A rat model of tibia fracture and recovery after plate fixation

Background Postoperative behavior and allodynia evaluation in rodents are commonly used to confirm preclinical disease models. In contrast, we are investigating pain and functional recovery after traumatic fracture and surgical repair. We created a tibial fracture in the rat and repaired the fracture internally with plating. We hypothesized that histological bone healing would be strongly correlated with functional recovery. Methods Sixteen male Sprague-Dawley rats underwent a metaphyseal transverse osteotomy of the proximal tibia. The defect was repaired by abutting the bone surfaces and fixing them in place using a 5-hole Y-plate with 4 screws. Fracture healing was investigated quantitatively and qualitatively at 2, 4, 6, and 8 weeks using micro-CT imaging, X-ray, and histology. Functional recovery was assessed using video recording and analysis of gait, static weight bearing, hind paw reflex response, and toe spread. Results The micro-CT and histological results demonstrated complete fracture healing at 8 weeks. Specific gait analysis parameters: temporal symmetry, hindlimb duty factor imbalance, phase dispersion, and toe spread showed longitudinal changes commensurate with fracture healing. Conclusions We aim to use this model to evaluate the efficacy of locally administered non-opioid analgesics with long-term effects on healing and function. Our long-term goal is to assess the local efficacy of drug delivery devices in improving post-surgical pain and function. The correlation in this tibia fracture model between bone healing and functional outcomes suggests that post-operative recovery can be monitored, and treatments can be compared using these endpoint measurements.