Patellar luxation

What is patellar luxation?

The patella (knee-cap) normally slides up & down within a groove on the femur (thigh bone), called the trochlear groove, as the knee moves. Patellar luxation is a condition where the patella slips out of this groove to the side. Luxation is usually medial (towards the inside of the joint) but can occasionally be lateral (towards the outside of the joint). There are four different grades of patellar luxation:

• Grade 1: The patella sits in the groove. It can be pushed out of the groove, but slips straight back in.
• Grade 2: The patella sits in the groove. It can easily be pushed in and out of the groove.
• Grade 3: The patella sits outside the groove, but can be pushed back in.
• Grade 4: The patella sits permanently outside the groove.

Patellar luxation is most commonly inherited, and is very common in toy and miniature breeds. Dogs with significant patellar luxation should therefore not be bred. About 50% of cases are bilateral (in both legs). Patellar luxation can also be secondary to trauma.

What are the signs of patellar luxation?

The signs of patellar luxation vary depending on the grade of the condition. Often dogs with mild patellar luxation will occasionally 'skip', carrying the knee bent for a few steps then returning to normal. They may kick backwards a few times in an effort to return the patella to its normal position. Dogs with more severe patellar luxation may be quite lame on the affected leg or legs. Usually signs become evident from a young age, but some dogs appear normal until later in life when arthritis or cruciate ligament disease arises secondary to chronic patellar luxation.

How is patellar luxation diagnosed?

Patellar luxation is diagnosed based on clinical examination. We will feel to see whether the patella sits in the groove, then apply gentle pressure to see whether the patella can be manipulated in and out of the groove. This tells us whether patellar luxation is present, but does not tell us whether this is the cause of any clinical signs you are seeing in your dog.

How is patellar luxation treated?

If we find patellar luxation on a routine examination but the condition is not causing problems, we may not recommend any treatment. On the other hand, if your dog is lame because of patellar luxation then surgical correction is the best option. The earlier we perform the surgery, the more we can minimise the risk of any secondary problems such as arthritis.

Patellar luxation surgery is usually a day procedure. Depending on the grade of patellar luxation, we may perform any combination of the following to stop the patella from luxating medially (towards the inside of the joint):

• Lateral imbrication / medial desmotomy – tightening the tissues on the lateral side of the joint and loosening the tissues on the medial side of the joint
• Patellar sling – using strong suture material to permanently pull the patella laterally
• Trochlear groove wedge osteotomy – deepening the trochlear groove
• Tibial Crest Transposition – moving the tibial crest, which is where the tendon of the patella inserts, laterally

Complete recovery generally takes 4–12 weeks, during which time we will recommend gentle physiotherapy involving bending and straightening of the leg and short, slow leash walks. After the surgical wound has healed, swimming is excellent exercise for the leg, as it is is low-impact and forces patients to use their legs. Overweight pets should start a weight loss program (see Obesity Information Sheet).