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Sensitivity of the jamar dynamometer in detecting submaximal grip effort
Sensitivity of the Jamar Dynamometer in Detecting Submaximal Grip Effort Roy F. Ashford, MD, Pasadena,CA, Steven Nagelburg, MD, Rodney Adkins, PhD, Downey, CA Twenty-two people with no extremity disability were tested in a standard fashion using the Jamar Dynamometer to establish their maximum grip strength. Each participant was asked to grip first right-handed then left-handed three consecutive times. The directions were reexplained so that each participant would give a consistent, less than optimal effort; three trials right and three trials left were recorded. The standard deviations of each set of these trials were calculated for both right and left hands. These standard deviations were then tabulated as scores for 44 trials of 22 patients, both hands, for maximal and submaximal efforts. These scores were then compared, maximal versus submaximal, using a paired t-test. We found no statistical difference in the two groups in comparing the variability of results. Therefore, the current protocol for Jamar testing can allow a patient to make a consistently submaximal effort, resulting in a false apparent loss of grip strength. (J Hand Surg 1996;21A:402-405.)
The evaluation of impairment of hand function has been determined by the J a m a r Dynamometer. Use of the J a m a r D y n a m o m e t e r has been an accepted test of grip strength and has been routinely part of the physical examination. 1~* The reliability and validity of the Jamar has been stressed and has been found to be the standard of objective grip strength measurements. 2-4 But the Jamar relies on full patient participation to give accurate results, as does other objective testing. Studies have standardized the use of the d y n a m o m e t e r as to position, timing, instructions,
From the Rancho Los Amigos Medical Center, Pasadena, CA, and the Spinal Cord Injury Project, Rancho Los Amigos Medical Center, Downey, CA. Received for publication May 11, 1995; accepted in revised form Sept. 2, 1995. Study performed at the Downey Orthopedic Medical Corporation, Downey, CA. No benefitsin any form have been receivedor will be receivedfrom a commercialpartyrelateddirectlyor indirectlyto the subjectof this article. Reprint requests: Roy E Ashford, MD, Rancho Los AmigosMedical Center, 1333 Lida Street, Pasadena, CA 91103.
402
The Journal of Hand Surgery
and repetition to improve the results and decrease interobserver error with good success. 3,4 It is recommended that three trials of grip strength be obtained and the mean of these numbers represents the most reliable result. 3 I f there is more than 20% variability in these readings, one can assume that the patient is not exerting a full effort. 4 In workers' compensation, the loss of grip strength is used to determine the physical impairment of the upper extremity, which in turn will assist the judge's decision for financial remuneration for that individual. Whereas the J a m a r has been a useful tool for the clinician to evaluate patients both pre- and postoperatively, to evaluate progress in therapy, and to assist in making functional recommendations, it is now apparent that some patients being evaluated for impairment m a y be biased toward performing poorly because of secondary gain. The Jamar has been found to be very accurate--better than _+2% to 5%,2,3--and reliable, but it does not tell the examiner if maximal patient effort has been applied. Maximal effort has been defined as consistent results that demonstrate less than 20% variability in three tests. 4
The Journal of Hand Surgery/Vol. 21A No. 3 May 1996
To date, no studies have shown that a submaximal effort can repeatedly give results with the same consistency, thereby convincing the examiner that they are truly weaker than they are. The purpose of this research is to determine if the Jamar Dynamometer can detect a submaximal effort.
Materials and Methods Twenty-two people, 15 women and 7 men, with no upper-extremity disability were evaluated with a single Jamar Dynamometer in a standard fashion. Each person was seated, the dynamometer was placed on a table top, the elbow was flexed about 90 ~, and the wrist was in neutral to slight ulnar deviation. The Jamar Dynamometer Was set in the second position on all tests. Each participant was instructed about the Jamar, told to grip maximally, then rest, first with the right hand, then the left, three consecutive times. The directions were then re-explained, telling each participant to give a purposeful and consistently less than optimal effort in order to convince the examiner that they were weaker than they were. The results were tabulated for maximal and submaximal efforts, three trials for the right and three for the left hands of each of the 22 people. The data were then analyzed for each of the three trials (Table 1), calculating the mean, range, and standard deviation. These standard deviations were set as scores for the 44 tests, 22 people with two hands each, for maximal and submaximal efforts. These scores were then compared with a Student's t-test to determine if a statistical difference exists.
