Cruciate ligament injury in dogs

The cruciate ligaments are an important part of the knee joint, that sit between the shin and the thigh bone, allowing it to work as a stable, hinged joint. Injury to the cruciate ligaments is one of the most common orthopaedic conditions seen in dogs that can often cause lameness, pain and future arthritis. So, what causes injury to the cruciate ligament, what are the signs to look out for and how is it treated?

What is a cruciate ligament?

The cruciate ligaments are fibrous bands that join the bones above (femur) and below (tibia) the knee joint. There are two cruciate ligaments in each knee. The cranial and caudal cruciate ligaments (called anterior and posterior in humans).

The cranial ligament runs from the front of the tibia to the back of the femur, while the caudal ligament attaches the other way. They cross over in the middle, hence the word cruciate which refers to cross-shaped.

In dogs the cranial cruciate ligament (CCL) is most commonly injured. In humans, the anterior cruciate ligament (ACL) is a common knee injury for athletes.

What causes injury to the cruciate ligament?

A cruciate ligament injury can occur for many reasons.

Athletic injury in a healthy dog – caused by twisting the knee joint. For example, the dog is running and changes direction suddenly. Or they could simply land awkwardly when running or jumping. The weight on the knee joint combined with excessive rotation on the cruciate ligaments results in injury.

Older, larger or overweight dogs – in these dogs the cruciate ligament progressively weakens or become stretched over time as a result of repeated trauma or arthritic disease. The injury could be a result of minor trauma such as stumbling over an object while walking or going downs some steps. These lead to partial tears and with ongoing use of the joint, the condition worsens until a complete rupture occurs. In these cases, they are more likely to rupture the cruciate ligament in the other knee.

Dogs with other knee problems – such as luxating patella, in which the kneecap (patella) moves in and out of its normal location. This can place stress on the cranial cruciate ligament and result in a rupture.

What are the signs of a cruciate ligament injury in dogs?

Common signs of a cruciate ligament injury in dogs include:

• Sudden lameness in hind leg

• Whimpering or yelping when bearing weight on affected leg

• Touching toe to ground but not bearing weight when standing

• Reluctance to walk or exercise

• Reduction in muscle mass around effected knee (muscle atrophy)

• Arthritic symptoms can develop if left untreated

If left untreated the lameness can sometimes reduce over a week or two as the acute inflammation resolves. However, arthritis will often develop inside the joint as a result of chronic instability. If your dog shows signs of lameness, pain or reduced activity it is best to have them examined by your vet as soon as possible.