power grip and precision handling · annalsoftherheumaticdiseases the shortening of one tendon...

Ann. rheum. Dis. (1962), 21, 164.

POWER GRIP AND PRECISION HANDLING

BY

J. M. F. LANDSMEERLaboratory ofAnatomy and Embryology, University ofLeiden, The Netherlands

The recent study by Napier (1956) of the prehensilemovements of the human hand is of outstandingimportance because it points out that the "natureof the intended activity finally influences the patternof the grip" (p. 906). He distinguishes between the"precision grip" and the "power grip" and statesthat these patterns, "either separately or in com-bination, provide the anatomical basis for allprehensile activities, whether skilled or unskilled"(p. 902). In the precision grip the thumb is abductedin both the metacarpophalangeal and the carpo-metacarpal joints, whereas in the power grip bothjoints are addicted.

With the abduction (combined with flexion) thethumb also rotates medially, so that the pulpsurface becomes directly "opposed to the pulpsurface of one or all of the remaining digits for thepurposes of (precision) prehension" (p. 908).

Napier (1952) positively stated that this abductionwith related rotation took place not only in thecarpometacarpal joint, but also in the metacarpo-phalangeal joint; this had been previously observedby Duchenne (1867) and Bunnell (1938), but neitherthey nor Napier offered any substantial evidencein support of this idea.

In the power grip the combined fingers form onejaw of the clamp with the palm as the other jaw.The fingers are more or less flexed according to thesize of the object, and they are laterally rotated andinclined towards the ulnar side of the hand. Thepower grip should therefore be manifested in grasp-ing a cylindrical object. The thumb-in theadducted position-is pressed with the pulp surfaceagainst the object to be grasped, and this, accordingto Napier, introduces an element of precision intothe power-grip complex. If the object is heavierand the possibility of precision more limited, thenthe thumb will gradually become more abductedand will be thrown over the object.

In the precision grip the abduction of the thumbensures that the pulp surfaces of the thumb and

fingers can place themselves opposite to each other;the fingers are now described as being flexed andabducted at the metacarpopbalangeal joints.The characteristics of both grips come into play

in grasping globular or cylindrical objects. Napierstates that the position of the hand is determinednot so much by the shape of the object as by thequality of the grip, which in its turn depends on thepurpose for which the instrument is grasped. Forexample, a pinhammer has about the same diameteras a pen or pencil and, although in both cases anelement of precision is involved, a pinhammer isclearly held and used differently from a pen.The problem which Napier raises is extremely

important, not only in the actual anatomy, but alsoin the evaluation of incongruity, the correction ofdeformities, and the reconstruction and rehabilita-tion of the hand. He gives very apt examples ofobjects with the same shape that can be used indifferent ways, according to the power or precisionrequired.

It is necessary for those concerned in the rehabili-tation of crippled or deformed hands to study thewhole subject of the various positions which thenormal hand is capable of assuming according tothe object grasped and the use to which it is to beput. Napier uses the terms "precision grip" and"power grip" "in a dynamic as well as a staticsense in the same way that flexion and extensionare employed to describe both the posture and themovement" (p. 903). The dynamics of grippingproduce a particular grip, and the static conceptindicates the final state of gripping. This conceptis given little consideration by Napier; he does notsay whether both forms of grip may be regardedas a variant of the final state, or whether the move-ments leading to this final state may be taken inboth cases as variants of an equivalent movementpattern.

Consequently it seems justifiable to attempt todiscover how the dynamic and static stages of these

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"grips" present themselves. In performing whatNapier calls the "power grip", the object must betaken hold of, and then the fingers must clenchthemselves around the object to hold it firmly.Thus, in the dynamic phase, the hand must beopen and the fingers and thumb must take up aposition suitable for grasping the object; the fingersin this position can then make closer contact with theobject, and further power can then be exerted forgripping or clenching. In this process the dynamicand static phases can be clearly distinguished. Theduration of the dynamic phase is unimportant; thefact that it is usually short does not mean that it isnot absolutely essential to the establishment of agood grip. It comprises a series of voluntary acts:

(a)(b)(C)

(d)

The opening of the hand;The positioning of the fingers;The approach of the fingers to the object;The transition to the static phase-theactual grip.

