Tension-Free Weight-Bearing Model of Steroid-Induced Osteonecrosis of Femoral Head in Rats

We primarily developed the rat model for weight-bearing interventions to investigate the efforts of weight-bearing exercise on osteonecrosis of the femoral head. Currently, most of the models are no weight-bearing models. However, the progressions of the osteonecrosis in the femoral head may be associated with weight-bearing exercises.

It's actually very difficult to secure with onto rest, as multi method severely restricted their movement, thereby feeling to achieve their purpose of weight-bearing exercises. To begin adaptation training, first place the rats in opaque cages. Keep them as far away as possible from non-modeled rats, ensuring the other rats are outside the maximum visual range.

Turn on the power and set the treadmill to 10 meters per minute with a zero degree incline. Place the rats on the treadmill and ensure the movements are as gentle as possible to avoid stress. After a 15-minute training, clean up the feces and urine left by the rats.

Spray the treadmill with alcohol to eliminate the animal odor. Continue training all animals for a week. Prepare two test tubes, a hook, and a loop fastener, approximately 80 centimeters long.

Place steel balls into the test tubes, ensuring that the initial combined weight of the test tubes, the hook and the loop fastener is 150 grams. Prepare test tubes with different total weights in 10 gram increments with the maximum weight being 350 grams. Now with gloved hands, hold the rat.

Wrap the hook and loop fastener of a tube on the back of the rat, about one centimeter from the midline. Change the tube from lower to higher weight until the rat is unable to stand when prodded or the experimenter leaves. Reduce the weight by 10 grams to allow the rat to stand.

This weight represents the rat's maximum weight-bearing capacity. To prepare the weight load, first use a one to 1.5 meter long elastic therapeutic tape to secure the fixation objects. With clay, adjust the weight of the test tubes to reduce the swinging of the load.

After weighing the test tubes and the fixation objects, add an appropriate amount of clay into the test tubes to adjust them to the target weight. Now, use a glass stirring rod to evenly spread the clay inside the test tubes. Clay concentrated at one end of the test tube may cause it to detach easily during training.

Adjust the total weight of the adjusted test tubes and clay at 50%of the rat's maximum weight-bearing capacity. To establish a steroid induced osteonecrosis of the femoral head or SONFH model, use an Albino rat. Intraperitoneal 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 the 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.