Anterior Cruciate Ligament Rupture

Anterior Cruciate ligament rupture is a common injury in dogs – especially in breeds like Labradors and Rottweilers where genetic risk factors causing cruciate degernerative changes may be involved. Large lively dogs need a surgery that will allow them to carry on being large and lively!

If you have been referred for TPLO surgery (Tibial Plateau Leveling Operation) for anterior cruciate ligament rupture then this will give you some idea of what the surgery involves and, importantly, the post-operative care that your dog will need.

How the Cruciate Ligament Works and What Happens When it Ruptures

When a dog is standing normally (or a human is standing on the ball of their foot) the knee is held firmly in position by the anterior cruciate ligament . It stops the tibia (shin bone) from sliding forwards relative to the femur (thigh bone). The tibia, Achilles tendon and associated muscles are also important in maintaining the joint’s stability.

If you stand on the ball of your foot with your knee slightly flexed you will feel that your calf muscles and Achilles tendon are taking the strain.

When the anterior cruciate ligament is ruptured the femur tends to be pulled backwards and the tibia is forced forwards and relatively upwards. This is known as tibial thrust and it causes the instability in the knee joint. The femur 'rolls backwards' down the top (plateau) of the tibia which is exacerbated by a tibial plateau that slopes backwards. Both complete rupture and partial tears prevent the dog taking full weight on the knee resulting in the dog becoming lame and the muscle on the front of the thigh becoming wasted.

Instability in the joint causes the release of various pro inflammatory mediators that initiate arthritis. The longer the joint is unstable the worse the arthritic changes become. It is common for a torn or sprained ligament to settle down and allow the dog to use its leg, especially with the use of powerful non-steroidal anti-inflammatory drugs (NSAIDs). However these cases have progressive arthritis and often end up with rupture of the ligament and complete lameness. By this time they have marked arthritic change within the joint. The instability has also allowed the meniscus (cartilage within the joint) to become torn compounding the lameness and the inflammation within the joint.

How the Surgery Works and What it Involves

Tibial plateau leveling is a technique that changes the slope of the tibial plateau (top of the shin bone that articulates with the thigh bone). This stops the femur 'rolling' back down the top of the tibia causing a mechanical lameness. The femur now rests in a more neutral position, with the tibial axis acting through the centre of the head of the femur. The net result is that when the dog stands on its knee the femur and tibia does not displace relative to each other and the dog is able to bear weight on the leg. Because tibial thrust has been abolished the injured ligament does not need repairing. Any strain on a torn ligament is removed.

The surgical technique is technically complicated requiring the tibial plateau to be isolated from the rest of the tibia by a circular cut with a special saw and blade. The plateau is then rotated to the correct position to reduce the slope. This is determined from measurements taken from the dog’s radiographs. This is why we have to make sure that we get good straight radiographs of the affected knee to make the measurements from before we embark on the operation. We canot see the damaged ligament on x-ray but we can do the measurements and also assess how much pre existing arthritis there is. The isolated part of the tibia is then fixed in position with a bone specially designed plate and screws.

Once the tibial plateau is ‘leveled’ the force in the knee acts directly down the tibia towards the tarsal (ankle) joint. When the dog bears weight the knee is no longer unstable and the joint feels comfortable. As well as superseding ligament replacement operations, it is an ideal technique for dogs with a torn/sprained ligament as it takes the strain off the injured ligament. Previously these dogs either had to wait for the ligament to rupture, which it usually did, or have the ligament chopped out and replaced.

Post-operatively, the dog becomes comfortable and sound very quickly but MUST be restrained until the cut through the bone has healed. Although this can take three months an x-ray examination is carried out at 6 weeks post-operatively to check that healing is progressing normally. Once healing is seen to be occurring the dog can have more exercise, on a flexi lead and the amount slowly increased.

After three months the dog should be able to exercise normally. Progressive arthritic changes are limited by this technique, unlike previous techniques where progressive arthritis was a problem for many dogs, especially the large ones.

Post-op Exercise Instructions

Tibial plateau leveling is a very successful method of treating cruciate injuries. However it a major operation and the post- operative care is as important as the surgery if we are to have a good result.

For the first two weeks, exercise must be very carefully limited. The surgery has basically created a (controlled) fracture that has to be allowed to heal. The isolated and rotated piece of bone is usually stable and will heal well but too much exercise too soon will compromise this.  However, too much early exercise, which includes allowing the dog to stand upright on its hind legs to peer over walls, out of windows etc., risks preventing the bone from healing or even damaging the plate and screws. The movement will rock the tibial plateau that is held by the plate. This will have several potentially catastrophic results. The bone may not heal and the screws may loosen allowing to tibial plateau to move causing the carefully measured slope to change. This causes the lameness to return as the joint becomes unstable again. The result will be further major surgery. In more minor cases, too much strain on the leg will cause a sprain of the patellar ligament or even a fracture of the tibial crest. This will heal in time without more surgery but will increase the time it takes for the dog to recover. A 30-60kg dog, as many of them are, can really test the metalwork!

The dog can be allowed into the garden on its own and with no temptations such as cats or squirrels present. If the dog cannot be trusted to be sensible it can only go into the garden on the lead under supervision. The rest of the time it must be supervised and if it has to be left it needs to go into a cage or crate or kennel in were it cannot jump up. It may not be loose in the house especially with another dog present.

Dogs that are going to boarding kennels during this time need to be in a kennel or crate which makes them stay on all fours rather than being able to stand up on their back legs with their front legs off the ground as this puts a lot of the dogs weight onto its bad leg.

After two weeks the dog can have a little more exercise, mainly for some mental stimulation.  100 yards twice daily, on a short lead, will be sufficient. A check up with us or at your own vet is advised at this time. Over the next three weeks this can be built up to 400 yards on a short lead twice daily. At home the dog still needs to rest and be restrained, especially when left on its own. It still needs to be prevented from standing up on its hind legs. Food may need restricting to avoid weight gain which needs to be avoided when recovering from orthopaedic surgery.

At 6 weeks after the surgery we usually see your dog here and take an x-ray to determine how the bone is healing. If this is progressing well we start to increase the exercise, usually by using a flexi-lead. The dog needs to walk on a level surface such as pavement or playing field. The first half of the walk should be on a short lead and once the excitement has worn off, the dog can be allowed to potter about on a longer lead.

By 3 months post op the dog can be exercising for periods of 20 minutes off the lead, but again needs the excitement ‘walking off’ on a lead before being allowed to run around.

In most cases the dogs are no longer lame and return to a normal active life. If the knee has a lot of arthritic changes then the dog may have some lameness. If this is the case it will have been discussed with you by the vet long term anti-inflammatory medication may be needed. Ideally the surgery has been done early enough to avoid this squeal.

It must be remember in all dogs with cruciate injury in one leg that there is likely to be some weakness in the other knee and that the other cruciate ligament is at risk of injury. This increases if the lameness is putting more strain on the sound leg. It is not uncommon for the second cruciate to become injured whilst the dog is recovering from the first and exercise restriction may also reduce this risk