of the hand in gripping. This muscle originates from the flexor retinaculum along with the palmar aponeurosis, the fleshy fibres are inserted into the skin of the hand. It is supplied by the superficial branch of the ulnar nerve.
The palmar aponeurosis
The deep fascia of the palm is specialised to form the palmar aponeurosis in the palm, the flexor retinaculum at the wrist and the fibrous flexor sheaths in the fingers. The palmar aponeurosis is triangular in shape, which forms the central deep fascia of the palm, and fixes the skin of the palm to improve grip, as well as providing protection of the underlying structures. Its apex fuses with the flexor retinaculum and receives the insertion of the tendon of palmaris longus. At its base it divides into four slips opposite the heads of the metacarpals of the medial four fingers, which in turn divide into two parts continuing with the fibrous flexor sheath of the digits. The lateral margin of the palmar apponeurosis is connected to the deep fascia that covers the thenar muscles, whereas the medial edge is connected to the deep fascia that covers the hypothenar muscles.
With regards to the cutaneous innervation of the hand, the ulnar nerve supplies the palmar and dorsal surface of the medial third of the hand, simultaneously with the palmar and dorsal aspects of the medial 1½ finger. The median nerve supplies the skin over the thenar eminence and the central part of the palm, the palmar surface of the lateral 3½ fingers and the dorsal surface of the distal 1/2 of the lateral 3½ fingers. The radial nerve supplies the skin of the lateral 2/3 of the dorsal surface of the hand and over the proximal phalanges of the lateral 3½ fingers. The radial nerve also supplies a small area of the skin on the palmar surface to the thenar eminence.
The palmaris brevis muscle
The skin of the palm, is considered to be thick skin, and has creases that increase the efficiency to grip. The superficial fascia of the palm contains the palmar cutaneous branch of the ulnar and median nerves, beside palmaris brevis that is used in cupping the palm of the hand in gripping. This muscle originates from the flexor retinaculum along with the palmar aponeurosis, the fleshy fibres are inserted into the skin of the hand. It is supplied by the superficial branch of the ulnar nerve.
The palmar aponeurosis
The deep fascia of the palm is specialised to form the palmar aponeurosis in the palm, the flexor retinaculum at the wrist and the fibrous flexor sheaths in the fingers. The palmar aponeurosis is triangular in shape, which forms the central deep fascia of the palm, and fixes the skin of the palm to improve grip, as well as providing protection of the underlying structures. Its apex fuses with the flexor retinaculum and receives the insertion of the tendon of palmaris longus. At its base it divides into four slips opposite the heads of the metacarpals of the medial four fingers, which in turn divide into two parts continuing with the fibrous flexor sheath of the digits. The lateral margin of the palmar apponeurosis is connected to the deep fascia that covers the thenar muscles, whereas the medial edge is connected to the deep fascia that covers the hypothenar muscles.
Figure1: Palmar aponeurosis and palmaris brevis.
Figure2: Palmar aponeurosis.
The flexor retinaculum and the carpal tunnel
A strong fibrous band called the flexor retinaculum stretches across the concavity of the carpal bones and converts it into a tunnel for the passage of the flexor tendons into the palm. It is attached laterally to the scaphoid tubercle and the trapezium, and medially to the pisiform and the hook of the hamate.
The structures passing superficial to the flexor retinaculum
The structures passing superficial to the retinaculum include the ulnar nerve and artery, the palmar cutaneous branches of the ulnar and the median nerves, and the tendon of the palmaris longus.
The structures passing deep to the flexor retinaculum
The structures passing deep to the flexor retinaculum are: the median nerve, the tendon of the flexor carpi radialis and its synovial sheath which passes in a separate compartment in front of the trapezium, the tendons of the flexor digitorum superficialis, flexor digitorum profundus, the tendon of flexor pollicis longus, the ulnar bursa (common synovial sheath surrounding the tendons of the flexor digitorum profundus and superficialis), and the synovial sheath of flexor pollicis longus.
