Development and Evaluation of a Rat Model of Full-Thickness Cartilage Defects

What this protocol not only mimics the occurrence and development of clinical FTCD, but also provides a reliable animal model for evaluating therapeutic treatments against FTCD. But this technique is easy to perform and enables growth observation immediately after the injury. This technique can successfully mimic clinical cartilage defects providing a platform for studying the pathological process of cartilage defects and developing corresponding therapeutic drugs.

This method could be applied to study traumatic cartilage defects, namely post-traumatic osteoarthritis. When trying this technique for the first time it is important to flex the tibia and the fibula at a 90 degree angle to fully expose the cochlear of the femoral condyle and keep the drill bit perpendicular to the cartilage surface. Begin by placing an anesthetized rat on the operating table in a supine position.

Place a sterile drape over the rat, exposing the shaven and disinfected knee joint. Using a number 11 scalpel blade make a one centimeter vertical incision in the middle of the knee joint. And cut the joint capsule and quadriceps femoris tendon along the medial patella edge.

Next, turn the patella outwards and flex the tibia and fibula at a 90 degree angle, To expose the femoral condyle cochlear. Using a 1.6 millimeter circular drill bit make a full thickness 0.1 millimeter deep cartilage defect in the femoral condyle cochlear. Wipe the surgical site with cotton balls soaked in 0.9%saline solution, and replace the patella.

Then keeping the knee in an extended position suture the incision layer by layer using non-absorbable 4-0 sutures. To measure the mechanical withdrawal threshold or MWT"of the rats, place the animal in a single plastic chamber on a wire mesh platform. Place the wire mesh base 50 centimeters above a table.

Begin the MWT measurement after 30 minutes of adaptation. Next, press the Von Frey filament perpendicularly on the planter surface of the rat's hind paw. Then bend the brush for two seconds avoiding the thickest part of the central portion of the paw.

Increase the stimulus weight gradually from 4 grams, until a positive response like paw withdrawal or licking occurs. 3 days post modeling the rats in the model group showed reduced MWT compared to the sham group. Suggesting hyperalgesia in the model group.

The MWT of the model group remained low even after 17 days. Indicative of the length of pain sensitivity. Histopathological staining of the sham group showed clear articular and intact cartilage surface, even distribution of the chondrocytes, and high expression of type-II collagen.

In contrast, the model group demonstrate depressed cartilage surfaces, lost chondrocytes, increased expression of matrix metalloproteinase MMP13, and decreased expression of type-II collagen. The most important thing to remember is patella must be reduced before suturing.