POSTGRAD MED. J. (i 963), 39, 5 I 8

MOVEMENTS OF THE THUMB IN RELATIONTO PERIPHERAL NERVE INJURIES

V. C. MARSHALL, F.R.A.C.S. R. D. MARSHALL, M.S.(Melb.), F.R.C.S., F.R.A.C.S.Department of Surgery, University of Melbourne, Royal Melbourne Hospital, Parkville, Victoria, Australia

THE movements of the thumb are complex andthe names of its muscles are confusing. Abductorsmay extend, abduct, or flex; flexors may flex,abduct, or oppose; and extensors may adduct aswell as extend. Nerve injuries may further compli-cate the picture by paralysing isolated muscles.This paper is an attempt to clarify the situation.

In contrast to the other digits, the thumb has anextremely free range of movement, and yet is astrong and stable structure. This is possible becauseit is well supplied with muscles which support thecarpo-metacarpal joint.

Little wonder, then, that when we come toconsider its functional anatomy, we are con-fronted with a complicated mechanism from whichit is difficult to sort out the components. The roleof each muscle (and, more fundamental still, thatof its nerve of supply) can often best be observedin absentia, when it is paralysed following a nerveinjury. However, the efforts of other muscles tocover up and to compensate for any resultantdisability tend to obscure the truth.

It is not surprising, therefore, that under-graduates experience considerable difficulty inanalysing the movements of the thumb when theyare trying to elicit signs of peripheral nerve injuryin the hand. We suspect that similar difficultiesmay plague their more senior surgical colleagues.

In this paper we have no original observationsto make. It is our aim only to analyse the normalmovements of the thumb as an introduction tobetter understanding of the disability whichresults when there is injury to the median, ulnaror radial nerve.

The Anatomy of the ThumbCarpo-metacarpal JointThis is a saddle-shaped synovial joint, with

reciprocally curved articular surfaces, surroundedby a thick, loose, capsular ligament. It is com-pletely separate from the other carpo-metacarpaljoints, and possesses a far greater degree ofmobility. There are thickenings in the capsulelaterally, anteriorly, and posteriorly. The anteriorand posterior ligamentous thickenings convergein their passage from the trapezium to the ulnarside of the first metacarpal. The configuration ofthe joint surfaces, and the ligamentous and muscu-lar attachments, make it impossible for flexion-

extension movements to occur without axialrotation of the digit.

Thumb MusculatureThe intrinsic muscles are the abductor pollicis

brevis, flexor pollicis brevis (superficial and deepheads), opponens pollicis, adductor pollicis, Istpalmar interosseous, and Ist dorsal interosseous.The extrinsic muscles are the long flexor andextensor, the short extensor and the long abductor.

Points worthy of emphasis are:(a) The abductor brevis and the superficial head

of the flexor brevis form a smooth swelling, makingup the visible part of the thenar eminence. Theyarise partly from the carpal bones, but mainlyfrom the flexor retinaculum, and insert into theradial sesamoid of the metacarpo-phalangeal joint(Fig. i). Usually both are supplied by the mediannerve. The superficial head of flexor pollicisbrevis is usually a small muscular slip, which willobviously have almost the same action as the shortabductor, except that its situation on the ulnarside of the larger muscle enables it more easily toact as a flexor of the metacarpo-phalangeal joint.

(b) Opponens pollicis lies deep to these twomuscles, and inserts into the radial aspect of themetacarpal shaft; its action is thus entirely on thecarpo-metacarpal joint (Fig. 2).

