Polyarthritis of the hand is a hallmark of rheumatoid arthritis (RA). Standard hand dynamometry registration of one-grip force or the recording of a series of multiple grips are commonly used to evaluate the function of the hand (1, 2). This provides an approximate measurement of handgrip strength, but not a detailed insight (3). A more detailed assessment would be useful for tailored rehabilitation of the hand in patients with RA, but also in patients with other non-rheumatic conditions involving the hand. Therefore, we developed a custom-designed electronic dynamic sensor in order to measure different minutely specified parameters for handgrip evaluation. The aim of this pilot study was to evaluate the hand grip in patients with RA using this new electrodynamic method.

This pilot study included 24 subjects, 12 patients with RA (6 women and 6 men, aged 35–55 years) in the early phase of the disease, and 12 healthy sex- and age-matched controls. The patients with RA were enrolled consecutively from the outpatient clinic according to the following inclusion criteria: newly diagnosed RA with disease duration < 6 months, age 35–55 years, and treatment with orally taken methotrexate 15 mg/week. In the evaluation of motor hand function a new expert electronic measuring system for dynamic measurements of the hand grip force, developed at the Ruđer Bošković Institute, was used (Figure 1). The device was calibrated in accordance with hand grip comparison on a mechanical dynamometric device with the same mechanical handrail. The dynamics of the dynamometric hand grip parameters in both groups was measured at the baseline and after 60, 120, and 180 days. All the patients were treated with the anchor disease-modifying anti-rheumatic drug (DMARD) methotrexate, and during the follow-up period its dosage was not changed. The patients had the option of taking NSAIDs and/or acetaminophen as an escape medication, but were required to stop the medication three days before each visit. The main dynamometric parameters of interest obtained were: maximum grip force (highest achieved power of each grip), fatigue (onset of decreasing tendency in maximum grip force in the grip series), grip velocity (ratio of maximum force and time in which the individual grip is achieved), and functional potential (composite measure combining the average grip force, average grip velocity, and fatigue). The evaluation of the hand’s functional deficit was performed by registering and extracting previously defined parameters in time and spectral domain over the processed time grip series of the dominant hand. The described pre-processing was conducted over a grip series (15 times) at baseline (moment t = 0) and at visits every two months thereafter. In order to minimize fluctuation and amplitude effects, Fourier analysis was used for each cycle. The best 10 from a total of 15 individual cycles were selected for each study participant, and the most irregular cycles, such as those containing more irregular maximums, uneven grip phase, or delay at the beginning and at the end of each grip, were removed. Statistical analysis included the T-test and the ANOVA test for repeated measures.

The two groups were well matched to age, and no significant difference was found between them (the mean and SD for age in RA patients was 54.7 ± 8.2 years, and in healthy controls 54.2 ± 8.2; P = 0.883). The baseline data on the dynamometric parameters of interest in the patients with RA and healthy controls are shown in Table 1. Compared to the control group, the RA patients had a significantly lower maximum grip force, fatigue (earlier occurrence of fatigue), grip velocity, and functional potential.

During the follow-up period, the measured dynamometric parameters in the patients with RA showed significant improvement at each visit as follows: maximum grip force – P = 0.040, fatigue – P = 0.032, grip velocity – P = 0.026, and functional potential – P = 0.014 (Table 2). Nevertheless, they did not reach the values measured in the healthy controls.

This pilot study presents the results of the application of a new measuring system, involving a unique data processing algorithm and proposed parameters of the hand function. It also considers the implications of this system for rheumatology. Previous studies based on single-grip measurement found that hand grip strength and net forces vary by sex, age, and anthropometric characteristics (4, 5). Generally, in conditions affecting the hand the observed dynamometric parameters increased, as strength, velocity, and grip stability grew (2). Compared to the baseline values, the increase in these parameters during the treatment represented a clear indicator of improvement of the hand function. The meticolous evaluation of the hand function using this new dynamometric system offers the possibility to plan appropriate exercises in order to obtain the best possible result. During a period of 6 months, the method showed good resolution at all stages.

It is important to note that within the framework of this study, data on grip force and velocity are primarily significant in relative relations. Hence, they should be considered with caution, whereas for accurate absolute values of the abovementioned parameters it would be necessary to perform a study on a larger number of subjects and with a stringently defined protocol of device calibration (6). The development of this expert diagnostic system could allow an objective hand functional status evaluation. For further research, along with net functional force and velocity in hand grip evaluation, and with adequate probe modification, it would also be possible to analyze the grip force of a specific group of digits – mostly that of the thumb plus one finger (“pinch testing”).

In this pilot evaluation study we present a new electronic dynamometric system for obtaining hand function parameters based on dynamic measurements. By comparing the results of healthy subjects and patients, and by recording the changes occurring during the treatment, we can conclude that this system measures the hand condition objectively. It can be safely used to monitor the status of individual patients during treatment and rehabilitation as a relevant indicator of recovery. Further studies with a larger number of patients are needed to confirm its value.

Conflict of interest statement: Authors declare no conflict of interest.

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Figure 1. Hand grip acquisition system

Table 1. Differences between patients and control group at baseline (T-test for independent groups)

Table 2. Changes in dynamometric variables during follow-up – patients with RA (n=12) (ANOVA)