The grip itself may be accomplished in very many

ways, a spherical object can be clenched in a powergrip with the thumb in opposition, and a cylindricalobject with the thumb in adduction or in opposition,to the other fingers.To distinguish Napier's so-called "precision grip"

from the "power" grip, it is necessary to charac-terize its quality, for the precision grip does notinvolve any forceful grasping of the object. As soon

as the taking hold is established, the pattern of thepower grip is present regardless of how much poweris exerted, but in the precision grip there can be no

such antagonism between the fingers (and thumb)and the middle hand (including the thenar andhypothenar) and a different form of antagonismis brought into use, namely an interdigital or

contradigital antagonism. The object is heldbetween the tips of the fingers, and because a verysmall degree of power is exerted the qualityindicated by the word "grip" is absent from themovement pattern. Nor is there any possibility ofa gradual transition to an increasingly more powerfulgrasp when the object is held in the finger tips. Itis possible to hold the object immobile between thefinger tips, but this is not typical for this form of"grip", the chief purpose of which is to operatethe object with precision by means of the fingers.This is the cardinal difference from the "power"grip, in which the static phase is characterized bythe fact that the gripping can retain a rigid relationto the object while it moves in relation to the wrist,elbow, or shoulder. In the precision "grip" thereis no question of a static phase, since the fingersthemselves manipulate the object, and there is no

point in distinguishing dynamic and static phasesin this movement pattern.For this reason the term "grip" is not applicable,

and it is therefore suggested that this manceuvreshould be called "handling".

In "precision handling", therefore, the firstrequirement is that the fingertips be so placed thatthe object can be held, and for this the opposition(with rotation) of the thumb is indispensable. Afterthis the motion of the fingers in relation to eachother perform the actual handling or manipulation.Napier explicitly states that the term "prehensile"

should be reserved for "movement in which anobject is seized and held partly or wholly within thecompass of the hand", whereas "non-prehensile"movements are those "in which no grasping orseizing is involved, but by which objects can bemanipulated by pushing or lifting motions of thehand as a whole or of the digits individually" (p. 902).It is therefore strange that Napier described pre-cision handling by the term "precision-grip".

ANATOMICAL AsPECTSPOWER GRIP

In recent studies on the anatomy of the articulatedfinger (Landsmeer, 1955, 1958, 1961), it was affirmedthat the movements of both interphalangeal jointswere coordinated. Because of the presence ofjoint clefts and bi-articular and polyarticular muscles,one may speak of a "chain of joints", in which eachbone except the terminal phalanx is an intercalatedunit. This process was described by Gilford, Bolton,and Lambrinudi (1943) in their paper on "linkjoints". In view of the anatomical evidence of theexistence of a joint chain, bridged by bi-articular andpolyarticular muscles, it is not sufficient to considerthe equilibrium or the motion (actually a series ofbalance states) of one joint; it must first of all bedetermined which grouping of joints or whicharticulated member can be considered as ananatomically-bonded entity. Because one of thelong flexors and also the extensor bridge both theelbow and wrist joints, the actual finger areas canbe considered separately because they can bestabilized independently. It is necessary, however,to investigate the significance of the flexors and theextensor in the articulation of the forearm.An intercalated bone in a bi-articular system,

bridged by two bi-articular antagonistic muscles,cannot be kept in equilibrium. A bi-articulartendon system can be shortened in its entirety onlyby a pattern of zigzagging, i.e. by changing theangles of the two joints in the opposite sense. Twomuscles can equilibrate only one joint. In sucha case the whole system cannot be shortened because

