Radial Palsy. retain even their proportional relationship after a period of wasting and generalized atrophy.

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for that muscle at that joint. are more memorable and because the use of many places of decimals might give a false wrist. I shall first summarize the balance of the aura of precision. normal wrist.

1 Palsy As the major effect of radial pals is at the subjects following selective parah sis. 126 CLINICAL NtECIIAMCS OF TIlE 11AM) retain even their proportional relationship after a period of wasting and generalized atrophy. X units 1 units active wrist extension moment (X). for that muscle at that joint. are more memorable and because the use of many places of decimals might give a false wrist. I shall first summarize the balance of the aura of precision. normal wrist. If a wrist is to be maximally stable with no need for finger movemetit, as when a fihter uses his clenched tist in boxing, both wrist movers and finger movers become wrist stabi lizers (Fig. 9-1). In such cases the total relative moment avail able for wrist extension is bout 25 and the to tal relative moment for wrist flexion 57. Thus the flexor side has about twice as much avail able moment as it needs for stability. The total relative moment for ulnar is 2. The total relative moment for radial is 2. When tinger and thumb movement is priman, the wrist needs stabilization chiefly to position the hand and to hold it against the destabili zation of the wrist caused by asymmetric and alternatitig movement of the digits. In such cases it is mainly the dedicated wrist-moving muscles that are used for wrist stability, leaving the linger-moving muscles free. The total rela tive moment for dedicated wrist extensors is about 1 and for wrist fiexion 22. devia tion is 17. and ulnar is 2. Wheti all the fingers and the thumb are to be maximally flexed for grasp, they exert a total relative fiexion moment at the wrist of about. This is in excess of the available (dedicated) wrist extension moment. Thus a free hand can never use its full potential for grasp, because it would force the wrist into flexion. 1-lowever, the full potver of grasp can be used when the hand of the wrist is maintained, in this case, by the weight of the body suspended from it. The same is true when carnring a heaw suitcase. ors may contract maximally. If there is need to extend all digits forcefully, the long digital extensors can exert a total rela tive moment of 12 at the wrist, which can eas ily be matched by dedicated wrist flexors. A yen common action of a normal hatid is when it grasps the handle of a hammer or axe and swings it downward into ulnar with the forearm midprone. This action is fbi lowed by the lulling of the hammer or axe into holds the branch of a tree and supports the body weight hanging from branch. The balance Gravity stabilizes the wrist so all the finger flex Gradually we shall obtain more measurements 1mm Lnlraoperative studies arid from normal One other source of error relates to the fact that in all normal use of the hand. joints are held stable by some simultaneous contraction of muscles that oppose eacit other. Thus if a wrist were to be used firmly in flexion, for ex ample, both flexors and extensors would con tract, but the flaxors would exert the greater moment. The extensors would exert just enough moment to keep the joints in firm congruent contact rather than to allow am angular tilting at the joint that might occur if the muscles on only one side were to contract. We have made no attempt to calculate this stabilizer function in the following studies. For example, I may slate that, in order to balance finger I lexors, the wrist extensors need X units of extensor moment. Perhaps I should have said that they really need X + V units, because the wrist flexors will also contract with a moment of V units. for the sake of stability. Thus the extensors and Ilexors of the wrist would each provide a moment of V for wrist stabilih. but the extensors would comract with an extra mo metit ofx units to balance the tinger fiexors. So that total wrist flexion extension moment would be: Wrist extension moment to balance linger fiexors = Wrist extension moment to balance wrist tlexors = rherelire wrist extensor moment needed lhr equilibrium = X + V units In our calculations we have omitted V and assumed simpfv that we need to balance active wrist flexion caused by finger tiexors (X) with All of the figures we use are relative. There are no absolute figures or even average figures for strength of muscles. We use the tension fraction (see Table 11 1) atid multiply it by the moment arm atid call that tie relative moment In the face of these various sources of error and speculation we have felt free to use whole numbers most of the time, both because they