A strong fibrous band called the flexor retinaculum stretches across the concavity of the carpal bones and converts it into a tunnel for the passage of the flexor tendons into the palm. It is attached laterally to the scaphoid tubercle and the trapezium, and medially to the pisiform and the hook of the hamate.
The structures passing superficial to the flexor retinaculum
The structures passing superficial to the retinaculum include the ulnar nerve and artery, the palmar cutaneous branches of the ulnar and the median nerves, and the tendon of the palmaris longus.
The structures passing deep to the flexor retinaculum
The structures passing deep to the flexor retinaculum are: the median nerve, the tendon of the flexor carpi radialis and its synovial sheath which passes in a separate compartment in front of the trapezium, the tendons of the flexor digitorum superficialis, flexor digitorum profundus, the tendon of flexor pollicis longus, the ulnar bursa (common synovial sheath surrounding the tendons of the flexor digitorum profundus and superficialis), and the synovial sheath of flexor pollicis longus.
Figure3: Flexor retinaculum.
Attachment of the flexor retinaculum
The flexor retinaculum is also the origin of some of the thenar muscles, the hypothenar muscles and palmaris brevis, and form the insertion of palmaris longus.
Fibrous Flexor Sheaths of the Fingers
The fibrous flexor sheaths of the fingers are mainly comprised from the thickened and arched deep fascia of the fingers. They are attached to the sides of the phalanges and extend from the head of the metacarpal to the base of the distal phalanx, playing a role in holding the flexor tendons in position during the flexion of the digits. The fibrous flexor sheath forms a blind osteofascial tunnel in which the flexor tendons of the fingers lie. This blind ended tunnel contains the tendon of the flexor pollicis longus, passing to the thumb, and the tendons of the flexor digitorum profundus and superficialis, passing to the medial four fingers of the hand.
The flexor retinaculum is also the origin of some of the thenar muscles, the hypothenar muscles and palmaris brevis, and form the insertion of palmaris longus.
Fibrous Flexor Sheaths of the Fingers
The fibrous flexor sheaths of the fingers are mainly comprised from the thickened and arched deep fascia of the fingers. They are attached to the sides of the phalanges and extend from the head of the metacarpal to the base of the distal phalanx, playing a role in holding the flexor tendons in position during the flexion of the digits. The fibrous flexor sheath forms a blind osteofascial tunnel in which the flexor tendons of the fingers lie. This blind ended tunnel contains the tendon of the flexor pollicis longus, passing to the thumb, and the tendons of the flexor digitorum profundus and superficialis, passing to the medial four fingers of the hand.
Figure4: Fibrous digital sheath.
Flexor Synovial Sheaths of the Hand
The flexor synovial sheath of the hand is a sort of bursa that contains the tendons passing in the osteofacial and carpal tunnels. The functions of the synovial sheath are to lubricate and reduce friction between the tendons passing through the tunnels. The flexor synovial sheaths of the hand are classified according to their position, as follows: the digital synovial sheaths, which line the osteofacial tunnels of the digits and the carpal synovial sheaths which line the carpal tunnel.
The digital synovial sheaths
The digital synovial sheaths independently cover the 2nd, 3rd and 4th fingers. Each digital synovial sheath ends proximally at the head of the metacarpal and distally to the insertion of the long flexor tendon. It continues proximally with the ulnar bursa (in the case of the little finger) and also continuous proximally with the radial bursa (in the case of the thumb).
The carpal synovial sheaths
The carpal synovial sheaths form the common flexor synovial sheath (ulnar bursa), the synovial sheath of flexor pollicis longus (radial bursa) and the synovial sheath of flexor carpi radialis. The common flexor synovial sheath is a large synovial sac passing deep to the flexor retinaculum (carpal tunnel), and encloses the tendons of flexors digitorum superficialis and profundus. The sheath starts just proximal to the flexor retinaculum and ends in the middle of the palm; its lower medial end is continuous with the digital synovial sheath of the little finger. The synovial sheath of flexor pollicis longus (radial bursa) surrounds the tendon of flexor pollicis longus, usually beginning one inch proximal to the flexor retinaculum; its lower part is continuous with the digital synovial sheath of the thumb. The synovial sheath of flexor carpi radialis extends distally to the insertion of that tendon.