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ANNALS OF THE RHEUMATIC DISEASESthe shortening of one tendon always requires thelengthening of its antagonist. In contrast, theshortening of one muscle in a bi-articular systemcan take place while the antagonist remains iso-metric. It will be clear that a tendon bridging abi-articular system can remain isometric only byzigzagging the system.The direction of this zigzagging-of the turning

of the intercalated bone-depends on the ratio ofthe distance from the tendon to the joint-axis in thetwo joints involved.The principle is illustrated diagrammatically in

Fig. 1(a), which shows only one of the muscles.Now, it is supposed that this muscle runs in sucha way that it remains isometric when the systemzigzags as the two joints change their angle by thesame degree. The question is, how does theantagonist run when it is shortened as a result ofthis zigzag pattern? The answer is that the tendonmust "gain" in the "flexing" joint more than it"loses" in the "extending" joint. Or that its distancefrom the axis in the "flexing" joint must exceed its

distance from the axis in the "extending" joint(Fig. ib). It may be deduced that, if the tendonsrun as assumed, their contraction will produce azigzag in the same direction, since in that eventthe entire tendon system shortens. In other words,a pair ofantagonistic bi-articular muscles will shortenas a system when the system zigzags in such a waythat the change of angle in each joint leads to theshortening of the tendon with the relatively largestbeam (Fig. lc).* So long as the shortening of thesystem as a whole cannot be prevented by some othereffect, e.g. by a third muscle, the zigzagging willproceed until one of the joints has reached itsend-state.

Thus, the proximal phalanx, considered as anintercalated bone, may be assumed to be bridgedby the long flexor and the extensor, and willimmediately arrive at its end-state, in which

* In a previous paper (Landsmeer, 1961), it was explained that the"relative beam", which can be measured directly, is generally areliable approximation for the "relative shortening"' the latter beinga more proper term for expressing the position of a muscle.

11R

(a) The joints change their angle in oppositedirections. Tendon R remains taut and thesame length. It is assumed that the tendonruns so that the joints change their angleto the same degree.

L o R L

(b) When tendon L gains more in Joint I thanit loses in Joint II, the whole tendinoussystem will become shorter. This will happenwhen d > b.

(c) The bi-articular bi-muscular system inits general form. When a/b > c/d the inter-calated bone will make a clockwise turn, aswhen muscles R and L both act.

Fig. 1.-Diagrams to explain the phenomenon of zigzagging in a bi-articular bi-muscular system.

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extension in the metacarpophalangeal joint andflexion in the proximal interphalangeal joint will occuruntil the possibility of excursion of one of them isexhausted. In theory, this could be established bythe fact that the ratio "distance extensor-joint axis:distance flexor-joint axis" for the metacarpo-phalangeal joint exceeds this ratio for the proximalinterphalangeal joint. The extensor has the rela-tively largest beam in the metacarpophalangealjoint, and the flexor profundus (and also thesublimis) in the proximal interphalangeal joint.By means of a third muscle, the intercalated bonecan be held in each state of equilibrium, providedthat this muscle can operate antagonistically. Thethird muscle can be either bi-articular or mono-articular. In this way the first phalanx can becontrolled by one of the flexors, the extensor, andthe bilateral wing-tendons of the interossei orlumbricales (Fig. 2). The fact that the flexorprofundus is not directly inserted on the middlephalanx does not prevent the inclusion of this musclein the bi-articular system, since the operation ofboth interphalangeal joints is co-ordinated (Lands-meer, 1958).

Opening the Hand.-This is a motion by whichthe interphalangeal and the metacarpophalangealjoints are moved simultaneously.

Choice of Finger Position.-This is more or lesssimultaneous with the preceding phase. The fingersare adjusted metacarpophalangeally while the desiredcurving is carried out interphalangeally. Thebilateral wing-tendons determine by mutual co-ordi-nation the position for abduction or adduction.

