functional assessment ofthe hand: reproducibility ...measuringresponseofpatients to...

Annals of the Rheumatic Diseases, 1987; 46, 203-208

Functional assessment of the hand: reproducibility,acceptability, and utility of a new system formeasuring strengthP HELLIWELL, A HOWE, AND V WRIGHT

From the Regional Rheumatology Centre, Royal Bath Hospital, Harrogate; and the Rheumatism ResearchUnit, University Department of Medicine, General Infirmary at Leeds

SUMMARY A new system for measuring strength of the hand using a torsion dynamometerlinked to a microprocessor is described. The system permits analysis of timed squeezes of bothgrip and pinch and is adjustable to all sizes of hand and degrees of hand deformity. Resultsobtained with the system were found to be reproducible, and the rigid device was acceptable to agroup of patients with arthritic hands. In rheumatoid arthritis there is a marked reduction inmaximum grip and pinch strength, together with a prolongation of the time taken to reach thismaximum, and increased fatigue. The limitations of grip strength as a measure of function of thehand are discussed.

Key words: grip strength, pinch strength, rheumatoid arthritis, microprocessor.

Despite the development of indices designed toassess the function of the rheumatic hand,' gripstrength assessment remains the cornerstone ofmost longitudinal studies designed to show func-tional change in the hand. Traditionally this ismeasured using a Davis bag, which is essentially apneumodynamometer. Despite the ready avail-ability, cheapness, and portability of this apparatusas an instrument for measuring strength, thepneumodynamometer has several drawbacks.Firstly, pressure produced in the system is de-pendent on force multiplied by the area over whichthis force is applied and with the Davis bag theposition of the patient's hand with regard to the bagcannot always be relied upon to be the same.Secondly, the pneumodynamometer is filled withair; since air is compressible, the system is liable tobe non-linear in response,2 though theoretically themagnitude of this error is likely to be small. Despitethese objections results with the pneumodynamo-meter are acceptable and reproducible,3 though inpractice the observer of three consecutive readingswith this device may be unconsciously smoothing thevalues.

Accepted for publication 29 August 1986.Correspondence to Dr P Helliwell, Rheumatology and Rehabili-tation Research Unit, School of Medicine, 36 Clarendon Road,Leeds LS2 9PJ.

Attempts to refine the pneumodynamometerhave been made. Filling the system with hydraulicfluid and enclosing the bag in an aluminium sleevelhave been tried to overcome the aforementionedproblems. Linking the pneumatic system via atransducer to a microprocessor and performinganalysis of the grip time curve has also beenattempted.4 These authors suggested that the rateof development of maximum grip was a moresensitive indicator of hand dysfunction than themaximum grip strength itself. Furthermore, it hasbeen suggested that changes in the rate of develop-ment of grip serve as a better discriminator inmeasuring response of patients to anti-inflammatorydrug therapy.6We have used a new strain gauged torsion

dynamometer linked to a microprocessor for analy-sis of a timed squeeze in a group of normal patientsand in a group of patients with rheumatoid arthritis.We have established normal values for the grip timecurve and have assessed reproducibility of succes-sive measurements. First impressions of the newsystem were that the rigid device caused morediscomfort to people with rheumatoid arthritis thanthe more malleable Davis bag. Therefore, a patientpreference study was carried out in a group ofpatients with rheumatoid arthritis in order to assessacceptability of the new device.

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204 Helliwell, Howe, Wright

Description of systemMax

The new digital grip analyser is shown in Fig. 1. Thedevice consists of two cushioned aluminium barsapproximately six inches long. The separation be-tween the two handles is adjustable to suit any handsize or deformity and the design allows for measure-ment of finger pinch and hand grip strength. Adigital readout facility in newtons force is providedwith the option of holding the maximum valueobtained. The grip strength analyser was interfacedwith a BBC model B microcomputer. The softwarefor use with the analyser provided a visual cue tostart the test and an audible cue for the patient torelease their grip.The computer program records force in newtons