The flexor synovial sheath of the hand is a sort of bursa that contains the tendons passing in the osteofacial and carpal tunnels. The functions of the synovial sheath are to lubricate and reduce friction between the tendons passing through the tunnels. The flexor synovial sheaths of the hand are classified according to their position, as follows: the digital synovial sheaths, which line the osteofacial tunnels of the digits and the carpal synovial sheaths which line the carpal tunnel.
The digital synovial sheaths
The digital synovial sheaths independently cover the 2nd, 3rd and 4th fingers. Each digital synovial sheath ends proximally at the head of the metacarpal and distally to the insertion of the long flexor tendon. It continues proximally with the ulnar bursa (in the case of the little finger) and also continuous proximally with the radial bursa (in the case of the thumb).
The carpal synovial sheaths
The carpal synovial sheaths form the common flexor synovial sheath (ulnar bursa), the synovial sheath of flexor pollicis longus (radial bursa) and the synovial sheath of flexor carpi radialis. The common flexor synovial sheath is a large synovial sac passing deep to the flexor retinaculum (carpal tunnel), and encloses the tendons of flexors digitorum superficialis and profundus. The sheath starts just proximal to the flexor retinaculum and ends in the middle of the palm; its lower medial end is continuous with the digital synovial sheath of the little finger. The synovial sheath of flexor pollicis longus (radial bursa) surrounds the tendon of flexor pollicis longus, usually beginning one inch proximal to the flexor retinaculum; its lower part is continuous with the digital synovial sheath of the thumb. The synovial sheath of flexor carpi radialis extends distally to the insertion of that tendon.
Figure5:Tendons of flexor digitorum superficialis and profundus.
The fascial spaces of the hand
The hand is divided into fascial compartments by the lateral and medial palmar septa, which extend from the palmar aponeurosis to the front of the third and fifth metacarpal bones, respectively. The lateral (thenar) compartment is located just lateral to the lateral palmar septum and contains the thenar muscles. The medial (hypothenar) compartment lies medially to the medial palmar septum and contains the hypothenar muscles. Another compartment is the intermediate compartment (midpalmar space), which is situated between the lateral and medial palmar septa, behind the palmar aponeurosis and contains the second, third, and fourth lumbrical muscles. The midpalmar space lies between the tendons of the long flexors of the middle, ring, and little fingers anteriorlly and the third, fourth, and fifth interossei posteriorlly.
The hand is divided into fascial compartments by the lateral and medial palmar septa, which extend from the palmar aponeurosis to the front of the third and fifth metacarpal bones, respectively. The lateral (thenar) compartment is located just lateral to the lateral palmar septum and contains the thenar muscles. The medial (hypothenar) compartment lies medially to the medial palmar septum and contains the hypothenar muscles. Another compartment is the intermediate compartment (midpalmar space), which is situated between the lateral and medial palmar septa, behind the palmar aponeurosis and contains the second, third, and fourth lumbrical muscles. The midpalmar space lies between the tendons of the long flexors of the middle, ring, and little fingers anteriorlly and the third, fourth, and fifth interossei posteriorlly.
Figure6: Superficial palmar arch.
The pulp space of the fingers
The pulp space of the fingers is considered to be subcutaneous tissue at the tips of the fingers and thumb, and it is divided into compartments by fibrous septa, which pass from the skin to the periosteum of the terminal phalanx. These compartments are full of fat and are passed through by branches of the digital arteries.
