Power grip, pinch grip, manual muscle testing or thenar atrophy – which should be assessed as a motor outcome after carpal tunnel decompression? A systematic review

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Power grip, pinch grip, manual muscle testing or thenar atrophy – which should be assessed as a motor outcome after carpal tunnel decompression? A systematic review

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  BioMed   Central Page 1 of 9 (page number not for citation purposes) BMC Musculoskeletal Disorders Open Access Research article Power grip, pinch grip, manual muscle testing or thenar atrophy –  which should be assessed as a motor outcome after carpal tunnel decompression? A systematic review JoGeere 1 , RachelChester* 1,2 , SwatiKale 1  and ChristinaJerosch-Herold 1  Address: 1 School of Allied Health Professions, University of East Anglia, Norwich, UK and 2 Physiotherapy Department, Norfolk and Norwich University Hospital NHS Trust, Norwich, UK Email: JoGeere-jo.geere@uea.ac.uk; RachelChester*-rachel.chester@nnuh.nhs.uk; SwatiKale-s.kale@uea.ac.uk; ChristinaJerosch-Herold-c.jerosch-herold@uea.ac.uk * Corresponding author Abstract Background: Objective assessment of motor function is frequently used to evaluate outcomeafter surgical treatment of carpal tunnel syndrome (CTS). However a range of outcome measuresare used and there appears to be no consensus on which measure of motor function effectivelycaptures change. The purpose of this systematic review was to identify the methods used to assessmotor function in randomized controlled trials of surgical interventions for CTS. A secondary aimwas to evaluate which instruments reflect clinical change and are psychometrically robust. Methods: The bibliographic databases Medline, AMED and CINAHL were searched forrandomized controlled trials of surgical interventions for CTS. Data on instruments used, methodsof assessment and results of tests of motor function was extracted by two independent reviewers. Results: Twenty-two studies were retrieved which included performance based assessments of motor function. Nineteen studies assessed power grip dynamometry, fourteen studies used bothpower and pinch grip dynamometry, eight used manual muscle testing and five assessed thepresence or absence of thenar atrophy. Several studies used multiple tests of motor function. Twostudies included both power and pinch strength and reported descriptive statistics enablingcalculation of effect sizes to compare the relative responsiveness of grip and pinch strength withinstudy samples. The study findings suggest that tip pinch is more responsive than lateral pinch orpower grip up to 12 weeks following surgery for CTS. Conclusion: Although used most frequently and known to be reliable, power and key pinchdynamometry are not the most valid or responsive tools for assessing motor outcome up to 12weeks following surgery for CTS. Tip pinch dynamometry more specifically targets the thenarmusculature and appears to be more responsive. Manual muscle testing, which in theory is mostspecific to the thenar musculature, may be more sensitive if assessed using a hand helddynamometer – the Rotterdam Intrinsic Handheld Myometer. However further research is neededto evaluate its reliability and responsiveness and establish the most efficient and psychometricallyrobust method of evaluating motor function following surgery for CTS. Published: 20 November 2007 BMC Musculoskeletal Disorders  2007, 8 :114doi:10.1186/1471-2474-8-114Received: 27 June 2007Accepted: 20 November 2007This article is available from: http://www.biomedcentral.com/1471-2474/8/114© 2007 Geere et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the srcinal work is properly cited.  BMC Musculoskeletal Disorders  2007, 8 :114http://www.biomedcentral.com/1471-2474/8/114Page 2 of 9 (page number not for citation purposes) Background Carpal tunnel syndrome (CTS) is the most common com-pression neuropathy, estimated to occur in 4% of the gen-eral population [1] with a higher prevalence in women(3% to 5.6%) than men (0.6% to 2.8%) depending ondiagnostic criteria used [1,2]. Surgical decompression of  the carpal canal is the treatment of choice in moderate tosevere cases and accounts for a large number of upper limb surgical procedures. To evaluate the effectiveness of different surgical techniques a range of outcome measureshave been used including objective assessment of motor function. Carpal tunnel syndrome presents with a range of symptoms including motor disturbance which can rangefrom weakness of the thenar muscles innervated by themedian nerve through to complete paralysis and atrophy.Surgical intervention may reverse these to a greater or lesser extent depending on the severity and duration of the condition [3]. The importance of improved motor function as an outcome may be undisputed however thequestions of what parameter should be assessed and with which instrument remain unanswered.Outcome measures need to be valid for the purpose