Reliability Study on Quantitative Detection of Extensor DigitorumBrevisStrengthwithNeedleElectromyographyand Nerve Conduction

GAO Dong,XIA Qing,RAN Dan,TIAN Dong,ZHU Guang-you,FAN Li-hua

（1.Shanghai Key Laboratory of Forensic Medicine,Institute of Forensic Science,Ministry of Justice,P.R.China,Shanghai 200063,China;2.Department of Hand Surgery,Huashan Hospital,Fudan University,Shanghai 200040,China）

Reliability Study on Quantitative Detection of Extensor DigitorumBrevisStrengthwithNeedleElectromyographyand Nerve Conduction

GAO Dong1,2,XIA Qing1,RAN Dan1,TIAN Dong2,ZHU Guang-you1,FAN Li-hua1

（1.Shanghai Key Laboratory of Forensic Medicine,Institute of Forensic Science,Ministry of Justice,P.R.China,Shanghai 200063,China;2.Department of Hand Surgery,Huashan Hospital,Fudan University,Shanghai 200040,China）

ObjectiveTo study the objectivity and reliability of needle electromyography and nerve conduction for detection of musculus extensor digitorum brevis strength,which may provide a basis for establishing a quantitative detection of muscle strength in forensic clinical study.MethodsForty-four healthy people were enrolled as the subjects,and during toe dorsiflexion,the following items including needle electromyography indexes,motor unit potential（MUP）amplitude,MUP count,recruitment reaction type, and nerve conduction detection indexes,compound muscle action potential（CMAP）amplitude,CMAP latent period and motor nerve conduction velocity（MNCV）,were simultaneously detected under the cooperation and disguise condition.ResultsUnder the cooperation condition,regardless of the same operator or different operators,there were good test-retest reliabilities in MUP amplitude,CMAP amplitude, CMAP latent period and MNCV,while there were normal test-retest reliabilities in MUP count and recruitment reaction type and the repeatability of the same operator was slightly better than the repeatability between different operators.Under the disguise condition,test-retest reliabilities of MUP amplitude, CMAP amplitude,CMAP latent period and MNCV were relatively high,while test-retest reliabilities of MUP count and recruitment reaction type were relatively low.ConclusionThere are good test-retest reliabilities in MUP amplitude,CMAP amplitude,CMAP latent period and MNCV,which can be conducive to comparison between different operators and results at various times;MUP count and recruitment reaction type,which can be easily affected by subjectivity of operators and examinees,can be used to differentiate whether an examinee disguises or not.The indexes used to objectively judge muscle strength remain to be further investigated.

forensic medicine;neural conduction;needle electromyography;musculus extensor digitorum brevis;muscle strength;reliability

Article IC:1004-5619（2013）06-0409-05

Introduction

Currently,inthefieldsofforensicclinical medicine and clinical practice,Lovett manual muscle assay is still adopted for strength assessment of muscles dominated by the nerve after common peroneal nerve injury.Since its invention,the method has been widely applied at home and abroad for its easy operation.However,it can be readily affected by subjectivities of examiners and subjects.And the assay can only divide muscle strength into several grades with poor sensitivity of difference among the grades.

In practice of forensic clinical medicine,muscle strength evaluation of a patient with peripheral nerve injury is related to the conviction and sentencing in a criminal case and compensation fordamage in a civil case;thus it is critically important to establish an objective and quantitative muscle strength evaluation method for peripheral nerve injury,especially for possible existence of disguised or exaggerated neurological dysfunction[1-2].The currentstudyenrolled44healthysubjectswhose strength of musculus extensor digitorum brevis was respectively measured by two operators under cooperation or disguise condition,and who simultaneously underwent neuroelectrophysiological monitoring with needle electromyography and nerve conduction detection.The statistic analysis on repeatability of measurement results was performed to screen good test-retest reliability indexes so as to provide a basis for establishing a method as an objective,reliable and quantitative muscle detection.

Subjects and methods

Subjects

A total of 44 healthy adults were enrolled in the current study,24 males and 20 females,who had no history of lower limb fractures,peripheralnerve injury,neurological diseases or diabetes.Their physical and neurological examination were reported to be normal,and their signed informed consents were obtained.

Strength measurement

When they were tested,the subjects squatted or stood.During toe dorsiflexion,they could not leave the bed so that the position was not affected by ankle dorsiflexion.After the test began,the subjects tried to stabilize dorsiflexion of toes with maximum strength for 10-20 seconds.The digital dynamometer,ranging from 0-100 Newton with 0.1 Newton as the measurement accuracy,was used to detect maximum toe dorsiflexion strength of the subjects. During toe dorsiflexion with maximum strength,neuroelectrophysiologicaldetection was simultaneously carried out.

