Cruciate Ligament Tears Surgery Service - Fleetwood Veterinary Clinic - Surrey, BC

ANATOMY

The canine knee joint, known as the stifle joint, is similar to a human’s knee in many regards. The joint is made up of the femur (thigh bone), tibia (shin bone), and the patella (kneecap) that are firmly held together by ligaments. Ligaments are strong, dense structures consisting of connective tissue that join the ends of two bones across a joint. The function of ligaments is to stabilize the joint.

The stifle has two very important ligaments called the cranial (CrCL) and caudal (CaCL) cruciate ligaments (cruciate means a cross or crucifix) that cross in the center of the joint. The CrCL (known as the ACL in humans) restrains the backward and forward motion of the joint, in addition to inward twisting and hyperextension of the joint. It is the structure that is most commonly injured in dogs. In fact, more than 600,000 dogs in the U.S. have surgery for this problem every year.

The stifle also has two half-moon shaped cartilage structures between the weight-bearing bone ends called menisci. There are two menisci in each stifle, one on the inner side of the joint called the medial meniscus and one on the outer side of the joint called the lateral meniscus. The menisci add support to the stifle and also serve as shock absorbers by spreading the weight load.

EFFECTS OF CrCL TEAR

The top of the tibia bone, called the tibial plateau is angled downward. When the CCL is torn, weight-bearing forces causes the femur bone to slide down this slope. Not only is this painful, but also causes the stifle to shift out of place during weight-bearing movement. As the femur slides down the tibial plateau, the meniscal cartilage—a cushion between the bones that acts as a shock absorber may be crushed.

In about 50% of the dogs with CrCL injuries, the meniscal cartilage has been injured as well. This type of injury is often accompanied by a “click” that can be heard when a dog walks. When the CrCL is weakened or torn, the most significant long-term change in the joint is the development of Clinical signs and diagnosis.

Most dogs with a complete CrCL tear show an immediate onset of lameness. While there may be some initial improvement over several days, there usually is a dramatic decline in limb function over time. Dogs that have a partial CrCL tear may have persistent lameness on the affected limb, yet others have stiffness or lameness on the limb after taking a nap or while exercising.

Your veterinarian may detect swelling in the knee and instability in the stifle upon examination of the joint. Dogs that have a partially torn CrCL may not have any detectable instability of the joint and x-rays of the joint may be needed to support the diagnosis arthritis.