The impact of various simulated arthrodesis angles of the proximal interphalangeal joint of the ring and middle finger on grip strength.

Abstract

Arthrodesis of the proximal interphalangeal (PIP) joint at 40° angle has been proposed by many authors. A smaller angle of arthrodesis results in weaker grip strength of the hand from the quadriga effect. However, arthrodesis at 40° compromises other aspects of hand function including poor aesthetic appearance. This paper aims to quantify the decrease in grip strength at 40°, 20°, and 0° of arthrodesis. Grip strengths of the hand were measured using a BASELINE dynamometer at settings II, III, and IV. Baseline grip strength of the subjects were first measured without wearing a splint. Thereafter, subjects wore thermoplastic splints to simulate arthrodesis of the middle and ring finger PIP joint at 40°, 20°, and 0°, and grip strengths were measured again. The grip strength of the hand with simulated arthrodesis was then calculated as a ratio of the baseline. There were 50 subjects yielding 100 sets of results. The results show that average grip strength ratio of the hand decreases progressively from 40° and 20° and to 0° of arthrodesis for both the middle and ring finger. However, the difference in grip strength ratio between 40° and 20° of arthrodesis was minimal. Simulated arthrodesis of the middle finger affected the grip strength ratio more than arthrodesis of the ring finger, and compromised gripping of a smaller handle more than a wider one. The decrease in grip strength from 40° to 20° simulated fusion of PIP joint was minimal. Therefore, in so far as grip strength loss is concerned, arthrodesis of the PIP joint at an angle less than 40° can be considered for patients with individual functional and aesthetic concerns.