Technical and measurement report Vibration testing: A pilot study investigating the intra-tester reliability of the Vibrameter for the Median and Ulnar nerves Gill James a, * , Claire Scott b a School of Health & Population Sciences, College of Medical and Dental Sciences, University of Birmingham, Edgbaston B15 2TT, United Kingdom b Solihull/HoEFT, Virtual Wards, Century House,100 Stratford Shirley, Solihull B90 3BH, United Kingdom article info Article history: Received 10 August 2011 Received in revised form 22 December 2011 Accepted 14 February 2012 Keywords: Intra-tester reliability Vibration threshold testing Vibrameter abstract The measurement of vibration thresholds (VTs) is a sensitive test for identifying and monitoring neuropathies. Such a test needs established reliability. The purpose of this research was to evaluate the intra-tester reliability of VT measurements of the Median and Ulnar nerves in asymptomatic participants. A double blinded repeated measures study was carried out. The VTs of the Median and Ulnar nerves were measured on two occasions with seven days between measurements. Participants were trained in identifying the sensation before commencing measurement. 22 participants who fulfilled the inclusion criteria were recruited. Intra-rater reliability was analysed used the intra-class correlation. The median nerve showed excel- lent reliability (ICC ¼ .922; standard error of the mean ¼ .0225 mm; ‘true’ SEM ¼ .045 mm; smallest real difference ¼ .062 mm). Ulnar nerve reliability was ‘substantial’ (ICC ¼ .632; standard error of the mean ¼ .0225 mm; ‘true’ SEM ¼ .055 mm; smallest real difference ¼ .085 mm). The VT measurements showed excellent to substantial reliability. The Vibrameter has the potential for excellent reliability providing manual therapists practice the technique of using it. It could usefully be considered by manual therapists to support their practice. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Measurements of vibration sensitivity are used both for detec- tion and monitering dysfunctions (Peters et al., 2003; O’Conaire et al., 2011). The test targets the large Ab fibres - which mediate the sensation of vibration and are sensitive to ischaemia. For example, vibration perception has been shown to be the first sensation to be lost in patients with diabetic neuropathies (Martina et al., 1998). In manual therapy, measurements of vibration thresholds (VTs) have been noted. For example, Greening and Lynn (1998) identified the existence of minor neuropathies (as exem- plified by raised VTs in the Median and Ulnar nerves) associated with computer usage. These findings suggest that manual thera- pists could utilise vibration perception outcome measures for monitoring and managing such conditions. However, if such measurements would be useful in screening and management of at-risk populations, the tool used must have acceptable levels of reliability. Without such an assurance the effectiveness of management and research programmes cannot be accurately identified. Various tools are available to assess vibration perception including the Vibrameter, tuning fork and nerve conduction tests. However, two-point discrimination or nerve conduction studies require more severe decreases in nerve function to produce significant results (Goldberg and Lindbolm, 1979; Szabo et al., 1984; Jetzer, 1991). The tuning fork is also less reliable and produces an output in time (seconds to extinction) (O’Conaire et al., 2011). Hilz et al. (1995) consider the Vibrameter to be the most sensitive tool for measuring vibration perception. However, studies evaluating the reliability of the Vibrameter have used different models of Vibrameter and different vibration frequency which makes comparison between studies difficult. The most directly compa- rable study was that undertaken by Peters et al. (2003) who carried out a large scale reliability study examining intra- and inter-rater reliability using asymptomatic participants. Their ICC measure- ments (.79, right hand; .73, left hand) may be classed as substantial (Landis and Koch, 1977). However, their protocol has three impor- tant aspects - the site of testing was in the Radial nerve distribution, the Vibrameter was supported rather than handheld and they recorded five measurements on each site. The two latter aspects would seem uncommon in clinical usage. * Corresponding author. Tel.: þ44 (0) 121 415 8598. E-mail address: [email protected](G. James). Contents lists available at SciVerse ScienceDirect Manual Therapy journal homepage: www.elsevier.com/math 1356-689X/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.math.2012.02.009 Manual Therapy 17 (2012) 369e372
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Manual Therapy 17 (2012) 369e372
Contents lists available
Manual Therapy
journal homepage: www.elsevier .com/math
Technical and measurement report
Vibration testing: A pilot study investigating the intra-tester reliabilityof the Vibrameter for the Median and Ulnar nerves
Gill James a,*, Claire Scott b
a School of Health & Population Sciences, College of Medical and Dental Sciences, University of Birmingham, Edgbaston B15 2TT, United Kingdomb Solihull/HoEFT, Virtual Wards, Century House, 100 Stratford Shirley, Solihull B90 3BH, United Kingdom
a r t i c l e i n f o
Article history:Received 10 August 2011Received in revised form22 December 2011Accepted 14 February 2012
1356-689X/$ e see front matter � 2012 Elsevier Ltd.doi:10.1016/j.math.2012.02.009
a b s t r a c t
The measurement of vibration thresholds (VTs) is a sensitive test for identifying and monitoringneuropathies. Such a test needs established reliability. The purpose of this research was to evaluate theintra-tester reliability of VT measurements of the Median and Ulnar nerves in asymptomatic participants.
