The Establishment of Calvarial Suture-Bony Composite Defects in Rats: A Standardized Model for Suture-Regenerative Therapy Investigation

Our research focuses on the detailed surgical procedures of calvarial suture-bony composite defects in rats, alongside the investigations into the short term and long-term prognosis of the model. The primary objective is to establish a standardized model that can be utilized for advancing suture regenerative therapies. For the current animal model, the primary challenge lies in completely removing the corona suture, while preserving the sagittal and frontal sutures with minimal other tissue removal.

Our protocol allows for more straightforward comparation through self-control by creating defects in both the left and the right half of the corona suture, and applying different interventions to each set. To begin, place the anesthetized rat in a prone position with the head naturally extending vertically. Using an electric shaver, remove the hair from the scalp between the nasal bridge and the cervical spine joint.

Disinfect the surgical area in circular motions, radiating from the center with 2%iodophor, followed by 75%ethanol. Employ a surgical drape to cover the dorsum of the animal and the fur surrounding the incision. Starting from the midpoint of the nasal bone, with a disposable scalpel, make a two centimeter longitudinal skin incision following the midline of the cranium.

Using a scalpel, make a midline periosteal incision mirroring the initial point and extent of the skin layer. Then gently lift the periosteum on both sides of the incision with a periosteal elevator to expose parietal bones, frontal bones, and coronal sutures. Apply vertical force with a 1.2 millimeter diameter round burr on the coronal suture until a sense of breakthrough is felt.

From the penetration point, move the burr laterally along the coronal suture to create an approximately four millimeter long positioning groove. Then remove bone tissue with the burr on both sides of the positioning groove to initially form a rectangular full thickness defect. Employ a 0.8 millimeter diameter round burr to refine details involving the grinding of right angles and the smoothing of defect margins.

Create two defects across the left and right halves of the coronal suture for self comparison. Regularly check the length width of the defects using a Verneer caliper to ensure consistency across all samples. After surgery, close the skin with 3/0 monofilament sutures.

Micro CT images and cross-sectional views of suture-bony composite defects at postoperative day zero confirmed the successful creation of a full thickness calvarial defect. Micro CT images and the corresponding statistical analysis at six weeks post-operation revealed a natural inclination towards defect closure with more pronounced tendencies 12 weeks after surgery, indicating potential suture fusion over time. Histological analysis using hematoxylin and eosin and Masson's trichrome staining two weeks postoperatively showed extension and continuity of the periosteum and dura mater, forming dense fibrous tissue that sealed the defect.

By 12 weeks, large pieces of new bone were observed in the defect center.