Optimisation and Validation of an Induced Membrane Technique Model to Assess Bone Regeneration in Rats

<b>Background:</b> The induced membrane (IM) preclinical models have been described in small animals, but few studies have looked at bone regeneration achievement. The optimisation and validation of such a preclinical model, considering the results obtained after the use of biomaterials as a substitute for bone grafting, could lead to simplifying the surgical procedure and enhance the clinical results. <b>Methods:</b> An in vivo model of the IM technique was developed on the femur of Lewis rats after a 4-mm critical bone defect stabilised with an osteosynthesis plate. A first optimisation phase was performed by evaluating different osteotomy methods and two different osteosynthesis plate sizes. The efficiency of the model was evaluated by the failure rate obtained 6 weeks after the first operative time. Thereafter, bone regeneration was evaluated histologically and radiologically at 24 weeks to confirm the critical nature of the bone defect (negative control), the effectiveness of the IM with a syngeneic bone graft (positive control) and the possibility of using a biomaterial (GlassBone Noraker) in this model. <b>Results:</b> Sixty-three rats were included and underwent the first surgical step. Nineteen rats subsequently underwent the second surgical step. The results obtained led to select piezotomy as the best osteotomy technique and 1-mm-thick plates with 2.0-mm-diameter screws as osteosynthesis material. Twenty-four weeks after the second surgical step, solely the group with both surgical steps and a syngeneic bone graft showed complete ossification of the bone defect. In contrast, the group without a graft did not present a suitable ossification, which confirms the critical nature of the defect. IM produced an incomplete bone regeneration using GlassBone alone. <b>Conclusions:</b> A piezotome osteotomy with an osteosynthesis plate of sufficient stiffness is required for this two-stage bone regeneration model in rats. The 4-mm bone defect is critical for this model and suitable for biomaterial evaluation.