every 0-2 seconds for a total time of 4 4 seconds.The grip versus time curve thus produced is graphi-cally displayed on the monitor and can be printedout on completion of the test (Fig. 2). The curve ismathematically described by the following para-meters: maximum grip strength in newtons; time tomaximum value in seconds; rate of loss of grip frommaximum value to the point of release of grip(described as the fatigue rate), expressed in newtonsper second; an expression of the amount of fatiguein terms of the percentage loss of grip from themaximum grip strength to the point of release of thegrip (this is given by the formula (MGS-FGS)100/MGS, where MGS is maximum grip strength andFGS is final grip strength); rate of loss of grip fromthe point of release to baseline value (described asthe release rate), expressed in newtons per second;

-

dou

0LL

RR

I%---~~~~~FR

I \/I\1,

Itm>I...I

O 1 1tO-9mnax Time (s)

Fig. 2 Schematic representation ofgripltime curve.Max=maximum grip strength in newtons. T... -=time tomaximum grip in seconds. t -time to 90% ofmaximum grip in seconds (see 'Discussion'). FR =rate ofloss ofgrip from maximum value to point of release innewtons per second. RR= rate of loss ofgrip from point ofrelease to baseline in newtons per second. Powerfactor isthe integral of the curve in newton seconds.

the integral of the curve (described rather loosely as'power factor'), expressed in newton seconds.The test was found to be easy to administer and

applicable to all patients with arthritic hands.Lateral pinch (between thumb pad and side of indexfinger) was used in all subjects. In approximately10% of patients with rheumatoid arthritis it wasnecessary to adjust the handle separation. This tookonly a few seconds and was standardised for each

Fig. 1 Digital pinchlgrip meter(MIE Medical Research Ltd).



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Functional assessment of the hand 205

subject by use of a graduated scale. Narrowing theseparation between the handles in some arthritic sub-jects does not confer on them an extra mechanicaladvantage: rather it enables them to employ thesame techniques of grip as their counterparts whoare able to grip the normally spaced handles.Provided that the amount of separation is constant,between subject comparability remains valid.When a patient first uses the system one or two

trial grips are undertaken to familiarise the patientwith the machine. The patient is asked to grip as fastand as hard as possible after the signal and to holdthe grip until the signal for release is given. Withinseconds an analysis of the grip/time curve is pre-

sented on the monitor and if it appears satisfactorythe test is completed. For a patient familiar with thesystem the time taken to obtain satisfactory curves

for both hands, assessing grip and pinch strength, isabout three minutes.

Patients and methods

In an attempt to define normality two groups ofnon-arthritic subjects were studied. Group A con-

sisted of 20 members of the nursing staff of theRoyal Bath Hospital, Harrogate, most of whomwere women aged 18-30. Group B consisted ofpatients waiting to see the doctor in a generalpractitioner's waiting room. No patient complainedof pain or stiffness in the hands. The age range ofthis group was 47-90 years, mean age 63, andconsisted of 20 women and 10 men. Group Cconsisted of inpatients with rheumatoid arthritis atthe Royal Bath Hospital, Harrogate. Age range forthis group was from 33 to 77 years, with a mean age

of 57, and consisted of 33 women and 13 men. Anydifferences between groups B and C were analysedusing a t test with Satterthwaite's approximation fornumber of degrees of freedom.7

Reproducibility of measurements was investi-gated by recording three successive attempts atgripping and pinching in a group of 20 subjects withrheumatoid arthritis. For the group as a whole meanvalues for each parameter at each attempt were

calculated and the results analysed using a one wayanalysis of variance.The patient preference study consisted of 26

subjects with arthritic hands (21 with rheumatoidarthritis, three with psoriatic arthritis, and two withosteoarthritis). In four subjects both hands were

tested because of a difference between hands in painexperience, swelling, or deformity. Subjects were

asked to squeeze each device three times, resting fora few seconds in between tests. When the Davis bagwas used subjects were asked to squeeze as hard as

possible for four seconds and the maximum valueobtained each time was recorded. The device on

which the patients were tested first was alternated toavoid any carry over effect if one device was foundto be more painful to use. For each patient mean

maximum grip strength with each device was re-

corded, together with a full Ritchie articular index8and a modified articular index.9 The modifiedarticular index consisted of the observer squeezingthe wrist, metacarpophalangeal joints as a group,and proximal interphalangeal joints as a group andscoring as with the Ritchie articular index from 0 to3 according to the painful response elicited. Thusthe maximum score for the modified index for eachhand was 9. The patients were asked at the end of

