[Comparison of mechanical qualities of cortical bone preserved by various freezing methods]

The purpose of this study was to compare the mechanical properties of the human cortical bone following three deep-freezing techniques: addition of D.M.S.O. (di-methyl-sulfoxide) and staged decrease of temperature with immersion into liquid nitrogen, immersion into nitrogen without cryoprotection, deep freezing in an electric device, down to -80 degrees C. Axial loading tests performed on two femurs (88 samples) allowed to determine the strain of failure fmax and the Young's modulus E. Torsion tests were undertaken on four femur (66 samples) to obtain the strain failure tmax and the Young's modulus G. We have taken several samples from the cortex, that we randomly divided into four groups, three of them being deep-frozen with one of the methods studied, the fourth being tested "fresh", after standard sample manufacturing. The results obtained at the fresh state were comparable with those published in the literature (fmax = 158 MPa, E = 9000 MPa, tmax = 60 MPa, G = 4000 MPa). The results obtained after deep freezing both in axial loading and in torsion, demonstrated significant differences, ever though of low value. The surgeon may use one of either freezing method, without fearing any deterioration of the mechanical properties that could threaten the primary stability of the graft. However, only liquid nitrogen permits a long lasting storage, and only the use of cryoprotection can give the hope of preservation of the chondrocytes in case of diaphyseal-epiphyseal grafts.