Measurement error in grip and pinch force measurements in patients with hand injuries.

Only data that have acceptable reliability and validity are valuable in the clinical decision-making process for determination of impaired function and comparison of surgical repair techniques to document progress during rehabilitation and to evaluate disability after injury. Such data will decrease the need for use of unsubstantiated opinions and will increase the physical therapist's ability to obtain reproducible findings and meaningful results. (1) Better reliability implies better precision of single measurements, which is a prerequisite for better tracking of changes in measurements in research and clinical practice. (2)

Generally accepted instruments in the evaluation of hand function measure grip and pinch force. Grip and pinch force measurements have been promoted as an important measure of outcome in, for example, the evaluation of peripheral nerve function. (3-5) For a correct interpretation of these force measurements, we contend information on the reliability (measurement error) of these measurements is required. The reliability of grip force measurements has been studied in patients with hand injuries (6,7) and in people without impairments of the hand. (8,9) It also has been studied in several other categories of patients, including women with nonspecific regional pain (NSRP) (10) and patients with reflex sympathetic dystrophy (RSD) (11) or epicondylitis, (12) and in people after a stroke. (13) The reliability of pinch force measurements has been studied in patients with RSD (11) and repetitive strain injury (RSI). (14)

The studies of Spijkerman et al (6) and Brown et al (7) on the reliability of force measurements in patients with hand injuries have important drawbacks. The study by Spijkerman et al included only 8 patients, and Brown et al, in their study of grip and pinch force measurements in patients with hand injuries, did not specify the measurement error. As in many studies, the intraclass correlation coefficient (ICC) was used as a measure of reliability. For clinical use, however, we believe the most relevant information is the magnitude of change between tests that is required to detect a real change, preferably quantified in the same units as the force measurement. (10,15) This magnitude of change is specified in the smallest detectable difference (SDD), which is calculated from the standard error of measurement (SEM), the absolute error component of the measurements, (16,17) The smaller the measurement error, the better the measure. (18)

Various factors relating to the patient's condition may influence the measurement error, such as the amount of pain and loss of normal function of the fingers or thumb after injury. The experience of the examiner also might influence the measurement error. However, studies on these aspects of grip and pinch force measurements for patients with hand injuries are scarce.

One aim of our study was to assess the SEM and related indexes of reliability for intraexaminer and interexaminer applications of grip (2 handle positions, with distances between the handles of 4.6 and 7.2 cm) and pinch (tip pinch and key pinch) force measurements for patients with hand injuries obtained with Lode handgrip and pinch-grip dynamometers (Fig. 1). * A second aim was to investigate whether the measurement error of grip and pinch force measurements differs between specific applications, such as measurements of injured and noninjured hands, measurements obtained by experienced and inexperienced examiners, and measurements between 2 handle positions for grip force and 2 different types of pinch force (ie, tip and key pinch force). A third aim was to judge whether the measurement error is small enough to justify use of these measurements to discern real changes in grip and pinch force in individual patients. Because no clear criteria to judge the SDD are available for grip and pinch force measurements, we compared our findings with the results of studies in which grip and pinch force measurements were examined in different patient categories (ie, patients with hand injuries, pain, RSD, or epicondylitis and people after stroke).

[FIGURE 1 OMITTED]

Method

Subjects

A consecutive sample of 33 patients (20 male, 13 female) who were seen in the Department of Rehabilitation Medicine of Erasmus MC-University Medical Center Rotterdam in the Netherlands participated in the study. They had a mean age of 36 years (SD 13.7, range=17-67). All patients had an injury on only one hand (6 with tendon lacerations, 9 with nerve lesions, 4 with fractures, and 14 with a combination of lesions or surgeries [eg, crush injury, finger amputation, arthrodesis]). During a period of 5 months, patients who were capable of being evaluated for grip and pinch force were asked to participate in this study. Patients who were not permitted to grip or pinch with maximum force because of injured tissue and patients who complained of pain were excluded. We presumed that pain would inhibit the patients from exerting full maximum force and that force measurements may reflect the amount of pain rather than the force-generating capacity of the patients. The participants were informed about the purpose of the study and gave informed consent.

