The patella (kneecap) is a small bone at the front of the stifle (knee) joint, positioned between the quadriceps (thigh muscle) and a tendon that attaches it to the tibia (shinbone). This is called the “quadriceps mechanism”. As the stifle flexes and extends, the patella glides up and down in a groove at the end of the femur (thigh bone). Occasionally, the patella slips out of the groove, this is called patellar luxation (or dislocation). The luxation usually occurs towards the inside (medial aspect) of the stifle, however, it can also luxate towards the outside (lateral aspect) or to both sides of the stifle. Patellar luxation can affect dogs and cats.

What causes patellar luxation?

If the quadriceps mechanism is not properly aligned with the groove, the patella will luxate. The cause of abnormal alignment can be complex, involving deformities of the femur and tibia. Patellar luxation is common in certain breeds which suggest that the condition may be genetic. It is commonly classified as a developmental problem with symptoms developing within the first year of age. Dislocation of the kneecap due to trauma is less common.

What are the signs of patellar luxation?

The signs can vary depending on severity of luxation (graded 1-4) and if one or both back legs are affected. The most common sign is skipping or hopping for a few steps. Dogs may also limp, hyperextend the hind limbs, swing the legs out to the side, or have a very crouched gait. If both legs are affected your pet may have trouble standing up.

Why has surgery been recommended for your dog?

Surgical correction of patellar luxation is recommended because each time the patella luxates, the cartilage on the back of the patella and on the femur wears away until there is bone rubbing on bone. Once this occurs the condition becomes quite painful and osteoarthritis is present. Early intervention is usually advised to prevent cartilage wear and to restore normal function of the quadriceps mechanism. Some dogs benefit from pain relief, weight loss and physiotherapy pre and post-operatively.

First the diagnosis of patellar luxation must be confirmed. Watching how your pet walks and palpation of the stifles to check for movement of the patella is the first step. Radiographs are obtained to check for deformities and to allow surgical planning rather than to confirm the diagnosis. This is because the patella can be mobile and is often in normal position when the radiographs are taken. In severe cases a CT scan may be required to assist with surgical planning.

Surgery usually involves a combination of the following depending on severity of the luxation.

Groove deepening surgery: A piece of bone and cartilage is removed from the groove, this area is deepened, then the piece of bone and cartilage is replaced. This makes the groove deeper while preserving its smooth cartilage surface. This procedure is called a trochleoplasty.

Soft tissue tightening and releasing procedures: the soft tissues can thicken and contract on the side that the patella is luxating to and stretch on the other side. For this reason, the soft tissues on the luxation side may need to be released (an incision called a desmotomy) and tightened (called an imbrication) on the other side.

Quadriceps realignment surgery: The aim of this surgery is to move a piece of bone at the top of the shinbone (the tibial tuberosity) that is attached to the patella, and reposition it so that the patella is correctly aligned with the groove in the femur. The piece of bone is most often reattached with two small pins +/- a wire. This procedure is called a tibial tuberosity transposition.

Some pets will have patellar luxation and tearing of the cranial cruciate ligament at the same time. In these cases, the procedures listed above can be combined with a TTO or extracapsular repair to correct both conditions simultaneously.

Patellar luxation repair is generally very successful with the vast majority of cases improving significantly, often within 6 to 8 weeks of surgery. Osteoarthritis in the joint may progress and cause lameness in the future.

What can go wrong?

Whilst the vast majority of procedures result in success, there are a number of potential complications that can occur. Every step possible is taken along the way to minimise the risk of complications and therefore maximise the chances of a good outcome.

Potential complications include:

• Excessive activity (running, jumping, stairs, playing with other animals) in the early stages after the operation can lead to failure of the repair and/or implants and even fractures. This risk is especially present in the first six weeks after surgery.

• Orthopaedic surgeries have a higher risk of postoperative infection than shorter, simpler surgeries. We take every precaution to minimise this risk at the time of surgery.

• The most common ‘reported’ complication is reluxation of the patella, however this is rare in the hands of an experienced surgeon (ie a Specialist). This can be resolved with a revision surgery if necessary.

Once a dog/cat is confirmed as a surgical candidate, a date for surgery will be arranged. Patellar luxation repair is an elective procedure, this means that it is not urgent but it should be performed prior to cartilage wear and development of osteoarthritis. Your vet can help you decide on the timing of surgery.

Most dogs are able to go home on the same day of surgery. We supply pain relieving drugs +/- antibiotics. Crate/pen confinement is essential in the first six weeks with short lead walks for toileting purposes. Most dogs start to use the leg within a week of surgery and improve steadily thereafter. Physical therapy (see below) is beneficial and can be started before surgery or within the first week after surgery. Your vet will usually check your dog a few times in the two weeks following surgery. At week six, your vet will re-examine your dog and may take a follow up radiographs to assess healing particularly if implants were applied. If all is going well at this stage, short lead walks with a gradual increase in activity back to normal activity will be advised.

What you need to do BEFORE the day of surgery:

• Read the Post Surgery Care Instructions for Patellar Luxation (link below).

• Have at least one area to confine your dog organised at home (eg a crate in your bedroom, tethered to a desk in your office and/or a pen in the lounge). You may need to purchase a crate, pen and/or gates and non-slip matting and get your dog used to this new arrangement.

• Arrange a skin check, and if necessary a pre-anaesthetic blood test, 7-10 days before surgery. If your dog has any skin lesions, a medicated body wash and antibiotics may be prescribed. If skin lesions are found on the day of surgery, this may result in the procedure being rescheduled to a later date due to the risk of infection.

• Wash your dog the weekend or day before surgery. This will reduce the time spent under anaesthesia cleaning your dog on the day of surgery.

• Consider “enrichment” for your dog in the postoperative recovery period (eg stuffed toys, sniffing games, food dispensing toys, chewing and licking time etc).

• Arrange pre and post operative physical therapy appointments before the day of surgery as there may be a wait for an initial appointment (see physical therapy contacts below).

View, download or print these post surgery care instructions for Patella Luxation Repair surgery.

Physio and Rehab contacts list