(c) Both the transverse and oblique parts of theadductor pollicis insert into the ulnar sesamoidof the metacarpo-phalangeal joint. The firstpalmar interosseous muscle (which is sometimeserroneously called the deep head of flexor pollicisbrevis), is a small slip running from the firstmetacarpal base to the ulnar sesamoid of themetacarpo-phalangeal joint. It is comparable to,but smaller than, the other palmar interossei(Fig. 3). The adductor and first palmar interos-seous are supplied by the ulnar nerve. A furthermuscle slip arising from the carpus, more or lessblended initially with the oblique adductor mass,passes deep to the tendon of flexor pollicis longus,across to the radial sesamoid of the metacarpo-phalangeal joint (Fig. 2). It is usually supplied bythe ulnar nerve. It matters little whether this iscalled a portion of adductor pollicis, or the deephead of flexor pollicis brevis, but it is important torealize that a muscle slip normally innervated by

by copyright. on M

arch 7, 2020 by guest. Protected

http://pmj.bm

j.com/

Postgrad M

ed J: first published as 10.1136/pgmj.39.455.518 on 1 S

eptember 1963. D

ownloaded from

September I963 MARSHALL and MARSHALL: Movements of the Thumb 519

Add. poll. r)

Add. polL (obi)FIG. i.-The superficial thumb muscles, the short

abductor and flexor, and the transverse and obliqueadductor.

Add. poll. (tu.)

F PL

FPB(deep head)

Opponens

Add. poll. (obL)

FPO\APB

FIG. 2.-The short abductor and flexor removed,showing the opponens, the transverse and obliqueadductor, and the ulnar innervated slip runningdeep to the long flexor tendon across to the radialsesamoid (deep head of flexor pollicis brevis).

the ulnar nerve passes to the radial side of theproximal phalanx.

Movements of the Thumb and the MusclesInvolvedThe configuration of the carpo-metacarpal joint,

and the position of the thumb in a different planefrom the other fingers, cause confusion indescribing movements of the thumb.

In the position of rest (which might well becalled the physiological position) the plane of the

Add pol. Z

1*\se. palm. int.

FPOFIG. 3.-The interossei (opponens removed).

thumb-nail is at right angles to the other nails,and its ulnar border is adjacent to the palmarsurface of the index finger. If the thumb is pulledback in a dorsal direction to its fullest extent, thenail is seen to rotate so that it is now almost in thesame plane as that of the other digits. This is thearbitrary 'anatomical position' which Britishanatomists have always used as the starting pointin describing thumb movements. If the thumb isbrought across the palm in the movement of'opposition' to meet the pad of the little finger, thethumb-nail is seen to be rotated through almostI80°, so that the pads of the thumb and littlefinger meet. This may be designated the 'opposedposition'.

Radial abduction of the thumb, denotingdivergence from the other fingers radially in theplane of the palm, and palmar abduction, denotingmovement away from the other fingers in a planeat right angles to the palm, are terms sanctionedby wide usage. Other anatomists have classedradial abduction as extension, and it is for thisreason that abductor pollicis longus used to becalled extensor ossis metacarpi pollicis.We have a clear picture of flexion and extension

in the other digits, and abduction and adductionentail respectively movements from and towardsmedius. Applying this to the thumb, and re-membering that flexion and extension do notoccur without rotation of the metacarpal on thecarpus (and this is due to the joint itself, not to theattachment of muscles), a logical nomenclaturearises.

Flexion is always accompanied by internalrotation, and extension by external rotation.Flexion (and extension) of the thumb is seen tooccur, through a curved plane, from a point wherethe thumb is in the same plane as the other fingers,to the point of full 'opposition' where it has rotated

by copyright. on M

arch 7, 2020 by guest. Protected

http://pmj.bm

j.com/

Postgrad M

ed J: first published as 10.1136/pgmj.39.455.518 on 1 S

eptember 1963. D

ownloaded from

520 POSTGRADUATE MEDICAL JOURNAL September I963extensioN

eddvctionabduction

fleKion

FIG. 4.-Cross-section throughthe metacarpal heads showinglocus of movement of thethumb metacarpal (stippledarea):(ia) 'Anatomical' position.(i b) Position of rest or 'physio-

logical' position.(ic) 'Opposed' position.The range of thumb movementis further increased by move-ment at the metacarpo-phalan-geal joint.

