carpal tunnel syndrome ( cts ) , caused by median nerve compression at transverse carpal ligament , is one of the most common entrapment neuropathy .
its major complaints are sensory component , such as tingling , pain , numbness3 ) .
sensory dysfunction of median nerve in cts can be evaluated by semi - quantitative assessment by comparing ulnar nerve sensory function of the same hand .
however , motor deficit , known to be present about 40% of the patients , also impedes patients ' functional status of hand , especially in severe case10 ) .
power and key pinch dynamometry , although used most frequently to assess the motor function of patients having cts , are known to be not so valid or responsive5 ) . in this study
we assessed the motor functions using devices measuring the abductor pollicis brevis power and evaluated its correlation with clinical , radiological and electrogianogsitc study ( eds ) findings .
device capable of measuring muscle power of abductor pollicis brevis ( apb ) was made by department of medical engineering , seoul national university hospital .
it was designed to measure strength using load cell in kilogram force from 0 to 50 with the maximum error of 0.15% ( mnt50l , cas , seoul , korea ) .
the device is composed of base plate with velcro straps for securing the forearm and palm , adjustable metal arm for proper positioning of load cell ( fig .
an analog - to - digital converter transfers signals from the load cell to the computer via universal serial bus .
it works under windows operating system ( win xp , microsoft , seattle , wa , usa ) .
it displays the change in measurement by graphs and it can display the maximum value of measurement with calibration before measurement ( fig .
2 ) . measurement of median nerve motor function was done by strength of thumb abduction and index finger flexion in a standardized fashion .
the base board was placed on desk , with the patient seated , the patient 's forearm was supinated on the base board .
the velcro straps were tightened around the patient 's hand and forearm to prevent any rotation of the forearm or wrist as well as other motions of wrist joint .
measurement was done three times , with a 20-second interval of rest between each attempt . before measurement
, the movement for motor power evaluation was demonstrated to the patient and the importance of exerting maximum effort was emphasized .
the tip of the load cell was placed at the radial border of the thumb interphalangeal joint flexion crease for measurement of thumb abduction strength ; at the distal interphalangeal joint flexion crease the load cell was positioned for index finger flexion strength ( fig .
thumb index ratio ( tir ) , the measure of median nerve motor function , was calculated as follows : tir=(average of 3 thumb abduction power)/(average of 3 index finger flexion power)1 ) subjects diagnosed as idiopathic cts , by eds and clinical features , were recruited for study .
the measurement was done in outpatient clinic after confirmed diagnosis , before operation , from july 2009 to december 2012 .
measurement was done in both hands for patients with bilateral disease , in one hand for patients with unilateral disease or patients previously got operated for cts .
bulk of thenar muscle was checked and presence or absence of thenar atrophy was recorded .
nerve conductive studies ( ncs ) were performed for diagnosis using standard techniques of surface stimulation and recording ( nicolet viking iv , madison , wi , usa ) .
skin temperatures were maintained above 31.0. median sensory nerve conduction velocity was orthodromically measured in the index finger - wrist segment , and the median distal motor latency from the wrist 5 cm proximal to the recording electrode at the abductor pollicis brevis .
the severity of cts was assessed based on the results of ncs using a previously reported neurophysiologic classification from negative to extremely severe8 ) .
usg of the carpal tunnel was performed for preoperative evaluation of median nerve in cases with severe symptoms showing poor response to conservative treatment .
the device used were hdi 3000 ( philips , netherland ) , sequoia 512 ( acuson , mountain view , ca , usa ) .
a 2 - 6 mhz linear array transducer was used . cross sectional area ( csa ) of median nerve
was measured using elliptical method at two points : one at mid - forearm , the other at just proximal to carpal tunnel , where the nerve swelling is most prominent .
the absolute value of nerve area at just proximal to carpal tunnel and ratio [ wrist to forearm ratio ( wfr ) ] of nerve swelling to mid - forearm was used for analysis .
statistical analysis was performed by spss ( version 20 , ibm spss statistics , armonk , ny , usa ) .
one - way analysis of variance ( anova ) and independent samples t - test and chi - square test were applied .
this study was approved by the institutional review board of our hospital ( 20090506/06 - 2009 - 60/83 ) .
device capable of measuring muscle power of abductor pollicis brevis ( apb ) was made by department of medical engineering , seoul national university hospital .
it was designed to measure strength using load cell in kilogram force from 0 to 50 with the maximum error of 0.15% ( mnt50l , cas , seoul , korea ) .
the device is composed of base plate with velcro straps for securing the forearm and palm , adjustable metal arm for proper positioning of load cell ( fig .
an analog - to - digital converter transfers signals from the load cell to the computer via universal serial bus .
it works under windows operating system ( win xp , microsoft , seattle , wa , usa ) .
it displays the change in measurement by graphs and it can display the maximum value of measurement with calibration before measurement ( fig .
measurement of median nerve motor function was done by strength of thumb abduction and index finger flexion in a standardized fashion .
the base board was placed on desk , with the patient seated , the patient 's forearm was supinated on the base board .
