Wrist & hand

Question 1

Outline the wrist joint.

Answer 1

• The radiocarpal or wrist joint is a biaxial synovial joint. At this joint the concave ellipsoid distal surfaces of the radius and the attached articular disc articulate with the convex proximal surfaces of the scaphoid, lunate and tri- quetral bones.
• The fibrocartilaginous disc, which holds the lower ends of the radius and ulna together, separates the radiocarpal joint from the distal radioulnar joint. It does not transmit thrust from the hand.
• The triangular facet on the lower end of the radius, whose apex is the styloid process, articulates with the scaphoid and the rectangular area next to it with the lunate, which also articulates with the disc.
• The triquetral articulates with the capsule where it is reinforced by the ulnar collateral ligament; it makes contact with the disc only in full adduction.
• A capsule surrounds the joint and is thickened to form palmar, dorsal and collateral ligaments.

Question 2

Describe the movements of the wrist joint.

Answer 2

• Movements at the joint are flexion and extension, adduction (ulnar deviation) and abduction (radial deviation).
• These four movements occurring in sequence produce circumduction.
• Some of the movement of flexion and extension is always accompanied by similar movement at the midcarpal joint.
• Of the total range of flexion (about 80˚), a greater proportion occurs at the midcarpal joint; in extension (60˚), there is a greater proportion at the wrist joint itself.
• The four movements are carried out by combinations of muscle groups.
• Flexion is produced by flexor carpi radialis and flexor carpi ulnaris as prime movers, aided by palmaris longus and the flexors of fingers and thumb and abductor pollicis longus.
• Extension is produced by the radial extensors (longus and brevis) and the ulnar extensor as prime movers assisted by the extensors of fingers and thumb.
• Abduction (limited to about 15˚ because of the distal projection of the radial styloid) is carried out by flexor carpi radialis and the two radial extensors acting together, assisted by abductor pollicis longus.
• Similarly adduction (45˚) is brought about by simultaneous contraction of flexor and extensor carpi ulnaris.
• In the resting position, the wrist is in slight adduction and extension.

Question 3

Outline the flexor retinaculum.

Answer 3

• The flexor retinaculum is a strong fibrous band, measuring 2–3 cm transversely and longitudinally, which lies across the front of the carpus at the proximal part of the hand.
• Its proximal limit lies at the level of the distal, dominant skin crease on the front of the wrist.
• It is attached to the hook of the hamate and the pisiform medially and to the tubercle of the scaphoid and the ridge of the trapezium laterally.
• The carpus is deeply concave on its anterior aspect, so a fibro-osseous canal, the carpal tunnel, lies between the flexor retinaculum and the carpal bones.
• The median nerve and all the long flexor tendons of the fingers and thumb pass through this tunnel. As they do so, the four tendons of the superficial flexor are separate and lie in two rows, with the middle and ring finger tendons in front of the index and little finger tendons.
• The tendons of flexor digitorum profundus lie deeply in one plane, with only the tendon to the index finger being separate from the others, which remain attached together till they reach the palm.
• All eight tendons of the superficial and deep flexors share a common flexor sheath, which does not invest them completely but is reflected from their radial sides, where arteries of supply gain access. It is as though the tendons had been invaginated into the sheath from the radial side.
• The tendon of flexor pollicis longus lies in its own synovial sheath as it passes through the fibro-osseous tunnel.
• At the lateral end of the tunnel a deep lamina from the flexor retinaculum is attached to the medial lip of the groove on the trapezium.
• The tendon of flexor carpi radialis, enclosed in its own synovial sheath, runs in the groove in this subcompartment of the carpal tunnel.
• The median nerve passes deep to the flexor retinaculum between the flexor digitorum superficialis tendon to the middle finger and the flexor carpi radialis tendon.
• The ulnar nerve lies on the front of the retinaculum lateral to the pisiform bone, with the ulnar artery lateral to the nerve. The ulnar artery and nerve are covered here by a slender band of fascia, forming the canal of Guyon in which the nerve may occasionally be compressed.
• The tendon of palmaris longus is partly adherent to the anterior surface of the retinaculum, and thenar and hypothenar muscles arise partly from it.
• The retinaculum is also crossed superficially by the palmar cutaneous branches of the ulnar and median nerves lying medial and lateral, respectively, to the tendon. The superficial palmar branch of the radial artery lies on the retinaculum further laterally.

Question 4

What are the 3 muscles of the thenar eminence?

Answer 4

• Abductor pollicis brevis
• Flexor pollicis brevis
• Opponens pollicis

Question 5

Abductor pollicis brevis:
* Origin
* Insertion
* Nerve supply
* Action

Answer 5

• Origin - flexor retinaculum and the tubercles of the scaphoid and trapezium.
• Insertion - radial side of the base of the proximal phalanx and the tendon of extensor pollicis longus.
• Nerve supply - muscular (recurrent) branch of the median nerve (mainly T1 but with some contribution from C8).
• Action - abducts thumb (moving it in a plane at right angles to the palm). By the slip to the tendon of extensor pollicis longus, it can assist in extension of the thumb.