The participants were in different phases of their rehabilitation process. Study entry was, on average, 22 months after injury or surgery when including one patient who had a 16-year period between the date of injury and time of examination. Excluding this patient, the average period was 9 months (SD=7.0, range 1-28) since injury or surgery. Force measurements of the hand are routinely obtained in our department during different phases of the rehabilitation process. Such measurements can be used to determine progression of muscle force recovery, the ability to perform in a vocation, and indications for continuing therapy and to assess longterm outcome after hand injuries.

Instrumentation

We used Lode handgrip and pinch-grip dynamometers (Fig. 1). The distances between the handles of the Lode handgrip dynamometer were adapted to create spaces between the handles comparable to those of the Jamar hand dynamometer. ([dagger]) For our study, the grip handle positions 2 (distance between handles=4.6 cm) and 4 (distance between handles=7.2 cm), which we designated "grip 2" and "grip 4," respectively, were used with the handgrip dynamometer.

[FIGURE 1 OMITTED]

With the Lode pinch-grip dynamometer, which is similar in design to the Preston pinch dynamometer, ([dagger],19) 2 types of pinch were measured: tip pinch and key pinch. Tip pinch force was measured with only the index finger on top and the other fingers flexed with the thumb below, and key pinch force was measured with the thumb on top and the radial side of the index finger below.

The grip handle is connected to an amplifier from which the values give a digital readout on a display. According to the manufacturer, the measuring range is 0 to 1,000 N, with an accuracy of 1% deviation for 2 to 500 N and 2% for 500 to 900 N. Calibration was done with suspended weights according to the method described by Mathiowetz et al. (8) We believe the use of strain gauge technology is preferable to dynamometers, which are spring-based or use a hydraulic pressure system, because such dynamometers might produce erroneous data due to the wear and tear of metal, slow leaks, and hysteresis. (20)

Procedure

Measurements were taken according to the recommendations of the American Society of Hand Therapists (ASHT). (21) Participants were seated at a table on which the dynamometers were positioned (Fig. 1). The subjects were told to keep their elbow flexed without resting their arm or the grip handle of the dynamometer on the table. The digital display was not visible to the subjects. Corresponding to the ASHT recommendations for each measurement, the mean of 3 repetitions was recorded. Measurements were obtained of the left and right hands alternately, which is the method of testing used at our clinic. Testing both hands, we contend, enables comparisons of the injured and noninjured hands, as proposed by Gaul. (22)

The side (injured or noninjured) at which measurements were started and the order of tests (grip 2, grip 4, tip pinch; or key pinch) were randomly selected. Both examiners obtained all the measurements twice for each subject; the order of examiners was randomly selected. During each measurement session, the examiners obtained 12 measurements (2 grip and 2 pinch measurements X 3 repetitions from one hand. Then the examiners were changed while the subject took a short break (2-3 minutes) and moved the arm and hand out of the testing position. In this way, we attempted to reflect practice with examiners independently testing subjects, except there was a short time interval between examiners. Both examiners participated in 2 sessions per patient, which resulted in 48 measurements per hand. The total time required for testing, including the breaks, was 35 to 40 minutes per patient.

Examiners

Because we were interested in the effect of experience of the examiner on measurement error, we selected 2 examiners with widely differing experience. The first examiner was a 54-year-old male physical therapist (JFvN) with 20 years of experience in testing hand function. The second examiner (JG) was a 22-year-old female medical student with no previous experience with these tests. During a 2-week period, the inexperienced examiner had 5 hours of training by an experienced physical therapist to become familiarized with the equipment and testing protocol. During the training, measurements were practiced on several subjects without hand injuries and some patients with hand injuries. We believe that the results obtained by this student are reasonably representative of those that could be obtained by an inexperienced examiner, regardless of whether this is a starting physician or physical therapist, because at this stage they have comparable (ie, limited) knowledge, attitudes, and skills concerning force measurements.

Data Analysis

Statistical analyses were done to determine intraexaminer reliability of data obtained in the 2 sessions performed by the same examiner both for the experienced examiner (Texp1 and Texp2) and the inexperienced examiner (Tinx 1 and Tinx 2) separately. Interexaminer reliability was calculated between the first sessions of the experienced examiner (Texp1) and the inexperienced examiner (Tinx1). Analyses of the measurements of the injured hands (n=33) and noninjured hands (n=33) were conducted separately.

