only on the proximal interphalangeal and metacar- pophalangeal joints. Extension at the interphalangeal joints is produced by the long extensors of the digits and also by the interosseous and lumbrical muscles acting through the extensor expansion. When the metacarpophalangeal joints of the fingers are fully extended, the long extensors are unable to act on the interphalangeal joints (see above) which can then only be extended by the lumbricals and interossei.
The lumbricals and interossei also flex the meta- carpophalangeal joints. When the lumbricals and interossei are paralysed, the long extensor muscles produce full extension of the metacarpophalangeal joint, and the long flexor muscles of the fingers act unopposed to flex the interphalangeal joints and produce the ‘claw hand’ which is characteristic of this paralysis.
In the thumb, the single interphalangeal joint is acted upon by the flexor and extensor pollicis lon- gus, and sometimes by the extensor pollicis brevis.
The abductor pollicis brevis (supplied by the medi- an nerve) may be partly inserted into the extensor expansion and able to produce extension. Thus, some extension of the interphalangeal joint of the thumb may still be possible when all the extensor muscles of the thumb are paralysed by destruction of the radial nerve.
The muscles acting on, and the movements of, the fingers and thumb are summarized in Tables 9.7, 9.8, 9.9, and 9.10. In these tables, the following ab- breviations are used: CM = carpometacarpal joint;
DIP = distal interphalangeal joint; IP = interphalan- geal joint; MP = metacarpophalangeal joint; PIP = proximal interphalangeal joint.
See Clinical Application 9.1 for a discussion of the condition known as claw hand.
the extensor digitorum tendon in place and pre- vents it from extending the interphalangeal joints when the metacarpophalangeal joint is extended.
When the metacarpophalangeal joints are straight or flexed, the extensor digitorum can extend the interphalangeal joints.
Sesamoid bones
A small, oval sesamoid bone is buried on each side of the palmar ligament of the metacarpophalan- geal joint of the thumb, where the tendons of the adductor pollicis and flexor pollicis brevis fuse with the ligament. Each bone articulates with the corresponding surface of the head of the metacar- pal. The tendon of the flexor pollicis longus lies in the groove between them. Smaller sesamoid bones may be found in the palmar ligaments of the other joints, particularly in the index and lit- tle fingers.
Movements at metacarpophalangeal joints
Based on the shape of the joint surfaces, flexion, extension, abduction, and adduction take place at the metacarpophalangeal joint. (Some amount of passive rotation is possible, but no voluntary rota- tion.) Abduction and adduction movements of the fingers are possible when the joint is extended and the collateral ligaments are relaxed. These move- ments are severely restricted in flexion because of the tightening of the collateral ligaments. Because the metacarpals are arranged in an arc convex dor- sally, the fingers converge on flexion and diverge on extension.
In precision movements, flexion of the meta- carpophalangeal joints of the medial four digits is produced mainly by the interossei and lumbricals.
Extension of these joints is produced by the exten- sor digitorum and by the extensor indicis and ex- tensor digiti minimi in the index and little fingers.
The extensors of the index and little fingers permit isolated extension of the index and little fingers when the middle and ring fingers are flexed at the metacarpophalangeal joints.
In the metacarpophalangeal joint of the thumb, the range of movements is much less in all directions. (A wide range of movements occurs at the carpometacarpal joint of the thumb.) Flex- ion is produced by the flexor pollicis brevis and longus, abduction and adduction by the short
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Interphalangeal joints
Table 9.7 Muscles acting on the fingers
Muscle Origin Insertion Action on fingers Nerve supply
Flexor digitorum superficialis
Humerus, medial epicondyle.
Radius anterior border
Middle phalanges Flexion, MP, and PIP Median
Flexor digitorum profundus
Ulna, proximal two-thirds, anterior and medial surfaces
Distal phalanges Flexion, all joints Median*
and ulnar Lumbricals Tendons of flexor digitorum
profundus
Middle and distal phalanges via extensor expansion
Flexion MP, extension IP Median and ulnar Extensor digitorum Humerus, lateral epicondyle Extensor expansion Extends all joints all fingers.
If MP fully extended, IP not extended
Radial*
Dorsal interossei Adjacent sides, metacarpals 1–5
Corresponding proximal phalanx, base through extensor expansion
Abduction of MP of index, middle, and ring fingers.
Extension IP
Ulnar
Palmar interossei Metacarpals, medial side 1 and 2, lateral side 4 and 5
Corresponding proximal phalanx, base through extensor expansion
Adduction of MP of thumb, index, ring, and little fingers.
Extension IP
Ulnar
Abductor digiti minimi
Pisiform. Flexor retinaculum Proximal phalanx, base medial side
Abduction MP (and CM) little finger
Ulnar
Flexor digiti minimi Hamate, hook. Flexor retinaculum
Proximal phalanx, base medial side
Flexion CM and MP Ulnar
Opponens digiti minimi
Hamate, hook Fifth metacarpal, medial side Lateral rotation of metacarpal. Flexion CM
Ulnar
Extensor indicis Ulna, posterior surface Extensor expansion Extension all joints index finger Radial*
Extensor digiti minimi
Humerus, lateral epicondyle Extensor expansion Extension all joints little finger. Abduction MP
Radial*
* Anterior or posterior interosseous branch.