the velcro straps were tightened around the patient 's hand and forearm to prevent any rotation of the forearm or wrist as well as other motions of wrist joint .
measurement was done three times , with a 20-second interval of rest between each attempt . before measurement
, the movement for motor power evaluation was demonstrated to the patient and the importance of exerting maximum effort was emphasized .
the tip of the load cell was placed at the radial border of the thumb interphalangeal joint flexion crease for measurement of thumb abduction strength ; at the distal interphalangeal joint flexion crease the load cell was positioned for index finger flexion strength ( fig .
thumb index ratio ( tir ) , the measure of median nerve motor function , was calculated as follows : tir=(average of 3 thumb abduction power)/(average of 3 index finger flexion power)1 )
subjects diagnosed as idiopathic cts , by eds and clinical features , were recruited for study . the measurement was done in outpatient clinic after confirmed diagnosis , before operation , from july 2009 to december 2012 .
measurement was done in both hands for patients with bilateral disease , in one hand for patients with unilateral disease or patients previously got operated for cts .
bulk of thenar muscle was checked and presence or absence of thenar atrophy was recorded .
nerve conductive studies ( ncs ) were performed for diagnosis using standard techniques of surface stimulation and recording ( nicolet viking iv , madison , wi , usa ) .
skin temperatures were maintained above 31.0. median sensory nerve conduction velocity was orthodromically measured in the index finger - wrist segment , and the median distal motor latency from the wrist 5 cm proximal to the recording electrode at the abductor pollicis brevis .
the severity of cts was assessed based on the results of ncs using a previously reported neurophysiologic classification from negative to extremely severe8 ) .
usg of the carpal tunnel was performed for preoperative evaluation of median nerve in cases with severe symptoms showing poor response to conservative treatment .
the device used were hdi 3000 ( philips , netherland ) , sequoia 512 ( acuson , mountain view , ca , usa ) .
a 2 - 6 mhz linear array transducer was used . cross sectional area ( csa ) of median nerve
was measured using elliptical method at two points : one at mid - forearm , the other at just proximal to carpal tunnel , where the nerve swelling is most prominent .
the absolute value of nerve area at just proximal to carpal tunnel and ratio [ wrist to forearm ratio ( wfr ) ] of nerve swelling to mid - forearm was used for analysis .
statistical analysis was performed by spss ( version 20 , ibm spss statistics , armonk , ny , usa ) .
one - way analysis of variance ( anova ) and independent samples t - test and chi - square test were applied .
this study was approved by the institutional review board of our hospital ( 20090506/06 - 2009 - 60/83 ) .
the mean age of patients was 57.6 years ( range from 28 to 81 ) .
eds was done in all patients , usg done in 102 wrists ( 56 patients ) .
the average of tir was 0.57 , with standard deviation of 0.16 ( range from 0.046 to 1.037 ) .
the average value of left wrist was 0.58 , and that of right was 0.55 , without any statistically significant difference .
the tir was significantly lower in patients with higher ncs grade ( anova , p<0.001 ) ( fig .
the tir of ncs extremely severe grade was significantly lower than those of other ncs grades in post - hoc analysis . in this analysis ,
one case with minimal ncs grade was excluded from analysis because the number of patient was too small for analysis .
the tir was significantly lower in patients with thenar atrophy ( 0.450.17 , meanstandard deviation ) than in patients without atrophy ( 0.610.14 , t - test , p<0.001 ) ( fig .
although the csa of median n at carpal tunnel showed not significant correlation with tir , the patients with higher wfr showed lower tir with statistical significance ( anova , p=0.042 ) ( fig . 5 ) .
the mean age of patients was 57.6 years ( range from 28 to 81 ) .
eds was done in all patients , usg done in 102 wrists ( 56 patients ) .
the average of tir was 0.57 , with standard deviation of 0.16 ( range from 0.046 to 1.037 ) .
the average value of left wrist was 0.58 , and that of right was 0.55 , without any statistically significant difference .
the tir was significantly lower in patients with higher ncs grade ( anova , p<0.001 ) ( fig .
the tir of ncs extremely severe grade was significantly lower than those of other ncs grades in post - hoc analysis . in this analysis ,
one case with minimal ncs grade was excluded from analysis because the number of patient was too small for analysis .
the tir was significantly lower in patients with thenar atrophy ( 0.450.17 , meanstandard deviation ) than in patients without atrophy ( 0.610.14 , t - test , p<0.001 ) ( fig .
although the csa of median n at carpal tunnel showed not significant correlation with tir , the patients with higher wfr showed lower tir with statistical significance ( anova , p=0.042 ) ( fig .
there have been several methods for evaluation of median nerve motor function in cts , such as power grip , pinch grip , manual muscle testing , and assessing the thenar muscle atrophy5,6 ) .
power grip , which has been used most extensively , does not exclusively evaluate the muscles affected by cts .
weakness of apb or opponens pollicis ( op ) may be masked by compensatory action of synergistic muscles , such as the flexor digitorum superficialis and flexor digitorum profundus , particularly to the ring and little fingers , therefore not significantly reducing power grip .
apb or op weakness may be compensated for during key pinch by synergistic muscle action or ' trick ' movements11 ) .