Results The average mean maximal effort was 38.4 kg, and the submaximal effort averaged 21.7 kg, a loss of 43%. Maximal effort showed an average range of 3.8 for each group of three tests, approximately an 11.3% variation, with a m a x i m u m range of 14.5 kg and a minimum o f 0 kg. Submaximal effort had an average range of 5.4 kg, a 26% variability, with a maximum of 11.4 and a minimum of 0 kg. The average standard deviation was 2.0 for the maximum group, compared to 2.4 for the submaximal group. The statistical analysis showed no difference between the two groups with regard to variability (t = -1.04; p = .305). We found a weak correlation of the two populations: r = -.301, and p = .047. In this study, variability was defined as the range (maximum result minus minimum result of the
403
three tests) divided by the mean of the three tests. We found that 8 of 44 (18%) maximal trials and 25 of 44 (57%) submaximal trials had a variability of 20% or greater. When we lowered the variability quotient to 10%, 20 of 44 (46%) maximal trials and 41 of 44 (93%) submaximal trials were greater than this standard.
Discussion The Jamar Dynamometer is accurate. 2-4 The factory specifications show reliability better than +5%, and studies have shown it to be less than +3%. 3 Interobserver erlor has been less than 1.2 to 1.4 kg 2 and most likely is a result of the error of the dynamometer itself. Our study showed an average range of 3.8 kg for maximal and 4.6 kg for submaximal effort. Taking into account the conservative standard error of +1.5 kg, our range becomes 2.3 to 5.3 kg and 3.1 to 6.1 kg. The spread of ranges in all trials is large, with standard deviations of 2.0 and 2.4, respectively. We found no statistical difference when comparing the ranges for each of the three tests of maximal versus submaximal. Our study had an average standard deviation of 2.0 with a mean of 38.4 kg for maximal effort and an average standard deviation of 2.4 with a mean of 21.7 kg for submaximal effort. Both average standard deviations are similar and they both demonstrated less than the 20% variability. Therefore, if an independent examiner was to look at both populations of data, based on current criteria of validity, he or she would say that population A is stronger than population B, even though they are the same people. We found no statistical difference when comparing the maximal and submaximal efforts based upon the range of test scores and the standard deviation of each of the three trials, but we did notice trends in variation on critical examination. If we used the standard 20% variability to determine maximal effort, the test would have called 18% of our maximal group not valid; in contrast, we could have separated out 57% of our submaximal group as malingerers. At 10% variability, we would accept only one half of the maximal trials as valid and we would have separated out over 93% of the submaximal group. If we eliminated the people with greater than 20% variability of results and accepted the people with less than 10% variability of results as being reliable, the people whose variability rate was greater than 10% and less than 20% would occupy a gray zone, leaving 28 of 88 patients (32%) unac-
404
Ashford et al. / Detecting Submaximal Grip Effort Table 1. Grip Strength Measurements
Submaximal Effort
Maximal Effort 1
Trials 2
55 56 61 61 34 34 36 38 38 32 55 49 55 49 25 27 34 23 39 39 32 20 26 23 30 28 24 27 59 57 36 37 50 52 51 43 27 31 38 33 43 38 64 50