The superficial palmar arch
The superficial palmar arch is formed mainly by the ulnar artery beside the superficial palmar branch of the radial artery. It lies superficial to the long flexor tendons and digital branches of the median nerve, but deep to the palmar aponeurosis. It has two branches, one palmar digital artery (for the medial side of the little finger) and the other for the three common palmar digital arteries, that descend in the 2nd, 3rd, and 4th intermetacarpal spaces, each one joined by the palmar metacarpal branch from the deep palmar arch before dividing into two palmar digital arteries.
The pulp space of the fingers is considered to be subcutaneous tissue at the tips of the fingers and thumb, and it is divided into compartments by fibrous septa, which pass from the skin to the periosteum of the terminal phalanx. These compartments are full of fat and are passed through by branches of the digital arteries.
The superficial palmar arch
The superficial palmar arch is formed mainly by the ulnar artery beside the superficial palmar branch of the radial artery. It lies superficial to the long flexor tendons and digital branches of the median nerve, but deep to the palmar aponeurosis. It has two branches, one palmar digital artery (for the medial side of the little finger) and the other for the three common palmar digital arteries, that descend in the 2nd, 3rd, and 4th intermetacarpal spaces, each one joined by the palmar metacarpal branch from the deep palmar arch before dividing into two palmar digital arteries.
Figure7: Thenar and hypothenar eminence.
The Short muscles of the Little Finger (Hypothenar eminence)
The short muscles of the little finger are located medially to the medial palmar septum and formed by 3 short muscles: the abductor, flexor and opponens digiti minimi. Combined they form the hypothenar eminence of the little finger. The deep branch of the ulnar nerve supplies all these muscles.
Abductor digiti minimi
Abductor digiti minimi helps in abduction of the little finger
Origin
It originates from the pisiform bone, pisohamate ligament, and the flexor carpi ulnaris tendon.
Insertion
It is inserted into the medial side of the base of the proximal phalanx of the little finger and in the extensor expansion of the little finger.
Nerve supply
The deep branch of the ulnar nerve supplies this muscle.
Figure8: Abductor pollicis brevis and abductor digiti minimi.
Flexor digiti minimi brevis
Flexor digiti minimi brevis flexes the proximal phalanx of the little finger.
Origin
It originates from the medial part of the flexor retinaculum and the hook of hamate.
Insertion
It is inserted into the medial side of the base of the proximal phalanx of the little finger.
Nerve supply
The deep branch of the ulnar nerve.
Flexor digiti minimi brevis flexes the proximal phalanx of the little finger.
Origin
It originates from the medial part of the flexor retinaculum and the hook of hamate.
Insertion
It is inserted into the medial side of the base of the proximal phalanx of the little finger.
Nerve supply
The deep branch of the ulnar nerve.
Figure9: Flexor digiti minimi brevis and abductor digiti minimi.
Opponens digiti minimi
Opponens digiti minimi rotates the fifth metacarpal laterally.
Origin
It originates from the hook of the hamate and the related medial part of the flexor retinaculum.
Insertion
It is inserted into the medial half of the palmar surface of the fifth metacarpal bone.
Opponens digiti minimi rotates the fifth metacarpal laterally.
Origin
It originates from the hook of the hamate and the related medial part of the flexor retinaculum.
Insertion
It is inserted into the medial half of the palmar surface of the fifth metacarpal bone.
Figure10: Opponens pollicis and opponens digiti minimi.
Figure11: Opponens pollicis and opponens digiti minimi.
The Short Muscles of the Thumb (Thenar eminence)
The short muscles of the thumb are four in number and occupy the lateral compartment of the hand, the first three are (the the abductor, flexor and opponens pollicis brevis) are generally supplied by the recurrent branch of the median nerve. However, the fourth muscle (the adductor pollicis) is supplied by a deep branch of the ulnar nerve.
Abductor pollicis brevis
Abductor pollicis brevis helps in abduction of the thumb.
Origin
It originates from the flexor retinaculum, tubercle of the scaphoid and the trapezium.
