Tibial Plateau Levelling Osteotomy Surgery (TPLO)

Last Updated September 2021

Cranial cruciate ligament injury

Damage to the cranial cruciate ligament is one of the most common orthopaedic conditions seen in dogs. There are two cruciate ligaments in the dog – the cranial and caudal cruciate ligaments, which cross over each other inside the knee (stifle) joint. These are the same structures as the anterior and posterior cruciate ligaments in the human knee, and while there are some anatomical differences, damage to the cranial cruciate ligament is essentially the same as damage to the anterior cruciate ligament (ACL) in humans. The cruciate ligaments are very important in stabilising the knee joint during weight bearing. A tear in the cranial cruciate ligament can happen suddenly due to excessive force during running and play, but quite often is the result of longer-term degenerative changes that cause progressive weakening and partial tears in the ligament until it eventually tears fully. A dog that has a cruciate ligament tear in one knee will often go on to tear the cruciate ligament in the other knee in the future. This will happen in up to 50% of cases. In some dogs, both knees may be affected at the same time.

Clinical Signs

Any breed of dog can be affected, from small dogs to giant breeds. A partial tear of the ligament can cause mild intermittent lameness (pain and difficulty walking) and swelling (effusion) in the knee joint. Affected dogs can have trouble sitting and will often hold the affected leg out to the side while sitting down. A completely torn ligament will usually cause severe lameness, and affected dogs will often bear little or no weight on the affected leg. In some cases the meniscus (cartilage pad) in the knee is torn due to abnormal forces on the cartilage in the unstable knee joint. This can result in a clicking noise that can sometimes be heard during walking.

Diagnosis

With a fully torn cranial cruciate ligament, the knee joint will be unstable during walking and the tibia (shin bone) will slip forwards relative to the femur (thigh bone) during weight bearing. This is called tibial thrust. This can sometimes be felt during examination of the dog’s knee. We test for positive tibial thrust and cranial drawer movement of the stifle, and if present this will confirm a torn ligament. Sometimes sedation or general anaesthesia is needed to be able to feel this. With partial ligament tears, the joint is still mostly stable but there will be effusion (swelling) in the joint and pain on manipulation of the joint. Radiographs are often needed to look for subtle signs of effusion and degenerative changes in the joint to help confirm a diagnosis.

Options for repair

There are multiple surgical options for repair of a cranial cruciate ligament tear or rupture. The gold standard option is now considered to be a Tibial Plateau Levelling Osteotomy (TPLO). Multiple studies have shown that a TPLO gives the best long-term outcome for return to function and the least degenerative changes in the joint. TPLOs can be done in both small and large breeds of dog. If your dog has had a different procedure done already on one leg, it can still have a TPLO done on the second leg. If a partial cruciate tear is diagnosed, early surgical intervention can be very beneficial before it progresses to a full tear. Outcomes can be much better in the long term as there will be less degenerative change (i.e. osteoarthritis) in the joint at the time of surgery, and there is less chance of damage to the meniscal cartilage. One major advantage of the TPLO is that a partially torn ligament can be left intact and can have some remaining function or even have some healing after surgery. Other types of surgical repairs generally involve cutting any remaining ligament fibres in order to perform the surgery. Another advantage is that post-operative meniscal tears are much less frequent following a TPLO compared to other procedures such as the TTA (Tibial Tuberosity Advancement). It will occur in around 5% of patients following a TPLO, compared to around 20% with a TTA. This means that where the meniscal cartilage is found to be intact (i.e. not damaged) at the time of surgery, it is usually left in place to continue performing its shock absorption role in the joint, and repeat surgeries to deal with a meniscal tear are much less commonly needed.

TPLO Procedure

Surgery involves first opening the stifle joint to inspect the torn ligament and the meniscal cartilages. Any torn parts of the meniscal cartilage will be removed. The TPLO procedure aims to stabilise the knee joint and eliminate tibial thrust. On average the slope of the normal tibia plateau is around 25 degrees. During surgery, the tibial plateau is “levelled” to 5 degrees to stop the sliding movement of the femur on the tibia (which occurs when the cruciate ligament is torn and damaged). This is achieved by cutting the top part of the tibia with a specially designed curved saw blade, and rotating it a precise amount that is calculated based on the preoperative X-rays. The bone is then fixed in the new position with a special bone plate and screws. The implants that are used are a special type known as a locking plate and screws, which is a much stronger system than previous types of plates. If both knees are affected, the worst affected leg will be done first, and the second leg can be done after healing is complete, generally around 3-4 months later.

Complications

Like any type of orthopaedic surgery, some complications can occur following the procedure. These can include swelling of the surgery site, infection, delayed healing of the bone, loosening or breakage of the implants, fracture of the tibial crest, and inflammation of the patellar tendon. In most cases, complications can be dealt with and patients will go on to have a good outcome. A second surgery can sometimes be necessary to deal with a complication, or remove implants once healing is complete. Post-operative damage to the meniscal cartilage is also possible, although as stated above it is fairly uncommon with this procedure. In some cases, it may be recommended to perform a meniscal “release” incision during surgery to prevent this from happening, although this is associated with an increase in degenerative changes in the joint. This can be discussed prior to surgery.

Aftercare and prognosis

Following surgery, your animal will be kept in hospital overnight. Most patients can be discharged the day after surgery. Pain relief medication will be provided to control post operative pain and inflammation, which will usually include a fentanyl patch which lasts for 3-5 days, plus one or two oral medications. In most cases oral antibiotics will also be given for a short period following surgery. To aid in healing and rapid return to function, post operative care will include:

• a series of six therapeutic laser sessions (two sessions per week for three weeks),

• a series of four injections of Synovan® to help with joint health and mobility, (one injection a week for four weeks),

• a treatment session with a rehab-focused veterinarian at our North Nowra practice. This is normally arranged for 1-2 weeks after surgery. Further rehab sessions can be organised if you wish to continue this.

Recovery after TPLO surgery is much the same as recovery after surgery for a broken bone. It will take at least 8-12 weeks for the bone to heal where it has been cut. In the immediate post operative period, you will need to confine your dog to a small area, ideally a crate or pen for the first two weeks, with only on-leash walking for toileting. Most dogs will be able to bear weight on the leg in the first few days, and function will improve gradually over the following weeks. Usually you can begin doing 5-minute leash walks from two weeks after the procedure, and increase exercise gradually over a period of 8 weeks. We will arrange to take post-operative radiographs around 8 weeks after surgery. These are often done under sedation, and are used to check that healing is progressing appropriately. Most dogs will be able to return to full off-leash exercise after around 12 weeks, and it is expected that most dogs will return to normal or near-normal function of the joint in the long term. Depending on how much damage and degeneration there was in the joint prior to surgery, there will likely be some ongoing care for osteoarthritis needed into the future. This will be much less than if surgery had not been performed.