An analysis of variance (ANOVA) was conducted with an SPSS/PC+ program ([double dagger]) to determine the multiple sources of measurement error. The variance attributed to differences among participants was designated "Var (P)." The variance attributed to differences between sessions by the same examiner (Texp1 and Texp2, Tinx1 and Tinx2) was designated "Var (S)." The variance ascribed to the different examiners (Texp1 and Tinx1) was designated "Var (T)." Variance due to interaction among participants for intraexaminer sessions was designated "Var (PXS)," and variance due to interaction among participants for interexaminer sessions was designated "Var (PXT)." The interaction components (PXS) and (PXT) were confounded by the residual error. In the intraexaminer analyses, Var (S) and Var (PXS) (ie, the variance within participants) constituted the error variance. Correspondingly, for the interexaminer analyses, the variance components Var (T) and Var (PXT) constituted the error variance.

From the error variance, the SEM was computed as its square root. (17) Based on the SEM, the SDD with 95% confidence was calculated as 1.96 X [square root of 2] X SEM. (23) This SDD can be applied in such a way that only differences between 2 consecutive measurements greater than the SDD can be interpreted with 95% certainty as real change in grip or pinch force. Intraclass correlation coefficients were computed as the ratio of variances among participants (ie, Var [P]) and the total variance. (15)

Comparing SEMs

In order to test whether differences existed in error variances of different applications of grip and pinch force measurements, a test of equality of variances for paired samples was applied. In this analysis, scores between sessions were compared by calculating the correlation coefficient (Pearson r) between the sum and difference of the difference scores and testing whether this correlation differed from zero. (16,24(pp171-172)) In this way, we tested whether differences existed in error variance, and thus SEM and SDD, between the experienced and inexperienced examiners, between measurements of the injured and noninjured hands, and between the 2 handle positions of the grip force measurements and between the 2 pinch force measurements.

Commonly accepted criteria to judge whether the SEM and SDD of measurements are adequate for application of the measurements to individual patients do not exist. Therefore, we compared the SEMs found in our study with those from other studies in which grip and pinch force measurements were investigated. For an adequate comparison, We selected studies from the literature in which values for SEM or SDD were reported and studies from which SEM and SDD can be estimated by using the formulas: SEM = SD [square root] (1-ICC) (15(p119),23) or SEM = [SD.sub.difference] /[square root of 2], (15(p120)) where SD=standard deviation. These studies included similar groups of patients as in our study (ie, patients with hand injuries or patients from different groups such as patients with pain, RSD, epicondylitis, and stroke).

Results

Descriptive values (mean and standard deviations) were calculated for all measurements (2 grip and 2 pinch measurements) for the injured and noninjured hands and for the 4 sessions conducted by the experienced and inexperienced examiners (Tab. 1). Evidently noninjured hands have stronger grip and pinch forces. The mean grip force in position 4 was less than in position 2. Key pinch had a considerably greater mean force than tip pinch.

Two scatterplots of measurements obtained for both injured and noninjured hands (n=66) are presented in Figures 2 and 3. Figure 2 shows the measurements of grip force with the second handle position for the 2 sessions conducted by the experienced examiner (Texp1 and Texp2). Figure 3 shows the measurements of the tip pinch force obtained by the 2 different examiners (Texp1 and Tinx1). Both scatterplots demonstrate that there was a high level of correspondence between the 2 sessions and the 2 examiners.

[FIGURE 2-3 OMITTED]

Table 2 contains the results of the ANOVA: the sum of squares, mean of squares, and estimated variance components attributed to different sources. Reliability indexes (ie, SEM, SDD, and ICC) for the intraexaminer grip and pinch measurements are presented, ordered by examiner (experienced and inexperienced) and by hand (injured and noninjured). The SEMs ranged from 4 to 29 N, and the corresponding SDDs ranged from 11 to 80 N. The lowest ICC was .82 and the highest ICCs were .97 which, according to the scale suggested by Shrout and Fleiss, (25) should be classified as excellent. The interexaminer data are presented in Table 3 and show comparable values.

No differences were found in the error variances of grip and pinch force measurements between injured and noninjured hands or performed by experienced and inexperienced examiners. Similarly, no differences were found in the error variances of the measurements between the 2 handle positions of grip force or between the 2 pinch techniques.

Tables 4 and 5 present comparisons among studies investigating grip and pinch force measurements, including the type of dynamometer used, characteristics of the subjects, means and standard deviations of force measurements, and reliability indexes (ie, SEM, SDD, and ICC). The measurement errors of the SEMs of grip force measurements are comparable in most of the studies, except for those of Nitschke et al (10) and Smidt et al, (12) in which relatively low values were found (Tab. 4). For pinch force measurements, the SEMs were 4 or 5 N, with the exception of the higher values of 11 N found by Geertzen et al (11) (Tab. 5).

