Grip strength characteristics using force–time curves in rheumatoid hands

The use of force–time curves in rheumatoid hands was investigated to assess peak force, average force, total grip time, area under the curve, and variability of the plateau region of the curves to identify the impact of different rheumatoid hand deformities on grip strength. We studied 43 patients — 10 men and 33 women — with established rheumatoid arthritis affecting their hands. Mean age was 61 years and mean duration of hand involvement was 13 years. Of the 86 hands, 38 had no finger deformity, eight had metacarpophalangeal joint ulnar deviation without any additional finger deformities, 16 had swan neck deformities, and 10 had boutonnière deformities. Fourteen hands had a combination of deformities. The hands with combined deformities were the weakest, had poor grip strength (34.7 N, SE 8), and were able to sustain grip for only a short time (22 sec, SE 3). Swan neck deformity also profoundly affects the magnitude (49.8 N, SE 7) and sustainability of grip (15 sec, SE 2). Even when only one finger had a swan neck deformity the mean strength was poor at 45 N. Swan neck deformity causes greater loss of strength than boutonnière deformity (82.7 N, SE 15). The strongest rheumatoid hands were those with only ulnar deviation deformities (90.8 N, SE 14). The area under the curve best predicted disability assessed using the Patient Evaluation Measure.