MOTOR CONTROL OF THUMB-INDEX SYSTEM IN HEALTHY POPULATION

Thumb and Index fingers are involved in many daily tasks, it is understandable how injuries, musculoskeletal, rheumatologic, and neurological diseases could affect hand function causing severe disability. The evaluation of motor control deficits of the thumb-index system is necessary to identify impairments and to propose specific therapeutic or surgical proposes. Pinch maximal voluntary contraction is the most investigated parameter, it is a valid estimator of general hand function. However, thumb and index are rarely involved at their maximal contraction, usually they are used in precision pinches at low submaximal forces exerted for a short-to-long time. For this reason other parameters must be investigated. In this dissertation, a multiparametric evaluation of thumb-index system was proposed. The battery of tests consisted of the maximal voluntary contraction (MVC) of pinch grip (TP, tip pinch and PP, palmar pinch) and of the opposite movement (E, extension of thumb and index), the endurance (SC, sustained contraction), the accuracy and precision of pinch force in a pinch and release task (DC, dynamic contraction) and the force coordination between hands in a bimanual simultaneous task (BSC, bimanual strength coordination). The tasks were measured with a measurement system consisted of two pinch gauges, connected to a PC, the visual feedback was displayed on a monitor through the graphical user interface of an ad-hoc developed software. To be usable in the clinical context, it is important to check the reliability of the tasks and collecting data in healthy samples permits on the one hand to analyse how values changes as function of anthropometric variables, hand dominance, dexterity, and on the other hand to define the reference values to compare pathological populations. Therefore this dissertation was conducted through test-retest reliability studies and cross-sectional studies to establish normative data of PP, TP, E MVCs, SC, DC and BSC in the Italian population. All the tasks proved reliable and consistent, MVC and SC showed high reliability, DC and BSC reliability was lower but clinically suitable. Strength, analysed through PP, TP, E MVCs, declined in line with the normal process of aging that also entails muscle fibers and the reduction of daily activities in older adults. In relative terms, E-MVC showed the highest strength loss in the over 75y. SC showed similar values in all age groups, variables of DC and BSC showed instead large effect related to age-decline. Women performed better than men only in SC, in MVC, DC and BSC men excelled. A hand dominance effect emerged only in TP and PP MVC. Correlations between tasks were very low to low, suggesting that different constructs were measured by the tasks. This Ph.D. project proposed novel tasks to evaluate pinch motor control which were showed reliable in healthy people and their normative data were obtained, representing a useful aid in the clinical field. The results become a starting point for future studies to highlight impairments of the thumb-index system in different neurological and musculoskeletal disorders and to guide the rehabilitation and the therapeutic intervention.