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- PATIENTS AND METHODS
- APPENDIX A: DESCRIPTION OF MPUT
Quantitative assessments of functional status, such as grip strength (GST) and walking time, have been widely used for several decades in studies on rheumatoid arthritis (RA) (1). These measures, as well as the button test (BT) (2) and questionnaires regarding activities of daily living (3, 4), are effective in documenting significant morbidity. Declines in functional status have been reported in most patients over the course of 9 years (5–7).
To evaluate patients with RA, quantitative assessment of functional status can provide valuable data on disability (7) and can be used as a long-term functional outcome measure (1). Quantitative assessment of functional status in patients with RA has been approached through simple, rapidly completed physical measures of performance, such as GST, walking time, and the BT (2). Those measures have advantages compared with self-report questionnaires: Some patients find it difficult to complete self-report questionnaires, especially those with low formal education levels who have an increased risk of developing progressive RA (8). Furthermore, clinicians might find it problematic to rely only on self-reported data of functional status as adjunct to clinical decisions (2).
Moreover, GST, walking time, and BT have been found to be highly reproducible measures concerning their interobserver and intraobserver reliability when used according to a standard protocol (2).
To assess hand function in patients with RA, GST is widely used and BT is less often used (7, 9–11). Compared with specific tests with a broad focus on different aspects of function, GST and BT values can be obtained quickly, which is especially important in busy clinic settings and long-term evaluations of RA patients.
Nevertheless, these tests have serious drawbacks. Patients with RA report pain when performing GST, which has to be done 3 times with each hand according to the standard protocol (2, 7). In joint protection instructions in occupational therapy, patients with RA are told to avoid maximum grip force and to respect their pain as an indicator to stop (12). To use GST as a measurement in rheumatology might be questionable under this perspective. Some patients use these arguments or complain about pain and refuse to have GST assessed at all. In addition, GST measures a single dimension of function whose importance for performing everyday tasks may be limited and thus severely impairs the applicability of the test for long-term observations.
BT is less often used in clinical practice than GST. The standard protocol requires a standardized button board (2) that is difficult to obtain. Wear and tear, replacement, or repair of the board change the performance conditions for the patients.
The Moberg pickup test (MPUT) was considered a possible alternative measure for assessment of functional status of the hand in patients with RA. MPUT consists of 12 small objects that have to be picked up while time is taken with a stop watch (Figure 1). A standard protocol has been established and interrater reliability has been found to be good (13). When administered blindfolded, MPUT has been described to assess sensory function grip of the hand (13). When administered with open eyes, MPUT could be used to assess precision grip in patients with RA. MPUT has not been used in RA patients so far. The aim of this study was to assess and compare the suitability of MPUT as an indicator of functional impairment in patients with inflammatory joint diseases. In this analysis, MPUT was compared with BT as an already established test for quantitative assessment of functional status in patients with inflammatory joint disease.
Figure 1. The 12 small objects of Moberg pickup test: These objects have to be picked up and put into the small container while time is taken with a stopwatch.
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- Top of page
- PATIENTS AND METHODS
- APPENDIX A: DESCRIPTION OF MPUT
In general, MPUT and BT show the same pattern of correlation with the other parameters, though the correlations are slightly stronger for MPUT than for BT. The most notable exception is GST on both hands, which correlates clearly stronger with the MPUT values. This allows a more consistent interpretation of the MPUT in relation to the other parameters. MPUT provides additional information compared with the BT. This notion is based on the following grounds.
There is a significant linear relationship between MPUT and BT; the measure of determination (R2 = 0.37) implies that this relationship explains approximately 37% of the variability of the values for both tests. We interpret this as the amount of variability due to the common aspects of functional ability that are measured by both tests, whereas the rest is due to different aspects of functional ability and random variation between patients. Under this assumption, we have 1) regressed MPUT on BT and 2) regressed BT on MPUT; the residuals from these regressions can be seen as corrected test values for 1) MPUT and 2) BT, after removal of the shared aspects of functional ability. Figure 5 shows the correlations of these corrected test values with the other tests: the corrected BT values show no significant correlation with any of the other parameters, whereas the corrected MPUT values are still significantly correlated with grip strength for the dominant hand and to a lesser degree also with ESR and CRP. From this we conclude that 1) MPUT measures specific aspects of functional ability that are not described by BT, but that correlate negatively with grip strength, CRP, and ESR; and 2) if BT measures any comparable specific aspects, these are not related to the other parameters.
Figure 5. Spearman rank correlations between the residuals of 1) regressing Moberg pickup test (MPUT) on button test (BT; dark bars) and 2) regressing BT on MPUT (light bars). The thin error bars show approximate 95% confidence intervals for the correlation coefficients, and the direction of the correlations is indicated by the signs at the right border of the plot. See Figure 4 for definitions.
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Both MPUT and BT values exhibit the population effects that one would expect from clinical practice: a tendency for slightly higher values for RA patients, and a slight increase of values with the age of the patients. Additionally, there is a strong sex effect for BT, which is completely absent from MPUT. A possible explanation is that the BT depends not only on functional ability, but also on skill, because there is no connection between sex and degree of impairment, and the skills required for the BT are more traditionally associated with women. This sex effect complicates test standardization for the BT.
Both MPUT and BT show a significant learning effect in that the time for the second attempt of the patient is on average shorter than for the first attempt. The MPUT protocol accounts for this learning effect by requiring the patient to use the dominant hand on both attempts. By recording only the better time, it allows patients to have a trial run first.
In case of the BT, the learning effect is strong enough to overcome the disadvantage of having to use the nondominant hand for the second attempt. This raises the question to what degree the value for the second attempt is influenced not only by learning the necessary motor skills, but also by the ability of the patient to use the nondominant hand for fine motor tasks. This problem is confounded by taking the average time of both attempts, so that both the learning ability and the degree of handedness of the patient influence the final value.
Interestingly, even though the MPUT does not measure performance of the nondominant hand, its values correlate better with grip strength of the nondominant hand than the BT values. From our clinical experience, MPUT refers to a domain of hand function that seems to be relevant for daily life, such as picking up money from a table or picking up paper clips. Thus, MPUT might have more relevance for daily life than BT (buttons have to be opened and closed by using one hand only, which is not done in daily life) and GST (using maximum grip force should be avoided in daily life by patients with RA). Nevertheless, further research is needed to determine to what level MPUT might be representative of hand function in general.
The limitation for all 3 (MPUT, BT, and GST) is that they are administered in a different environment according to a standard protocol that might not allow for the patient to use his or her normal coping strategies. The relevance for daily life can be questioned under this perspective.
Because fine motor tasks may be particularly severely affected by RA's stiffness and finger joint immobility, a test that measures these domains may have great practical value for RA patient assessment. So far, no gold standard exists for measuring hand function in rheumatology and the available tests have limitations in standardization (BT), practicability (Jebsen-Taylor-Hand-Function Test &lsqbr;24&rsqbr;) and practical value (grip strength). To define a gold standard for functional testing, an international consensus on a set of functional outcome measures in rheumatology would be highly useful.
In conclusion, we found in our comparative survey that both MPUT and BT show population effects as expected (higher values for RA and older age). MPUT, compared with BT, exhibits no sex and a smaller learning effect and correlates better with several core set parameters. A significant linear relationship between MPUT and other function-related tests, BT and grip strength, could be demonstrated. Additionally, MPUT seems to have more relevance to everyday life than grip strength and BT. Thus, we consider MPUT a possible alternative to GST and BT for measuring functional ability of patients with inflammatory joint disease. Further research is needed to determine the usefulness of MPUT in monitoring RA patients over long-term periods.