Animals and surgical procedure

The Institutional Animal Care and Ethics Committee of Chonbuk National University approved all experimental procedures in this study (Ethics number: CBNU 2017-0108). We used male Sprague-Dawley rats (10 weeks of age, 320-350 g). All rats were caged individually at 22°C and 50% humidity in controlled rooms having 12-h light/dark cycles. For anesthesia, we administered Zoletil (150 mg/kg) through intraperitoneal injection. We performed ischemic osteonecrosis of femoral head surgery (n=10) and sham surgery (n=10), as previously described [5]. To confirm the effect of metformin on INFH, metformin was dissolved in physiologic saline. During the week after surgery, we administered metformin (25 mg/kg) once a day by intraperitoneal injection to the experimental group, whereas only saline (the vehicle) was injected in the control group. Rats were euthanized by exsanguination under sodium pentobarbital anesthesia 4 weeks after surgery.