Impairment of electrical activation of wrist flexor and extensor muscles during gripping and functional activities in the early stage of hand osteoarthritis: A cross-sectional study

Abstract Study Design This is a cross-sectional study. Introduction The wrist extensor muscles have a fundamental role in the stabilization of the wrist while performing manual activities. However, it is unknown if the clinical signs of hand osteoarthritis (HOA) cause impairment in the activation of these muscles Purpose of the Study The purpose of this study was to investigate whether early-stage HOA affects the magnitude of activation and coactivation between the wrist extensor and flexor muscles Methods Thirty-two subjects were divided into two groups: control group (n = 16; 55 ± 7.42 years) and a group with HOA grades 2 or 3 (HOAG; n = 16; 57 ± 7.82 years). Muscle activation was measured in m. flexor digitorum superficialis, m. flexor carpi ulnaris (FCU) and extensors (EXT) during the evaluation of grip strength and three manual activities (write, cut a paper with scissors, and close and open a bottle). The coactivation index was calculated between the electromyography of the flexors (FCU and FSD) and wrist EXT. Results HOAG presented reduced muscle activation in all tasks, with a statistical difference for the flexor digitorum superficialis and EXT in the scissors activity, and for the FCU in the bottle activity. No differences were found between groups for the coactivation index and grip strength. Discussion The reduced muscle activity may be due to an inability of the patients of the HOAG to recruit all motor units or to an inhibition related to the presence of pain. Conclusion In the early stages of HOA, there is a functional deficit associated with a reduced muscle activity of the wrist muscles during manual activities.