A double blinded repeated measures study was carried out. The VTs of the Median and Ulnar nerveswere measured on two occasions with seven days between measurements. Participants were trained inidentifying the sensation before commencing measurement. 22 participants who fulfilled the inclusioncriteria were recruited.
Intra-rater reliability was analysed used the intra-class correlation. The median nerve showed excel-lent reliability (ICC ¼ .922; standard error of the mean ¼ .0225 mm; ‘true’ SEM ¼ .045 mm; smallest realdifference ¼ .062 mm). Ulnar nerve reliability was ‘substantial’ (ICC ¼ .632; standard error of themean ¼ .0225 mm; ‘true’ SEM ¼ .055 mm; smallest real difference ¼ .085 mm).
The VT measurements showed excellent to substantial reliability. The Vibrameter has the potential forexcellent reliability providing manual therapists practice the technique of using it. It could usefully beconsidered by manual therapists to support their practice.
� 2012 Elsevier Ltd. All rights reserved.
1. Introduction
Measurements of vibration sensitivity are used both for detec-tion and monitering dysfunctions (Peters et al., 2003; O’Conaireet al., 2011). The test targets the large Ab fibres - which mediatethe sensation of vibration and are sensitive to ischaemia. Forexample, vibration perception has been shown to be the firstsensation to be lost in patients with diabetic neuropathies (Martinaet al., 1998). In manual therapy, measurements of vibrationthresholds (VTs) have been noted. For example, Greening and Lynn(1998) identified the existence of minor neuropathies (as exem-plified by raised VTs in the Median and Ulnar nerves) associatedwith computer usage. These findings suggest that manual thera-pists could utilise vibration perception outcome measures formonitoring and managing such conditions. However, if suchmeasurements would be useful in screening and management ofat-risk populations, the tool used must have acceptable levelsof reliability. Without such an assurance the effectiveness of
.
All rights reserved.
management and research programmes cannot be accuratelyidentified.
Various tools are available to assess vibration perceptionincluding the Vibrameter, tuning fork and nerve conduction tests.However, two-point discrimination or nerve conduction studiesrequire more severe decreases in nerve function to producesignificant results (Goldberg and Lindbolm,1979; Szabo et al., 1984;Jetzer, 1991). The tuning fork is also less reliable and produces anoutput in time (seconds to extinction) (O’Conaire et al., 2011). Hilzet al. (1995) consider the Vibrameter to be the most sensitive toolfor measuring vibration perception. However, studies evaluatingthe reliability of the Vibrameter have used different models ofVibrameter and different vibration frequency which makescomparison between studies difficult. The most directly compa-rable study was that undertaken by Peters et al. (2003) who carriedout a large scale reliability study examining intra- and inter-raterreliability using asymptomatic participants. Their ICC measure-ments (.79, right hand; .73, left hand) may be classed as substantial(Landis and Koch, 1977). However, their protocol has three impor-tant aspects - the site of testingwas in the Radial nerve distribution,the Vibrameter was supported rather than handheld and theyrecorded five measurements on each site. The two latter aspectswould seem uncommon in clinical usage.
Fig. 1. (a) Testing position for Median Nerve. (b) Testing position for Ulnar Nerve.
G. James, C. Scott / Manual Therapy 17 (2012) 369e372370
Studies on the reliability of the Vibrameter have often beencarried out with symptomatic participants and, whilst thisapproach is clinically relevant, it is difficult to assess the extent towhich the measurement is stable from test to test. Any variation inthe readings may therefore be a reflection of true clinical change oras a result of unreliable measurement techniques. Therefore, anyreliability study that uses inherently unstable clinical participantshas a built-in confounded error. A true measure of the technique’sreliability should be conducted with a stable, non-clinical pop-ulation. Direct generalisability to a symptomatic population islimited but such a decision facilitates control of potential con-founding variables.