Table 9.8 Movements of fingers
Movement Muscles Nerve supply
Flexion All fingers
All joints: MP, PIP, DIP
Flexor digitorum profundus Median* (index and middle) Ulnar (ring and little)
MP and PIP Flexor digitorum superficialis Median
MP only Lumbricals Median (index and middle)
Lumbricals Ulnar (ring and little)
Interossei Ulnar
CM and MP, little finger Flexor digiti minimi Ulnar
CM only, little finger Opponens digiti minimi Ulnar
Extension All fingers
All joints: MP, PIP, DIP
Extensor digitorum Radial*
Index: MP, PIP, DIP Extensor indicis Radial*
Little finger: MP, PIP, DIP Extensor digiti minimi Radial*
IP only when MP fully extended Lumbricals Median (index and middle)
Ulnar (ring and little)
Interossei Ulnar
Abduction at MP
(Continued)
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The joints of the upper limb
Table 9.9 Muscles acting on the thumb
Muscle Origin Insertion Action on thumb Nerve supply
Flexor pollicis longus Radius, anterior surface middle two-quarters
Distal phalanx, base Flexion all joints Median*
Flexor pollicis brevis Trapezium, tubercle.
Flexor retinaculum
Proximal phalanx, base Flexion CM and MP Median
Abductor pollicis brevis Scaphoid, tubercle. Flexor retinaculum
Anterior aspect Abduction CM and MP Median
Opponens pollicis Trapezium, tubercle. Flexor retinaculum
Metacarpal, anterior surface
Medial rotation and flexion of CM
Median
Abductor pollicis longus Radius and ulna, dorsal surfaces distal to supinator
Metacarpal base, anterior aspect
Abduction of CM, some extension
Radial*
First palmar interosseous First metacarpal, base Proximal phalanx base Adduction of MP Ulnar Adductor pollicis Metacarpal, base of 2 and 3,
body of 3
Proximal phalanx base posterior aspect
Adduction CM and MP Ulnar
Extensor pollicis longus Ulna, posterior surface middle third
Distal phalanx Extension all joints, especially with CM laterally rotated
Radial*
Extensor pollicis brevis Radius, posterior surface Proximal (and distal) phalanx base
Extension of CM, MP (and IP), especially when thumb opposed
Radial*
* Anterior or posterior interosseous branch.
Table 9.10 Movements of the thumb
Movement Muscles Nerve supply
Flexion
All joints Flexor pollicis longus Median*
CM and MP Flexor pollicis brevis Median
CM only Opponens pollicis Median
Extension
All joints Extensor pollicis longus Radial*
CM and MP (IP) Extensor pollicis brevis Radial*
CM only Abductor pollicis longus Radial*
IP only Abductor pollicis brevis Median
Abduction
CM only Abductor pollicis longus Radial*
CM and MP Abductor pollicis brevis Median
All fingers, except little finger Dorsal interossei Ulnar
Little finger Abductor digiti minimi Ulnar
Adduction at MP
All fingers, except middle Palmar interossei Ulnar
Opposition at CM of little finger Opponens digiti minimi Ulnar
* Anterior or posterior interosseous branch.
Table 9.8 Movements of fingers (Continued)
Movement Muscles Nerve supply
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Interphalangeal joints
Table 9.10 Movements of the thumb (Continued)
Movement Muscles Nerve supply
Adduction
CM and MP Adductor pollicis Ulnar
MP only First palmar interosseous Ulnar
Opposition
Medial rotation, CM Opponens pollicis Median
* Anterior or posterior interosseous branch.
CLINICAL APPLICATION 9.1 Ulnar claw Claw hand is an abnormal hand position that develops
due to damage of the ulnar and/or median nerves. The affected fingers are hyperextended at the metacarpo- phalangeal joints, and flexed at the distal and proximal interphalangeal joints. The primary cause of this deform- ity is the paralysis of the lumbricals and interossei which normally flex the metacarpophalangeal joint and extend the interphalangeal joints. When they are paralysed, the extensor action of the long extensors on the metacar- pophalangeal joint and the flexor action of the long flex- ors on the interphalangeal joint are unopposed. Patients with a claw hand will be unable to abduct and adduct their fingers (due to paralysis of the interossei).
An ulnar claw results from a lesion in the ulnar nerve in the hand. The third and fourth lumbricals are paralysed, resulting in clawing of the fourth and fifth fingers. As the ulnar nerve also supplies the interossei, they too are par- alysed. The lumbricals of the index and middle fingers
are not affected, and clawing of these fingers is not seen (even though the interossei are paralysed).
A paradoxical condition is seen when the ulnar nerve is damaged at the elbow. The effects of the lumbrical paralysis are unchanged. But because, in this condition, the medial half of the flexor digitorum profundus is also denervated, flexion of the interphalangeal joints of the ring and little fingers is weak. The claw-like appearance of the hand is reduced (and not worsened, as one would expect from a higher-level injury). As reinnervation and healing occur along the ulnar nerve after a high lesion, the claw hand deformity will get worse as the patient recovers. Claw hand can be demonstrated in yourself.
Fully extend your fingers at all joints, and note the taut extensor tendons on the back of your hand. Keeping the metacarpophalangeal joints fully extended, flex your in- terphalangeal joints, and note that this can be done with- out any movement of the extensor tendons.
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CHAPTER 10
The nerves of the upper limb
Introduction
An upper limb neurological examination is part of general neurological examination and is used to assess the integrity of motor and sensory nerves which supply the upper limb. Fig. 10.1 shows the cutaneous distribution of the main nerves of the upper limb. Clinical Applications 10.1 and 10.2 at the end of this chapter will explore the practical application of this knowledge.