Discussion

In our study, high ICCs were found for the reliability of grip and pinch force measurements in subjects with hand injuries. In our view, however, a high ICC should not be interpreted as a small measurement error because, in an ICC, measurement error and real variability between subjects are expressed in relative terms. Expressing the reliability as a dimensionless ratio of variances does not allow us to interpret the reliability in terms of an individual score. To decide whether a person's grip force has changed after a period of rehabilitation, a physical therapist must know which part of the change measured was real and which part by is due to measurement error. To accomplish this, we calculated the SEM and SDD.

In our study, the SDD of the grip force measurements (second handle position) of the injured hands was 61 N for measurements obtained by the experienced examiner (Tab. 2). This finding means that for grip force measurements taken by the experienced examiner (Texp), a change in force of at least 61 N is needed between 2 sessions to be 95% confident that a real change has occurred. The 2 different types of pinch force measurements (tip pinch and key pinch) showed a much smaller SDD; for the experienced examiner, the SDDs for the injured hands were 11 to 12 N (Tab. 2).

In the case of our 2 examiners with widely differing experience, comparison of the SEMs showed no differences between them. Thus, for grip and pinch force measurements, it appears that a brief training period was sufficient for an inexperienced examiner to reach a level of reliability comparable to that of an experienced examiner. Given the small number of examiners in our study, however, this cannot be stated with certainty.

More examiners, however, would entail a longer measurement time, which might fatigue the patient or decrease his or her concentration, both of which may influence the measurement error. We attempted to compensate for the small number of examiners by selecting 2 examiners with what we considered maximally different experience. Given that no differences in measurement error between the 2 examiners were found, we contend that having more examiners (eg, with intermediate levels of experience) obtain the measurements would not have affected our conclusions. Although we do not have data to support this view, we believe it is a reasonable interpretation.

Other factors also may influence the measurement error. For example, we also examined the difference in SEMs between grip and pinch force measurements of the injured and noninjured hands. The measurement error, however, did not differ between the injured and noninjured hands. No differences were found between the SEMs of grip force measurements in the 2 handle positions or between both types of pinch force measurements. Therefore, for applications in clinical practice, we contend one SEM value can be applied for grip force measurements for both handle positions and one SEM value can be applied for pinch force measurements, irrespective of injury and experience of the examiner.

Accepted criteria to judge the SDD of grip and pinch force measurements do not exist. Therefore, we compared our findings with those of 6 studies in which grip and pinch force measurements were investigated in similar and different patient categories (ie, patients with hand injuries, (6,7) women with NSRP, (10) patients with RSD, (11) patients with epicondylitis, (12) and patients after a stroke (23) (Tab. 4). The SEMs of grip force measurements in these different studies are comparable. However, the differences in means and ranges of the measured force levels in these studies are remarkable (eg, the mean grip force levels in the affected hands ranged from 84 to 300 N). To determine the value of a particular measurement in a population during clinical practice, we believe it is essential to know in which range the changes of muscle force take place. For example, in people with hand injury, the grip force will be lower shortly after the trauma. During later phases of rehabilitation, the increased muscle force will generally reach a plateau after many months. If the difference in the grip force between the start and end of the rehabilitation is, for example, 100 N, an SDD of 80 N will mean the measurement is inadequate to detect changes. If the range in which the forces change is as wide as 300 N, an SDD of 30 N is certainly sufficient to detect changes during the rehabilitation process. In this latter example, a virtual scale of 10 steps is achieved.

To determine whether the calculated measurement error is small enough to make a test valuable in clinical practice, different methods have been applied in the studies we cite. Geertzen et al (11) concluded that the SDD is too large in relation to the mean force measured to be useful in patients with RSD. Smidt et al (12) suggested that an SDD less than 10% of the total range of the measurements would be acceptable. The range, however, is determined by the extreme values of the measurement, whereas the standard deviation is less influenced by the extreme values. In our study, therefore, we re-examined the SDD in relation to the standard deviation of the measurements by calculating the SDD/standard deviation ratios. The SDD/standard deviation ratios were 0.5 to 0.6 for grip force measurements using the second handle position and 0.6 to 0.7 when using the fourth handle position. These findings mean that 6 to 7 steps of changes in force level can be detected within the 95% distribution ("virtual scale") of impaired to normal levels of grip force. In our opinion, this SDD/standard deviation ratio is useful in order to gain better insight as to whether measurements can be used to detect clinical meaningful changes. A more definitive conclusion concerning the usefulness of the measurements can be made by relating the SDD relative to the magnitude of changes in force measurements in a prospective study of patients throughout the entire rehabilitation process.

