Validation of Spring Forces Applied in Dynamic Outrigger Splinting

Abstract

Theoretically, when an outrigger or a pulley is used on a dynamic splint, the amount of spring force lost to friction could be substantial enough to invalidate the use of a premeasured spring system. This study had three purposes: 1) to establish length-tension relationships for 1-inch custom-made and 2-inch commercial springs, 2) to determine how much force was lost when an outrigger or a pulley was added to a simulated dynamic splint, and 3) to develop a “clinically friendly” method for measuring the actual amount of force applied with a dynamic outrigger splint. The force measurement system consisted of two Haldex force gauges that were tested for calibration and reliability. Lengthtension curves for 1-inch custom-made and 2-inch commercial 200-g springs placed on 100-500 g of tension at 50-g intervals were obtained by applying vertical tension to the springs with precision weights and horizontal tension to the springs with the force gauge. Next, the lengths of the 1-inch and the 2-inch springs and the amount of force applied were measured when a brass brazing rod outrigger and a Phoenix pulley were added to simulate a variety of dynamic splinting conditions. The results of this study demonstrated that: 1) custom-made 1-inch springs and commercial 2-inch 200-g springs maintain reliable length-tension relationships in the test range of 100–500 g and 2) friction between the dynamic components of a splint and a brass brazing rod outrigger or a Phoenix pulley does affect spring length-tension relationships. These results suggest that friction in this simulated dynamic splint experiment does affect the spring length-tension relationships and the amount of resultant force applied. Because each spring had to be lengthened to accommodate for friction in order to generate the desired force, the validity of the forces applied by a premeasured spring system is questionable. An alternate method of validating the actual forces applied by a spring on dynamic outrigger splints is discussed.