Optimal Grasp Distance and Muscle Loads for People With Rheumatoid Arthritis Using Carpometacarpal and Metacarpophalangeal Immobilization Orthoses.

Abstract

The objectives of this study were to investigate whether people with rheumatoid arthritis (RA) require greater muscle loads to equal the grip strength of healthy adults and to find the optimal grip distance for people with RA using carpometacarpal and metacarpophalangeal immobilization orthoses as measured by electromyography of the forearm muscles. A 2 × 2 (Group × Orthosis) experiment and a 2 × 3 (Orthosis × Grasp Distance) factorial were conducted. Grip strength and muscle load were measured. Grip strength was significantly lower, and muscle load was greater, in 18 participants with RA than in 18 healthy adults. No effect of orthosis use on grip strength and muscle load was found. Muscle load was lower for the 42.25-mm diameter dynamometer handle than for handles with larger diameters. People with RA require more muscle load than healthy adults to produce the same exertion, and 42.25 mm is recommended for people with RA as the optimal grasp distance.