Behavioural welfare assessment of unilateral and bilateral femoral defects in rats

This study compared behavioural outcomes and welfare indicators in rats undergoing unilateral or bilateral femoral osteotomy during the first stage of the Masquelet technique. Twenty-five male Sprague–Dawley rats underwent creation of a mid-diaphyseal femoral defect (uni- or bilaterally) filled with polymethylmethacrylate and stabilised with locking plates. Behaviour was assessed using video recordings analysed according to the NC3Rs rat ethogram before surgery and at predefined postoperative time points following the first surgical stage only. Twenty animals (unilateral n = 9; bilateral n = 11) completed the behavioural evaluation. No significant differences were observed between unilateral and bilateral groups for any behavioural parameter or body-weight evolution ( p > 0.05). In contrast, both groups showed significant transient reductions in movement, maintenance, climbing and exploratory sniffing behaviours 2 h after surgery, followed by progressive recovery over subsequent days. Eating, sleeping and play behaviours remained relatively stable throughout the observation period. Overall, these findings indicate that perioperative welfare impairment was driven primarily by the surgical intervention itself rather than by surgical laterality. Under appropriate multimodal analgesia, postoperative monitoring and refinement strategies, bilateral femoral osteotomy did not produce measurable additional behavioural impairment compared with unilateral surgery, supporting its use when scientifically justified within the framework of the 3Rs.