Enhancement of bone apposition to stainless steel cortical screws by surface modification using heat treatment: An experimental study

Objective: The purpose of the present study was to test whether the surface of stainless steel cortical screws modified by an oxidation process (heat treatment) resulted in enhancement of bone apposition as a consequence of better bone apposition to the metal surface. Design: Control and heat-treated commercial cortical screws (stainless steel 316L) were inserted alternately into the tibiae of eight goats with a fixed insertion torque. Fluorochrome bone label was given during the six-week experimental period, after which the goats were killed and the extraction torque force measured. The screws and the adjacent bone were processed for histology. Main Outcome Measure: It was hypothesized that the heat-treated transcortical metal screws would have a greater extraction torque than untreated control screws. Results: The extraction torque of the heat-treated screws was 0.59 ± 0.06 newton-meters, which was significantly (p < 0.0001) higher (1.7-fold) than that of the control screws (0.35 ± 0.02 newton-meters). Histomorphometric measurements demonstrated a 65 percent, significant (p < 0.05), increase in the area of fluorescence (indication of new bone deposition) adjacent to the heat-treated implant versus the control screws. Conclusions: Heat treatment of the cortical screws prior to insertion significantly increases fixation strength to the host bone in a large animal model. The clinical applicability will be to achieve bone apposition similar to that seen with titanium implants but with a stiff low-cost material.