Table 1 Mean values (SEM): three consecutive grips in 20 patients with rheumatoid arthritis

1 2 3 F ratio

Maximum (N) 91-4 (20-4) 89-5 (20.0) 91 2 (20 4) 0 004tm;.X (s) 2-9 (0-3) 2-49 (0 35) 2-40 (0-24) 1.05Fatigue rate (N/s) 13-1 (4-6) 675 (2.5) 10-7 (1-81) 095Fatigue (%) 10-2 (1.9) 11-25 (1.9) 11-2 (1-7) 0-11Release rate (N/s) 154-6 (31) 186-3 (35) 205-9 (39) 0 54Power factor (N.s) 392-4 (67.5) 374 7 (64.2) 379-5 (62-0) 0-02

Table 2 Mean values (SEM): three consecutive pinches in 20 patients with rheumatoid arthritis

1 2 3 F ratio

Maximum (N) 37.9 (5-3) 36-4 (4-9) 39-1 (5-7) 006tm.lx (s) 2-36 (0-3) 1-76 (0.3) 2 06 (0.3) 0-98Fatigue rate (N/s) 6-65 (2-6) 3 2 (0-6) 7-1 (2-0) 1t23Fatigue (%°) 15-1 (3-0) 14-2 (2-8) 18 5 (3-8) 0-5Release rate (N/s) 94 7 (14 0) 94 1 (13-3) 100-5 (16-0) 0-06Power factor (N.s) 155-2 (22.9) 148-2 (20-6) 154-1 (23.5) 0-03



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the test the following question: 'If you had tosqueeze these devices each day as part of yourassessment, which would you prefer?' Device pre-ference was thus noted. Any difference between thetwo groups was analysed using the Fisher exactprobability test.

Results

REPRODUCIBILITYReproducibility for grip and pinch is shown inTables 1 and 2 respectively. For the group as awhole, reproducibility was acceptable for all para-meters for both grip and pinch. On an individualbasis the maximum grip strength and power factorwere highly reproducible, but the values for tmaxtended to be somewhat erratic. Therefore cautionneeds to be taken when studying individuals or smallgroups.

COMPARATIVE STUDIESMean values for the three groups for grip and pinchstrength are presented in Tables 3 and 4 respec-tively.

Little difference was seen between the two non-arthritic groups despite the marked difference in agerange. Values for maximum grip strength showedthat in rheumatoid arthritis grip strength was ap-proximately 25% that of a non-arthritic population,with a reduction in pinch strength of approximately40%. Occasionally pinch strength exceeded gripstrength in patients with rheumatoid arthritis, andmany patients commented that they relied on tripodor lateral pinch in their everyday activities. Time tomaximum grip strength in the rheumatoid group wassignificantly prolonged for grip, while pinch timeswere also prolonged but not significantly more thancontrols. Compared with the elderly normal popula-tion, subjects with rheumatoid arthritis showed

Table 3 Mean values (SEM) for grip strength ofnurses(A), non-rheumatic patients (B), and patients withrheumatoid arthritis (C)

Group p Value(B v C)

A B C

Maximum (N) 256 (16) 238 (16) 60 (5) <0-001tm,,x (s) 1-5 ()-2) 16 (0-1) 2-3 (0-2) <0-005Fatigue rate

(N/s) 23 (4-0) 12-3 (1-2) 6-8 (2-5) <0-1Fatigue (%) 112 (1-4) 71 (0-9) 11-8 (1-7) <0-025Release rate