1.1. Clinical relevance
The measurement of vibration thresholds could be developed asa powerful diagnostic tool for optimising the identification andmanagment of neuromusculoskeletal dysfunctions. However, it isimportant to investigate the reliability of the tool under conditionsas near to the clinical application as possible. The Vibrameter can bedifficult to use, because the head is heavy and cumbersome. Thisdisadvantage could limit its clinical application and adverselyaffect its reliability. Identifying its reliability may provide evidencefor using the Vibrameter clinically, despite the perceiveddisadvantages.
This study documents an intra-reliability study on the groundsthat intra-tester reliability (where the same test is administered bythe same measurer over time) is considered superior to inter-testreproducibility (Croft et al., 1994). Clinically, it is probable thatthe outcome measurements would be carried out by one physio-therapist, thus addressing the utility of this decision. An inter-raterreliability study would be of more relevance where multiple raterswere taking measurements over time.
2. Methodology
2.1. Design & rationale
A repeated measures test-retest design with seven daysbetween test and retest was employed. The individual taking themeasurements and the participant were blinded to the results tominimise bias. Power calculations documented by Walter et al.(1998) suggest a sample size of greater than eighteen wasrequired in order for the study to have validity. Participantsprovided written consent and the protocol was not invasive. Ethicalapproval was granted by the University of Birmingham.
2.2. Participants
A convenience sample was recruited by email. They wereasymptomatic (to control for the chance of changes in VT due topathological changes) and aged between 18 and 30 years (to controlfor the possibility of age related changes in VT). Gender, handdominance and height were not considered to be significant vari-ables in the arm (Peters et al., 2003). The Median and Ulnar nervesof the hand were targeted for measurement, because this area hasbeen the target of research (Greening & Lynn, 1998; O’Conaire et al.,2011). Participants were screened for diabetes (Dyck et al., 1987;Deursen van and Sanchez, 2001), history of injury of the neck orupper limb and systemic disease.
2.3. Apparatus & methods
A Vibrameter� (Mark lV; frequency of 100 Hz, Somedic Ab,Sweden), an adjustable plinth and standard chair was used. Any
jewellery was removed to ensure it did not compromise themeasurements. The forearm was positioned in 135� supinationon the plinth with the hand supported by a bean bag. The probewas positioned upon the palmar surface of the 2nd (MedianNerve) and 5th (Ulnar nerve) Metacarpal heads (see Fig. 1a andb), since these sites encompass the supply and dermatomaldistribution of these nerves in the hand (Marchettini et al.,1990).
The Vibrameter� was calibrated according the manufacturers’recommendations. The sensation was demonstrated on the non-dominant hand and the dominant hand was used for measure-ments. All the measurement were taken by the same person (CS)following training and development of the measurement protocol.The measurer was a student at a UK university studying physio-therapy. The training period was important prior to testing andthis stage revealed that the measurer’s forearm required supportto stabilise the head of the Vibrameter. The measurer could seethe display to ensure the pressure of the Vibrameter was consis-tent, but the amplitude of vibration (in microns e mm) was con-cealed and recorded by an assistant. Data acquisition used themethod of limits whereby Vibration Perception Threshold (VPT)and Vibration Disappearance Threshold (VDT) were eachmeasured three times with a 10 s rest between measurements.Mean values (VTs) are then calculated. This method is reported tobe reliable, simple, quick and less error prone (Gerr and Letz,1988; Stuart et al., 2003). The room used for testing was quietand temperature controlled at 21 �C.
Table 1Inferential and descriptive statistics.
ICCa Lower bound Upper bound Mean (SD) SEM (true SEMb) SRDc
a ICC average measures; two way random effects model.b true SEM ¼ 1.96*SEM.c SRD ¼ 1.96*O2*SEM.
G. James, C. Scott / Manual Therapy 17 (2012) 369e372 371
2.4. Data handling & analysis
The one-way ANOVA intra-class correlation co-efficient (ICC) isa key indicator of reliability (Rankin and Stokes, 1998:; Bruton et al.,2000). ICC values of between .81 and 1.0 could indicate almostperfect agreement (Landis and Koch, 1977). A Bland-Altman limitsof agreement analysis (1986) was carried out to visually quantifythe measurement error. Standard error of measurement (SEM)calculates variability of measurements in the same individual. The‘true’measurement is calculated as 1.96*SEM (Borstad et al., 2007).Smallest real difference (SRD) is the smallest change that can beinterpreted as a real difference (Beckerman et al., 2001; Borstadet al., 2007). It is calculated as SRD ¼ 1.96*O2*SEM.