Insertion
It is inserted into the lateral side of the base of the proximal phalanx of the thumb and in the extensor expansion of the thumb.
Nerve supply
It is supplied by the recurrent branch of the median nerve.
The short muscles of the thumb are four in number and occupy the lateral compartment of the hand, the first three are (the the abductor, flexor and opponens pollicis brevis) are generally supplied by the recurrent branch of the median nerve. However, the fourth muscle (the adductor pollicis) is supplied by a deep branch of the ulnar nerve.
Abductor pollicis brevis
Abductor pollicis brevis helps in abduction of the thumb.
Origin
It originates from the flexor retinaculum, tubercle of the scaphoid and the trapezium.
Insertion
It is inserted into the lateral side of the base of the proximal phalanx of the thumb and in the extensor expansion of the thumb.
Nerve supply
It is supplied by the recurrent branch of the median nerve.
Flexor pollicis brevis
Flexor pollicis brevis plays a role in flexing the proximal phalanx of the thumb.
Origin
It originates from the flexor retinaculum and trapezium, but it also has some deep fibres from the trapezoid and capitate and related ligaments.
Insertion
It is inserted into the lateral side of the base of the proximal phalanx of the thumb.
Nerve supply
It is supplied by the recurrent branch of the median nerve.
Flexor pollicis brevis plays a role in flexing the proximal phalanx of the thumb.
Origin
It originates from the flexor retinaculum and trapezium, but it also has some deep fibres from the trapezoid and capitate and related ligaments.
Insertion
It is inserted into the lateral side of the base of the proximal phalanx of the thumb.
Nerve supply
It is supplied by the recurrent branch of the median nerve.
Figure12: Flexor pollicis brevis and flexor digiti minimi.
Figure13: Muscles of the thumb.
Opponens pollicis
Opponens pollicis opposes the thumb to the other fingers by flexing the first metacarpal on the trapezium.
Origin
It originates from the tubercle of trapezium and the adjacent flexor retinaculum.
Insertion
It is inserted into the lateral half of the anterior surface of the first metacarpal bone.
Nerve supply
It is supplied by the recurrent branch of the median nerve.
Opponens pollicis opposes the thumb to the other fingers by flexing the first metacarpal on the trapezium.
Origin
It originates from the tubercle of trapezium and the adjacent flexor retinaculum.
Insertion
It is inserted into the lateral half of the anterior surface of the first metacarpal bone.
Nerve supply
It is supplied by the recurrent branch of the median nerve.
Adductor pollicis
Adductor pollicis helps in the adduction of the thumb.
Origin
Adductor pollicis has two heads, as follows: the oblique head which originates from the capitate and the adjacent bases of the second and third metacarpals, and the transverse head originates from the front of the third metacarpal.
Insertion
It is inserted into the medial side of the base of the proximal phalanx of the thumb and into the extensor expansion of the thumb.
Nerve supply
It is supplied by the deep branch of the ulnar nerve.
Adductor pollicis helps in the adduction of the thumb.
Origin
Adductor pollicis has two heads, as follows: the oblique head which originates from the capitate and the adjacent bases of the second and third metacarpals, and the transverse head originates from the front of the third metacarpal.
Insertion
It is inserted into the medial side of the base of the proximal phalanx of the thumb and into the extensor expansion of the thumb.
Nerve supply
It is supplied by the deep branch of the ulnar nerve.
Figure14: Adductor pollicis.
Figure15: Median nerve.
Median Nerve in the Hand
The median nerve passes through the carpal tunnel into the hand just below the flexor retinaculum. It terminates at the distal border of the flexor retinaculum by splitting into recurrent and palmar digital divisions. The recurrent division originates from its lateral side and provides four muscular branches which supply a number of muscles, including: abductor pollicis brevis, flexor pollicis brevis, opponens pollicis and the first lumbrical muscle. It also has palmar digital branches which supply the lateral two lumbricals. Cutaneous branches are also present to supply the palmar surface of the lateral three and a half fingers and the distal part of the dorsal surface of the same fingers.
