The overall goal of this surgical intervention is to evaluate transpedicular screws using an in vivo porcine lumbar spine model. This method can help answer key questions about such complications of the spine, such as the loosening of pedicle screw. The main advantage of this technique is that we can compare long-term stability of different type of screws.
Maintain 12-month-old miniature pigs in the experimental unit for at least one week. After this acclamation period, give each pig a clinical exam, measure respiratory rate, heart rate, and body temperature. Prior to the anesthesia, starve the pigs for 12 hours.
To sedate a pig, inject atropine into the lateral cervical muscle region behind the ear. Once sedated, press a hand around the base of the ear and then clean the ear with alcohol. Then, place an over the needle plastic catheter into the ear vein.
Then, flush the catheter with heparinized saline and secure it with tape. Now, induce anesthesia using ketamine and xylazine via the catheter. To intubate the pig, position it in sternal recumbency.
And with the help of an assistant, hold open the jaw using a suitable sling. Then, pass the tip of the laryngoscope into the pharyngeal cavity to displace the epiglottis from the soft palate. Once intubated, listen to the respiration in both lungs.
Then, fill the cup of the endotracheal tube with air using a 10 milliliter syringe, and fix the tube to the snout, using adhesive tape. Next, begin providing 2%isoflurane through the tube. Then, test the pig's corneal and palpebral reflexes to confirm a surgical plane of anesthetization.
Now, apply ointment on the eyes and set up vital sign monitors, which should be checked at least every five minutes. 30 minutes before the surgery, provide a bolus of cefazolin via the ear vein catheter. Then, switch the IV line to administer 37 degree Celsius saline and fentanyl for pain management.
To begin, shave the pig's back 10 centimeters to either side of the midline. Then, clean the skin with alternating scrubs of povidone iodine solution and 70%ethanol. Now, make a longitudinal midline incision from the second spinous process of the lumbar spine to the first median sacral crest.
Then, dissect through the subcutaneous tissue and fascia down to the tip of the spinous processes. Next, using a Cobb elevator, elevate the paraspinal muscles subperiosteally from the underlying lamina. Then, dissect along the spinous process and lamina at the facet joints.
At the entry point, which is just inferior to the mamillary process from L3 to L5, use a burr or rongeur to open the superficial cortex. Then, insert the guide pen parallel to the superior end plate and at a 20 degree angle to the spinous process. Now, take posterior anterior lateral X-rays to define the insertion points for the pedicle screws.
Then, insert a pedicle probe up to 25 millimeters and confirm a complete intraosseous trajectory using the sounding device and palpation. Now, insert six pedicle screws. Make sure that the screw heads are well-seated.
Pay attention to the orientation of the site opening and the horizontal position which must line up with the rod. Then, insert two rods into both sides of the pedicle screw heads. Next, attach sleeves and nuts to the screw's head.
First tighten the nuts loosely with a straight socket wrench and then tighten them with a counter torque wrench. Then, confirm the positions of the pedicle screws using X-rays. Once the site is ready to close, irrigate it with three liters of normal saline.
Then attach a silicone drain and take out the silicone tip. Now, close the paraspinal muscles and subcutaneous tissues using absorbable sutures, and then close the skin with nonabsorbable nylon sutures. After suturing, disinfect the site with povidone iodine and apply a dressing.
Once a strong swallowing reflex is apparent, extubate the pig and transfer it to a recovery room. Once fully conscious, provide the pig food and water and check its gate patterns. Monitor the hind limb movement to assess the implant and provide pain relievers for three days.
12 weeks after the implantation, euthanize the pig. To harvest a spinal section, make a longitudinal midline incision at the previous surgery scar legion. Then, dissect the soft tissue and paraspinal muscles to fully expose the implant from L3 to L5.Now, remove the nuts using a counter torque wrench.
And then remove the rods. Next, using an oscillating saw, cut the L2-3 disc space and the L5-S1 disc space. Then, dissect both sites in the middle and anterior part of the L3-5 spine with a Cobb elevator and tower forceps.
If the spinal section cannot be immediately analyzed, store it in saline-soaked gauze at minus 20 degrees Celsius. The bonding strength between the pedicle screws and bone was evaluated for three screw types. Uncoated, hydroxyapatite-coated, and titanium-coated.
The main extraction torsional peak torque, or bond strength, was greatest with the titanium-coated pedicle screws. The region of interest can be evaluated by a micro-CT program for the analysis of the bone volume fraction, bone surface density, and specific bone surface. Scanning a spinal section with Goldner trichrome shows the interface between the pedicle screw and bone.
The fibrous tissue is red, and the bone is blue. When using uncoated pedicle screws, only fibrous tissue was observed at the interface. However, new bone formation was found at the interface for both types of coated screws.
It was even observed that with titanium-coated pedicle screws, the space between the screw threads in the bone was completely compacted. Once mastered, this technique can be done in three hours if it is performed properly. While attempting this procedure, it's important to focus on proper positioning of the the pedicle screws so the misplacement of the pedicle can be prevented.
After its development, this technique paved the way for researchers in the field of the spine surgery to explore loosening of pedicle screws in patients with osteoporosis.
