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Background
The cranial cruciate ligament is one of a pair of ligaments that stabilise the knee (stifle) joint.
The two ligaments connect the femur (thigh bone) to the tibia (lower leg bone and prevent backward and forward movement between the upper and lower limb. They get their name because they cross over in the centre of the joint.
The most common injury to the stifle joint is damage to the cranial cruciate ligament. The ligament can break in one of two ways – it can be subject to increased stress over time (often due to the dog's conformation, or exercise type) – this can produce low grade inflammation and sometimes fraying of a few fibres at a time, or it can snap suddenly due to a direct and sudden stretch (a sporting injury).
Dogs with a frayed or inflamed ligament become gradually lame and may show reduced willingness to exercise. They may be stiff after rest and may show swelling of the joint.
Dogs with a broken ligament will usually not use the limb at all. A classic story is a terrier who was fine one minute, chased a squirrel in the garden and now won't put any weight on one back leg.
Inflamed ligaments may sometimes become less painful and be able to perform their stabilising duties. They can be weaker and the chances of a full tear increase following a minor injury. Full ruptures of the ligament should be surgically repaired if the health of the dog allows. If the joint is left without the support that the ligament provides, terrible arthritis will follow quickly, causing pain and reduced life expectancy for the dog.
How it is repaired
There are several methods of repair for the cruciate ligament. The type of repair is chosen to give the dog the best chance of recovery and full future use of the limb.
In small dogs of less than 20 kilos in weight, the usual choice of repair uses a prosthetic ligament, (a fabello-tibial suture). Surgery is performed to remove damaged tissues from the joint. The cartilage shock absorbers or “menisci” are examined for damage. The joint is repaired and a strong piece of surgical nylon is threaded around anchor points to mimic the action of the ligament, but with the prosthetic ligament on the outside of the joint, not the inside.
In large dogs of over 25 kilos (or in dogs with steep angulation of the top of their tibia) and in cats the treatment of choice is a procedure called a TPLO – a tibial plateau levelling osteotomy. This procedure involves precisely cutting a section of bone at the top of the tibia and rotating it through a measured angle to reduce the forward movement of the tibia during weight bearing. The cut bone is secured in its new position using a metal plate and screws. The procedure is highly technical, but very successful. It is more appropriate for heavy dogs because their problem is solved mechanically rather than relying on a prosthesis which could break under the forces created by the dog's weight. Highly active or strong dogs may also benefit from this procedure over the prosthesis.
Both repair methods require a period of extremely strict rest after surgery to allow the repair to become stable. 6-8 weeks of house/cage rest is required. Physiotherapy and hydrotherapy can be useful in aiding recovery. Pain relief is always provided for dogs undergoing these procedures.
Prevention rather than cure
Prevention of cruciate injuries can be difficult as some dogs are predisposed, but avoiding rotation and jumping together is useful (Frisbees are a good source of income for veterinary orthopaedic surgeons!).
If your dog is unlucky and has already had a cruciate ligament injury, there is much that can be done to slow the onset of degeneration (arthritis) in the joint, though we would still expect the joint to become arthritic with age.
For preventative measures for arthritis, please see our arthritis section.