(N/s) 584 (65) 432 (45) 125 (13) <0-001Power factor

(N.s) 1107 (71) 1133 (74) 255 (29) <0-001

Table 4 Mean values (SEM) for pinch strength ofnurses(A), non-rheumatic patients (B), and patients withrheumatoid arthritis (C)

Group p Value(B v C)

A B C

Maximum (N) 83 (3) 78 (5) 32 (2) <0 001tm,,x (s) 1-5 (0-3) 1-6 (0.2) 2-0 (0-2) <0-2Fatigue rate

(N/s) 7-8 (1-1) 6-5 (0-8) 3-2 (0-6) <0-005Fatigue (%) 13 (2-2) 10-5 (1-3) 14-8 (2.3) <0-1Release rate

(N/s) 195 (24) 173 (20) 83 (7) <0-001Power factor

(N.s) 362 (15) 354 (23) 139 (12) <0-001

considerably more fatigue during the grip test, andthe trend was towards increased fatigue in thepinch test, though this did not achieve statisticalsignificance.

INTER-RELATIONSHIP OF STRENGTHVARIABLESTable 5 gives the Pearson's r correlation coefficientsfor maximum grip strength compared with theadditional parameters for the three groups ofpatients studied. As expected, maximum gripstrength was strongly related to power factor.Maximum grip strength was also strongly related torelease rate in these three groups, though this maynot be so for other disease states such as, forexample, myotonia. There was no correlation be-tween maximum grip strength and time taken toreach this maximum value, so these two variablesprovide independent information on the grip. Maxi-mum grip strength was positively related to fatiguerate, as expected. The maximum grip strength wasindependent of the percentage fatigue, though therewas a trend towards a negative relationship in thegroups studied.

Table 5 Correlations between variables in the three groups

Grip RA Pinch RA Grip Gripgroup A group B

Max v tm;ix -009 0-13 -0-13 -0-1Max v FR 0.47* 0-51* 0-24 0-45*Max v F% -0-29* -0-20 -0-16 -0-25Max v RR 0.87* 0.78* 0-61* 0.81*Max v PF 0-99* 0.99* 0-98* 0-99*

*Denotes significant at 5% level.RA=rheumatoid arthritis; A=nurses; B=non-rheumatic patients;FR=fatigue ratio; F=fatigue; RR=release rate; PF=power factor.



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Functional assessment of the hand 207

Table 6 Pneumodynamometer and torsion dynamometer:patient preference study in 26 patients with rheumatoidarthritis*

PD preference TD preference DK p Value

Number 16 13 1Sex 4M, 12F 3M, IOFMAI 3-71 (0-54) 3-58 (0-62) NSRI 18 2 (2-07) 15 5 (1.85) NSMGS (N) 273 (44-3) 301 5 (62.9) NSMGS (mmHg) 92-4 (8-7) 93-2 (13-5)

PD=pneumodynamometer; TD=torsion dynamometer; DK=don't know; MAI=modified articular index; RI=Ritchie articularindex; MGS=maximum grip strength.Values are means (SEM).*In four patients both hands were tested because of a differencebetween hands in pain experience.

PATIENT PREFERENCE STUDYResults of the patient preference study are pre-sented in Table 6. Sixteen patients preferred thepneumodynamometer rather than the torsiondynamometer and 13 the reverse for the handtested, with one patient undecided. There was noparticular preference by gender and the values forthe modified articular index and the Ritchie articu-lar index were not significantly different for bothgroups.

