HEAT GENERATION IN BONE CUTTING-IMPLICATIONS FOR THERMAL NECROSIS

摘要

A bunion is a common foot disorder caused by an abnormal outward projection of the joint and inward turning of the toe. Surgery to correct the malformation involves cutting the first metatarsal head, repositioning and setting it; the bone is then left to heal itself over time. A potentially serious by-product of the bone cutting is the frictional heat generated. While the heat susceptibility of individual bone cells varies throughout bone and is difficult to quantify, studies have shown that when injured, bone may not always heal as bone but rather as a fibrous tissue of varying degrees of differentiation. Prolonged heat exposure at or above critical temperatures may also lead to fat and bone cell resorption, a subsequent fat cell degeneration of the tissue, local swelling of cells as well as denaturation of the enzymatic and membrane proteins (Eriksson & Albrektsson, 1983, Li et al, 1999). In his vital-microscopic study in the rabbit, Eriksson concluded that bone regeneration is significantly impaired when bone is exposed to a temperature of 47 deg C for one minute, (1984). Other studies have also shown that there are critical temperatures and exposure times that should not be exceeded during the surgical procedure if healing is not to be compromised. It is the goal of this work to delineate the heat generation and resulting temperature field in the vicinity of the first metatarsal bone during a simulated bunion surgery. This is accomplished by making in situ Measurements of the time-varying temperature field in the bone during the cutting procedure. The hope is to develop an empirical model that directly correlates bone properties and mechanical parameters-force, pressure applied, depth of cut-with the maximum temperature reached in the cortical and trabecular bone. With such a model, it may be possible to modify instrumentation and/or surgical technique so as to avoid exceeding the critical temperature(s).