andpopulation, repeatable over time and across testers and beable to reflect clinically important change [4,5]. There is no lack of available instruments which quantify motor function, however they may not meet the rigorous psy-chometric criteria required of an outcome measure to thesame degree. Whilst several outcome measures are neededto capture the impact of a disorder like CTS on the indi- vidual, the use of multiple outcome measures whichaddress the same domain such as motor function shouldbe avoided as it places an unnecessary burden on thepatient and clinician. The primary aim of this review was to identify the meth-ods used to assess motor function following surgical inter- ventions for CTS in published clinical trials and toevaluate the extent to which they reflect clinical changeafter decompression. A secondary aim was to review thoseassessments of motor function which reflect change andare psychometrically robust. This may contribute towardsa consensus view of how motor function should beassessed in future trials which in turn would facilitatemeta-analysis of results [6]. Methods  A systematic review was conducted to identify rand-omized controlled trials of surgical interventions for car-pal tunnel syndrome which included assessment of motor function as a primary or secondary outcome. Search strategy and review criteria  The bibliographic databases Medline [1950 to June 2006],CINAHL [1982 to June 2006] and AMED [1985 to June2006] were searched using a combination of terms: rand-omized controlled trial or controlled clinical trial, carpaltunnel and surgery or decompression or release. The titlesand abstracts of those studies retrieved were read and full-text was obtained for those studies which met the follow-ing inclusion criteria: prospective, randomized or quasi-randomized trials, the experimental or comparator inter- vention included surgical release, the patients had a con-firmed diagnosis of carpal tunnel syndrome madethrough physical examination and clinical history with or  without confirmatory electrophysiological testing and theoutcomes were described. Only English language publica-tions were considered and irrespective of the year of pub-lication. Studies which assessed motor function throughpatient-rated questionnaires such as the Boston Carpal Tunnel Questionnaire [7] only were excluded. Each study  which met the inclusion criteria was independently readby two reviewers and a data extraction form completed which detailed the type of motor assessment, equipment used, method of assessment, scaling and results. Results  A total of 28 studies were identified which met the inclu-sion criteria. Of these 22 included an assessment of motor function using performance-based tests [8-29]. The other  six studies assessed motor function through patient-reported questionnaires only. The instruments and methods used to evaluate motor out-come following carpal tunnel surgery included i) meas-urement of grip and pinch strength with dynamometry or  vigorimeters, ii) manual muscle strength testing and iii)presence or absence of thenar atrophy. Grip and pinch strength measurement Nineteen of the 22 studies used power grip strength as anoutcome measure post surgery. 14 studies assessed bothpower and pinch grip. Tables 1 and 2 summarise the tools and methods used to assess grip and pinch strength ineach study. The amount of detail given on measurement procedure varied greatly and several studies did not statethe tool of measurement, the handle position used,number of trials, whether the value reported was a scorederived from one attempt, the average or the best of threetrials, or the statistical unit of measurement. Only onestudy reported the positioning of the upper limb during dynamometry [29]. One study [12] adjusted figures for  age, sex and gender according to Mathiowetz et al [30].In order to compare the overall magnitude of changeacross these studies pre-operative and post-operative val-ues from each study were extracted. Of the 19 studies which assessed power grip strength, only six studies[17,19,20,24,26,29] reported actual pre-operative, early   BMC Musculoskeletal Disorders  2007, 8 :114http://www.biomedcentral.com/1471-2474/8/114Page 3 of 9 (page number not for citation purposes) and late post-operative values which have been plotted ona line graph (Fig 1).Figure 1 shows a marked decline in power grip within thefirst 2 weeks post surgery. By 6 weeks power grip hadrecovered to, or close to, pre-operative levels. Three fur-ther studies [11,13,16] which displayed grip strength graphically only showed a similar trend for values up to12 weeks post-operatively. Whilst these nine studiestogether demonstrate similar patterns of recovery, trendsin the studies reporting later recovery (greater than 12 weeks) [8,9,11-14,16,17,20,22,24,25,27,29] were less consistent. The differences in later results did not appear to be related to the time at which final post operativeassessment took place.Key, tip and tripod pinch were similarly analysed. Figures2 