To establish a steroid induced osteonecrosis of the femoral head, or SONHF model, use an albino rat. Intraperitoneally inject lipopolysaccharide into the midline of the rat's abdomen every 24 hours. After the last lipopolysaccharide injection, inject methylprednisolone into alternate unilateral gluteal muscle every 24 hours after regular feeding.
Next, mark the rat's back midline at one to two centimeters on both sides as a reference point for the weight load. Make sure that the marks are appropriately positioned to prevent the rat from tipping or hindering movement during treadmill training. Now, with the help of another investigator, hold the rat with gloved hands.
Place one hand under the rat's armpit to secure the forelimb and jaw. Then use the other hand to secure the hind limbs and tail. Stick the elastic therapeutic tape to the test tube without applying tension to secure the load on the rat's back.
Ask the second investigator to fix the test tube to the rat's back parallel to the rat's spine. To minimize the suffering of the rat, perform fixation without applying tension. Stick the test tube with adjusted weight onto the elastic therapeutic tape.
Then wrap the test tube around the rat's body using a tension-free technique. Place the rat in an open space or a single cage, and monitor its breathing and direction. Promptly, release the rat if it breathes rapidly or opens its mouth.
Ideal immobilization should allow the rat to move freely and perform activities like drinking, lifting forelimbs, and feeding. Release and re-immobilize after 20 minutes if immobilization is unsatisfactory. Next, turn on a treadmill and set the speed to one meter per minute with a zero-degree incline.
Gently transfer the rat onto the treadmill and begin the timer. If the rat cannot complete the 30-minute training, place it in a cage for a 10-minute rest without removing the fixation. After the training, clean up the feces and urine left by the rats and spray alcohol to eliminate the animal odor.
Handle the animals as gently as possible to prevent animals from vocalizing and causing traumatic stress to other rats. Immediately release the rat from fixation after the completion of training.