54 56 62 59 32 33 41 42 36 30 50 50 55 50 26 23 36 27 36 39 34 20 25 16 30 25 20 19 55 55 36 37 47 50 47 41 25 31 40 35 43 39 60 51
Averages:
3 55 56 60 55 33 34 41 37 35 27 50 48 55 48 25 22 35 27 39 37 34 18 18 20 31 26 21 20 48 50 36 36 48 47 36 34 23 31 40 32 41 39 58 45
Mean (kg)
SD
54 56 61 58 32 33 39 39 36 29 51 48 54 48 25 23 35 25 38 38 33 19 23 19 30 26 21 21 53 53 36 36 48 49 44 39 25 31 39 33 42 38 60 48
0.52 0 1.14 3.47 0.95 0.79 2.62 2.41 1.82 2.29 2.62 1.14 0.52 1.14 0.79 2.92 0.91 2.62 1.46 0.79 1.31 1.14 4.48 3.47 0.95 1.64 2.29 4.3 5.72 3.47 0 0.26 1.46 2.5 7.5 4.81 1.82 0 1.2 1.36 1.2 0.45 2.84 3.09
38.4
2
Range Variability (kg) (%) 1 0 2 7 2 1 5 5 4 5 5 2 1 2 / 5 2 5 3 1 2 2 8 7 2 3 5 8 11 7 0 0 3 5 15 9 4 0 2 3 2 1 5 6 4
2 0 3 12 6 3 13 13 11 17 10 4 2 4 4 22 6 20 8 3 6 11 35 37 7 12 24 38 21 13 0 0 6 10 34 23 16 0 5 9 5 3 8 13
\
11.3
c o u n t e d for. A l l o f t h e s e o p t io n s l a c k sufficient sensi-
1
Trials 2
40 41 41 36 20 16 36 30 25 24 25 25 45 46 18 14 6.8 7.3 6.8 14 10 4.5 9.1 5 23 20 6.8 8.2 21 24 25 27 41 41 14 25 16 18 27 23 19 20 31 31
36 41 40 39 20 20 34 33 20 20 20 27 45 36 15 13 7.7 9.1 5 6.8 8.6 5 9.1 4.1 18 22 6.8 9.1 16 20 23 20 45 43 16 24 16 27 27 26 15 22 30 30
43 36 36 41 20 13 31 30 27 20 27 20 52 41 14 14 5.9 6.8 4.1 2.3 6.8 4.1 7.3 5 28 19 5.5 9.5 16 22 18 25 41 43 18 18 21 27 24 18 16 20 27 30
Mean (kg)
SD
Range Variability (kg) (%)
39 39 39 38 20 16 33 30 24 21 24 24 47 41 15 13 6 7 5 7 8 4 8 4 22 20 6 8 17 21 22 23 42 42 15 22 17 24 26 22 16 20 29 30
3.41 2.62 2.41 2.27 0 3.67 2.73 1.84 3.47 2.41 3.47 3.47 4.22 4.77 2.33 0.69 0.91 1.2 1.39 5.72 1.6 0.45 1.05 0.52 4.77 1.36 0.79 0.69 3.15 1.6 3.53 3.22 2.36 0.95 1.82 3.78 3.03 5.25 1.84 4.12 1.98 1.2 2.15 0.79
7 5 5 5 0 7 5 3 7 5 7 7 8 10 5 1 2 2 3 11 3 1 2 1 10 3 1 1 5 3 7 6 4 2 4 7 5 9 3 8 4 2 4 1
18 13 13 13 0 44 15 10 29 24 29 29 17 24 33 8 33 29 60 157 38 25 25 25 45 15 17 13 29 14 32 26 10 5 27 32 29 38 12 36 25 10 14 3
21.7
2.39
5
26
tent p e o p l e in the m a x i m a l trials tended to b e m o r e
tivity or specificity in d e t e r m i n i n g with certainty that
c o n s i s t e n t in the s u b m a x i m a l trial. C o n v e r s e l y , the
an i n d i v i d u a l has g i v e n full effort.
p e o p l e w i t h the g r e a t e s t variability o f results in the
W e did find a w e a k c o r r e l a t i o n o f the t w o p o p u l a tions, w i t h a c o e f f i c i e n t o f - . 3 0 1
(p = .047). This
w e a k c o r r e l a t i o n s u g g e s t s that the t w o p o p u l a t i o n s are the same, w h i c h i n d ic a t e s that the m o s t c o n si s-
m a x i m a l trials h a d m o r e variable results in the subm a x i m a l trial. This is to say that greater v ar i ab i l i t y in testing is m o r e intrinsic to e a c h patient rather than a f u n c t i o n o f effort applied.
The Journal of Hand Surgery/Vol. 21A No. 3 May 1996
Our test did show a greater variation when giving a suboptimal effort; however, this was not with statistical significance. With variation greater than 20%, we found that three times more people were faking a test (57% vs 18%), and it seems reasonable to use this as an estimate. But this means that almost half of the patients could still fake an objective test. We presume that if patients had secondary gain for motivation and possible coaching, they might improve their scores, but this will need to be confirmed in future studies. It is possible that increased time intervals between each trial (ie, hours or days) might further delineate submaximal tests.