to 4 show the change from pre-operative to early post- operative pinch strength for key pinch, tripod and tippinch, respectively. Only studies where actual values werereported have been included. There was a similar patternto that observed with power grip, reporting an early post-operative decrease in pinch strength. The trend was for anincrease in tip and tripod pinch strength at 12 weeks com-pared to pre-operative values.In order to compare the relative responsiveness of power and tip pinch effect sizes were calculated. Effect size(mean change divided by standard deviation of initialscore [31]) is a standardised score which is unit free andallows comparison between different scales and alsobetween studies. However several of the studies includedin this review did not report means or standard devia-tions, therefore it was not possible to calculate an effect size from the data given. The severity of motor weaknessmay also differ within study and between study popula-tions and a high degree of heterogeneity is likely to result in a higher standard deviation of the baseline score (thedenominator in the equation) which could result in asmall effect size. It was therefore decided to only calculateand compare the effect sizes within studies, that is whereboth power and tip or tripod pinch were assessed on thesame sample and where the data for this could beextracted from the article.Only two studies [17,29] included both grip and pinch strength and also reported means and standard deviationsor 95% confidence intervals for pre- and post-operativeassessments. Tables 3 and 4 give the effect sizes for grip and pinch strength at six and 12 weeks post-operatively.In the study by Dias et al [29] the responsiveness of power grip is low indicated by a small effect size of 0.22 or less. Tip pinch strength scores show moderate to large effect sizes suggesting that it is more responsive to change thanpower grip. The effect sizes in Nakamichi and Tachibana's[17] study are moderate to large in both power and pinch Table 1: Summary of studies evaluating power grip StudyInstrumentUnit of measurementHandle positionPatient positioning Agee et al., 1992 [9]Jamar%all 5 settingsNRBhattacharya et al., 2004 [28]Jamar%2NRBrown et al., 1993 [10]JamarlbsNRNRBrüser et al., 1994 [18]Jamar%NRNRCitron and Bendall, 1997 [16]Martin VigorimeterkpaNRNRDias et al., 2004 [29]JamarkgNRYDumontier et al., 1995 [14]JamarkgNRNRErdmann, 1994 [11]JamarlbNRNRFerdinand and Maclean, 2002 [22]Baseline hydraulicIbNRNRFoulkes et al., 1994 [12]Jamarlb2 2 NRHelm and Vaziri, 2003 [26]Baseline hydraulickgNRNRMacDermid et al., 2003 [24]digit grip device 1 kgNR but cites refsNR but cites refsMackenzie et al., 2000 [19]Baseline hydraulickg2NRMackinnon et al., 1991 [8]NRkgNRNRNakamichi & Tachibana, 1997 [17]NRkgNRNRSaw et al., 2003 [25]JamarkgNRNRSennwald & Benedetti., 1995 [13]Jamarkg2NRTrumble et al., 2002 [20]Jamarkgall 5 settingsNRWong et al., 2003 [27]NR%NRNR 1 NK Biotechnical Corp, Minneapolis, MN, USA; 2 data adjusted for age, sex, and side.% = percent change from preoperative valueNR = not reportedlb = poundskpa = kilopastelskg = kilograms  BMC Musculoskeletal Disorders  2007, 8 :114http://www.biomedcentral.com/1471-2474/8/114Page 4 of 9 (page number not for citation purposes) strength however reflect a change in the wrong direction,that is at 6 weeks and 12 weeks both power and key pinchhad deteriorated from pre-operative values. Even at thefinal follow-up which in Nakamichi and Tachibana's [17]study was as long as 2 years the mean scores for power returned to pre-operative values only. Lateral pinch wasonly slightly improved at 2 years after surgery.  Manual Muscle Testing  Eight of the 22 studies reviewed used manual muscle test-ing as an outcome measure, five of these included it as well as power or pinch strength [8-10,15,17,20-22]. Table 5 summarises the scale, grading system and muscle(s)tested in each study. Comparison of results was not possi-ble due to the different scales used and several studies didnot report pre- and post-operative values. The Abductor Pollicis Brevis (APB) muscle was tested in six studies[8,10,15,17,20,22], two studies [9,21] did not specify the muscle tested. Three studies gave descriptive statistics for pre- and post-operative values [10,15,17]. In Nakamichi and Tachibana's [17] study the 2 year follow-up valueshad improved from a mean grade of 2.5 (± 2.1) to 3.9 (±1.9) in the experimental group and from 2.3 (± 2.0) to 4.3(± 1.7) in the comparator group. A grading of 0–5 wasused however no reference is made to which classificationsystem was used. Brown et al [10] used the AOA criteriaand a grading of 0 to 5. Mean pre-operative grades were4.4 and 4.5 for comparator and experimental groupsrespectively, increasing to 4.6 to 4.7 post-operatively.  