Question 6

Flexor pollicis brevis:
* Origin
* Insertion
* Nerve supply
* Action

Answer 6

• Origin - lies to the ulnar side of the abductor. It arises by a superficial head from the flexor retinaculum and trapezium and by a deep head from the trapezoid and capitate.
• Insertion - radial sesamoid of the thumb and so to the radial side of the base of the proximal phalanx.
• Nerve supply - muscular (recurrent) branch of the median nerve (mainly T1 but with some contribution from C8). However, nerve supply of flexor pollicis brevis is subject to more variation than that of any other muscle in the body. It may be from the muscular branch of the median nerve or the deep branch of the ulnar nerve, or it may have a double supply from both nerves.
• Action - flexes the proximal phalanx and draws the thumb across the palm.

Question 7

Opponens pollicis:
* Origin
* Insertion
* Nerve supply
* Action

Answer 7

• Origin - lies deep to the former two muscles. It arises from the flexor retinaculum and the trapezium.
• Insertion - whole of the radial border of the metacarpal bone of the thumb.
• Nerve supply - muscular (recurrent) branch of the median nerve (mainly T1 but with some contribution from C8). The opponens usually has a double supply.
• Action - opposes the metacarpal of the thumb.

Question 8

Describe the movements of the thumb.

Answer 8

• Flexion at the metacarpophalangeal and interphalangeal joints of the thumb is brought about by flexor pollicis longus and brevis, and extension by extensor pollicis Iongus and brevis.
• In palmar abduction (often termed abduction) the thumb moves away from the index finger in a plane at right angles to the palm, and the thumbnail remains in a plane at right angles to that of the four fingernails. This movement is produced by abductor pollicis brevis.
• In radial abduction (often termed extension) the thumb is moved away from the index finger in the plane of the palm by abductor pollicis longus and extensor pollicis brevis.
• The opposite to both these movements, which brings the thumb alongside the index finger, is adduction and is produced by adductor pollicis.
• Further transpalmar adduction is effected by flexor pollicis brevis, which also flexes the interphangeal joint of the thumb.
• In opposition of the thumb adduction is combined with internal rotation of the first metatarsal at its joint with the trapezium, by opponens pollicis, and extension of the thumb at the metacarpophalangeal and interphalangeal joints. This composite movement makes the thumbnail lie parallel with the nail of the opposed finger.

Question 9

Outline the muscles of the hypothenar eminence.

Answer 9

• In name the muscles that form the hypothenar eminence on the ulnar side of the palm are similar to the three thenar muscles.
• Abductor digiti minimi is the most medial of the group. It arises from the pisiform bone and the tendon of flexor carpi ulnaris and is inserted into the ulnar side of the base of the proximal phalanx and into the extensor expansion.
• Flexor digiti minimi brevis arises from the flexor retinaculum and the hook of the hamate and is inserted into the ulnar side of the base of the proximal phalanx.
• Opponens digiti minimi also arises from the flexor retinaculum and the hook of the hamate and is inserted into the ulnar border of the fifth metacarpal bone.
• Nerve supplies - by the deep branch of the ulnar nerve (mainly T1).
• Actions - all three hypothenar muscles help to cup the palm and assist in the grip on a large object.

Question 10

Outline the long flexor tendons of the hands.

Answer 10

• In the palm the tendons of flexor digitorum superficialis lie anterior to those of flexor digitorum profundus.
• From the latter tendons the four lumbrical muscles arise.
• The superficial tendons overlie the profundus tendons as they pass, in pairs, into the fibrous flexor sheaths of the fingers.

Question 11

Outline the lumbricals.

Answer 11

• Lumbrical muscles arise from the four profundus tendons and pass along the radial sides of the metacarpophalangeal joints on the palmar surface of the deep transverse metacarpal ligament, to be inserted by their tendons into the extensor expansions on the dorsum of the proximal phalanges.
• Nerve supply - characteristically, the two ulnar lumbricals are innervated by the ulnar nerve and the two radial lumbricals by the median nerve (C8, T1). The proportion of ulnar and median distribution to the lumbricals follows that of the parent bellies of the tendons in the forearm. Lumbricals supplied by the ulnar nerve are bicipital, each arising by two heads from adjacent profundus tendons, while those supplied by the median nerve are unicipital and arise from one tendon only.

Question 12

Adductor pollicis:
* Origin
* Insertion
* Nerve supply
* Action

Answer 12

Lies deeply in the palm.
* Origin - transverse head - whole length of the palmar border of the 3rd metacarpal. Oblique head - bases of the 2nd and 3rd metacarpals and capitate.
* Insertion - transverse head - ulnar sesamoid of thumb, ulnar side of the base of the proximal phalanx and tendon of extensor pollicis longus. Oblique head - ulnar sesamoid.
* Nerve supply - deep branch of the ulnar nerve (C8, T1).
* Action - to approximate the thumb to the index finger, whatever the original position of the thumb.