405
References 1. Harkonen R, Purtoma M, Alaranta H. The grip strength and hand position of the dynamometer in 204 Finnish adults. J Hand Surg 1993;18B:129-132. 2. Harkonen R, Harju R, Alarante H. The accuracy of the Jamar Dynamometer. J Hand Ther 1993;6:259-262. 3. Mathiowetz V, Weber K, Volland G, Kashman N. Reliability and validity of grip and pinch strength evaluations. J Hand Surg 1984;9A:222-226. 4. Swanson A, Swanson G, Goran-Haggert C. Evaluation of hand impairment. In: Hunter J, Schneider J, Mackin E, eds. Rehabilitation of the hand. 3rd ed. St Louis: CV Mosby, 1990:108-138.
The evaluation of impairment of hand function has been determined by the J a m a r Dynamometer. Use of the J a m a r D y n a m o m e t e r has been an accepted test of grip strength and has been routinely part of the physical examination. 1~* The reliability and validity of the Jamar has been stressed and has been found to be the standard of objective grip strength measurements. 2-4 But the Jamar relies on full patient participation to give accurate results, as does other objective testing. Studies have standardized the use of the d y n a m o m e t e r as to position, timing, instructions,
From the Rancho Los Amigos Medical Center, Pasadena, CA, and the Spinal Cord Injury Project, Rancho Los Amigos Medical Center, Downey, CA. Received for publication May 11, 1995; accepted in revised form Sept. 2, 1995. Study performed at the Downey Orthopedic Medical Corporation, Downey, CA. No benefitsin any form have been receivedor will be receivedfrom a commercialpartyrelateddirectlyor indirectlyto the subjectof this article. Reprint requests: Roy E Ashford, MD, Rancho Los AmigosMedical Center, 1333 Lida Street, Pasadena, CA 91103.
402
The Journal of Hand Surgery
and repetition to improve the results and decrease interobserver error with good success. 3,4 It is recommended that three trials of grip strength be obtained and the mean of these numbers represents the most reliable result. 3 I f there is more than 20% variability in these readings, one can assume that the patient is not exerting a full effort. 4 In workers' compensation, the loss of grip strength is used to determine the physical impairment of the upper extremity, which in turn will assist the judge's decision for financial remuneration for that individual. Whereas the J a m a r has been a useful tool for the clinician to evaluate patients both pre- and postoperatively, to evaluate progress in therapy, and to assist in making functional recommendations, it is now apparent that some patients being evaluated for impairment m a y be biased toward performing poorly because of secondary gain. The Jamar has been found to be very accurate--better than _+2% to 5%,2,3--and reliable, but it does not tell the examiner if maximal patient effort has been applied. Maximal effort has been defined as consistent results that demonstrate less than 20% variability in three tests. 4
The Journal of Hand Surgery/Vol. 21A No. 3 May 1996
To date, no studies have shown that a submaximal effort can repeatedly give results with the same consistency, thereby convincing the examiner that they are truly weaker than they are. The purpose of this research is to determine if the Jamar Dynamometer can detect a submaximal effort.
Materials and Methods Twenty-two people, 15 women and 7 men, with no upper-extremity disability were evaluated with a single Jamar Dynamometer in a standard fashion. Each person was seated, the dynamometer was placed on a table top, the elbow was flexed about 90 ~, and the wrist was in neutral to slight ulnar deviation. The Jamar Dynamometer Was set in the second position on all tests. Each participant was instructed about the Jamar, told to grip maximally, then rest, first with the right hand, then the left, three consecutive times. The directions were then re-explained, telling each participant to give a purposeful and consistently less than optimal effort in order to convince the examiner that they were weaker than they were. The results were tabulated for maximal and submaximal efforts, three trials for the right and three for the left hands of each of the 22 people. The data were then analyzed for each of the three trials (Table 1), calculating the mean, range, and standard deviation. These standard deviations were set as scores for the 44 tests, 22 people with two hands each, for maximal and submaximal efforts. These scores were then compared with a Student's t-test to determine if a statistical difference exists.