Neuroelectrophysiological detection

The Keypoint multifunctional nerve evoked potential instrument（Danish Medtronic Company）was used at ambient temperature and the surface temperature of the instrument was maintained at above 30℃.The conduction detection method of the common peroneal motor nerve:the electrical stimulations were given on the ankle and the fibular head, respectively,with a stimulation device,and stimulus intensity gradually increased from weak to strong, to reach a superstrong stimulus to ensure that the nerve fibers to be tested could maintain complete excitation,and the surface electrodes were placed on the musculus extensor digitorum brevis for recording.Test indexes covered the amplitude and latent period of compound muscle action potential（CMAP）and motor nerve conduction velocity（MNCV）.The disposable concentric needle electrodes were used to measure amplitude,count,and recruitment reaction type of motor unit potential（MUP）during maximum dorsiflexion of the musculus extensor digitorum brevis.Among them,recruitment reaction types were divided into four types,a small amount of MU,purephase,mixedphaseandinterference phase.Given that the subjects were healthy volunteers and asked to perform toe dorsiflexion with certain strength,there was no non-MU type,which was not included in the current study.When common peroneal nerve conduction was detected and needle electromyographywas used to detect the musculus extensor digitorum brevis,stimulator stimulation location,recording electrode placement location,needle electrodes entering location and measurements of all indexes referred to the methods recommended by Huashan Hospital affiliated to Fudan University[3].

Test procedure

Under the cooperation condition,34 subjects performed toe dorsiflexion with maximum muscle strengths.The measurement was repeatedly performed in three ways,by operator Atwice,operator B twice and operator A and B once,respectively.The interval between two measurements lasted more than 10 minutes.

Under the disguise condition as disguising muscle dysfunction,44subjects performed toe dorsiflexion with arbitrary muscle strengths.The measurement was performed twice by operator A.

Statistical analysis

Statisticalsoftware SPSS11.0 was used for analysis.Under the cooperation condition,the testretestreliabilityanalysis,ofwhichthespecific method was intra-class correlation coefficients（ICC）test,was employed to analyze two measurement results from the same operator and different ones. Under the disguise condition for test-retest reliability analysis,ICCtest was applied to an analysis of two measurement results from the same operator.

Results

Under the cooperation condition,regardless of the same operator or different ones,there were goodtest-retestreliabilitiesinMUPamplitude, CMAP amplitude,CMAP latent period and MNCV, but normal test-retest reliabilities in recruitment reaction type and MUP count were observed.The repeatability of the same operator was slightly better than that between different operators.The test-retest reliability statistical results of allindexes of the same operator or different operators under the cooperation condition were showed in Table 1.Under the cooperation condition,regardless of the same operator or different ones,recruitment reaction types were detected to be only two types,the interference phase and mixed phase.The percentages of the two types were shown in Table 2.

Table 1 Test-retest reliability of electrophysiological indexes during toe dorsiflexion

1 ）measurements performed twice by one operator;2）measurements repeatedly performed by two operators

Table 2Composition of various recruitment reaction types during toe dorsiflexion [cases（%）]

Under the disguise condition,the same operator performedtwomeasurementsoneafteranother. There were good test-retest reliabilities in MUP amplitude,CMAP amplitude,CMAP latent period and MNCV,and poor test-retest reliabilities in MUP count and recruitment reaction type.The test-retest reliabilitystatisticalresults ofthe same operator were shown in Table 1.Under the disguise condition,recruitment reaction types were found to be four types,a small amount of MU,pure phase,mixed phase and interference phase.The percentages of various recruitment reaction types were shown in Table 2.

Discussion

Since the advent ofnerve electromyography technology in the 19th century,it has been widely applied at home and abroad for its important value in positioning,qualitative,quantitative,and prognostic evaluation and efficacy evaluation for peripheral nerve injury,and well acknowledged in clinical and forensic medicalcommunities to be an objective electrophysiologicalexamination method to reflect nerve and muscle functions[1-2,4].In clinical medical diagnosis and treatment practice as well as scientific research,mainlythroughmonitoringdynamic changes of nerve electromyography detection indexes,the change of the outcome of peripheral nerve function is reflected;therefore the effects of different treatment methods after peripheral nerve injury can be evaluated.For the muscle dominated by the nerve,its function evaluation is based on Lovett manual muscle assay founded by American orthopedic surgeon Professor Robert Lovett in 1916.The method is used to assess if muscle strength is normal and the lowered degree of muscle strengths[5]. In 1983,based on Lovett grading standard,Medical Research Council（MRC）further graded muscle strengths according to motion amplitude and the strength of the resistance,and developed a MRC grading standard[5].Manual muscle assessment method is simple and requires low hardware,but the requirements for an examiner’s experience and an examinee’s cooperation degree are extremely high, and the tests between different examiners and the tests of the same examiner during different periods may make evaluation results be significantly different;therefore repeatability andsensitivity are not high and it is difficult to reflect an examinee’s muscle strength objectively and accurately.During the clinical diagnosis and treatment process,a patient with nerve injury can follow a clinician well for cooperating with the clinician to carry out accurate diagnosis and treatment;thus manual muscle test results are relatively reliable and accurate.However,in the practice of forensic clinical identification,a patient with nerve injury wants to get more financial compensation or to increase punishment to a perpetrator,or to escape deserved punishment, which could result in deliberately disguising or exaggerating limb dysfunction.For a patient with nerve injury who may disguise or exaggerate injured nerve dysfunction,therefore,it is difficult to show his or her real state of muscle function only based on Lovett manual muscle assay.To address the issue, there have been reports on muscle function test methods in clinical medical and forensic medical communities.

