THE MOVEMENTS OF Function 2. M. A. From Muscles retain position for another influenced by that which not is simply The The shunt “ of in the while during movement. nineteenth while These century. spurt “ is the “ is possible to anatomical arrangement. words were distinguish shunt SHUNT A shunt muscle is one across it ; whereas distinction becomes that in which the bones make an the joint is inserted far from which arises if any, This far from muscles the with even for rule. The most posterior spurt ischial muscles joint origins is true to the spurt into of the function “ by muscles its the ; the phasic action are it is clear the joint of their two that kinds of muscle above it remain pubic by more English simple fibres and that the difference origins and insertions. is, of course, more nearly (Fig. The the along muscle are in the of their two types for the than There are they act. to be an exception whereas the brachialis anticus shunt muscles. From is the relative the joint do those most are these distance from action of the in main that muscles whose length beyond parallel to the moving bone than near a muscle very few, which muscles, distinction The to arises hand, on appears the bone which other joints and are the than along it. of full extension muscle. spurt brachii these reason the the at first brachio-radialis The descriptive. engineers A muscle On from biceps between 1). muscle. which of this is muscles inspection force to it is a spurt muscle, muscles. teres other near functions of the MUSCLES equidistant magnus shunt pronator examples is inserted in a field with movement in a curve, curve. As a general rule it contractile a shunt insertions adductor are each with it is clearly and and anterior fibres angle change out bone in the direction of the joint, the curved path which it traverses SPURT more and and mechanics spurt or they is carried a spurt muscle directs more of its force across the bone effective as soon as the joint moves from the position one and postural “ AND directs between force associated tangent to that from MUSCLES function) functions along the bone along introduced muscles (postural arrangement Shunt “ is the centripetal force which acts along the “ Cork of these and “ College, position distinction function IRELAND University Each refers to the force which is transmitted spurt refers to the force which pulls the JOINTS Musculature in a given it is reflected AND CORK, function). gravity. terms the Department of a joint (phasic for of MACCONAILL, A natomy bones academic, themselves. Shunt the the BONES is greater than of the opposite type, and thus direct more of their force along the bone. It is possible to develop the thesis in a mathematically precise manner (MacConaill 1946) ; but this is not necessary for the practical grasp and application of the principle. This principle finds two chief applications, namely, interosseal parts a mechanical expansions, basis which explains and an understanding of the musculature The more sheaths transmit, that the 100 clinical than serve importance bursae, the FUNCTION of tendon ancillary simple close against “vaginate” and lumbricoof the several of joints. THE no the sites of tendon sheaths of the sequence of contraction purpose to OF synovial the fibrous of retaining the bone in all positions muscles, as we may call TENDON SHEATHS sheaths has sheaths the obscured beneath tendons, the which and fact they therefore that they run. the are Fibrous forces they of the joint. The effect of this function is them, are shunt rather than spurt muscles, THE JOURNAL OF BONE AND JOINT SURGERY THE except the for digit the joints in the at case which of the the explanation It makes the art not longus BONES AND digitorum. of ballet example, This LUMBRICAL ankle and wrist dancer and the AND is shown The the instinct sheaths perhaps deeply more shocked. in Fig. joints over sheath and 1 FIG. Scheme between proximal examination extensor than that candidate is less entitled to show Spurt and the difference shunt muscles. The spurt muscle (A) pulls more directly across the bone in most positions other than full extension. The shunt muscle (B) pulls more directly along the bone. to the paper by pull the direction the a sheath Sunderland (1945), CISARTICULAR The distance movement from of a joint the may AND origin made are the -is (Fig. the muscle The ratio When muscle muscle that A in Fig. ; but if the then proof the the axis length. to is primarily (MacConaill ratio has a special part and upon cases and to the and this action will than be The application VOL. 31 B, NO. is enhanced 1, FEBRUARY are lumbrical inserted into These the expansions