Conclusions

According to the ICC values obtained in our study, the reliability of grip and pinch force measurements is excellent. However, assessment of the measurement error and detectable change in muscle to force between 2 consecutive measurements demonstrated that, in grip and pinch force measurements in individual patients, only relatively large changes can be adequately detected.

Measurement error did not differ between the experienced and inexperienced examiners or the injured and noninjured hands. Similarly, no differences were found in the grip force measurements for the 2 handle positions or in the tip pinch and key pinch force measurements. The limited number of examiners and the use of subjects who were pain-free should be considered when applying our results. Further study of the SDD/standard deviation ratio is needed to develop clear criteria to judge whether measurement error is acceptable to detect changes in individual patients.

Table 1.
Grip and Pinch Force Measurements (in Newtons) Obtained by Experienced
and Inexperienced Examiners for Both Hands of Participants With Hand
Injury of One Hand (N=33)

                         Experienced Examiner

                         Session 1   Session 2

Hand         Test (a)    [bar]X   SD    [bar]X   SD

Injured      Grip 2      250      123   253      125
             Grip 4      231      110   231      111
             Tip pinch    39       17    39       16
             Key pinch    63       22    64       22
Noninjured   Grip 2      370      116   364      115
             Grip 4      326      110   323      108
             Tip pinch    55       13    53       12
             Key pinch    87       18    86       19

                         Inexperienced Examiner

                         Session 1   Session 2

Hand         Test (a)    [bar]X   SD    [bar]X   SD

Injured      Grip 2      241      122   245      117
             Grip 4      231      113   223      109
             Tip pinch    37       16    38       16
             Key pinch    63       25    62       24
Noninjured   Grip 2      345      115   359      118
             Grip 4      325      112   317      109
             Tip pinch    54       12    54       12
             Key pinch    86       20    84       20

(a) Grip 2=measurements of grip force in the second handle position,
grip 4=measurements of grip force in the fourth handle position.

Table 2.
Intraexaminer Measurements of Grip and Pinch Force (in Newtons) of
Injured Hands of Participants  (N=33) Obtained by Experienced and
Inexperienced Examiners (a)

Examiner        Hand         Test        Source             SS

Experienced     Injured      Grip 2      Between patients   972270
                                         Within patients     15841
                             Grip 4      Between patients   758462
                                         Within patients     20257
                             Tip pinch   Between patients    16035
                                         Within patients       603
                             Key pinch   Between patients    30373
                                         Within patients       510
Inexperienced   Injured      Grip 2      Between patients   899327
                                         Within patients     12989
                             Grip 4      Between patients   772010
                                         Within patients     12443
                             Tip pinch   Between patients    15234
                                         Within patients       657
                             Key pinch   Between patients    36315
                             (n=32)      Within patients      1316
Experienced     Noninjured   Grip 2      Between patients   835322
                                         Within patients     22198
                             Grip 4      Between patients   738201
                                         Within patients     26918
                             Tip pinch   Between patients     9482
                                         Within patients       539
                             Key pinch   Between patients    21601
                                         Within patients       754
Inexperienced   Noninjured   Grip 2      Between patients   822792
                             (n=32)      Within patients     21624
                             Grip 4      Between patients   769145
                                         Within patients     13478
                             Tip pinch   Between patients     8858
                                         Within patients       892
                             Key pinch   Between patients    23848
                                         Within patients      1383