In 2004,Liu et al.[6]measured abduction strength of the abductor pollicis brevis of 297 normal volunteerswith an improvedportable dynamometer produced by J Tech Company.In their study,there were high test-retest reliabilities between repeated measurement results of the same operator and between measurement results ofdifferent operators, the reliability coefficients as 0.92 within the group and0.89betweengroups,indicatingthatthe portable dynamometer method produced a high detection stability and reliability.Therefore,the researchers believed that compared with manual muscle assay,this method could more objectively,accurately,sensitively reflect the strength of the abductor pollicis brevis.In 2005,Li et al.[7]studied the correlation between abductor digiti minimi strength, the first interosseous muscle strength,flexor carpi ulnaris strength and ulnar nerve conduction velocity, latent period,amplitude in 25 patients with ulnar nerve injury,and concluded that there was a significant correlation between manual strength examination results of the three muscles and ulnar nerve conduction velocity,amplitude,and proposed that degree of strength loss of related muscles could initially be speculated according to the motor nerve conduction velocity and other indexes.When Aberg et al.[8]compared the efficacy of two kinds of nerverepair methods in 2009,12 patients with complete forearm or wrist nerve（median nerve or ulnar nerve）injury randomly underwent different surgical nerve stump suture repairs,and then their motion and sensory functions were examined according to the British MedicalCouncil’s Lovett manualmuscle strengthgradingmethodandsenseclassification method 2 weeks,3,6,9,12 and 18 months after operations.Among them,the sensory functions of six patients with ulnar nerve injury were gradually improved with time,but the researchers failed to study the dynamic change rule of muscle with time.

Recently,there has been much literature at home and abroad[4,9]which aimed at the comparison of different treatment method efficacies of nerve injury.Their findings reflected a characteristic that electromyography detection indexes and limb functions showed dynamic changes and their changing trends were similar to some degree after peripheral nerve injury had been treated.The investigations showed that some peripheral nerve electrophysiological detection indexes were certainly related to muscle function so that it was feasible to apply neuroelectrophysiological indexes to objectively assessing limb function.However,EMG indexes were still not overall,and needle electromyography indexes to reflect muscle function were not reported;furthermore,to examine limb motor function still relied on manualmuscle strength grading,and muscle strength evaluation method itself lacked good objectivity and comparability,when compared with instrumental muscle strength detection method.

Based on the previous studies,the current study, which combined the advantages of each instrumental strength detection method and neuroelectrophysiological method,used a portable dynamometer to measure musculus extensor digitorum brevis strength, andsimultaneouslyneedleelectromyographyand nerve transmission detection to monitor the dynamic changes of neuroelectrophysiological indexes of the musculus extensor digitorum brevis.The musculus extensor digitorum brevis was chosen as the object of study,mainly because identifying common peroneal nerve injury in the current forensic clinical practice is common,and the musculus extensor digitorumbreviscanprovidethemostimportant strength of toe dorsiflexion,especially the second to the fifth toes,so that interference factors can be remarkably reduced and the relationship between neuroelectrophysiologicalindexes and muscle strength can be studied well.

Reliability is an extremely important index in deciding whether the means of research is objective and accurate or not.Therefore,the current study designed repeated measurements by the same operator and then by different operators,respectively,in order to ensure reliability and test-retest stability of theneuroelectrophysiologicalmethodsinmuscle strength evaluation.According to the statistical results in Table 1,regardless of the same operator or different operators,under the cooperation condition there were good test-retest reliabilities in MUP amplitude,CMAP amplitude,CMAP latent period and MNCV.And test-retest reliabilities of MUP count and recruitment reaction type were acceptable,but were slightly lower than those of the four indexes. The overall test-retest stability of detection indexes of the same operator was slightly better than that between different operators.It was similar to the statisticalresults under the cooperation condition that under the disguise condition test-retest reliabilities of MUP amplitude,CMAP amplitude,CMAP latent period and MNCV were relatively high;however,test-retest reliabilities of MUP count and recruitment reaction type were lower than those under the cooperation condition（ICC coefficients as 0.52 and 0.57,respectively）.