postural the bulk mechanism of the limb, of the and they from axis its full length to concept muscles the B the ‘I the this Hence by enclosure in 1949 there muscle behaves Where there muscle, two it is a shunt a synovial to show the of a fibrous Where author’s over 2 FIG. Scheme action Further passing to it. of war. of in underlying far distal theatre natural (C) to as muscle. in Pacific the ratio CIT muscle to the unity, found the length, the insertion of These measurements a shunt 1946). is inserted the LENGTHS is but formed a joint-stabilising tendon sheath. sheath (A) the a spurt muscle. sheath bound elbow (its by joint, the bones. muscle. on the above to the the the action distance muscle (B), to as a shunt a short or postural sheath as being on the no is behaves joints. The biceps brachii may be taken as an example. It is a muscle which acts upon the shoulder j oint and also radio-ulnar j oint is irrelevant to this discussion). It arises shoulder say, of the they of the digits cisarticular is stretched to of the cisarticular is greater statements who is why the extensor in a palmar (or plantar) the tendon in close apposition with 1, then the muscle is primarily a spurt ratio be less than unity, as in the muscle muscle of these paper ratio than, tendon. TRANSARTICULAR transarticular length (T)-that is to say, a guide to the functional relation of the joint. B, while 3). based of a muscle be called and the distance from that muscle is the transarticular length posture. joint, is to be at the correspondfunction served by a by expansions extensor form the of of the examiner who cannot see where of the They between range candidate who assigns tendons of the fingers is to also muscles tendon of the and thus keep bone. joints rather than move phasic. In this enable the fingers (or toes) to be used effectively over a wide range of posture. Attachments to the more distal a similar function at the joints of the fingers. For a first-hand nerve injury upon the functions of these muscles the reader is parts of the tendon subserve account of the effects of referred is served parts of MUSCLES sound The interosseous joint 2. a wide flexor beneath a metatarso-phalangeal forgiven, because the range of angulation ing joints is comparable. In fact, the flexor terminal acrobat. of the to the index-extensor the bones together rather than INTEROSSEOUS tendon 101 JOINTS ensheathed-for muscles tend to press than mobilisers-postural stability of the THE OF are shunt rather of the possible they flexor It will thus be clear that them. They are stabilisers lies MOVEMENTS the shoulder, and by 102 the M. prolongation of the sheath along the elbow and is inserted but spurt or phasic muscle for the elbow. to other muscles which are disposed long head of the biceps femoris had of the knee, acts on two joints and We a spurt THE bicipital groove. are muscle led, then, to one and REVERSIBILITY OF MUSCLE at the joint. cisarticularlength (T) of a muscle. of the joint the spurt interchange musculature for muscles tendons (C) See The influence environment ; and assessment lifting is a constant of muscles power measure factor must THE The magnitude of this direction a bone of its conof movement moment of contraction an added loads put in attempts they So actfar from as spurt the muscles are therefore shunt action is not their cisarticular and those which exceptions, have lumbrical it appears that and reserve efficiency. power, than the load, is one of the the for any in action which given of a parallelogram load. at varies We of forces time ; it with the have thus which if the ratio J/W were known, respectively. The law which underlies balances the pull of gravity whether acts at total load, the directional could I k FIG.4 ‘ , , The - parallelogram of forces of a joint at rest (or moving at minimal uniform speed). ‘ (W) Total load (weight oflimb plus extraneous forces all forces MUSCULATURE Weight- rather towards the centre force is the resultant of gravity the upon them. at numerical which have a resultant directed the joint (Fig. 4). The other muscle is of in our two without to scale in moving overcome or lines a muscle the limb. The weight of the may often be comparable force the TO analogous upon the of squint. limb, with is fixed : when the shunt effect when they act from they act from anatomical insertions. and conversely. This restriction absolute force, of the muscles and are thus to the tests which an ophthalmologist makes oculomotor apparatus of a patient suspected In all important cases the weight of the centre of a muscle tendons, nor for Apart from these GRAVITY of gravity of muscular tests OF the the maximal extraneous