The median nerve passes through the carpal tunnel into the hand just below the flexor retinaculum. It terminates at the distal border of the flexor retinaculum by splitting into recurrent and palmar digital divisions. The recurrent division originates from its lateral side and provides four muscular branches which supply a number of muscles, including: abductor pollicis brevis, flexor pollicis brevis, opponens pollicis and the first lumbrical muscle. It also has palmar digital branches which supply the lateral two lumbricals. Cutaneous branches are also present to supply the palmar surface of the lateral three and a half fingers and the distal part of the dorsal surface of the same fingers.
Figure16: Ulnar nerve and artery.
Ulnar Nerve in the Hand
The ulnar nerve is the main nerve in the hand. It passes into the hand superficial to the flexor retinaculum on the lateral side of the pisiform and medial to the ulnar artery. It terminates just distal to the flexor retinaculum by dividing into superficial and deep terminal branches. The superficial branch provides a muscular branch and cutaneous branches. The muscular branch supplies palmaris brevis. The cutaneous branches supply the medial side of the little finger and the adjacent sides of the ring and little fingers. The superficial branch passes subcutaneously between the pisiform and hook of the hamate. The deep branch accompanies the deep branch of the ulnar artery and runs between abductor digiti minimi and flexor digiti minimi, passing through opponens digiti minimi before joining the course of the deep palmar arch posterior to the long flexor tendons. It passes in the concavity of the deep palmar arch giving the following branches: muscular branches to the three hypothenar muscles, which are abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi. It also supplies the two medial lumbricals, the four dorsal interossei, the four palmar interossei and adductor pollicis. It also supplies the wrist joint with articular branches
The ulnar nerve is the main nerve in the hand. It passes into the hand superficial to the flexor retinaculum on the lateral side of the pisiform and medial to the ulnar artery. It terminates just distal to the flexor retinaculum by dividing into superficial and deep terminal branches. The superficial branch provides a muscular branch and cutaneous branches. The muscular branch supplies palmaris brevis. The cutaneous branches supply the medial side of the little finger and the adjacent sides of the ring and little fingers. The superficial branch passes subcutaneously between the pisiform and hook of the hamate. The deep branch accompanies the deep branch of the ulnar artery and runs between abductor digiti minimi and flexor digiti minimi, passing through opponens digiti minimi before joining the course of the deep palmar arch posterior to the long flexor tendons. It passes in the concavity of the deep palmar arch giving the following branches: muscular branches to the three hypothenar muscles, which are abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi. It also supplies the two medial lumbricals, the four dorsal interossei, the four palmar interossei and adductor pollicis. It also supplies the wrist joint with articular branches
The Long Flexor Tendons in the Hand
A number of tendons are present in the hand as described below:
- The tendon of flexor pollicis longus that enters the palm posterior to the flexor retinaculum and is inserted into the terminal phalanx of the thumb,
- The tendons of flexor digitorum superficialis that has four tendons for the medial four fingers and travels into the palm behind the flexor retinaculum opposite the proximal phalanx, each of these tendon divides into two to allow the passage of the tendon of flexor digitorum profundus. The two divisons reunite again and finally divide and are inserted into the sides of the shaft of the middle phalanx.
- Other tendons include the tendons of flexor digitorum profundus that forms four tendons for the medial four fingers, entering the palm deep to the flexor retinaculum and giving origin to the four lumbricals. These tendons pass through the opening in the tendon of flexor digitorum superficialis to be inserted into the palmar surface of the base of the distal phalanx
Figure17: Lumbricls and flexor digitorum profundus tendons.
The Lumbrical Muscles in the Hand
There are four lumbrical muscles in each hand and their action is to flex the metacarpophalangeal joint and extend the interphalangeal joints at the same time.
