Optimal Dorsal Strap Placement and Angulation to Resist Foot Displacements in Orthoses and Footwear. In Vitro Study
Kogler, Géza F.
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A dorsal strap on a lower extremity orthosis (e.g., ankle foot orthosis) is one of the most common addition to a device to control foot motion. The aim of this study was to establish clinical guidelines that orthotists could target when determining the placement and angulation of a dorsal foot control strap in an orthosis. An in vitro experimental study was designed that simulated the movement of heel rise with respect to an orthosis. Cadaveric limbs (n=5) were mounted in a test fixture. where the first and second toes were affixed to the base via a plate and screw and a 111 N weight attached to a cable and pulley mechanism lifted the limb and foot vertically. A round aluminum bar (1.0 cm in diameter) attached to a load cell was used to measure the force applied to the foot, simulating the dorsal control strap function in an orthosis. Nine test conditions were evaluated. The force application points studied were oriented along the longitudinal axis of the foot starting proximally at the talus with a middle and distal location 2.0 cm apart respectively. Forces were measured at each of the three longitudinal axis locations at three angles (i.e. 75°, 90°, 105°). Results demonstrated that the more proximally positioned force application point had a lower measured force compared to a corresponding distally placed position (p<0.05). In addition. an acute angle (75°) force application point resulted in a higher force output compared to an obtuse angle (105°) force application (p<0.05). while the perpendicular and obtuse force application pOints were statistically similar. The data suggests that the optimal placement of a dorsal foot control strap should be proximally positioned and the angle of force application should be oriented perpendicular whilst erring to an obtuse angle for the most efficient orthotic control of foot movements in an orthosis.