Biomechanical analysis of hindfoot fixation using an intramedullary rod.

To measure the stiffness of the hindfoot when fixed with an intramedullary rod placed in a retrograde manner, two biomechanical experiments were carried out on five matched pairs of cadaveric below knee specimens. Experiment 1: In the right leg of each pair, an intramedullary rod was placed in a retrograde fashion through the calcaneus, talus, and into the tibial intramedullary canal. Biomechanical testing was done to determine hindfoot stiffness, with and without distal and proximal transverse interlocking screws. The uninstrumented left leg of each pair was tested as a control. Experiment 2: A series of similar biomechanical experiments were done on the same specimens to determine the effect on hindfoot stiffness of an intramedullary rod with one distal screw as compared with a method of tibiotalocalcaneal fixation using three cross-cannulated screws. The results show that an intramedullary rod placed in a retrograde manner stiffens the hindfoot and the placement of interlocking screws enhances that effect (Experiment 1). The intramedullary rod with one distal screw inserted provides more stiffness to the hindfoot than does three cross-cannulated screws (Experiment 2).