The level for rejection of the null hypothesis was specified asp � 0.05. The data should be normally distributed with 95% of
Fig. 2. (a) Bland Altman plot for Median Nerv
values at test and retest lying within two standard deviations ofthe mean.
3. Results
Twenty two participants were recruited (Female¼ 17;Male¼ 5)with an age range 22e30 years of age (mean ¼ 25.5; SD � .9), handdominance (Left ¼ 6; Right ¼ 16)). The KolmogoroveSmironov testwas non-significant for both nerves - it was concluded the datawere normally distributed.
The ICC values and descriptive statistics are shown in Table 1.Reliability is better for the Median than the Ulnar nerve. The SEMand SRD values provide further information about the reliabilityand amount of change needed to indicate real differences.
e. (b) Bland Altman plot for Ulnar nerve.
G. James, C. Scott / Manual Therapy 17 (2012) 369e372372
Fig. 2a,b show the Bland and Altman (BA) plots for the Medianand Ulnar nerves. Both BA plots show that only two data points(derived from different participants) do not fall within the limits ofdifference. The wider distribution of the difference between testand retest illustrate visually the lower ICC values obtained for theUlnar nerve.
4. Discussion
The ICC results for the Median nerve indicates almost perfectagreement (Landis and Koch, 1977 with an ICC of .922 (limits ofagreement at 95% were .06 (upper) and �.13 (lower)). The Ulnarnerve reliability was substantial (ICC ¼ .632. limits of agreement at.24 (upper) and �.36 (lower) (Landis and Koch, 1977).
Comparison of these results with the study conducted by Peterset al. (2003) reveals that the intra-tester reliability for the Mediannerve was greater than recorded by their ICCs. Their protocol useda stand to support the Vibrameter, whereas our protocol providedforearm support. Nevertheless it appears that the instrument canbe highly reliable when handheld. Although Peters et al measuredover the dermatomal distribution of the Radial nerve and our sitewas over the distribution of the other nerves, these results shouldbe comparable despite the larger age range of Peter et al’s study.Wealso used a relatively inexperienced measurer and undertooktraining and practice prior to acquiring the reliability data. Judgingby the reliability results we would suggest that the Vibrameter canbe easier to use than commonly thought.
The BA plots demonstrate that, with the exception of two points,all scores are contained within the limits of agreement. Bland andAltman (1986) state if the data is normally distributed then 95%of the data will fall within the limits of difference. For the Mediannerve the majority of points are clustered around the mean ofdifference and the mean of VT. However, for the Ulnar nerve, thepoints are more dispersed from the mean difference and mean VTvalues, which illustrates the lower ICC value. The standard error ofmeasurement (SEM) values of .023 mm (test) and .022 mm (retest)for theMedian nerve and .022 mm (test) and .033 mm (retest) for theUlnar nerve are quite small. These SEMs represent a measurementerror for the Median nerve of �11.4%(test) and �9.36% (retest); forthe Ulnar nerve the error is �9.36% (test) and �9.7% (retest). TheSRD values suggest that changes of .062 mm (Median nerve) and.085 mm (Ulnar nerve) would be required before it could beconcluded actual change had occurred.
Our major concern is the difference in reliability in the twotesting sites. Results from the Ulnar nerve are less reliable and theretest measurements may be the source of error. Since themeasurement technique appears more awkward for the measurer,developing this technique may improve this situation. A possibleexplanation may relate to localised tension in Guyon’s canal,although it should not affect the results since a reliability studyevaluates the consistency of measurement between test and retest.A relatively small sample size was used, although it was adequateaccording to Walter et al’s calculations (1998).
4.1. Clinical implications & further research
VT measurements are important as it is the first sensory loss inneuropathy development (Martina et al., 1998). The Vibrameter isacknowledged to be sensitive and can demonstrate excellent
reliability. However, it appears not to be used in clinical practice,because of difficulties in the measurement technique, the time ittakes and cost. However, our results suggest that the technique andthe time factors can be addressed using a suitable protocol and timefor training in the technique. Measuring both nerves in this studytook approximately 5 min to complete and the reliability wassubstantial to excellent. It is important however, to emphasize thatfurther research investigating symptomatic populations, a widerrange of asymptomatic participants and inter-rater reliability isneeded. Once the reliability is established the Vibrameter wouldseem to be fit for purpose for manual therapists to incorporate intotheir clinical practice for diagnosis and monitoring managementprogrammes.
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