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

The carpometacarpal (CMC) and metacarpophalangeal (MP) immobilization orthosis was one short thumb immobilization orthosis that did not cover the thumb interphalangeal and wrist joints, and the orthosis was custom-molded by an occupational therapist with more than 6 years of experience. Participants wore the orthosis with their right hands for the duration of the testing procedure, approximately 30 minutes. The grasp distance was the distance between the handle and the main shaft of the dynamometer. We designated the first, second, and third handle positions on the dynamometer as the grasp distances: Distance 1 (D1) was 42.25 mm, Distance 2 (D2) was 54.64 mm, and Distance 3 (D3) was 68.90 mm. This study required only a single test session for each participant. Each participant performed three trials per condition for a total of 21 trials (maximal grip × 3 trials and 3 distances × 2 orthoses × 3 trials). The level of orthose factor was two: with or without orthosis. The order of the (distance × orthoses) conditions was randomly assigned. Rest periods of 1 minute were given between each trial, and periods of 5 minutes, between each condition. The participants could prolong the resting time if tired. Grip Strength Measurement. Participants sat on a chair, and the seat height was adjusted so that their feet were flat on the floor with their knees and hips flexed at about 90 degrees. They then placed their right forearm on the table with the shoulder in adduction, the elbow at 60 degrees to 90 degrees flexion, the forearm in neutral position between pronation and supination, the wrist in neutral position between the ulnar and radial deviation, and the wrist at 10 degrees to 20 degrees extension, and they concurrently grasped a Baseline digital hand dynamometer (Model 12-0112; Fabrication Enterprises, White Plains, NY). The values displayed by the dynamometer were recorded. This participant positioning was adopted from Mathiowetz et al. (1985); however, the dynamometer was reversed to allow participants to see the readings. The forearm was placed on the table to help support the weight of the dynamometer.