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Hand function is of great importance in the many daily activities that require well-coordinated hand and arm movements. Measurement of hand function is an essential element in the rehabilitation process, in order to facilitate medical diagnosis and determine developmental stages, functional levels, and the efficacy of treatment interventions. Basic requirements for any measurement used in clinics are that they are easy to use, relevant to the function being assessed, and valid and reliable. When scrutinizing the literature on hand function, important gaps were found with regard to measurement. For example, the reliability of grip strength with the Grippit in children has yet to be determined, and there are few evaluations of hand function measurements in Charcot-Marie-Tooth disease (CMT). Furthermore, laboratory measurements of hand function, which have the potential to provide more detailed information and insight into hand control, such as the role of the cerebellum in reactive grip control – have not been fully explored. The overall aim of the thesis was to achieve more knowledge on hand function; on the evaluation of measurements in different target populations; and on movement control of the hand.

In the first study, the aim was to evaluate the test-retest reliability of the peak and sustained grip strength with Grippit in a sample of healthy children (n=58, 6-, 10- and 14-y-olds). This was followed by two studies examining hand function in an adult sample (n=20) diagnosed with CMT. The test-retest reliability of grip and pinch strength using Grippit, sensation with the Shape Texture Identification test (STI) and dexterity with the Box and Block Test (BBT) and Nine-Hole Peg test (NHP) were studied. The impact of the disease on daily life, measured with the Disability of the Arm, Shoulder and Hand questionnaire (DASH), and correlations between disability and various aspects of hand function, were also explored in this condition. The aim of the fourth study was to examine grip force response to unpredictable loadings of an object held in a pinch grip in subjects (n=9, 22-48 yrs) who had been diagnosed with a cerebellar lesion, compared with a healthy control group (n=11). The first study showed that test-retest reliability was good for both peak and sustained grip strength in healthy children. The mean and best of three trials were equally reliable, but differences in reliability were detected within different age groups. For example, the peak grip strength, best of three trials, was more reliable for the 6-y-olds (intraclass correlation coefficient (ICC)=0.96, standard error of measurement in percentage (SEM%)=6.3) and 14-y-olds (ICC=0.96, SEM%=5.2) compared with the 10-y-olds (ICC=0.78, SEM%=12.5). In the second study, evaluating measurements of hand function in subjects with CMT, grip strength proved to be reliable (ICC=0.99, coefficient of repeatability (CR)=26.7 N, coefficient of variation (CV)=6.6 %), but pinch strength was less reliable. The reliability was also good for the BBT (ICC=0.95, CR=11.5 blocks/min, CV=8.4%) and the NHP (ICC=0.99, CR=4.3 s, CV=3.9 %). However, a bias towards higher values was noted on the second test occasion with the BBT. The reliability of the STI test (kappa=0.87) was also very good in subjects with CMT. A limitation in this latter test was noted in terms of its ability to describe subjects either performing very well or very poorly. The results of the third study showed that hand function in CMT was reduced (p<0.001) to about 60% of that in healthy controls in each of the separate outcome measures, as well as by a constructed summary index of hand function. The median DASH score was 38.8 (range 0-66.7) and was clearly related to hand function (r=0.64-0.83). The results of the final study in subjects with cerebellar lesions showed that the ipsilateral hand had delayed and more variable response latencies e.g. 278±166 ms for loads delivered at 2 N/s, compared with healthy subjects (HS) 80±53 ms (p=0.005). The cerebellar subjects also used a higher pre-load grip force with the ipsilateral hand (1.6±0.8 N) than the HS (1.3±0.6 N (p=0.017)). Even the contralateral hand in subjects with unilateral cerebellar stroke showed a delayed onset of the grip response.

In conclusion: Grip strength assessment in children with Grippit results in good reliability for peak and sustained grip strength, although the 10-y-olds were less reliable. In CMT the tested instruments can all be used to evaluate hand function, but certain factors, such as the number of trials used should be taken into consideration. The CMT subjects’ hand function was reduced and correlated with their self-experienced disability. However, clinicians should be aware that patients might score lower than expected on DASH, possibly due to a long process of adaptation. Cerebellar lesions can impair the reactive grip control in both the ipsilateral and the contralateral hand. These investigations have thus, as intended increased the knowledge of hand function. The studies have evaluated some measurements in different samples, which will help clinicians testing hand function.