Results The average mean maximal effort was 38.4 kg, and the submaximal effort averaged 21.7 kg, a loss of 43%. Maximal effort showed an average range of 3.8 for each group of three tests, approximately an 11.3% variation, with a m a x i m u m range of 14.5 kg and a minimum o f 0 kg. Submaximal effort had an average range of 5.4 kg, a 26% variability, with a maximum of 11.4 and a minimum of 0 kg. The average standard deviation was 2.0 for the maximum group, compared to 2.4 for the submaximal group. The statistical analysis showed no difference between the two groups with regard to variability (t = -1.04; p = .305). We found a weak correlation of the two populations: r = -.301, and p = .047. In this study, variability was defined as the range (maximum result minus minimum result of the
403
three tests) divided by the mean of the three tests. We found that 8 of 44 (18%) maximal trials and 25 of 44 (57%) submaximal trials had a variability of 20% or greater. When we lowered the variability quotient to 10%, 20 of 44 (46%) maximal trials and 41 of 44 (93%) submaximal trials were greater than this standard.
Discussion The Jamar Dynamometer is accurate. 2-4 The factory specifications show reliability better than +5%, and studies have shown it to be less than +3%. 3 Interobserver erlor has been less than 1.2 to 1.4 kg 2 and most likely is a result of the error of the dynamometer itself. Our study showed an average range of 3.8 kg for maximal and 4.6 kg for submaximal effort. Taking into account the conservative standard error of +1.5 kg, our range becomes 2.3 to 5.3 kg and 3.1 to 6.1 kg. The spread of ranges in all trials is large, with standard deviations of 2.0 and 2.4, respectively. We found no statistical difference when comparing the ranges for each of the three tests of maximal versus submaximal. Our study had an average standard deviation of 2.0 with a mean of 38.4 kg for maximal effort and an average standard deviation of 2.4 with a mean of 21.7 kg for submaximal effort. Both average standard deviations are similar and they both demonstrated less than the 20% variability. Therefore, if an independent examiner was to look at both populations of data, based on current criteria of validity, he or she would say that population A is stronger than population B, even though they are the same people. We found no statistical difference when comparing the maximal and submaximal efforts based upon the range of test scores and the standard deviation of each of the three trials, but we did notice trends in variation on critical examination. If we used the standard 20% variability to determine maximal effort, the test would have called 18% of our maximal group not valid; in contrast, we could have separated out 57% of our submaximal group as malingerers. At 10% variability, we would accept only one half of the maximal trials as valid and we would have separated out over 93% of the submaximal group. If we eliminated the people with greater than 20% variability of results and accepted the people with less than 10% variability of results as being reliable, the people whose variability rate was greater than 10% and less than 20% would occupy a gray zone, leaving 28 of 88 patients (32%) unac-
404
Ashford et al. / Detecting Submaximal Grip Effort Table 1. Grip Strength Measurements
Submaximal Effort
Maximal Effort 1
Trials 2
55 56 61 61 34 34 36 38 38 32 55 49 55 49 25 27 34 23 39 39 32 20 26 23 30 28 24 27 59 57 36 37 50 52 51 43 27 31 38 33 43 38 64 50
54 56 62 59 32 33 41 42 36 30 50 50 55 50 26 23 36 27 36 39 34 20 25 16 30 25 20 19 55 55 36 37 47 50 47 41 25 31 40 35 43 39 60 51
Averages:
3 55 56 60 55 33 34 41 37 35 27 50 48 55 48 25 22 35 27 39 37 34 18 18 20 31 26 21 20 48 50 36 36 48 47 36 34 23 31 40 32 41 39 58 45
Mean (kg)
SD