Assessment of thenar atrophy  Presence of thenar atrophy was reported in 5 studies[8,10,20,21,23] (see Table 6). Thenar atrophy can only be assessed subjectively as being present or absent. A four-point categorical scale was used in two studies [8,10]. The overall trend was, as expected, a decrease in proportionsof those with thenar atrophy. Discussion  The primary aim of this review was to identify what meth-ods and instruments have been used to assess motor out-come and to examine their usefulness as an indicator of change over time. Dynamometry of power and pinch grip,manual muscle testing and presence or absence of thenar atrophy, were the three main methods of objectively quantifying motor outcome. Subjective rating of weak-ness is also included in some of the patient-oriented out-come measures, for example the Symptom Severity Scaleof the Boston Carpal Tunnel Questionnaire [7] ( Do youhave weakness in your hand or wrist? ), however the focus of this review was to compare performance based outcomemeasures of muscle weakness. Table 2: Summary of studies evaluating pinch grip ReferenceInstrumentUnit of measurementProtocolPositionKey PinchTip PinchTripod Pinch Agee et al., 1992 [9]NR% 2 NRNR  ✓ ✓ Brown et al., 1993 [10]JAMARlb 3 NRNR  ✓ Brüser et al., 1994 [18]B%NRNR  ✓ ✓ Dias et al., 2004 [29]JAMARkgNRNR  ✓ Erdmann, 1994 [11]JAMARlbNRNRNot specifiedFerdinand & Maclean, 2002 [22]B&LNRNRNR  ✓ Foulkes et al., 1994 [12]B&LlbNRNR  ✓ ✓ ✓ MacDermid et al., 2003 [24]pinch device NK 1 kgNR 3 NR 3 ✓ ✓ Mackenzie et al., 2000 [19]B&LkgNRNR  ✓ Mackinnon et al., 1991 [8]NRNRNRNRNot specifiedNakamichi & Tachibana 1997 [17]NRkgNRNR  ✓ Sennwald & Benedetti, 1995 [13]B&LlbNRNR  ✓ Trumble et al., 2002 [20]pinch meter 2 kgNRNR  ✓ ✓ Wong et al., 2003 [27]NR%NRNRNot specifiedTotal1043% = percent change from preoperative valueNR = not reportedlb = poundskg = kilogramsB&L pinch gauge (B&L Engineering, Santa Fe, CA) 1 NK Biotechnical Xorp, Minneapolis, MN 2 Therapeutic instruments, Clifton, New Jersey 3 Reference to reliability studies provided.  BMC Musculoskeletal Disorders  2007, 8 :114http://www.biomedcentral.com/1471-2474/8/114Page 5 of 9 (page number not for citation purposes)  Assessment of grip strength with dynamometry was themost common method of reporting motor outcome. Theusefulness of power grip as an indicator of change in bothearly (up to 6 weeks post-operatively) and later recovery (>6 weeks) from carpal tunnel release is questionable. Although Simpson [32] states that grip strength is particu-larly useful to evaluate outcome following carpal tunnelrelease, she also cautions that it should not be used wheretissue healing is incomplete and testing would cause pain.Early post-operative power grip strength showed that val-ues initially decreased and coincides with the assessment of pillar or scar pain or tenderness where higher painscores were reported in the early post operative phase. Although none of the studies were designed to investigatean association between pain and grip strength, it is likely that the reduction in grip strength reflects pain inhibition with muscle contraction or increased sensitivity to pres-sure over the pillar region or scar. Contraction of musclessrcinating from the flexor retinaculum might cause painby transmitting tension to the cut and healing transversecarpal ligament or retinaculum. The dynamometer handlemay produce discomfort over the scar or pillar region dur-ing power grip dynamometry. Ludlow et al [33] comment that whilst grip and post-operative scar tenderness havebeen shown to predict return to manual work, it is unclear  whether these are distinct or whether the discomfort of the handle against the pillar area contributes to low gripresults. If the aim is to quantify pain or tenderness to pres- Line graph of pre and post-operative tip pinch strength Figure 4Line graph of pre and post-operative tip pinch strength . EG = experimental group, CG = comparator group.Line graph of pre and post-operative key pinch strength Figure 2Line graph of pre and post-operative key pinch strength . * Statistically significant difference between groups reported. EG = experimental group, CG = comparator group.Line graph of pre and post-operative power grip strength Figure 1Line graph of pre and post-operative power grip strength . EG = experimental group, CG = comparator group. * studies which measured power grip at more than one time point between 12 and 104 weeks demonstrated minimal change in values. 12 to 104 weeks*3 to 6 weeks1 to 2 weekspreoperative week 40.020.0       K     g Nakamichi CGNakamichi EGHelm and Vaziri CGHelm and Vaziri EGDias CGDias EGTrumble CGTrumble EGMacKenzie CGMacKenzie EGMacDermid CGMacDermid EG Line graph of pre and post-operative tripod pinch strength Figure 3Line graph of pre and post-operative tripod pinch strength . Trumble et al. [20] reported a significant differ-ence (p < 0.05) between groups until the 3 rd post-operative month but does not report actual 2 week values. MacDermid et al. [24] reported no significant differences between groups. EG = experimental group, CG = comparator group. 120 week 7.06.56.05.55.04.5        k      g Trumble CGTrumble EGMacDermid CGMacDermid EG
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