EPL *a

tIJW

FIG. 5A.-The anatomia poitinmedially through almost i800. At any point alongthis line movement of the thumb at right-anglesto the curve can occur; abduction being away fromthe other fingers, and adduction being towards theother fingers. This is illustrated in Fig. 4 whichis a cross section through the metacarpal heads.The range of movement of the thumb is limited

by tension of the ligaments and muscles, and alsoby tension of the skin of the first web and of thethenar eminence, as is well seen in full abductionat right an les to the palm when tightness andcreasing of the skin over the metacarpal head andthenar eminence occur.

It is important to realize that the names of themuscles cannot tally completely with the move-ments of flexion, extension, abduction and adduc-tion. The line of action of a given muscle usuallymoves the thumb in a single direction. However,because of the inbuilt rotating action of thethumb metacarpal, dependent directly on thejoint, this single direction may have a differentdescription from point to point in the locus ofthumb movements.

Thus, abductor pollicis longus produces a radialdivergence of the thumb from the other fingersand this is correctly called abduction if the startingpoint is the anatomical position (Fig. 5a). How-

FIG. 5B.-The physiological position.Metacarpal rotation occurs during the arc ofopposition, so that abductor pollicis longus changesfrom an abductor to an extensor, and the thenarmuscles from flexors to abductors.

ever, if the starting point is the physiologicalposition (Fig. 5b), the movement is extension.

Similarly abductor pollicis brevis producesmovement of the thumb in a line away from thepalm. It thus acts as a flexor from the anatomicalposition (Fig. 5a), and as an abductor from thephysiological position (Fig. 5b).

Extensor pollicis longus, from its point ofangulation around the posterior radial tubercle,will pull the thumb dorsally from the physiologicalposition, acting as an extensor. It has, however, anadditional and quite powerful action of adductingthe thumb from a position of radial divergence(see below).Adductor pollicis is the prime mover in adduc-

tion from both the anatomical and physiologicalpositions. It will also, however, in company withthe short abductor, initiate flexion from theanatomical position (Fig. 5a). A list of the musclesproducing movements follows, those contributingbut slightly being enclosed in brackets; however,

by copyright. on M

arch 7, 2020 by guest. Protected

http://pmj.bm

j.com/

Postgrad M

ed J: first published as 10.1136/pgmj.39.455.518 on 1 S

eptember 1963. D

ownloaded from

MARSHALL and MARSHALL: Movements of the Thumb

all that is required in practice is a knowledge ofwhat each individual muscle can do, which is onlypossible if the peculiarities of the carpo-metacarpaljoint are appreciated.

Muscles Producing Thumb MovementsThe Arc of FlexionFlexor pollicis brevis (both heads)Abductor pollicis brevisOpponens pollicisFlexor pollicis longus(Adductor pollicis)

The Arc of ExtensionExtensor pollicis longusExtensor pollicis brevisAbductor pollicis longus

Abduction(i) In the plane of the palm (or radial abduction

from the anatomical position).Abductor pollicis longusExtensor pollicis brevis(ii) Away from the plane of the palm inside

the radial margin of the index finger (or palmarabduction from the physiological position).Abductor pollicis brevisFlexor pollicis brevis (both heads)(Opponens pollicis)(Abductor pollicis longus by means of a slip to

abductor pollicis brevis can on occasion impart afew degrees of true palmar abduction, butattempts to increase the range immediately resultin radial abduction of the thumb.)