Discussion

Grip strength assessment is frequently used inclinical trials and has been shown to be a sensitiveindicator of disease activity.9 Grip strength is acomposite measure and may be influenced bydysfunction in muscles, tendons, and any of thesmall joints of the hand and wrist. In addition,accurate reliable assessment requires maximal efforton every occasion. The patients may be motivatedfor a variety of reasons and this motivation may beinfluenced in many ways, consciously or uncon-sciously, by the assessor. Thus although reproduc-ibility figures outside the trial may be acceptable,other factors may be contributing to a change in gripstrength in a longitudinal trial design. With theselimitations in mind a more detailed assessment ofhand function has been designed.' Although thesefunctional indices are undoubtedly more compre-hensive and provide a better guide to overall handfunction, the time required to complete each indexis prohibitive for clinical trial work, where manypatients may be assessed in a session.As a measure of grip and pinch strength we feel

the system described here has several advantagescompared with the Davis bag. The rigid straingauged device provides more accurate data for

immediate display. The design of the handles is suchthat the instrument is not sensitive to changes ofposition of the applied force, which is a problemwith the pneumodynamometer. The main advantageof the digital analyser, however, is that a more indepth analysis of a timed grip can be obtained byinterfacing with a microcomputer. As we haveshown this provides information on the dynamicquality of grip in addition to the maximum gripstrength. Furthermore, software is available topermit analysis of grip strength endurance, whichmay be of value in certain circumstances, such asstroke rehabilitation. This facility may also be usedfor assessing treatment efficacy in, for example,myasthenia gravis.

First impressions were that the rigid device wasmore uncomfortable for the patient to use than thesofter Davis bag, but the patient preference studyshowed that this was not so in a group of patientswith arthritic hands. The results show that prefer-ence is independent of the degree of pain in thejoints of the hand and wrist, and our overallimpression is that if one device caused pain onsqueezing then the other device also caused pain.Patients chose a particular device on the basis ofhow well they thought that device represented theirgrip strength. In other words, if they found theDavis bag slipping out of their hand then they wouldchoose the rigid device. Patients choosing the Davisbag found the rigid device somewhat unwieldlydespite its adjustable handles for any hand size ordeformity.No attempt was made to give the patients a choice

between peak or sustained grip during the prefer-ence study. It has been shown by Grindulus andCalverley that patients with rheumatoid arthritisprefer peak grip assessment. "' These workers foundthat very few of their patients could sustain a grip forfive seconds. We found initially that having an eightsecond timed grip was too long for arthritic patients,but once the program was changed to a 4-4 secondtimed grip all patients were able to grip adequatelyfor this period.

Reproducibility of maximum grip strength andpower factor using this system compares favour-ably with reported reproducibility of the pneumo-dynamometer.3 Reproducibility of tmax and fatiguerate on an individual basis is not very good andcaution must be used in interpreting these para-meters on individual patients. For a group ofpatients as a whole reproducibility is adequate. Inthe normal groups and in the patients we studied thearea under the curve, fatigue rate, and release ratewere closely related to maximum grip strength andprobably do not provide any additional information.The values tmax and percentage fatigue were inde-



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pendent of maximum grip strength, and in thisgroup of patients these three values are of thegreatest interest.

Patients with rheumatoid arthritis had approxi-mately a 75% reduction in maximum grip strengthand a 60% reduction in maximum pinch strengthcompared with non-arthritic controls. These figurescompare favourably with those obtained by otherworkers.1 12 Quite often lateral pinch is strongerthan grip strength in rheumatoid arthritis, andpatients frequently rely on this manoeuvre in theireveryday activities. In addition, surgical stabilisationof the first metacarpophalangeal joint is likely toaugment the execution of this movement, and weare currently studying the effect of surgical pro-cedures on the function of the hand in this way.

Patients with rheumatoid arthritis take a signifi-cantly longer time to reach maximum grip strengththan normal subjects. This has been noted before byMyers et al,4 though the absolute values obtainedwere quite different from ours. There is invariablyan initial steep rise in the grip time curve with asubsequent slower climb to peak grip. If the time to90% maximum is estimated this second slow climbcan be eliminated and this possibly explains thedifference between our results and those obtainedby the New Zealand group. We have now changedthe program to measure time to 90% of maximumgrip and have obtained times equivalent to those ofthe New Zealand group.