Approach.-The movement of metacarpophalan-geal joint is independent of the interphalangealjoints; as the fingers approach the object the meta-carpophalangeal joint moves while the interphalan-geal joint changes but little.

Grip.-As the fingers take hold of the object,they are powerfully drawn by the flexor profundus,so that they remain in a position which ensures anefficient grip. The so-called phalangeal tendonsof the interossei, which include that of the abductordigiti V, are pre-eminently suited to contribute thepower involved in the actual grasping. They arepresent on only one side of each finger; the ulnarside of the little and ring fingers and the radialside of the first and middle fingers. These tendonshave no identical antagonist, which is certainlyremarkable for a muscle in a lateral position. Thisanatomical situation suggests that the phalangealtendons will hold the metacarpophalangeal jointin a terminal abducted position, and will work

(a) Bi-articular system composed of the proximal interphalan-geal and the metacarpophalangeal joints bridged by theextensor and both flexors.

(b) The proximal phalanx in this system will make a coun-ter-clockwise turn.

(c) The interosseous (wing tendon) acts antagonistically tothe common effect of the extensor and flexors.

Fig. 2.-Diagrams of a finger with its tendinous system.

antagonistically not in relation to a heterolateralpartner (which occurs only exceptionally in themiddle finger), but in relation to other functionalunits of the hand. The osseous insertion of theinterossei will cause abduction (and rotation) of theextended proximal phalanx, but rotation only of theflexed proximal phalanx.

The choice of position and the final position inwhich the grasp is made are principally determinedby the shape of the object. With a sphericalobject, the metacarpophalangeals of the little andring fingers are in maximal ulnar abduction, andthe lateral rotation of these joints is obvious. Thefirst finger is in maximal radial abduction, which isotherwise limited in relation to the axis of themetacarpal. The middle finger can be in an inter-mediate position. The thumb is in opposition tothe other fingers, while the little and third fingersare laterally rotated, the index finger shows nomedial rotation whatever, and the middle finger

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ANNALS OF THE RHEUMATIC DISEASES

retains a free choice according to the needs of thesituation (Fig. 3).

Fig. 3.-Position of the fingers in the spherical grip. Notice theopposition of the thumb and the lateral rotation of both the ring and

little fingers.

The part played in this pattern by the phalangealtendons on the ulnar side of the little and thirdfingers and on the radial side of the first finger isclear. These fingers are abducted in a terminalposition.

In grasping a cylindrical object, the situation issomewhat different (Fig. 4). The little and ringfingers are now more sharply bent. The phalangealinterossei bring the metacarpophalangeal joints toa state of maximal lateral rotation. Both fingersare projected over the palm of the hand. The indexand middle fingers with the thumb, which lies in thepalm of the hand, form a pincer, and the phalangealtendon on the radial side of the index and middlefingers is now in antagonism to an adducted pollux.Thus an initial dynamic phase and a terminal staticphase can be observed in anatomical terms in thepower grip.

Precision HandlingThe central fact in "handling" is that the object

can be manipulated by means of the fingers. Themetacarpophalangeal and interphalangeal joints

Fig. 4.-Position of the fingers in the cylindrical grip. The ring andlittle fingers are laterally rotated to a maximum.

move independently. When the profundus is active,the terminal phalanx will move in a co-ordinatedpattern with the middle phalanx. When the sublimisacts as the flexing muscle, the terminal phalanx isbeyond muscular control. With pressure on thevolar side it will consistently turn dorsally, evenwhen the proximal interphalangeal joint is flexed.This situation is far from rare; it occurs frequentlyin the index finger in the manipulation of a pen.Brand (1958), discussing the paralytic claw-hand,

precisely stated that "as soon as the metacarpo-phalangeal hyperextension is relaxed in beginningto close the hand, the interphalangeal joints againlose all extension power. The patient thereforealways closes the hand by closing his terminaljoints first" (p. 618). The patient can grasp onlylittle objects, for with larger objects "the presentingfinger tips and nails push the object out of the palminstead of surrounding it by the palmar surface andpulps of the fingers which should reach out toencircle it. This reaching out of the fingers isa purely intrinsic action and is the preliminary to allnormal grasp and pinch" (p. 619).