2 OI ERATIONS To RESTORE MUSCLE BALANCE TO THE HAND 129 of the ith no fighter wrist stabi availthe to Thus avail ie total 2. The [1 is 2. imafl, )Osition stab lii EDC EIP,EPL 1 EDCM DC R jedq EDCL._ 2 E P LII rela isors is 1 devia re to be APL FCR FDPI FOPR FD P1 A Z-FDSL FDSM FDSR FC U p1 licated) ver, the ie hand )rts the balance by the it. The ;uitcase. ger flex tefullv, al rela :an CBS.5. hand is r or axe eviation n is fbiaxe into Flexion Fig This is not an anatomical diagram; it is a simplified mechanical statement of the Ca pability of each muscle to affect the wrist joint. The positions of the tendons in relation to the axes of flexion-e.xtension and of ulnar-radial represents their moment arms at the wrist. The number of dots in each cluster is an indication of tl1e tension capability of that muscle-tendon unit rounded off to the nearest whole number. iwl, Abductor pollicis longus;, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus;, extensor carpi ulnaris; EDCI, extensor digitorum communis (index); EDCL, extensor digitorum communis (little); EDCM, extensor digitorum communis (middle); EDCR, extensor digitorum communis (ring); EDQ, extensor digiti quinti; El?, extensor indicis proprius; EPE, extensor pollicis brevis; EPL, extensor pollicis longus; PCI?. flexor carpi radialls;, flexor carpi ulnaris; ED?!, flexor digitorum proftindus (index); FDPL, flexor digitorum profbndus (little); FDPM. flexor digito rum profundus (middle); FDPR, flexor digitomm profbndus (ring); FDSL, flexor digitonim supethcialis (little); FUSI. flexor digitorum supefficialis (index); FDSM, flexor digitomm su pethcialis (middle): FflSR, flexor digitorum superticialis (ring); PL, palmaris longus.

10 CLINICAL MECHANICS OF TIlE HAND O1 FmtTWNS To RESTORE MUSCLE BALANCE TO TiLE hand 11 radial and then by continued alter tia t ion between ulnar and radial devia t ion.

time. In flict the radiodorsal would be 10 and the ulnar-dorsal (in the midprone position) would be only, because the extensor carpi ulnaris in the midprone position has a very small moment arm for

Since active ulnar cievia lion with the tist clenched demands a strong extensor carpi ulnaris action, and since the extensor carpi ulnaris lies close to (lie flexor-extensor axis when the forearm is

3 10 CLINICAL MECHANICS OF TIlE HAND O1 FmtTWNS To RESTORE MUSCLE BALANCE TO TiLE hand 11 radial and then by continued alter tia t ion between ulnar and radial devia t ion. If the ulnar dorsal and radiodorsal quadrants of wrist extensors were each to relax in turn when the other contracted, the available wrist extension moment would be variable, oni half being used at a time. In flict the radiodorsal would be 10 and the ulnar-dorsal (in the midprone position) would be only, because the extensor carpi ulnaris in the midprone position has a very small moment arm for wrist exten sion (p. 208). Since active ulnar cievia lion with the tist clenched demands a strong extensor carpi ulnaris action, and since the extensor carpi ulnaris lies close to (lie flexor-extensor axis when the forearm is fttlh pronated, it fol lows that hammering must be cliflicult and weak with a pronated forearm (It ist try it) In foci in nianv such reciprocal actions 11w flexor carpi ulnads and extensor carpi ulnaris act to gether and alternate with the extensor carpi ra diabs brevis and longus. On the downstroke there is marginal wrist support for grasp. A glance at Fig. [-2 shows the total imbal ance that results from radial palsy. No active tendon crosses the wrist dorsal to the flexor-ax tensor axis. Am active flexton of the fingers must result in wrist Ilaxion. which leaves the tinger fiaxors using the weakest part of their muscle tension curve. The hand is almost use less. The first priority of the sitrgeon is to place a strong muscle dorsal to the tlaxion-extension axis, so that the fingers and thumb can flax strongly again. The second priority is 10 con sider ulnar radial stability. If the first transfer is to be delayed for am reason, the wrist must be supported in a splint, to allow continued use of the hand and to prevent progressive short ening of the muscle fibers of all fiaxors. Almost all hand surgeons have used the pronator teres as the motor for wrist extension in radial palsy. Such unanimity suggests that the choice has been good. The tension fraction of the protnttor teres is 5,5 compared to 12 for the preparttlysis total of wrist axtensors. The to tal tension of all radial supplied muscles that cross the wrist is 429i, of the lotal of all muscles crossing the wrist. So the total available strength of all muscles that cross the wrist after radial pal is only 58% of the total before pa rah sis. For perfect balance afier radial palw, all actions would have 58% of the moment they had before radial pal. Thus the pronator teres is not so far short of the tension needed for bal ance of the wrist at this reduced level. Moreover PS ECRI R- depl,edcm,edcr (X -,,,,EDQ Q() EDCL PT 2 0 cc 0 GD 00 C) E PB APL 1 2 U FCR FDSI FDSL FDSM FDSR 444 PLA = Unparalyzed = Paralyzed FC U Flexion Fig. 9. palsy: cued itt the wrist. In this tiiagrath each tendon that crosses site wrist is represen tec I 1w a group cit circles, earl i of wit id tlenu his 1.0 ut sit 00 our scale of t ela t Ye tension (six p. 194). se have used I Ire nearest whole nunibet. Each tendon lies in its me clianic;tl relationship to the axes of lexinn extension anti of radial and ulnar, the black circles are normal tmtscles and he white circles are paralyzed. (See Fig. 9 1 legend for abl revia t ions.) - Flexian = Unparalyzed o = Paralyzed Fig. 9. palsy. A way to maintain t adiat ultiar balance at the wrist vhett the pro nator teres is attarhed to the extensor r;rrpi radialis brevis as the wrist extensor. sut: When normal muscle is transf en t ed to the site of paralyzed mttscle 0, the symbol $ indicates activation of pat-alyzed tendon, while the original tendon becomes 0.