fact has to be kept in mind This have sheathed into them. RELATION this force as well as move parts moved by muscles with rule muscles which are prime movers, and shunt muscles which are joint approximators, their roles with reversal of their directions of contraction. That is to say, of a joint is mechanically reversible as a whole, but not by parts. THE far to the other. action is concerned, the reversible. But their reversible ; for in general is indicated. which inserted it arises ACTION of the transarticular lengths are unequal ; and the greater anatomical origins, the less will be that effect when The cisarticular length then becomes the transarticular, does not hold and interosseous general the origin muscle or fromfibres,the whether insertion. 3 . hand solely upon the moment force taken about the axis independent FIG other muscle effect depends tractile meaningsof length of motion the to this a shunt The To illustratethe and transarticular text. The axis On a short distance distal to it. It is therefore a powerful The example of the biceps brachii is extended readily similarly. In particular, Haines (1934) showed that the little phasic effect upon the hip joint when it acted as conversely. it is chiefly MACCONAILL the above a motor A. of of the but of moving part load). (M) Muscular force required to keep the part at rest, shown acting through centre of gravity of the moving part. This is the resultant of all the actual muscle forces in operation. (J) The resultant of the other two forces, acting across the joint. It is shown in the text to be equal in magnitude to the total load. be drawn J and W being the total shunt the concept of this parallelogram the joint be at rest or in uniform THE JOURNAL OF force and the total load is that musculature motion. BONE AND JOINT SURGERY THE limb It is an anatomical is not retained say, the has will be amount the fact that automatically centripetal curve, to MOVEMENTS or shunt be supplied which the AND structure assistance must In constant during uniform movement. will be proportional to the square of a joint is such that of muscles is required be present musculature.* 103 JOINTS so far when we have as this is true, In accordance of the rate of turn the swinging : that is to movement the along shunt a J, force, with the laws of physics the of the bone about the axis of joint. then What equal to the of the and is the J of when the joint large tonus arc at is present, the part is on the same rate and the swing. That is, in the limit, to the load (W) and is constantfor It follows that when the weight joint, as in the upraised forearm muscles will be in minimal action. rehabilitation of cases of infantile agreement argument. between Further traction of the expectation evidence several Let bone, rest that force centripetally rapid be the require place of surface his hands his elbows. of marked reversed. first case are anti-gravity 31 B, looked and the typical for in each be added free “) top For practical NO. 1, FEBRUARY a the upon is the of the of con- musculature the be the of the the of a joint joint force along the which acts joint. bone. Any more That force cannot along the curve as of the movement. nature muscles The is most experiment of a door the is much summarise muscles name force the truth sequence acceleration shunt case. brachio-radialis The the can therefore as the * the the uniform ; that difference easily is to then to the in positions implies, have purposes the 1949 ease aided by pull rOle of the other a special say, arc of movement nearly may play be the those subject the by complete regarded that extension swing at the to bending in advance have been a moderately by saying of expect subject slowly, contraction raise in rapid order would marked contraction and shunt muscles musculature to asking up of muscular the than part as one by himself of observation making between observed, is to be checked and that We also are by the It “ or shunt downwards movement will then be seen to come into biceps, for the roles of spurt weight. muscles, uniform is excluded available be say, should to inward It will The brachio-radialis contraction of the (forearm over is proper is considered. joint. an for possibility anatomy. upon, the proper joint than the prime movers. Thus we should expect that the teres, and the brachio-radialis, would come into increased conthis can easily be felt and seen to be the case. These four muscles to some extent throughout the movement ; it is an increase of origins on grounds of the impart only is to its be moved as towards would The biceps can and has “ force that they This which joint directed along muscles, of