Less-Invasive Technique for Non-stabilized Mandibular Fracture in Mouse Models

The scope of research is mandibular endochondral bone repair. We aim to develop a technique for non-stabilized mandibular fracture with minimal bone loss and soft tissue injury to best represent endochondral bone repair process. The bone repair process is influenced by the forces exerted on the bone callous and depends on the anatomical sites.

Few authors report the study of mandibular bone repair. The diffusion of our protocol will facilitate research development in this specific field. Our protocol has the advantage of avoiding excessive bone loss and soft tissue damage at the site of mandibular bone fracture to best represent endochondral bone repair.

To begin, place the anesthetized mouse on its back on a heating plate covered by a sterile field kept at 37 degrees Celsius throughout the procedure. Apply eye lubricant to both eyes to prevent dryness caused by general anesthesia. Fit a mask on the snout for continuous isoflurane inhalation.

Then secure the mouse's extremities with adhesive tape. After putting on sterile gloves, disinfect the skin with several swipes of 10%povidone iodine solution and alcohol. To perform the submandibular cutaneous approach, using micro scissors, make a skin incision from the mandibular angle to the junction of the horizontal branch of the mandible.

Dissect the subcutaneous tissues to expose the masseter muscle. Now use a periosteal elevator to detach the masseter muscle attachments from the inferior border of the mandible. Elevate the masseter muscle in a subperiosteal plane along the mandibular ramus with the elevator.

Using the piezoelectric bone surgery device with saline serum irrigation anterior to the mandibular angle in the posterior part of the concavity, create a small osteotomy at the inferior border of the mandible. Locate the posterior border of the mandible and the coronoid notch. Then complete the fracture using small straight scissors inserted along the mandibular ramus to avoid additional meed muscle aperture and injury.

Place the scissors perpendicular to the inferior border of the mandible to allow the correct orientation of the fracture. Now check for total mobility between the two bone segments during gentle manipulation with forceps to ensure complete fracture. Close the skin incision using separate stitches.

Take cephalic lateral x-rays to verify the fracture's direction. Prepare a mouse cage without kibbles and hard enrichment to prevent any masticatory forces. Isolate the operated mouse in a single cage for the first week until the skin has completely healed.

Administer buprenorphine by subcutaneous injection at 4, 24, 48, and 72 hours after the procedure. Feed the mice a soft diet gel from day zero to the end of the consolidation period to avoid pain and secondary displacement of the fracture. Weigh the mice daily from day zero to day four post-fracture in the morning before buprenorphine injection, and then three times per week until animal sacrifice.

The histological images confirm the development of a soft callus with a cartilaginous template 14 days after the fracture in a wild type mouse.