Biomechanical Strength of Large Diaphyseal Deep-frozen Allografts

The aim of this paper is to study the biomechanical strength of deep-frozen allografts as they heal. Twenty-eight adult cats were used with the tibia as the experimental model site. Deep-frozen allografts stored at -80 degrees C were used to reconstruct a large tibial defect (at least two-thirds of the diaphysis). An intra-medullary rod was used for fixation. The healing was studied by X-ray at observation periods of 4, 6, 8, 12, 16, 24 and 36 weeks. Post-transplantation biomechanical testing was performed using the Shimadzu Universal Testing Machine DCS series with a torsion test device of 50 kg force metre. Parameters studied included maximum torque, torsional stiffness and energy of absorption. The transplanted grafts were compared to the mechanical properties of the internal controls of the normal opposite tibia of each cat. The results of the mechanical tests demonstrated that deep-frozen allografts did not regain normal strength. At nine months, only about 60% of normal torque strength and about 80% of normal torsional stiffness was achieved. Clinically, it is important to employ strong and rigid internal fixation using intra-medullary nailing rather than plating to allow for immediate mobilisation and reduce the rate of graft fracture.