In this important observation Brand touchedupon the true nature of the bi-articular system, con-trolled by two muscles only; in such a system one ofthe joints will always fall into a terminal position,

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because of the zigzagging tendency. For the systeminvolved in handling, the terminal position for thecombined interphalangeal joints is flexion and thatfor the metacarpophalangeal joint is extension.This holds good as long as the intrinsics are out ofaction. The first metacarpal tends to turn dorsally,a movement which can be equilibrated by theinterossei or lumbrices (Fig. 2). The intrinsicsbeing disregarded, either the metacarpophalangealjoint will be extended, or the interphalangeal jointswill beflexed. The finger can be moved in accordancewith a well-defined pattern; the interphalangeal jointscan be flexed and extended only when the metacarpo-phalangeal joints remain extended, while the meta-carpophalangeal joints can be flexed and extendedonly when the interphalangeal joints are flexed.Starting from the extended position, the inter-phalangeal joints will be flexed first, and only whenthey are fully flexed will the metacarpophalangealjoints be taken into flexion. The invalidity of thehuman hand in cases of functional disorder of theintrinsics is identical with the fixed pattern ofmovement.As for the abductory action of the so-called

phalangeal interossei, Eyler and Markee (1954)have commented on the dorsal bipennate part ofthe dorsal interossei (our phalangeal tendon):"The dorsal component of each dorsal interosseusis anatomically best suited to forcefully deviate itsrespective digit"; and on the wing-tendons: "Eachvolar interosseus and volar component of eachdorsal interosseus is in position to exert greatestforce on the lateral bands of the extensor apo-neuroses, to forcibly flex the metacarpophalangealjoint, extend the interphalangeal joints, and to a lessdegree deviate its digit" (p. 8).

Finally, the position of the grasping hand inrelation to the forearm is important. The humanhand can grasp cylindrical objects so that the pro-supination movements are translated as a rotationof the object. In this way a screwdriver is held ina cylindrical power-grip and the same applies to theposture of the hand in fencing. But in unscrewingthe lid of a jar, in the initial phase of loosening thelid, the spherical power grip gives the hands a firmcontact with both the lid and the jar. The forearmsare then used as levers in line with the radius of thelid and of the jar. By means of the upper arms,tangential forces are applied to the proximal endsof the forearms, and these considerably enhancethe effort.

SummaryOn the basis of a fresh analysis of the pattern of

movement and posture of the human hand, a dis-tinction is suggested between power-grip and

precision-handling. In the former, a dynamic,initial phase can be distinguished from a static,terminal phase, and the position of the fingersdepends upon the shape of the object; in the latterthere is no static phase.The dynamic phase includes the opening of the

hand, the positioning of the fingers, and the graspingof the object. The functional anatomical processesof these movements have been subjected to closeranalysis.The finger represents a chain of joints, bridged by

bi-articular and polyarticular tendons. Two bi-articular systems can be discerned: that of themetacarpophalangeal joint and proximal inter-phalangeal joint, with the proximal phalanx as theintercalated bone; and that of the interphalangealjoints, with the middle phalanx as the intercalatedbone. The latter is a co-ordinated system, butin the former two joints can be moved independently.Abductions in the metacarpophalangeal joint areaccompanied by rotations. The movementsinvolved in "gripping" and "handling" are furtheranalysed, with remarks on the position of thegrasping hand in relation to the forearm, and thespecific manner in which the object or tool is to beused.