From the statistical data of the current study,it can be seen that during electrophysiological test an operator might affect repeatability of detection indexes to some degree,especially those depending on subjective judgment of the operator（such as MUP count and recruitment reaction type）,but on the whole the operator did not affect the data.Therefore,there were good comparability and test-retest stabilities in the six indexes whether between the same operators or between different operators.According to statistical results,regardless of the cooperation condition or the disguise condition,the repeatability of MUP count and recruitment reaction type was lower than that of the other four indexes. Especially under the disguise condition,test-retest reliabilities of the two indexes were lower than those under the cooperation condition,and from Table 2 it can be seen that under the disguise condition 7% of a small amount of MU and 20%of pure phase were included in recruitment reaction types besides interference phase and mixed phase which also emerged under the cooperation condition.By analysis we thought that the main reasons behind the results were the detection methods selected for detecting indexes and detection influential factors.

CMAPamplitude,CMAPlatentperiodand MNCV are indexes to detect nerve conduction,and the main factors to impact detection accuracy of the three indexes are electric stimulator placement point selection,the intensity of electrical stimulation and other technical factors.Because anatomical landmarks are much clearer and more readily identified when common peroneal nerve conduction is detected,there is generally no significant difference in placement point selection of an electrical stimulatorand during the test process,as long as the intensity of electrical stimulation is gradually increased until maximum intensity is ensured,the choice of the intensity of electrical stimulation will not significantly impact the results,either.MUP amplitude,different from the three indexes,belongs to needle electromyography test indexes,but it essentially reflects the electrophysiological characteristics of measured muscle motor unit itself and under particular movement conditions（e.g.light muscle contraction）it is mainly affected by the nature and the status of the motor unit itself and is less affected by externally subjective and human factors;therefore the test-retest reliability under each condition is higher.Though MUP count and recruitment reaction type as well as the MUP amplitude all belong to the needle electromyography indexes,but the former two test processes are easily affected by the experiences of an examiner,test methods and other technical factors,as well as a examinee’s physiological and pathological conditions,cooperative degree and other subjective and objective factors[10].Thus test-retest reliability is lower,especially when an examinee deliberately disguises himself or herself and does not cooperate in a test.This can be seen from the difference between test-retest reliabilities of the same operator under the cooperation condition and those under the disguise condition.

Although test-retest reliabilities of MUP count and recruitment reaction type in the current study were the lowest of the selected six indexes,their value as objective evaluation indexes ofmuscle strength did not seem to be the lowest.Because there is significant test-retest reliability difference of MUP count and recruitment reaction type between the cooperation and the disguise condition,the two indexes could be valuable to judging if there was disguise in an examinee and how big it was.In general,when the muscle strength of an examinee is tested in forensic clinical medicine,the cooperative degree of an examinee may be suspected,but an objective basis is lacked to reflect the presence of disguise or degree of disguise.We believe that MUP count and recruitment type selected in the current study can exactly be used as monitoring indexes of disguise.If the same operator repeatedly tests a subject and the repeatability of the two indexes is good,there can be no disguise or possibility of little disguise;if the same operator does the same with poor repeatability,there is disguise and discrete degree of repeated test data can be used to judge disguising severity.

In the current study,muscle strength test methods were simpler and more convenient than manual muscle test methods.Combined with neuroelectrophysiological indexes with good test-retest reliability, they can be conducive to ensuring the comparability ofstrength measurementduringdifferentperiods longitudinallyand different operators horizontally. Therefore,the objectivity and quantitative value of muscle strength evaluation method of instrumental measurement combined with neuroelectrophysiology can meet the needs of the forensic clinical identification and research well.To judge objectively,real muscle strength with neuroelectrophysiologicalindexes still merits further investigations.

Acknowledgements

The research was supported by the fund of the 12th Five-year National Plan for Science and Technology Support（2012BAK16B03）and Public Welfare Fund of Ministry of Science and Technology for Research Institute（GY1104）.

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（Received date:2013-08-27）

（Editor:WANG Ya-hui）

DF795.1Document code:A

10.3969/j.issn.1004-5619.2013.06.003

Author:GAO Dong（1981—）,Ph.D in forensic science of peripheral nerve injury identification;E-mail:gaodong811204@ sina.com

FAN Li-hua,research fellow,master tutor in forensic clinical medicine;E-mail:fanlh@ssfjd.cn