Comparative Biomechanical Evaluation of Bone Healing in the Dog

Abstract

SUMMARY A project was devised to compare the ultimate strength and stiffness of normal bone to healing bone 10 weeks after fixation of midshaft (femur) fractures with intramedullary (i.m.) pin, i.m. pin and half Kirschner (½ K.) splints, or a tension bone plate. The ½ K. devices were removed at the 4th postoperative week, the i.m. pins (from both groups) were removed at the 6th postoperative week, and the bone plates were removed after euthanasia, which was 10 weeks for all cases. Percentage recovery (healing) was derived by determination of ultimate strength and stiffness in normal and healing femurs of the same dog. The i.m. pin and ½ K. was the most satisfactory and the bone plate was the least satisfactory means of achieving healing. It was believed the bone plates performed less effectively because “stress protection” (a phenomenon in which the normal physiologic stresses of bone responsible for its architecture, consequently its strength and stiffness) was markedly altered by the plate. Because bone plates assume all stresses, fractured bones underneath either heal slowly and perhaps incompletely or may atrophy from disuse because of lack of physiologic stimulation.