I 12 CLINICAL MECIIAMCS OF Tilt 11AM) OPERATIONS TO RESTORE MUSCLE BALANCE TO THE hand 1 if the pronator teres is put into an insertion such as the extensor carpi raclialis brevis with its large

However, although there is agreement that the pronator teres is the right muscle, not all surgeons agree about the insertion, and here is where a little mechanics should help.

The pronator teres is inserted into both the extensor carpi radiatis longus and the extensor 012, carpi radialis birvis. This is a yoke insertion j: using both tendons on the radial side of the axis?

It results in a strong link between extension and radial. In neutral extension of the wrist the extensor carpi radialis brevis tendon would become slack (see Fig.

If the wrist is in a neu tral flexed position, only (lie extensor carpi ra dialis brevis insertion win be effective.

The extensor carpi radialis bwvis is used as the only insertion.

It is no use expecting the flexor carpi ulnaris to restore radial ulnar balance because the flexor carpi ulnaris cannot ulnar deviate without also exerting significant flexion moment.

4 I 12 CLINICAL MECIIAMCS OF Tilt 11AM) OPERATIONS TO RESTORE MUSCLE BALANCE TO THE hand 1 if the pronator teres is put into an insertion such as the extensor carpi raclialis brevis with its large moment arm, its total relative nioinetit will turn out to be 52% of t]ie total moment of the nornial wrist extensors. some of which have small moment arms. However, although there is agreement that the pronator teres is the right muscle, not all surgeons agree about the insertion, and here is where a little mechanics should help. Consider some of the alternative suggestions for insertion of the pronator teres. 1. The pronator teres is inserted into both the extensor carpi radiatis longus and the extensor 012, carpi radialis birvis. This is a yoke insertion j: using both tendons on the radial side of the axis?. This has often been recom mended, perhaps because the tendon of the ex tensor carpi radialis longus lies temptingly close beside the tendon of the pronator teres. It results in a strong link between extension and radial. In neutral extension of the wrist the extensor carpi radialis brevis tendon would become slack (see Fig. 4-26) and only the extensor rarpi radialis longus would be the efiective insertion, and this has a small mo ment arm fbi extension. If the wrist is in a neu tral flexed position, only (lie extensor carpi ra dialis brevis insertion win be effective. This pattern is so obviously foolish that the double extensor rarpi radialis brtn is erterisor car-pi rn thahs longus insertion shouki never be used. 2. The extensor carpi radialis bwvis is used as the only insertion. This gives a good moment arm for extension but it does have a significant radial moment too, and there is no ulnar deviating extensor moment to balance it. It is no use expecting the flexor carpi ulnaris to restore radial ulnar balance because the flexor carpi ulnaris cannot ulnar deviate without also exerting significant flexion moment. Thus each time the flexor caqi ulnaris is used to add ul nar side stabilization, the wrist would lose its essential extension support. A hammer or axe would fly out of the hand each time an ulnar swing took place, because the wrist could not ulnar deviate without flexing and this would loosen finger fiexion. a. A possible solution to the excess radial de viation when the pronator teres is at tached to the extensor carpi radialis brevis would be to link the extensor carpi ulnaris and the flexor carpi ulnaris into a yolce, with two insertions and a single motor, to make the flexor carpi ulnaris