Adduction(i) In the plane of the palm (ulnar adduction).Adductor pollicisExtensor pollicis longusIst palmar interosseous(Ist dorsal interosseous)(ii) In the plane at right angles to the palm

(palmar adduction).Adductor pollicisExtensor pollicis longus(ist palmar interosseous)(Ist dorsal interosseous)

'Opposition'This movement is, in fact, the movement of full

flexion of the carpo-metacarpal joint of the thumbas previously described, in which the thumb iscarried out from the palm and as far as possibletowards the little finger. The placing of thepads of the thumb and little finger togetherdepends on the thumb movement (flexion) andon reciprocal flexion of the little finger. Itwould be better if the name 'opponens pollicis'

were discarded for a muscle which is virtually apure flexor of the carpo-metacarpal joint, as itimplies falsely a major importance of this musclein the action of 'opposition'. In summary, it isclear that the source of confusion with the nomen-clature of the thenar muscles rests in our deter-mination to describe joint movements with suchterms as abduction-adduction, and flexion-exten-sion, even if the corresponding movements donot exist. The fact is that no simple movementin a single plane can occur in the joint at the baseof the thumb.

The Effects of Nerve LesionsWe shall now consider the deformities in ulnar,

median and radial nerve lesions and the expectedloss of movements. Trick movements due tocompensation by unparalysed muscles are readilyappreciated if the functional anatomy is kept inmind.One is concerned here with the fully developed

picture seen several weeks after a nerve lesion,when wasting and deformity have reached theirpeak. The recent nerve injury does not producethese effects, since the muscles retain their bulk,and the position of rest remains normal because ofthe elasticity of the muscle bellies. Thus im-mediately after a complete median nerve lesionthe thumb will spring back to the position of restif it is forcibly adducted and then all the musclesare relaxed. This can easily be misconstrued asactive abduction if the thenar muscles are notpalpated during the performance of the movement.A month later, the thenar eminence is wasted, thethumb has assumed the 'ape-like' position, and theloss of palmar abduction is obvious and complete,apart from trick movements to be considered.

Ulnar Nerve PalsyThe thumb muscles paralysed are the first dorsal

and first palmar interossei, the adductor pollicisand the deep head of flexor pollicis brevis. Wastingof the adductor pollicis and first dorsal interos-seous causes hollowing of the web between thumband index. Disability of adduction would beexpected, and is the basis of tests of ulnar nervefunction. However, in practice compensation forloss of the adductor is often seen as adduction canbe performed from a position of palmar or radialabduction by extensor pollicis longus. Movementof the thumb across the palm towards the littlefinger can then be continued by flexor pollicislongus, which simultaneously flexes the terminalphalanx. In any test of adduction, therefore, thetendon of extensor pollicis longus and the positionof the terminal phalanx should be carefullyobserved.

-September I963 52I

by copyright. on M

arch 7, 2020 by guest. Protected

http://pmj.bm

j.com/

Postgrad M

ed J: first published as 10.1136/pgmj.39.455.518 on 1 S

eptember 1963. D

ownloaded from

522 POSTGRADUATE MEDICAL JOURNAL September I963

.::~~~..: ..................................... ...

! I|1"|..........ElE| 111! -.................

