The cranial cruciate ligament is a tough band of fibrous tissue within the knee joint that attaches the femur to the tibia, and it prevents the tibia moving forward relative to the femur.
In humans, the ligament often snaps due to sudden trauma (rugby and soccer players) but in dogs it is most often a very different scenario. In dogs, the ligament slowly degenerates over time, almost like a fraying rope. The cause is usually unknown but factors that play a role are genetics, (certain breeds are more susceptible), weight of animal, individual conformation and certain inflammatory conditions and also activity of an animal.
THE SIGNS:
Limping is the most common sign. It may start suddenly or build up gradually over weeks, or it could be intermittent, often over months.
INSIDE THE JOINT:
The fraying ligament starts an inflammatory reaction in the knee causing pain and lameness. Arthritis begins to set in at an early stage. At a critical point of fraying, the ligament loses its’ normal mechanical function and the painful lameness is accompanied by a mechanical lameness. An important factor that influences the mechanical lameness is the backward slope at the top of the tibia. Every time the dog puts weight on the leg the femur will tend to roll down this slope. In some dogs this will lead to damage to the meniscus, the cartilage pad between the femur and tibia.
DIAGNOSIS:
Laxity in the joint, using a specific manipulation technique, will confirm the diagnosis (which often has to be done under sedation). In dogs with partial tears/chronic fraying, other tests such as x-rays and joint aspirates may be helpful. Puffiness in the joint, remodelling of the bones around the knee, how the dog holds the leg when sitting all help make the diagnosis.
TREATMENT:
Medical management
This is only recommended where the anaesthetic risk is too high or in an extremely old and very small dog. This includes weight management, physiotherapy and pain killers.
Surgery
There are 2 types of surgical repair. The one method tries to replace the ligament with an artificial one and the other makes the ligament redundant by realigning the forces acting on the joint.
1) Ligament replacement techniques.
These have the ability to return many animals to near normal function. The disadvantages of this technique are the unpredictability during the early stages of recovery and the mechanical limitations in heavy or athletic dogs. Some dogs become transiently more lame before improving. Others take many weeks to improve and a small proportion will have on-going knee pain and instability. Usually this technique is recommended for traumatic rupture of the cruciate and in small dogs. In the long term more arthritis will develop with this technique
This technique involves opening the joint, cleaning out the remains of the torn ligament, inspecting the menisci and trimming where damaged, closing the joint capsule then implanting the artificial ligament. The material is anchored behind a small bone at the back of the femur (fabellum) and through a bone tunnel and small “button”in the tibia.
We have a choice of 2 materials. A reinforced surgical mono nylon is the cheapest, anchored with stainless steel crimps. The disadvantage of this technique is that dogs have been known to snap the implant before the joint has stabilised. In large dogs we use a double implant.
The other material is a strong synthetic material called LigaFiba. This is available in up to 230Kg breaking strain so is very unlikely to break, even in very large dogs. It is a little more expensive than the nylon and there is a slightly higher risk of infection due to it being a braided material.
2) TTAR (Tibial Tuberosity Advancement Rapid)
This is where the anatomy of the joint is altered making the cruciate ligament redundant (correcting the underlying cause of the problem)
The main supporting muscle of the leg, the quadriceps is attached to the tibial crest. By moving the tibial crest forward the forces within the knee are altered, neutralising the tendency of the femur to slide down the sloping tibial plateau. Because bone healing is more efficient than ligament healing, this repair is more robust than the surgery to replace the ligament. A major practical benefit is the dog will be using the leg within 1-3 days. The mechanical advantages plus the rapid return to function are especially important in heavy and athletic dogs and in early mild cases where ligament replacement could make them more lame initially
As a general rule, over 90% of animals return to normal activity after TTAR with far less arthritis developing long term. This procedure is very important in young, very large dogs.
This technique involves opening the joint, cleaning out the remains of the torn ligament, inspecting the menisci and trimming where damaged, closing the joint capsule. Then using special instruments, the tibial crest is sawn loose and moved forward, and a titanium cage is fitted in the defect and anchored using 6 titanium screws. The size of the cage fitted is predetermined after measurements are made on the x-rays taken of your dogs’ leg.
If you think your dog may have a cruciate injury or if you would like more info, please do not hesitate to contact us at the practice!