REFERENCESBraithwaite, F. O., Channell, G. D., Moore, F. T., and

Whillis, J. (1948). Guy's Hosp. Rep., 97, 185.Brand, P. W. (1958). J. Bone Jt Surg., 40B, 618.Bunnell, S. (1938). Ibid., 20, 269.Duchenne, G. B. (1867). "Physiologie des mouve-

ments." Bailliere, Paris.Eyler, D. L., and Markee, J. E. (1954). J. Bone Jt Surg.,

36A, 1.Gilford, W. W., Bolton, R. H., and Lambrinudi, C.

(1943). Guy's Hosp. Rep., 92, 52.Landsmeer, J. M. F. (1955). Acta anat. (Basel), 25,

Suppl. 24.(1958). Acta morph. neerl.-scand., 2, 59.(1961). Ibid., 3, 287, 304.

Napier, J. R. (1952). J. Anat., 86, 335.--- (1956). J. Bone Jt Surg., 38B, 902.

Capacite de saisir et precision manuelie. Une analysedes movements prehensiles de la main humaine

RESUMESur la base d'une analyse nouvelle du mecanisme des

mouvements et de la position de la main humaine,on propose une distinction entre la capacity de saisir et laprecision manuelle. Dans le premier cas on peut di,-tinguer une phase initiate dynamique d'une phase ter-minale statique et la position des doigts depend ducontour de l'objet; dans le deuxieme cas la phase statiqueest absente.La phase dynamique comprend l'ouverture de la main,

la mise en position des doigts et l'action de saisir l'objet.6

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ANNALS OF THE RHEUMATIC DISEASES

Le fonctionnement anatomique au cours de ces mouve-ments fut soumis a une analyse detaillee.Le doigt represente une chaine d'articulations relive

par des tendons bi- et poly-articulaires. On peut dis-tinguer deux systemes bi-articulaires: celui de l'articula-tion metacarpo-phalangienne et de l'interphalangienneproximale, ou la phalange proximale est un os intercale,et celui des articulations interphalangiennes, avec laphalange moyenne comme os intercale. Ce dernier estun systeme coordine, mais dans le premier les deuxarticulations peuvent etre mues independemment. Lesabductions dans l'articulation metacarpo-phalangiennes'accompagnent de rotations.On proceda a d'autres analyses des actions de saisir

et de manipuler, et on nota la position de la main aumoment de saisir par rapport a l'avant-bras et la manierespecifique dont un objet ou un outil doivent Wtremanipules.

Poder de asimiento y precision manual. Un analysis de losmovimientos prensiles de la mano humana

SUMARIOSobre la base de un analisis reciente del tipo de movi-

mientos y de la postura de la mano humana se sugiere

una distinci6n entre powder de asimiento y precisionmanual. En el primero puede distinguirse una faseinicial dinamica de una terminal estatica y la posici6nde los dedos depende del contorno del objeto; en elsegundo no existe fase estatica.La fase dinamica comprende la apertura de la mano,

colocacion de los dedos y el asimiento del objeto. Elfuncionamiento anatomico del proceso de estos movi-mientos fue sometido a un analisis mas detallado.

El dedo represents una cadena de articulacionesponteadas por tendones inter y poli-articulares. Dossistemas inter-articulares pueden ser puestos de mani-fiesto: el de la articulaci6n metacarpo-falangiana y de lainterfalangiana proximal con la falange proximal comohueso intercalado, y el de las articulaciones interfalan-gianas, con la falange media como hueso intercalado.El ultimo es un sistema coordinado, pero en el primerolas dos articulaciones pueden ser movidas indepen-dientemente. Abducciones en la articulaci6n metacarpo-falangiana son acompanadas de rotaciones.Mas adelante se analizan los movimientos de asir

y de manipular y se nota la posici6n de la mano al asiren relaci6n con el antebrazo y el modo especifico en queel objeto o herramienta ha de ser usado.

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power grip and precision handling · annalsoftherheumaticdiseases the shortening of one tendon...

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