-~~~.I. ....

~~~.

FIG. 6.-Ulnar nerve palsy:Froment's sign positive.

- l.:62.46 ; .. ,. t.' -°t~~~............................F'.RD85. 02FIG. 7. Left ulnar nerve palsy. Froment's sign nega-

tive. Note prominence of tendon of extensorpollicis longus.

Froment's SignThis is based upon the compensatory action of

flexor pollicis longus in ulnar adduction of thethumb. A piece of paper is held against resistancebetween the straight thumb and the radial marginot the index finger and palm. Flexion of theterminal joint of the thumb by flexor pollicislongus so that the paper is held by a pincer actionis a sign of failure of the adductor to perform theaction (Fig. 6). However, extensor pollicis longusacting alone may provide firm adduction so thatflexion of the interphalangeal joint does not occur,and under these circumstances the adductorpollicis may be thought to be functioning unlessthe tendon of extensor pollicis longus is observedand palpated during the performance of the test(Fig. 7).

Opposition of the Thumb and Little FingerNormal opposition is a combination of the full

movement of flexion and internal rotation of thethumb, and flexion of the little finger at themetacarpo-phalangeal joint, aided by cupping ofthe palm and a forward elevation of the relativelymobile fifth metacarpal head by the hypothenarmuscles. It is customarily tested by placing thepads of the digits in contact, with the thumb andlittle finger extended at the interphalangeal joints(Fig. 8).

In ulnar nerve palsy the thumb component ofthe movement can be carried out adequately inthe absence of the adductor by the median-innervated short abductor and flexor, opponensand flexor pollicis longus. The little finger isunable, however, to reciprocate, and the hypo-thenar paralysis prevents the necessary elevationof the fifth metacarpal head. The thumb com-pensates for this by full flexion of the terminalphalanx which may enable it to contact the side ofthe terminal phalanx of the flexed and abductedlittle finger (Fig. 9). Sunderland (I944a) haspointed out that the flatness of the knuckles inopposition due to the failure of elevation of thefifth metacarpal head contrasts with the cupping ofnormal opposition and is an excellent test of ulnarparalysis. The test is best viewed from the dorsalor end-on aspect.

Median Nerve PalsyInspection may reveal the so-called 'simian

hand', the thumb being pulled into extension andexternal rotation by the unopposed action ofabductor pollicis longus and extensor pollicislongus and brevis. Muscle wasting causes flatten-ing of the thenar eminence, crinkling of the skin,and prominence of 'the first metacarpal shaft(Fig. io).

by copyright. on M

arch 7, 2020 by guest. Protected

http://pmj.bm

j.com/

Postgrad M

ed J: first published as 10.1136/pgmj.39.455.518 on 1 S

eptember 1963. D

ownloaded from

MARSHALL and MARSHALL: Movements of the Thumb

FIG. 8.-Normal opposition.

Abduction of the Thumb at Right Angles to the PalmThis is the most useful test for median nerve

palsy, and should always be tested against re-sistance from the physiological position, with thethumb inside the radial margin of the palm andindex finger. We have seen that the slip fromabductor pollicis longus to abductor pollicisbrevis may give a weak palmar abduction fromthe anatomical position but this should not causeconfusion if the test is performed as above.

Palmar abduction in median nerve palsy dependson the following:

(a) The size of the ulnar-innervated slip to theradial sesamoid (deep head of flexor pollicisbrevis). This will hypertrophy in long-standingcases and may stand out as a visible ridge. It cancause weak palmar abduction and internal rotation.

(b) Anomalous innervation of the thenar muscu-lature by the ulnar nerve. Clinical and anatomicalstudies have suggested (Sunderland and Hughes,1946; Clifton, 1948; Rowntree, 1949) that anoma-

FIG. 9.-Opposition in ulnar nerve palsy. Note failureof little finger component.

lous innervation is relatively frequent, and thatonly in about 85% of cases does the normaldistribution prevail. Sparing of the thenar musclesin median nerve palsies may be found in about 4%of hands, and sparing of the muscles usuallyinnervated by the ulnar nerve in about 3%/0 of handsin ulnar nerve palsies (Clifton, 1948). Confirma-tion of anomalies may be obtained by electricalstimulation or blocking of the suspected nerve ofinnervation.

Opposition of the Thumb and Little FingerThe full sweep of flexion and internal rotation