54 56 61 58 32 33 39 39 36 29 51 48 54 48 25 23 35 25 38 38 33 19 23 19 30 26 21 21 53 53 36 36 48 49 44 39 25 31 39 33 42 38 60 48
0.52 0 1.14 3.47 0.95 0.79 2.62 2.41 1.82 2.29 2.62 1.14 0.52 1.14 0.79 2.92 0.91 2.62 1.46 0.79 1.31 1.14 4.48 3.47 0.95 1.64 2.29 4.3 5.72 3.47 0 0.26 1.46 2.5 7.5 4.81 1.82 0 1.2 1.36 1.2 0.45 2.84 3.09
38.4
2
Range Variability (kg) (%) 1 0 2 7 2 1 5 5 4 5 5 2 1 2 / 5 2 5 3 1 2 2 8 7 2 3 5 8 11 7 0 0 3 5 15 9 4 0 2 3 2 1 5 6 4
2 0 3 12 6 3 13 13 11 17 10 4 2 4 4 22 6 20 8 3 6 11 35 37 7 12 24 38 21 13 0 0 6 10 34 23 16 0 5 9 5 3 8 13
\
11.3
c o u n t e d for. A l l o f t h e s e o p t io n s l a c k sufficient sensi-
1
Trials 2
40 41 41 36 20 16 36 30 25 24 25 25 45 46 18 14 6.8 7.3 6.8 14 10 4.5 9.1 5 23 20 6.8 8.2 21 24 25 27 41 41 14 25 16 18 27 23 19 20 31 31
36 41 40 39 20 20 34 33 20 20 20 27 45 36 15 13 7.7 9.1 5 6.8 8.6 5 9.1 4.1 18 22 6.8 9.1 16 20 23 20 45 43 16 24 16 27 27 26 15 22 30 30
43 36 36 41 20 13 31 30 27 20 27 20 52 41 14 14 5.9 6.8 4.1 2.3 6.8 4.1 7.3 5 28 19 5.5 9.5 16 22 18 25 41 43 18 18 21 27 24 18 16 20 27 30
Mean (kg)
SD
Range Variability (kg) (%)
39 39 39 38 20 16 33 30 24 21 24 24 47 41 15 13 6 7 5 7 8 4 8 4 22 20 6 8 17 21 22 23 42 42 15 22 17 24 26 22 16 20 29 30
3.41 2.62 2.41 2.27 0 3.67 2.73 1.84 3.47 2.41 3.47 3.47 4.22 4.77 2.33 0.69 0.91 1.2 1.39 5.72 1.6 0.45 1.05 0.52 4.77 1.36 0.79 0.69 3.15 1.6 3.53 3.22 2.36 0.95 1.82 3.78 3.03 5.25 1.84 4.12 1.98 1.2 2.15 0.79
7 5 5 5 0 7 5 3 7 5 7 7 8 10 5 1 2 2 3 11 3 1 2 1 10 3 1 1 5 3 7 6 4 2 4 7 5 9 3 8 4 2 4 1
18 13 13 13 0 44 15 10 29 24 29 29 17 24 33 8 33 29 60 157 38 25 25 25 45 15 17 13 29 14 32 26 10 5 27 32 29 38 12 36 25 10 14 3
21.7
2.39
5
26
tent p e o p l e in the m a x i m a l trials tended to b e m o r e
tivity or specificity in d e t e r m i n i n g with certainty that
c o n s i s t e n t in the s u b m a x i m a l trial. C o n v e r s e l y , the
an i n d i v i d u a l has g i v e n full effort.
p e o p l e w i t h the g r e a t e s t variability o f results in the
W e did find a w e a k c o r r e l a t i o n o f the t w o p o p u l a tions, w i t h a c o e f f i c i e n t o f - . 3 0 1
(p = .047). This
w e a k c o r r e l a t i o n s u g g e s t s that the t w o p o p u l a t i o n s are the same, w h i c h i n d ic a t e s that the m o s t c o n si s-
m a x i m a l trials h a d m o r e variable results in the subm a x i m a l trial. This is to say that greater v ar i ab i l i t y in testing is m o r e intrinsic to e a c h patient rather than a f u n c t i o n o f effort applied.
The Journal of Hand Surgery/Vol. 21A No. 3 May 1996
Our test did show a greater variation when giving a suboptimal effort; however, this was not with statistical significance. With variation greater than 20%, we found that three times more people were faking a test (57% vs 18%), and it seems reasonable to use this as an estimate. But this means that almost half of the patients could still fake an objective test. We presume that if patients had secondary gain for motivation and possible coaching, they might improve their scores, but this will need to be confirmed in future studies. It is possible that increased time intervals between each trial (ie, hours or days) might further delineate submaximal tests.
405
References 1. Harkonen R, Purtoma M, Alaranta H. The grip strength and hand position of the dynamometer in 204 Finnish adults. J Hand Surg 1993;18B:129-132. 2. Harkonen R, Harju R, Alarante H. The accuracy of the Jamar Dynamometer. J Hand Ther 1993;6:259-262. 3. Mathiowetz V, Weber K, Volland G, Kashman N. Reliability and validity of grip and pinch strength evaluations. J Hand Surg 1984;9A:222-226. 4. Swanson A, Swanson G, Goran-Haggert C. Evaluation of hand impairment. In: Hunter J, Schneider J, Mackin E, eds. Rehabilitation of the hand. 3rd ed. St Louis: CV Mosby, 1990:108-138.