Cruciate Ligament Injuries

What are they?

The cruciate ligaments are two fibrous bands that cross over each other inside the knee joint. They function to allow the knee to flex and extend whilst stopping the adjacent bones from sliding apart as weight bearing occurs. Humans have a very similar set up and cruciate ligament rupture is a common knee injury of athletes. Once a cruciate ligament is torn the joint becomes unstable and painful: the pet will present with varying degree of lameness.

How does the injury occur?

Classically cruciate injuries are caused by a sudden twisting motion. This is seen commonly in people and in dogs especially when they run or jump with a sudden change in direction. It is generally the anterior (front) ligament that is torn.

There are a number of factors that make it more likely that rupture of the anterior cruciate ligament will occur. These factors are

  • Genetic predisposition where there is abnormal conformation of the back legs such that there is constant abnormal forces acting on the joint. This is increasing common in large breed dogs over about 15 to 25 kg.
  • Obesity greatly increases the risk of rupture
  • Old age with osteoarthritis causing chronic damage to the ligaments.



  • The history gives us a lot of information from how and when an injury occurred to any previous episodes of lameness.
  • The physical examination will often confirm our suspicion as the animal is often very lame (toe touching) and when we examine the leg we will be able to demonstrate that there is laxity in the joint. The laxity we are looking for is called an anterior drawer sign as it demonstrates that the Anterior ligament has ruptured.
  • Some pets will not allow this to be done awake due to pain. We will generally anaesthetise those pets to conform the diagnosis. At that stage radiographs are taken to rule out other problems and allow us to assess for preexisting arthritis.
  • At times it is not possible to show that the anterior ligament has been torn due to scar tissue around the joint – in those dogs once we have ruled out other problems then we would proceed to surgery to explore the joint.
  • Inside the knee joint are pieces of cartilage called menisci. At times these cartilages are also damaged when the cruciate ligaments rupture. They are inspected at the time of surgery and are removed if damaged.


Is it a surgical problem?


Generally the answer is yes. In very small dogs under about 5 to 8 kg you may find that the animal copes without surgery. Most small dogs will end up needing surgery. All larger dogs should go straight to surgery.

The standard surgery we perform is to repair the damage by placing artificial surgical material to mimic the ligament out side the joint. During surgery the joint is opened to allow us to clean out the damaged material. This is the time we check the menisci for damage. They are removed if this is found as they can cause on going pain.

In dogs over about 15 to 20 kg we offer referral to the specialist surgeons as the external tie technique is often not able to withstand the forces generated within the joints. These forces can lead to tearing of the implant. The surgeons in these bigger dogs will change the weight bearing angles on the knee joint to reduce these forces on the repairs. This advanced surgery is called a Tibial Plate Leveling Osteotomy (TPLO) and should only be done by registered specialists. This specialist surgery is not for every one due to the cost – we have very good success with the standard surgery on these bigger dogs if a referral is not possible.


What happens after surgery?


Our standard recommendation post cruciate surgery is

        Strict rest for 8 to 12 weeks – over this time there will be a slow return to walking. We assess the pet regularly over this time period.
        Never run your dog again and do not throw balls etc for them.
        Start using Cartrophen as recommended by your vet.
        Feed Eukanuba Joint Mobility diet (correct level Fatty Acid levels and also glucosamine) for life.
        Keep your dog trim, mobile and healthy. Use pain killer/antinflammatory medications as prescribed by your veterinarian.


Can the same injury happen to the other knee?

The simple answer is – Yes. The other knee joint will suffer an anterior cruciate rupture in about 60% of dogs. Occasionally an animal will present with both knees having just had the anterior cruciate ligaments rupture – these dogs present as if they can not walk. Surgery is need regardless of the size dog.