It has been suggested that prolongation of time tomaximum grip is equivalent to the subjective experi-ence of stiffness in rheumatoid disease.'3 This mayresult from several factors. Firstly, increased resist-ance to passive motion in the metacarpophalangealjoint has been recorded by Wright and Johns,'4though more recent studies with a new fingerarthrograph moving the joint laterally have beenunable to confirm these findings. 15 Secondly, pain inthe small joints of the hand and wrist may beinhibiting the rate of development of the grip.Thirdly, inherent disease in the muscles may becontributing. Electrophysiological techniques haveshown that both subclinical polymyositis and abnor-mal muscular fatiguability are common in rheuma-toid arthritis.'6 17

Ultimately, the utility of the information on thedynamic qualities of grip stength would be deter-mined in therapeutic intervention studies. Myers etal have suggested that the rate of development of

grip is a better discriminator than maximum gripstrength for measuring response to anti-inflam-matory drugs.6 We are currently studying thediurnal variation of these parameters in untreatedpatients with rheumatoid arthritis, in addition to theeffect of standard therapies such as anti-inflam-matory drugs, physiotherapy, intra-articular steroid,and pulsed intravenous steroid.

This work was supported by research grants from the Arthritis andRheumatism Council. We thank Miss Anne Laville and Mrs SheilaCoombes for help in preparation of the manuscript.

References

1 Clawson D K, Souter W A, Carthum C J, et al. Functionalassessment of the rheumatoid hand. Clin Orthop 1977; 77:203-10.

2 Kondraske G V. Measurement of the quality of hand contrac-tions. Med Biol Eng Comput 1985; 23: 399.

3 Lee P, Baxter A, Dick W C, Webb J. An assessment of gripstrength measurement in rheumatoid arthritis. Scand J Rheuma-tol 1974; 3: 17-23.

4 Myers D B, Grennan D M, Palmer D G. Hand grip function inpatients with rheumatoid arthritis. Arch Phys Med Rehabil1980; 61: 369-73.

5 Duym B W, Pfurtscheller G. Measurement of the quality ofhand contractions. Med Biol Eng Comput 1984; 22: 245-50).

6 Myers D B, Wilson K, Palmer D G. Relative changes inmaximum grip strength, work and power output during handgrip assessment of rheumatoid patients in a drug trial. ProcUniv Otago Med Sch 1979; 57: 64-5.

7 Snedecor G W, Cochran W G. Statistical methods. 7th ed. Iowa:Iowa State University Press, 1980: 7.

8 Ritchie D M, Boyle J A, McInnes J M. et al. Clinical studieswith an articular index for the assessment of joint tenderness inpatients with rheumatoid arthritis. Q J Med 1968; 37: 393-406.

9 Rhind V M, Bird H A, Wright V. A comparison of clinicalassessments of disease activity in rheumatoid arthritis. AnnRheum Dis 1980; 39: 135-7.

10 Grindulus K A, Calverley M. Grip strength: peak or sustainedpressure in rheumatoid arthritis? J Chron Dis 1983; 36: 855-8.

11 Jones A R, Unsworth A, Haslock I. A microcomputercontrolled hand assessment system used for clinical measure-ment. Eng Med 1985; 14: 191-8.

12 Walker P S, Davidson M D, Erkman M J. An apparatus toassess function of the hand. J Hanid Surg 1978; 3: 189-93.

13 Myers D, Wilson K, Palmer D G. An objective measurement ofchange in morning stiffness. Rheumatol Int 1981; 1: 135-7.

14 Wright V, Johns R J. Quantitative and qualitative analysis ofjoint stiffness in normal subjects and in paticnts with connectivctissue disease. Ann Rheum Dis 1961; 20: 36-46.

15 Howe A. Microprocessor mediated metacarpophalangeal jointstiffness measurement. University of Leeds, 1985. (PhD thesis.)

16 Steinberg V L, Wynn Parry C B. Electromyographic changes inrheumatoid arthritis. Br Med J 1961; i: 630-2.

17 Lenman J A R, Potter J L. Electromyographic measurement offatigue in rheumatoid arthritis and neuromuscular disease. AnnRheum Dis 1966; 25: 76-84.



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