Left untreated, the instablility of the knee causes chronic pain, arthritis, and imminent degenerative joint disease. Treatment is surgical stabilization of the knee joint. However, conservative medical management with joint health supplementation, anti-inflammatory medication, and weight management are sometimes successful in cats and small dogs.
There are many different surgical procedures utilyzed for cranial cruciate ligament rupture in dogs and cats. My procedure of choice is the extracapsular lateral fabellar suture. For dogs weighing 80 pounds or more, there is some controversy whether a surgical technique called the tibial plateau leveling ostetomy (TPLO) should be used in favor of the extracapsular approach. Clinically, I have not appreciated a difference in results using either procedure. Therefore, I tend
to utilize TPLO mainly only for giant breed dogs weighing 150 or more pounds. With cats, I have not had to surgically intervene, as conservative medical management tends to be very successful.
Specifically, the affected dog or cat presents at first with toe-touching to non-weight bearing lameness. There is often significant swelling of the affected knee joint, with moderate to severe pain when the joint is manipulated. On physical examination, dogs and cats that have ruptured their cranial cruciate ligament, have what is called a cranial drawer sign. This is when the femur (thigh bone) is held stationary, and the veterinarian can pull the tibia (chin bone) forward. This should not occur in a normal knee joint.
In the lateral fabeller suture procedure, the stifle (knee joint) is surgically opened to examine the inside of the joint. We typically perform a mini-approach to the joint, which minimizes the healing time after surgery. The remnants of the cruciate ligament are excised and torn meniscal cartilages are debrided (trimmed up). If the medial meniscus is not torn, a prophylactic release of the caudal (back) pole of the meniscus is performed in order to help prevent a tear in the future.
Heavy suture material (monofilament nylon) is passed from the lateral fabella to the tibial crest and tied in order to eliminate joint instability (drawer movement). With time scar tissue develops around the stifle joint which helps to stabilize the joint. The build up of scar tissue will also decrease the range of motion of the joint.
The illustration of the stifle joint (side view) that has implanted nylon bands which stabilize the joint. The blue short line represents the cranial cruciate ligament and the red lines represent the nylon bands that are passed around the fabella bone (which sits on the back of the femur bone), and through a hole that has been drilled in the front part of the tibia bone. The nylon bands (red lines) are in the same orientation as the cruciate ligament.
When the cruciate ligament is ruptured, the slope of the tibial plateau, along with the forces exerted by the calf and quadriceps muscles cause the femur bone to slide down the top of the tibia bone called the tibial plateau. This in essence causes the tibial plateau to thrust forward with each weight-bearing stride and is called cranial tibial thrust. This thrusting results in excessive wear of the cartilage of the joint. In addition, as the tibia thrusts forward it stretches the tissues which surround the joint, which causes pain.
Excessive cranial tibial thrust also can tear of one of the cartilage pads in the knee called the medial meniscus. This usually results in a meniscal bucket handle tear or crush injury. The tibial plateau leveling osteotomy or TPLO can eliminate cranial tibial thrust, thus creating a dynamically stable stifle and sound gait.
The first part of the surgery involves removing the torn ends of the cruciate ligament and examining the medial and lateral meniscus cartilages. If a tear of either meniscus is found, the damaged part of the meniscus is removed. The tibial plateau leveling osteotomy - TPLO involves making a curved cut in the top of the tibia bone (osteotomy) to include the tibial plateau. The tibial plateau (the dashed line denotes the top of the tibial plateau) is then rotated along the curved osteotomy in order to level the slope. A plate and screws are used to hold the tibial plateau in place so that the bone can heal well. Below is an illustration demonstrating the curved cut in the tibia bone and rotation of the the tibial plateau; below right is photo of a plastic bone model demonstrating the TPLO; take note of the metal plate and screws that hold the bone together while healing takes place.
The cranial cruciate ligament is an important stabilizing ligament of the knee joint. Specifically, it prevents forward thrusting of the tibia whenever the animal steps. This tendency for forward thrusting of the tibia is a natural process and due to the distribution of tendon forces exerting tension in the area. Rupture of this ligament leads to acute, severe instability of the knee joint. This injury occurs most commonly in medium to large breed dogs, but is seen occasionally in small dogs and cats.