Examiner        Hand         Test        Source              MS

Experienced     Injured      Grip 2      Between patients   30383
                                         Within patients      490
                             Grip 4      Between patients   23702
                                         Within patients      633
                             Tip pinch   Between patients     501
                                         Within patients       19
                             Key pinch   Between patients     949
                                         Within patients       16
Inexperienced   Injured      Grip 2      Between patients   28104
                                         Within patients      406
                             Grip 4      Between patients   24125
                                         Within patients      389
                             Tip pinch   Between patients     476
                                         Within patients       21
                             Key pinch   Between patients    1135
                             (n=32)      Within patients       41
Experienced     Noninjured   Grip 2      Between patients   26104
                                         Within patients      694
                             Grip 4      Between patients   23069
                                         Within patients      841
                             Tip pinch   Between patients     296
                                         Within patients       17
                             Key pinch   Between patients     675
                                         Within patients       24
Inexperienced   Noninjured   Grip 2      Between patients   26542
                             (n=32)      Within patients      698
                             Grip 4      Between patients   24036
                                         Within patients      408
                             Tip pinch   Between patients     277
                                         Within patients       28
                             Key pinch   Between patients     745
                                         Within patients       43

                                                            Estimated
Examiner        Hand         Test        Source             Variance

Experienced     Injured      Grip 2      Between patients    14947
                                         Within patients       490
                             Grip 4      Between patients    11534
                                         Within patients       633
                             Tip pinch   Between patients      241
                                         Within patients        18
                             Key pinch   Between patients      483
                                         Within patients        16
Inexperienced   Injured      Grip 2      Between patients    13849
                                         Within patients       402
                             Grip 4      Between patients    11868
                                         Within patients       406
                             Tip pinch   Between patients      228
                                         Within patients        21
                             Key pinch   Between patients      547
                             (n=32)      Within patients        41
Experienced     Noninjured   Grip 2      Between patients    12705
                                         Within patients       694
                             Grip 4      Between patients    11114
                                         Within patients       841
                             Tip pinch   Between patients      140
                                         Within patients        18
                             Key pinch   Between patients      326
                                         Within patients        24
Inexperienced   Noninjured   Grip 2      Between patients    12922
                             (n=32)      Within patients       698
                             Grip 4      Between patients    11823
                                         Within patients       408
                             Tip pinch   Between patients      124
                                         Within patients        28
                             Key pinch   Between patients      351
                                         Within patients        43

Examiner        Hand         Test        Source             SEM   SDD

Experienced     Injured      Grip 2      Between patients
                                         Within patients    22    61
                             Grip 4      Between patients
                                         Within patients    25    70
                             Tip pinch   Between patients
                                         Within patients     4    12
                             Key pinch   Between patients
                                         Within patients     4    11
Inexperienced   Injured      Grip 2      Between patients
                                         Within patients    20    56
                             Grip 4      Between patients
                                         Within patients    20    56
                             Tip pinch   Between patients
                                         Within patients     5    13
                             Key pinch   Between patients
                             (n=32)      Within patients     6    18
Experienced     Noninjured   Grip 2      Between patients
                                         Within patients    26    73
                             Grip 4      Between patients
                                         Within patients    29    80
                             Tip pinch   Between patients
                                         Within patients     4    12
                             Key pinch   Between patients
                                         Within patients     5    13
Inexperienced   Noninjured   Grip 2      Between patients
                             (n=32)      Within patients    28    77
                             Grip 4      Between patients
                                         Within patients    20    56
                             Tip pinch   Between patients
                                         Within patients     5    15
                             Key pinch   Between patients
                                         Within patients     7    18

Examiner        Hand         Test        Source             ICC

Experienced     Injured      Grip 2      Between patients
                                         Within patients    .97
                             Grip 4      Between patients
                                         Within patients    .95
                             Tip pinch   Between patients
                                         Within patients    .93
                             Key pinch   Between patients
                                         Within patients    .97
Inexperienced   Injured      Grip 2      Between patients
                                         Within patients    .97
                             Grip 4      Between patients
                                         Within patients    .97
                             Tip pinch   Between patients
                                         Within patients    .92
                             Key pinch   Between patients
                             (n=32)      Within patients    .93
Experienced     Noninjured   Grip 2      Between patients
                                         Within patients    .95
                             Grip 4      Between patients
                                         Within patients    .93
                             Tip pinch   Between patients
                                         Within patients    .89
                             Key pinch   Between patients
                                         Within patients    .93
Inexperienced   Noninjured   Grip 2      Between patients
                             (n=32)      Within patients    .94
                             Grip 4      Between patients
                                         Within patients    .97
                             Tip pinch   Between patients
                                         Within patients    .82
                             Key pinch   Between patients
                                         Within patients    .89

(a) Grip 2=measurements of grip force in the second handle position,
grip 4=measurements of grip force in the fourth handle position.
SS=sum of squares, MS=mean squares, SEM=Standard error of measurement,
SDD=smallest detectable difference, ICC=intraclass correlation
coefficient.