Origin
They originate from the tendons of flexor digitorum profundus in the palm. The medial two lumbricals are bipennate. The first one originates from the tendon of the middle and ring, whilst, the second one originates from the tendon of the ring and little fingers. The lateral lumbricals are unipennate; the third lumbrical originates from the tendon of the index, whilst the fourth originates from the tendon of the middle finger.
Insertion
They are inserted into the extensor expansion of the medial four fingers.
Nerve supply
The lateral two lumbricals are supplied by the median nerve, whereas the ulnar nerve supplies the medial two.
Figure18: Lumbricals.
Figure19: Radial artery.
The Radial artery in the palm
The radial artery curves around the lateral margin of the hand and then in the floor of the anatomical snuffbox in order to reach the palm by running between the two heads of the first dorsal interosseous. It then passes between the oblique and transverse heads of adductor pollicis muscle to form the deep palmar arch with the deep branch of the ulnar artery. It gives off the radialis indicis to the radial side of the index finger and the princeps pollicis which, in turn, divides into two digital branches for the thumb.
The Deep Palmar Arch
The deep palmar arch is formed mainly from the terminal part of the radial artery in the palm with the deep branch of the ulnar artery. It is located deep to the flexor tendons and lumbricals.
Figure20: Deep palmar arch.
The Dorsal Interossei
The dorsal interossei of the hand are muscles that occupy the space between the metacarpals. In the hand there are four dorsal interossei which are situated in the dorsal aspect of the intermetacarpal spaces. These muscles abduct the index, middle and ring fingers at the metacarpophalangeal joints.
Origin
The dorsal interossei originate as two heads from the adjacent sides of two metacarpal bones (between which it lies).
Insertion
The insertion of the first is into the lateral margin of the index finger. The second is inserted into the lateral side of the base of the proximal phalanx of the middle finger. The third is inserted into the medial side of the base of the proximal phalanx of the middle finger. The fourth is inserted into the medial side of the base of the proximal phalanx of the ring finger.
Nerve supply
All the dorsal interossei are supplied via the deep branch of the ulnar nerve.
Figure21: Dorsal interossei.
The Palmar Interossei
These four muscles of the hand are located on the palmar surfaces of the metacarpals. These muscles adduct the thumb, ring, index and little fingers to the midline at the metacarpophalangeal joints. The first palmar interossei is considered to be part of adductor pollicis or flxor pollicis brevis.
Origin
It originates by one head from the adjacent sides of the metacarpals. The origin of the first palmar interosseous is from the base of the first metacarpal. The second, third and fourth palmar interossei muscle originate from the anterior surface of the second, fourth and fifth metacarpals.
Insertion
The first interosseous muscle is inserted into the extensor expansion and into the medial side of the base of the proximal phalanx of the thumb. The second is inserted into the medial side of the extensor expansion of the index finger. The third is inserted into the lateral side of the extensor expansion of the ring finger. The fourth interosseous muscle is inserted into the lateral side of the extensor expansion of the little finger.
Nerve supply
All these muscles are supplied by the deep branch of the ulnar nerve.
These four muscles of the hand are located on the palmar surfaces of the metacarpals. These muscles adduct the thumb, ring, index and little fingers to the midline at the metacarpophalangeal joints. The first palmar interossei is considered to be part of adductor pollicis or flxor pollicis brevis.
Origin
It originates by one head from the adjacent sides of the metacarpals. The origin of the first palmar interosseous is from the base of the first metacarpal. The second, third and fourth palmar interossei muscle originate from the anterior surface of the second, fourth and fifth metacarpals.
Insertion
The first interosseous muscle is inserted into the extensor expansion and into the medial side of the base of the proximal phalanx of the thumb. The second is inserted into the medial side of the extensor expansion of the index finger. The third is inserted into the lateral side of the extensor expansion of the ring finger. The fourth interosseous muscle is inserted into the lateral side of the extensor expansion of the little finger.
Nerve supply
All these muscles are supplied by the deep branch of the ulnar nerve.