into a pure ulnar deviator (Fig. 9-).?. A yoke attachment is macic of the pronator teres to the extensor carpi radialis brevis and the extensor carpi ulnaris insertions. This would balance radial ulnar, but the extensor carpi ulnaris hasaven small moment for extension and would limit the total exten sion nioment of the pronalor teres (as the ex tensor carpi radialis brevis did in I above.) This is riot reronirnended, 4. The pronator teres may be attached by a yoke insertion between the extensor carpi radi alis brevis and a tendon graft to an ulnar side insertion that has a moment arm for extension siniilar to that of the extensor carpi radialis brevis. There are two ways tlus can be done. a. Attach the pronator teres to the extensor carpi radialis brevis and the extensor carpi radialis longtis together proxinialb. Then detach the extensor carpi radialis longus from its insertion, ptlll it out prox imal lv and tunnel it to t lie base of the tburt Ii metacarpal where it can be at taclied to dorsal liganietits or bone or both (Fig. 9-4). b. The extensor carpi ulnaris tendon ma be cut proximally and the tendon pulled out distally at its metacarpal insetion. Then the proximal end mat be tunnelled obliquely across the forearm to join the extensor carpi radialis brevis at the point where the pronator teres is attached. It will be found that the rerouted extensor carpi ulnaris tendon will have a reduced ulnar moment arm and an en hanced extensor moment arm, making it comparable to the extensor carpi radialis brevis on the other side. RECOMMENDATION I suggest that 4a is a good choice and makes for lateral stability; 2o is acceptable and has the advantage of retaining active ulnar devia tioti. If a tendon transfor for utist extension is done early, to restore activity to a hand in which it is still possible that some radial nerve recoven may take place, then I suggest trans forring the pmnator teres to the extensor carpi H 0 radialis brevis only, with the extensor carpi ra dialis brevis in continuity. This will give good usable wrist extension. Later, if the nerve recov ers, nothing will have been lost. If the nerve does not recover, an ulnar-side yoke may be added later, especially for a manual worker who recognizes the need for it. FINGER EXTENSION IN RADIAL PALSY PT 2 4( C C Flexian A r, EDQ * S = Unparalyzed = Paralyzed Fig Iütclial 1xt1 sv. ha lancer I wrist tx tension achiever I b to nsfër o C tim,rom, I or I eres (FF) to he extensor carpi rtcliilis beet-is and base of the tbnrth metacarpal (using the exien stir L arpi rinlialis loneus as a grati in silt,). Null:: When nr,rmii muscle is transfrn ed iii the site otjxiwh zerl muscled, the symbol S indicates activation nf jsirahved tendon, while the original tendon becomes 0. A ten common pattern of transfer has been that of the flexor carpi ulnads to all finger cx tensors? and the palmads longus to the exten sor pollicis longus (Fig. 9-5). The flexor carpi ulnaris has a tension fraction of about 6.5 and this is mow than adequate for finger extension, Hon ei er, there are two objec tions to tins transfer. 1. The muscle fibers of the flexor carpi ul naris are very short. They are just ade quate for wrist movement, but inadequate for finger extension plus wrist movement (Fig. 11-il, B). 2. It leaves no prime ulnar deviator for the wrist stabilization of the wrist is of great importance and ulnar is a t en significant movement and should not be sacrificed lightly. This was clraniaticallv illustrated for me while I was giving the Bunnell memorial lec ture in San Francisco some years ago. I had

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