Cruciate Ligament Rupture

The knee joint contains two bands of fibrous tissue, called the cruciate ligaments, which join the femur and tibia together. This ensures the knee works as a stable joint. The knee joint is held together by multiple ligaments and lacks interlocking bones – this creates a somewhat unstable joint.

The cranial cruciate ligament (known as ACL in humans) is in charge of preventing the lower half of the leg from displacing forward when the dog/cat puts weight on the leg. The most common injury in dogs is a rupture of this ligament. When the ligament snaps, the joint becomes very unstable and this leads to arthritis and damage to the cartilage. The cartilage inside the knee joint is known as menisci. Menisci act as shock absorbers. They are often damaged when the cruciate ligament ruptures. The repair is done at the same time when the cruciate ligament is repaired.

The most common causes of this rupture are trauma and degeneration of the ligaments in the joint.

Traumatic/Acute ruptures are due to twisting injuries of the knee. They are sudden and occur when the dog is running and decides to change directions abruptly. Acute cruciate ligament ruptures and extremely painful. In obese dogs, minor traumas such as tripping up the stairs, can result in rupture.

Chronic ruptures are due to repeated excessive force applied on the joint. With continued use, the stress of the ligament worsens until it ruptures.

The most common sign seen by owners is sudden crying or stopping while running/during exercise and then not being able to bear weight on one of the hind legs. Some pets might place a small amount of weight on the affected leg, this is known as “toe touching”.

Your veterinarian will perform a cranial drawer test, which showcases the abnormal forward movement of the tibia in front of the femur. If the patient is too anxious or the condition has been left for some time before seeking veterinary advice, this might not be easy to demonstrate. An x-ray of the stifle will be needed in these cases.

In most cases, surgical intervention is needed.

We normally suggest a tibial plateau levelling osteotomy (TPLO) for dogs heavier than 10 kgs. TPLO is the surgery of choice for very active dogs regardless of size. The surgery changes the angle and therefore the relationship between the femur and the tibia. The levelling of the surfaces within the knee joint helps with the stability of the joint and creates more of a normal shape and reduces mechanical stress.

To better understand the purpose of levelling the tibia, we often use the analogy of a wagon on a hill. Imagine a wagon tied to a post on the slope of a hill. If the rope holds, the wagon does not roll downhill. If we add excess weight (or downward force) to the wagon, the rope could break, and the wagon will roll down the hill. However, if the wagon is on level ground, it will not roll with added weight, even if the rope is broken.

In this example, the wagon is the femur, and it slides down the slope of the tibia when the CCL is ruptured. This instability leads to damage and destruction of the cartilage and bones of the knee joint. TPLO surgery levels the tibia to prevent the femur from sliding forward, thereby stabilizing the joint.” – sourced from VCA animal hospitals.

Healing from TPLO surgery is generally rapid, but does depend heavily on owner compliance.

Extracapsular techniques (meaning the repair is outside the joint capsule of the knee joint) can be used in dogs less than 10 kg. The surgeon examines the joint, removing fragments of the ruptured ligament and restoring the menisci if needed, then places an artificial ligament (usually placed outside of the joint capsule) to stabilize the joint and prevent abnormal motion.

Exercise levels must be restricted post-operatively for 6 to 8 weeks.

Regardless of the surgical method use, the risk of development of arthritis is very high. The progression and development of it significantly reduces with surgery but is not preventable. Life long weight control and joint supplements are beneficial.