the and a force to act bone. contraction is true, give force spurt contraction above to shunt the closer to the biceps, brachialis, pronator traction in that order, and are, of course, contracted be CONTRACTION possible the with it may swing,” pendulum “ movements slowest by are known a greater as one along which pendulum “ not of itself demonstrate nature is available if the for all positions well muscles that possible degree of tonus arm is hanging vertically centripeta.l MUSCULAR stated gravity the will of to W. This arc, but the the same with OF law same throughout movement provided the with being It appears or on the ankle in standing, the prime movers or spurt This is well known and has been applied admirably to the cerebral palsy by Phelps and his school (Collis 1947). This concerned that combines ? is a minimal When the when the joint is at rest the all positions of the joint. of the part is acting vertically SEQUENCES it be assumed is at with and event does of a confirmatory muscles THE which moving threshold is equal a small therefore pendulum equal is not load, musculature, this value W. The argument is thus : there consistent with security of the joint. total centripetal force which balances the weight rate of swing. A pendulum swings through VOL. BONES the form and ; the active force by OF spurt ; while joint. as the arc of a circle. in the heavy muscles shunt 104 M. It is understood, at the start than inhibition out upon of course, of the of the the that movement. MACCONAILL moving Very the often, antagonistic experimenter A. fibres. himself. limb such An against gravity acceleration seems experiment Practise calls to be is instructive relaxing the for acceleration gained by muscles, no more be carried those of the ; it has to especially upper limb : in particular, let the arms hang heavily by the sides ; sit-or better, stand-with the two arms hanging by the sides in that way ; now let them bend at the elbows ; do not even try to bend them actively. If the shoulder muscles be relaxed completely the forearms will be felt to float upwards, much as if they were floating in salt water. The “ “ “ sensation is remarkable attain considerable fixed upon “ and quite angulation a distant different of object so the that from elbow the that in increase the rOle and finger the elbow. in the of shunt muscles flexors utmost This account in which the and value. which concept been purpose statements of spurt has of the be have two part at be seen in if others a slight, shunt to have but demonstrate of the wrist musculature of muscular of muscular all be tone of the of the synovial will psychological will survey aspects be experiments preliminary are to if possible, normal There The increases served of fresh the mechanism not been grounds from It is possible should, exhaustive to or flexion. eyes clenched. these muscles chiefly lightly will the and an shunt The elbow. fingers to the given either writer upon and been fists of the elbow, to way. detachment the the an introduction treated made clenching over intended than Attention have The pass is not as no more of flexion ; for which intended speed of deliberate this concomitants of cubital flexion may be attained. The experiment may be repeated with the perceptible, “ “ of action joints, ; it a particular relevance arrangement and standard works upon are stimulated to is a mechanism action the subject. question the experiment. SUMMARY 1 . Muscles displacement acting upon any or spurt muscles, 2. which Muscles shunt muscles. 3. The fibrous arise far tendon 4. The lumbrical 5. The arrangement joint and from sheaths and can be muscles the are muscles musculature joint cavity during movement is supplied rest or mainly uniform by the 6. described are are to spurt joint-stabiising interosseous of the Experiments joint divided into of stabilisation muscles ; those which : muscles arise near of it are mechanisms. are muscles is such these of stabilisation as to movement. shunt muscles. illustrate two principal groups or shunt muscles. ensure The of the a constant necessary digits. pressure centripetal across force the during observations. REFERENCES (1947) : Reablement of Children with Infantile R. W. (1934) : On Muscles of Full and of Short MACCONAILL, M. A. (1946) : Some Anatomical Factors Irish Journal of Medical Science, 6th series, 160. COLLIS, E. HAINES, SUNDERLAND, Muscles. S. American (1945): The Journal Actions of Anatomy, of the 77, Extensor Cerebral Action. affecting Digitorum Palsy. Lancet, Journal the H, 239. of Anatomy, Stabiising Communis, 69, 20. Functions Interosseous of and Muscles. Lumbrical 189. THE JOURNAL OF BONE AND JOINT SURGERY