Question 13

Outline the interosseous muscles.

Answer 13

• The interossei are in two groups, palmar and dorsal. * The former are small and arise from only one (their own) metacarpal bone; the latter are larger and arise from the adjacent metacarpal bones of the space in which they lie.
• The palmar interossei are only seen from the palmar aspect of the interosseous spaces, but the dorsal can be seen from both dorsal and palmar aspects.
• It is easy to recall the attachments of the interossei by appreciating their functional requirements. The formula ‘PAD and DAB’ indicates that palmar adduct and dorsal abduct the fingers relative to the axis of the palm, which is the third metacarpal bone and middle finger.
• The tendons of palmar and dorsal interossei all pass on the posterior side of the deep transverse metacarpal ligament to reach their distal attachments. They are inserted chiefly into the appropriate side of the extensor expansion, proximal to the insertion of the lumbricals but partly also into the base of the proximal phalanx.
• All the interossei are supplied by the deep branch of the ulnar nerve (C8, T1).

Question 14

Describe the palmar interossei.

Answer 14

• The palmar interossei adduct the fingers.
• The thumb requires no palmar interosseous as it already possesses its own powerful adductor pollicis muscle.
• Nevertheless a few fibres are sometimes found passing from the base of the metacarpal of the thumb to the base of its proximal phalanx; when present these fibres represent the first palmar interosseous muscle.
• The middle finger has no palmar interosseous; it cannot be adducted towards itself.
• The second, third and fourth palmar interossei arise from the middle finger side of the metacarpal bone of the index, ring and little fingers and are inserted into the same side of each respective finger.

Question 15

Describe the dorsal interossei.

Answer 15

• The dorsal interossei, more powerful than the palmar, abduct their own fingers away from the midline of the palm.
• The thumb and little finger already possess their proper abducting muscles in the thenar and hypothenar eminences.
• Thus there are dorsal interossei attached only to index, middle and ring fingers.
• In the case of the index and ring fingers they are inserted into the side of the finger away from the middle finger. The middle finger itself has a dorsal interosseous attached on both sides. All four dorsal interossei arise by two heads, one from each metatarsal bone bounding the interosseous space.

Question 16

Describe the fibrous flexor sheaths.

Answer 16

• From the metacarpal heads to the distal phalanges all five digits are provided with a strong unyielding fibrous sheath, attached to the margins of the phalanges in which the flexor tendons lie in a fibro-osseous tunnel.
• In the thumb the fibrous sheath is occupied by the tendon of flexor pollicis longus alone.
• In the four fingers the sheaths are occupied by the tendons of the superficial and deep flexors, the superficial splitting to spiral around the deep within the sheath.
• The proximal ends of the fibrous sheaths of the fingers receive the insertions of the digital slips of the palmar aponeurosis. * The fibrous flexor sheaths of the fingers are reinforced by annular pulleys situated anterior to the metacarpophalangeal joint (A1), the middle third of the proximal phalanx (A2), the proximal interphalangeal joint (A3) and the middle third of the middle phalanx (A4).
• In between these annular pulleys are cruciform pulleys (C1, C2, C3).
• In the thumb the A1 pulley is anterior to the metacarpophalangeal joint and the A2 pulley just proximal to the interphalangeal joint.
• An oblique pulley is situated over the middle third of the proximal phalanx.

Question 17

Outline the extensor tendons and expansions.

Answer 17

• The extensor tendons to the four fingers have a characteristic insertion.
• Passing across the metacarpophalangeal joint, the tendon blends with the central axis of a triangular fibrous expansion on the dorsum of the proximal phalanx.
• The base of the triangle is proximal and extends around the metacarpophalangeal joint to link with the deep transverse metacarpal ligament.
• The margins of the expansion are thickened by the attachments of the tendons of the lumbrical and interosseous muscles (the so-called ‘wing tendons’), which also contribute transverse fibres to the expansion.
• As the extensor tendon approaches the proximal interphalangeal joint it splits into a middle slip and two collateral slips.
• The middle slip is attached to the base of the middle phalanx.
• The collateral slips are joined by the thickened margins of the expansion and converge to be inserted together into the base of the distal phalanx.
• The retinacular ligaments are fibrous bands attached to the side of the proximal phalanx, with the fibrous flexor sheath attachment. They extend distally to merge with the margins of the extensor expansion and thereby gain attachment to the base of the distal phalanx.
• Extension of the proximal joint draws them tight and limits flexion of the distal joint. Flexion of the proximal joint slackens them and permits full flexion of the distal joint. The two joints thus passively tend to assume similar angulations.