The cranial cruciate ligament is one of the main stabilizing structures of the stifle joint (in humans this joint would be called the knee). The cranial cruciate ligament serves to prevent forward movement of the tibia bone (shin bone) relative to the femur bone (thigh bone), to prevent internal rotation of the tibia bone, and to limit hyperextension of the stifle.
Two meniscal cartilages located inside of the joint are crescent-shaped pads that serve as cushions, provide stability to the joint, and help to push the nourishing joint fluid into the cartilage of the femur and tibia bones.
Several other ligaments also hold the stifle together, however, these infrequently rupture in dogs.
To the right is a photo of the ligaments of the stifle joint as viewed from the front—the kneecap and patellar ligament have been removed; C=cranial cruciate ligament; M=medial meniscus.
Cranial cruciate ligament rupture
Cranial cruciate ligament rupture is the most common orthopedic condition that we treat and affects all breeds of dogs, and occasionally cats and ferrets.
The ligament may undergo partial tearing over a period of months, or may suddenly rupture during normal physical activity.
Most dogs are middle-aged or older when the rupture occurs, however some breeds such as Labrador Retrievers, Rottweilers, and Mastiffs may develop partial or complete tears when they are puppies.
The cause is unknown, but conformation of the limbs and genetics may play a role.
Partial ligament tears may be difficult to diagnose and frequently occur in both legs at the same time.
When the ligament tears, the stifle becomes unstable. The femur and tibia bones that form the joint then rub back and forth on each other (termed “drawer movement”). This results in pain due to stretching of the joint capsule, potential damage to the meniscal cartilage, and inflammation of the joint (called arthritis). In about half of the patients that we operate, the meniscal cartilage on the inner side of the joint (medial meniscus) has been torn and the damaged portion must be removed.
Candidates for the lateral fabellar surgery
This technique is used most commonly for small dogs and cats.
We have noted that dogs that have a steeply-sloped tibial plateau should receive the TPLO instead of the lateral imbrication technique regardless of their size. The lateral imbrication technique cannot overcome the forces on the stifle joint caused by a steep slope and frequently the nylon band will tear or loosen in the postop period.
All dogs that are going to have cruciate surgery should have a correctly positioned x-ray taken to measure the slope of the tibia so that an informed decision can be made on the appropriate type of surgery that should be performed. In my experience, dogs that have a steep tibial slope (especially large breeds) do much better with the TPLO surgery. This may not be an important factor in small breeds even with a steep tibial slope, but the clients should be aware of the fact that a steep tibial slope will put much greater force on the nylon bands, therefore they may break.
The stifle 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 torn ends of the cruciate ligament are removed and the medial and lateral meniscus cartilages are examined for tears.
To the right is an illustration of the front view of the stifle—note the medial meniscus, the cranial cruciate ligament, and the lateral meniscus
The medial meniscus is concurrently torn in about 40 to 50% of dogs that have a torn cruciate ligament.
When the femur bone shifts backwards the femur bone pinches the medial meniscus, causing it to tear from the back part of the stifle joint and flip forward. A torn meniscus will make a patient much more painful than a cranial cruciate ligament tear alone. As the patient walks the torn part of the meniscus may flip back and forth resulting in an audible popping or clicking noise.
Every attempt is made to save as much of the normal meniscus as possible and only trim out the damaged portions of this structure. This is called a partial menisectomy. It is believed that a partial menisectomy results in less arthritis than a complete menisectomy.
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.
An alternative to using the lateral fabellar technique is the tibial plateau leveling osteotomy. This is an excellent technique for large dogs, highly athletic dogs (hunting, agility), or show dogs. I prefer this technique over the lateral fabellar technique, as these patients recover quicker and develop less degenerative arthritis of the stifle.
The illustration on the right shows the implanted nylon bands which stabilize the joint. The blue 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 pull the femur back into place on the tibia.
Contralateral cruciate tears
About one third of the dogs will also tear the cruciate ligament in the opposite limb.
These dogs frequently have arthritis in the knee joint even before the tear in the cruciate is obvious on physical examination, but early changes such as mild joint swelling may be detected with x-rays.
An x-ray may be recommended to predict if the opposite stifle joint is going to develop a tear.
Expected convalescent period
By 2 weeks after the surgery your pet should be touching the toes to the ground at a walk.
By 8 weeks the lameness should be mild to moderate.
By 6 months after the surgery your pet should be using the limb well.
With the extracapsular technique, about 85% of the cases are significantly improved from their preoperative state. With the extracapsular technique, we can expect that 50% of these dogs will have some degree of lameness, whether it is mild or intermittent following heavy activity. On the other hand about 50% regain normal function of the limb.
Even though this surgery may not return the limb to perfectly normal function, these dogs usually are greatly improved over their condition prior to surgery.
The lateral fabellar suture technique will not stop the progression of arthritis that is already present in the joint. As a result, your pet may have some stiffness of the limb in the mornings. In addition, your pet may have some lameness after heavy exercise or during weather changes. To help with stiffness, chondroitin sulfate and glucosamine may be given.
Anesthetic death can occur, but is rare
Infection at the surgical site
Sterile reaction to the nylon bands
Premature loosening or breakage of the nylon bands
If the meniscal cartilages were not found to be damaged at the initial surgery, it is possible that damage may occur at a later date, thus requiring a second surgery. The sign of a meniscal tear is a sudden onset of lameness.
Entrapment of the peroneal nerve by the nylon sutures is very painful and can result in permanent functional impairment of limb function.
Abbreviated Post-op care
Icepack the stifle three times daily, 10 minutes per session for the first 2 days to help reduce the swelling and pain.
Passive range of motion of the joint involves flexing and extending the stifle joint, and should be done for 10 minutes. After the range of motion exercises have been completed, a cold compress is applied to the stifle for about 5 to 10 minutes.
The rehabilitation therapy should be done until your pet is bearing a significant amount of weight on the limb.
During the first two months, activity is restricted to short leash walks outside.
Running, jumping, and rough play are forbidden.
Gradually increasing the activity during the third month after surgery allows for a safe return to function.
Unleashed activity can take place after four months.