muscle function evaluated by hand held dynamometer ( rotterdam intrinsic handheld myometer , rimh ) has been suggested for better evaluation of motor functions of cts .
it is equipped with easy - to - hold , ergonomic handgrip , and capable of detecting minute changes in hand muscles9 ) .
it uses load cell which generate digital output , easy to read with good reproducibility as demonstrated in rimh9 ) .
graphic display of measured strength is useful for detecting steady state of muscle power , preventing mislead by ' peak ' of instant high power .
it is operated on solid base , obviating the possible variance of power applied by the examiner .
one of the distinguished merits compared to other studies measuring apb strength is its ability of internal control1,7 ) .
the measured apb strength is compensated by flexor strength of index finger ; therefore it can be a measure of apb strength corrected for each cases intrinsic variation of muscle bulk or strength .
it is known that muscle power of right hand is higher in about 10% that of left hand4 ) .
our data shows no statistically significant difference in tir of right and left hands , which supports the validity of internal control .
ncs grade used in our study gave higher grade in cases with abnormal responses in median nerve motor component8 ) .
significantly lower tir in extremely severe grade in our series reflects the dysfunction in motor components of median nerve .
there has been a report that indicated no significant difference in tir between ncs grades , which classified by prolongation of distal motor latency1 ) .
it might suggest delicate variation in distal motor latency is not well correlated with median nerve motor function , although presence or absence of motor ncs is correlated with tir difference .
the difference of tir in accordance of presence of thenar muscle atrophy shows objective measurement of strength is well correlated with qualitative assessment of median nerve motor dysfunction .
the absence of correlation between apb emg abnormality and tir might be caused by the number of cases . in our hospital ,
apb emg was not done for all of the patients with cts , only 36 of 119 wrists underwent apb emg . the lack of correlation between tir and apb emg support this speculation .
the lower tir in patients with more severe median nerve swelling in usg has not been reported previously .
our data shows wfr , the relative swelling of median nerve , rather than absolute csa of median nerve is a better reflection of median nerve dysfunction in cts .
it is known that severe median n swelling is correlated with higher ncs grade , supports the concepts that morphological change of median nerve is correlated with functional derangements of median nerve2 ) .
it has been suggested that there might be a cut off value for diagnosis of cts by median nerve motor dysfunction1 ) .
we think that it is impractical because median nerve motor dysfunction develops in severe cases of cts , not in all of the patients .
the larger variation in tir in cts patients , compared to normal control suggests that normal controls show relatively uniform values , whereas mixed values of normal and abnormal values appear in cts patients1 ) .
there might be a cut off value for normal or abnormal value in tir ; however it requires large population data with normal control .
although there might be a cut off value of tir , it would better for use it for assessment of median n motor function , rather for diagnosis of cts .
our data show objective measurement of median nerve dysfunction is possible and its correlation with gross thenar muscle atrophy , ncs grade , and usg findings
. it might be helpful for detecting patients with median nerve motor dysfunction without objective thenar muscle atrophy , thus to treat the patients before obvious muscle wasting and functional loss .
it can be done without any discomfort , so it might be a good substitution for apb emg , especially in repeated measurement for detecting recovery of motor function after surgery .
measurements of median nerve motor function using load cell is a valuable evaluation tool in cts .
it makes possible to objectively evaluate median nerve motor function without any discomfort to the patient .
 objectivemajor complaints of carpal tunnel syndrome ( cts ) are sensory components . 
 however , motor deficit also impedes functional status of hand . 
 contrary to evaluation of sensory function , the objective , quantitative evaluation of median nerve motor function is not easy . 
 the motor function of median was evaluated quantitatively using load cell and its correlation with findings of electrodiagnostic study ( eds ) was evaluated.methodsobjective motor function of median nerve was evaluated by load cell and personal computer - based measurement system . 
 all of the measurement was done in patients diagnosed as having idiopathic cts by clinical features and eds findings . 
 the strength of thumb abduction and index finger flexion was measured in each hand three times , and the average value was used to calculate thumb index ratio ( tir ) . 
 the correlation of tir with clinical , eds , and ultrasonographic findings were evaluated.resultsthe tir was evaluated in 67 patients ( 119 hands ) . there were 14 males and 53 females , mean age were 57.6 years ( range 28 to 81 ) . 
 the higher preoperative nerve conductive studies grade of the patients , the lower tir was observed [ p<0.001 , analysis of variance ( anova ) ] . 
 tir of cases with thenar atrophy were significantly lower than those without ( p<0.001 , t - test ) . 
 tir were significantly lower in patients with severe median nerve swelling in ultrasonography ( p=0.042 , anova).conclusionmeasurements of median nerve motor function using load cell is a valuable evaluation tool in cts 
 . it might be helpful in detecting subclinical motor dysfunction before muscle atrophy develops . 
INTRODUCTION
MATERIALS AND METHODS
Device for motor function evaluation
Measurement of motor function
Patients, EDS, USG
Statistical analysis
RESULTS
Demographics
TIR
Correlation of TIR with other variables
DISCUSSION
CONCLUSION