of the thumb requires the action of median-innervated muscles. 'Pseudo-opposition' occurscharacteristically in median nerve palsies-the bentthumb is swept straight across the palm by adduc-tor pollicis and meets the side of the flexedterminal phalanx of the little finger (Fig. ii).However, opposition may be normally carried outin median nerve palsies in cases of ulnar innerva-

Selptember I963 523

.i

.II

....

by copyright. on M

arch 7, 2020 by guest. Protected

http://pmj.bm

j.com/

Postgrad M

ed J: first published as 10.1136/pgmj.39.455.518 on 1 S

eptember 1963. D

ownloaded from

POSTGRADUATE MEDICAL JOURNAL

FIG. io.-Median nerve palsy showing thenar atrophy.

tion of the short abductor and flexor, or opponenspollicis.

Flexion of Terminal Phalanx of the ThumbFlexor pollicis longus is paralysed in a high

median nerve palsy. The test is valid only if it iscarried out against resistance in the position ofrest, with the thumb inside the margin of theindex finger and palm, and with the wrist in neutralposition.

Trick flexion is produced by hyperextension ofthe wrist and full radial abduction of the thumbso that the stretched tendon of flexor pollicislongus causes passive flexion (Sunderland, I944b),or by hyperextension and abduction of the thumbfollowed by sudden relaxation of the extensorscausing rebound flexion (Wood Jones, I949).

Combined Median and Ulnar Nerve PalsyAll thumb muscles are paralysed apart from the

long abductor and extensor, and the short exten-

FIG. I i.-Median nerve palsy-attempted opposition.

sor. However, the previous remarks concerningFroment's sign apply, as extensor pollicis longusis still capable of adduction from a position ofradial divergence, and a weak degree of abductionaway from the palm may be produced by the slipfrom abductor pollicis longus to the short muscles.

Radial or Posterior Interosseous Nerve PalsyThe thumb muscles paralysed are the long and

short extensor and long abductor. The thumb liesin the position of rest and flexion and oppositionmovements are normally carried out, but thethumb cannot be extended and radially abductedaway from the margin of the index finger. Exten-sion of the terminal phalanx of the thumb may besimulated by passive rebound from the flexedposition (Fig. i2a and b), but if the movement istested against resistance lack of function will beobvious.

SummarySome points in relation to the anatomy of the

carpo-metacarpal joint and thenar musculature arediscussed. It is stressed that flexion and extension

-September I963524

by copyright. on M

arch 7, 2020 by guest. Protected

http://pmj.bm

j.com/

Postgrad M

ed J: first published as 10.1136/pgmj.39.455.518 on 1 S

eptember 1963. D

ownloaded from

September I963 MARSHALL and MARSHALL: Movements of the Thumb

47S

FI IZA

FIG. I2BPosterior interosseous nerve palsy-extension of

terminal phalanx ofthumb simulated by rebound.

are always accompanied by axial rotation of thedigit, and a nomenclature of thumb movements isdescribed. Because of rotation of the thumb duringflexion-extension, the movement produced by anindividual muscle will have a varying descriptionfrom point to point throughout the range of thumbmovement.The effects of thumb paralysis in peripheral

nerve palsies are considered. Compensatory actionof unparalysed muscles may cause difficulty in

interpretation of tests of nerve function unlessthe anatomy of thumb movements is clearlyappreciated.

We are grateful to Mr. D. H. Patey and Mr. L. P.Le Quesne, Department of Surgical Studies, MiddlesexHospital, for permission to study their patients, and toProfessor M. R. Ewing, Professor of Surgery, Univer-sity of Melbourne, for advice in the preparation ofthis paper.

REFERENCESCLIFTON, E. E. (1948): Unusual Innervation of the Intrinsic Muscles of the Hand by Median and Ulnar Nerve,

Surgery, 23, 12.ROWNTREE, T. (I949): Anomalous Innervation of the Hand Muscles, J3. Bone Jt Surg., 3xB, 505.SUNDERLAND, S. (I944a): The Significanca of Hypothenar Elevation in Movements of Opposition of the Thumb,

Aust. N.Z.J'. Surg., 13, 155.(I944b): Flexion of the Distal Phalanx of the Thumb in Lesions of the Median Nerve, Ibid., I3, 157.and HUGHES, E. S. R. (1946): Metrical and Non-metrical Features of the Muscular Branches of the Ulnar Nerve,

J. comp. Neurol., 85, I13.WOOD JONES, F. (1949): 'The Principles of Anatomy as Seen in the Hand', Second Edition, p. 222. London: Bailliere,

Tindall and Cox.

by copyright. on M

arch 7, 2020 by guest. Protected

http://pmj.bm

j.com/

Postgrad M

ed J: first published as 10.1136/pgmj.39.455.518 on 1 S

eptember 1963. D

ownloaded from