This method causes acute cartilage damage to the weight-bearing surface of the rabbit knee and reliably induces post-traumatic osteoarthritis. This model mirrors joint trauma that is relevant to clinical practice. It will allow for the evaluation of novel therapeutics to mitigate post-traumatic arthritis.
The main technical hurdle is placement of the Steinmann pin into the femoral shaft. Misplacement will result in femoral shaft fracture. We recommend practicing this model first on rabbit cadavers.
To begin, place the stainless steel front leg block under the end of the impact platform and cover the platform with a heating pad. Place the anesthetized rabbit in the prone position on the heating pad. Place a padded bump under the contralateral hip.
Using silk tape, gently retract the tail superior and contralateral to the operative extremity. Clean the surgical site with chlorhexidine and 70%alcohol-soaked sterile gauze, starting from the posterior knee with a circular sweep outward. Place a sterile glove over the operative foot up to the ankle and wrap it with a sterile cohesive wrap.
Drape the surgical site using three drapes by placing one directly under the operative extremity and the other two covering the rest of the body. Secure the drapes with towel clamps. Palpate the position of the patella anteriorly to estimate the position of the knee joint.
Using a 15 blade, make a three to four-centimeter incision along the posterior aspect of the extended knee from the level of the superior pole of the patella distally. Perform blunt and sharp dissections through the underlying superficial fascia. After developing the interval between the skin medially and the medial gastrocnemius laterally, place a self retaining Weitlaner retractor in this interval.
Then dissect laterally to the saphenous and retract the vasculature medially and the gastrosoleus complex laterally. Continue dissecting distally until a small mobile fabella is identified over the posteromedial femoral condyle. Perform an arthrotomy demobilize the fabella superolateral, exposing the underlying medial femoral condyle.
Retract the soft tissue. While maintaining the condyle exposed, place a 0.062-inch Steinmann pin at the superior aspect of the medial femoral condyle and centered in the anterior posterior direction of the medial femoral condyle, roughly five millimeters from the posterior aspect of the condyle. Next, using a battery-powered Steinmann pin driver, drive the pin laterally through the bone and lateral skin parallel to the joint surface.
Remove the retractors and close the skin incision with a 3-0 Polysorb suture in a running fashion. Cover the incision with sterile gauze. Remove the drape under the operative limb.
Adjust the heights of the lower aspects of the Steinmann pin clamps so that they match the height of the pin. Secure the Steinmann pin on both sides of the knee by attaching the top aspects of the clamps and tightening the screws. Remove the suture and reopen the incision.
Use self-retaining Weitlaner and cricket retractors to expose the medial femoral condyle. Attach the sterile three-millimeter impacter head to the drop tower carriage. Bring the drop tower over the operative extremity and place its base underneath the impacting platform.
Gently lower the impacter onto the center of the posteromedial femoral condyle. Move the rabbit or tower to ensure the impacter head is centered over the medial femoral condyle. Once appropriate trajectory is ensured, clamp the tower onto the platform with the toggle clamps.
Next, set the impacter on the drop tower at seven centimeters above the medial femoral condyle. In the lab view data acquisition software, click on the start button just before freeing the spindle stop to release the carriage and allow it to drop under the force of gravity. Perform visualization of the cartilage surface to determine whether appropriate cartilage damage has occurred.
To analyze the data using the MATLAB code, move the data file from the sensors to the same folder as MATLAB and run the code. Inspect the load time curve and ensure that it is smooth, indicating that no fracture has occurred. Remove the drop tower from over the operative extremity, placing all used surgical tools aside.
After wearing the new sterile gloves, reapply a sterile drape to the lower extremity. Then re-expose the medial femoral condyle. Thoroughly rinse the surgical site with 50 to 60 milliliters of sterile saline.
Close the posterior capsule using a 5-0 Polysorb suture, followed by skin closure with a 4-0 Monosorb suture. Remove the height adjustable screw mechanism securing the Steinmann pin. Remove the Steinmann pin from the femur with the powered wire driver.
Dress the wound with a non-adhesive dressing, followed by adhesive tape. Perform an X-ray of the operative extremity to ensure no fracture occurred and appropriate pin placement. The success of the surgical procedure was monitored through visualization of the condyle and radiography to confirm no fracture.
Improper Steinmann pin placement resulted in an osteochondral fracture on impact. In this model, the average peak impact stress was 82 megapascals, and the average loading rate was 37 megapascals per millisecond. Cartilage damage was not observed in the contralateral uninjured femoral condyle and was mainly localized to the impact site.
Impacted 16-week medial femoral condyles, or MFCs, had higher OARSI scores compared to the control MFCs. Further, impacted knee MFCs also displayed higher OARSI scores compared to the MTP, LTP, and LFC. In contrast, no differences in OARSI scores were observed among the MFC, LTP, MTP, and LFC compartments of the contralateral non-impacted knee.
There were no significant differences between the impacted and non impacted LFC, MTP, and LTP joint surfaces. Articular cartilage from impacted MFC had higher levels of tunnel positivity, indicating increased chondrocyte apoptosis compared to non-impacted MFCs. At the end of the procedure, the pain behavior of the rabbits can be tracked.
After the study, the development of post-traumatic osteoarthritis will be evaluated using imaging techniques, histology, and other methods. We're using this model to test therapeutics and devices that aim to mitigate post-traumatic osteoarthritis. The model may also help us to better understand the progression of this disease.