Table 3.
Interexaminer Measurements of Grip and Pinch Force of Injured and
Noninjured Hands of Participants (N=33) (a)

                                                             Estimated
Hand         Test        Source             SS    MS         Variance

Injured      Grip 2      Between patients   948096   29628   14584
                         Within patients     16279     493     493
             Grip 4      Between patients   763813   23869   11508
                         Within patients     27279     852     852
             Tip pinch   Between patients    15805     494     234
                         Within patients       855      28      29
             Key pinch   Between patients    33541    1048     509
             (n=32)      Within patients       955      30      30
Noninjured   Grip 2      Between patients   835379   26106   12899
                         Within patients     35320    1104    1111
             Grip 4      Between patients   774343   24198   11857
                         Within patients     15495     484     484
             Tip pinch   Between patients     9579     299     136
                         Within patients       857      27      27
             Key pinch   Between patients    21771     680     315
                         Within patients      1594      49      50

                                            SEM   SDD
Hand         Test        Source             (N)   (N)   ICC

Injured      Grip 2      Between patients
                         Within patients    22    62    .97
             Grip 4      Between patients
                         Within patients    29    81    .93
             Tip pinch   Between patients
                         Within patients     5    15    .89
             Key pinch   Between patients
             (n=32)      Within patients     5    15    .94
Noninjured   Grip 2      Between patients
                         Within patients    33    92    .92
             Grip 4      Between patients
                         Within patients    22    61    .96
             Tip pinch   Between patients
                         Within patients     5    14    .84
             Key pinch   Between patients
                         Within patients     7    20    .86

(a) Grip 2=measurements of grip force in the second handle position,
grip 4=measurements of grip force in the fourth handle position.
SS=sum of squares, MS=mean squares, SEM=Standard error of measurement,
SDD=smallest detectable difference, ICC=intraclass correlation
coefficient.

Table 4.
Comparison of Intratester Measurements From 6 Grip Force Studies With
Data From Our Study (a)

              Handheld
Study         Dynamometer        Subjects                          n

Spijkerman    Prototype          No injuries                       16
  et al (6)     Lode             Hand injuries                      8
Brown et      Dexter             Hand injuries                     30
  al (7)        grip (b)
Nitschke et   Jamar              Women with no                     32
  al (10)                          injuries
                                 Women with                        10
                                   NSRP
Geertzen et   CITEC              RSD             Unaffected hand   29
  al (11)       grip (c)                         Affected hand
Smidt et      Jamar              Epicondylitis   Uninvolved hand   50
  al (12)                                        Involved hand
Boissy et     Lafayette          Not affected                      10
  al (13)       grip (d)         Stroke                            15
Our study     Lode grip handle   Hand injuries   Noninjured hand   33
                position 2                       Injured hand
              Lode grip handle                   Noninjured hand
                position 4                       Injured hand

Study         [bar]X   SD    SEM   SDD   ICC

Spijkerman    231       18   14    39    98
  et al (6)   434       10   25    59    98
Brown et      267      115   30    84    93
  al (7)
Nitschke et   325       69   20    57    93
  al (10)     174       62   18    59    95
Geertzen et   123       66   24    66    97
  al (11)      84       51   25    71    94
Smidt et      340      100   13    37    98
  al (12)     300      110   14    39    98
Boissy et     382       87   33    92    86
  al (13)     130       84   25    69    91
Our study     367      115   26    73    95
              252      123   22    61    97
              324      109   29    80    93
              231      109   25    70    95

(a) NSRP=nonspecific regional pain syndrome, RSD=reflex sympathethic
dystrophy, SEM=standard error of measurements, SDD=smallest detectable
difference, ICC=intraclass correlation coefficient (except for study
by Nitschke et al, in which Pearson correlation coefficient were
calculated). All data converted to newtons (data in studies by
Nitschke et al. Geertzen et al, and Smidt et al were in kilograms of
force and were converted to newtons by multiplying by 10; Brown and
colleagues' within-patient data were in pounds were multiplied
by 4.448). Data are for intratester measurements, except for Geertzen
et al and Smidt et al, who reported intertester data. Data from Brown
et al are the mean of 3 testers. Figures in italics are estimated from
ICC values presented in the studies.

