Improved Methodology for Studying Postnatal Osteogenesis via Intramembranous Ossification in a Murine Bone Marrow Injury Model

Our research is focused on understanding bone repair mechanisms using the bone marrow injury model. We aim to uncover how intramembranous ossification is regulated during healing, and to explore therapeutic approaches that can be harnessed to enhance bone regeneration. Recent studies in the field established surface markers defining skeletal stem and progenitor cells revealing their critical roles in bone development and repair.

Our protocol enables investigation of these cells'contributions during intramembranous ossification, which allows us to explore their regulation and potential for therapeutic targeting during bone repair. Our protocol addresses the gap in understanding bone repair solely through intramembranous ossification in postnatal context, using a model that is clinically relevant. In contrast to other injury models used to study intramembranous ossification, our protocol provides a more controlled environment and reproducible injury responses, specifically in the long bones.

In the future, our lab will utilize the bone marrow injury model alongside localized pharmacological approaches to transiently modulate epigenetic regulators of osteogenesis. Our goal is to enhance bone regeneration and healing through novel therapeutic approaches. To begin, prepare and disinfect all the working surfaces with a clinical-grade disinfectant cleaner.

Cover the heating platform with a sterile surgical pad. Gather and arrange all sterile instruments as well as reagents. Now, weigh the mouse using a precision balance.

Based on the available formulation of buprenorphine, calculate the required volume for analgesic administration. After anesthetizing the mouse, carefully remove it from the induction chamber. Place the animal on the sterile surgical pad in a supine position and fit the nose cone over the mouse's head.

Briefly remove the mouse from the nose cone and inject the calculated dose of extended release buprenorphine analgesic via the subcutaneous route. Then carefully place the mouse back into the nose cone anesthesia unit. Fill a three milliliter syringe equipped with a 26-gauge needle with sterile saline, and place it to the side.

Remove the fur from the hind limb where the procedure will be performed using electric or battery-operated clippers. Using sterile cotton-tipped applicators, apply a 10%povidone-iodine scrub to the surgical site, followed by application of 70%isopropyl alcohol scrub and let the area dry completely. Now place the mouse on its back and flex the knee of the operative leg.

Hold the leg with the non-dominant hand such that the knee is bent over the middle finger. The second finger rests on the femur and the thumb rests on the tibia. Using a scalpel, make a small, shallow horizontal incision just below the patella.

Locate the joint space with the needle placed horizontally across the bent knee and feel for the space between the femur and tibia. Use this anatomical guide to manually drill into the distal femur from the knee toward the proximal side with a 25-gauge needle. Insert the needle through or around the patella.

Confirm the proper placement of the needle in the medullary cavity with an x-ray, ensuring it is as close to the center as possible. After removing the 25-gauge needle, immediately insert a 26-gauge needle into the same hole within the marrow cavity. Ream the sides of the medullary cavity in a circular motion at least five times until it feels smooth.

Then remove the 26-gauge needle, and flush the cavity with 1.5 to 2 milliliters of saline until the backflow runs clear. Safely dispose of the syringe and needle in a designated container. Next, close the skin wound using a topical adhesive suture.

Immediately after surgery, administer the remaining dose of extended release buprenorphine as calculated earlier. Monitor the animal on the heating pad for signs of normal, unobstructed breathing.