(b) Dexter Extremity Evaluation & Therapy Systems, Cedaron Medical
Inc, PO Box 2100, Davis, CA 95617.

(c) CITEC hand-held dynamometer, CIT Technics, Rijksstraatweg 384,
9752 CR Haren, the Netherlands.

(d) Lafayette Instrument Co, 3700 Sagamore Pkwy N, PO Box 5729,
Lafayette, IN 47903.

(e) Figure from study by Smidt et al are estimated from the
[SD.sub.diff] values they reported. These values of the SDD differ
from the values reported by Smidt et al, who submitted an erratum on
this point.

Table 5.
Comparison of Data From Earlier Pinch Force Measurement Studies With
Data From Our Study (All Data in Newtons) (a)

              Handheld
Study         Dynamometer   Subjects

Geertzen et   CITEC         RSD          Unaffected side   Key pinch
  al (11)                                Affected side
Brown et      Dexter        Hand                           Tip pinch
  al (7)                      injuries                     Jaw pinch
Our study     Lode          Hand         Noninjured hand   Tip pinch
                              injuries     Injured hand
              Lode                       Noninjured hand   Key pinch
                                           Injured hand

              Handheld
Study         Dynamometer   n    Tester         [bar]X   SD     SEM

Geertzen et   CITEC         29   Intertester    67       19     11
  al (11)                                       56       23     11
Brown et      Dexter        30   Intratester    48       18.2    4
  al (7)                           (mean of 3   64       22.7    4
                                   testers)
Our study     Lode          33   Intratester    53       11.7    4
                                                39       15.6    4
              Lode                              86       19      5
                                                64       22.4    4

              Handheld
Study         Dynamometer   SDD    ICC

Geertzen et   CITEC         30     ... (b)
  al (11)                   31     ... (b)
Brown et      Dexter         7.1   .96
  al (7)                     8.5   .96
Our study     Lode          12     .89
                            12     .93
              Lode          14     .93
                            11     .97

SEM=Standard error of measurement, SDD=smallest detectable difference,
ICC=intraclass correlation coefficient, RSD=reflex sympathetic
dystrophy.

(b) No data available.

This article was received February 24, 2003, and was accepted May 19, 2003.

* Lode Medical Technology, Zernikepark 16, 9717 AN Groningen, the Netherlands, Distributed in the United States by ElectraMed Corp, G-5332 Hill-23 Dr, Flint, MI 48507.

([dagger]) Sammons Preston/Rolyan, 4 Sammons Ct, Bolingbrook, IL 60440.

([double dagger]) SPSS Inc, 233 S Wacker Dr, Chicago, IL 60606.

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TAR Schreuders, PT, is Physical Therapist, Department of Rehabilitation Medicine, Hand Therapy Unit, Erasmus MC-University Medical Center Rotterdam, PO Box 2040, 3000 CA Rotterdam, the Netherlands ([e-mail]). Address all correspondence to Mr Schreuders.

ME Roebroeck, PhD, is Assistant Professor, Department of Rehabilitation Medicine, Erasmus MC-University Medical Center Rotterdam.

J Goumans, MD, is Medical Student, Erasmus MC-University Medical Center Rotterdam.

JF van Nieuwenhuijzen, PT, is Research Therapist, Department of Rehabilitation Medicine, Erasmus MC-University Medical Center Rotterdam.

TH Stijnen, PhD, is Professor of Biostatistics, Department of Epidemiology and Biostatistics, Erasmus MC-University Medical Center Rotterdam.

HJ Stam, MD, PhD, is Professor of Rehabilitation Medicine and Chairman, Department of Rehabilitation Medicine, Erasmus MC-University Medical Center Rotterdam.

Mr Schreuders, Dr Roebroeck, and Dr Stam provided concept/idea/research design. Mr Schreuders and Dr Roebroeck provided writing. Dr Goumans and Mr van Nieuwenhuijzen provided data collection, and Mr Schreuders, Dr Roebroeck, Dr Goumans, and Dr Stijnen provided data analysis. Mr Schreuders and Dr Goumans provided project management. Dr Roebroeck and Dr Stam provided fund procurement and facilities/equipment. Dr Stijnen and Dr Stam provided consultation (including review of manuscript before submission).

The Ethical Committee of the Erasmus Medical Center, the Netherlands, approved this study.