Sub-Luxating Patella (Loose Kneecap)

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Also known as slipping kneecaps, patella luxation is the kneecap slipping out of position. This leads to pain in some cases (but not all), but far more importantly, increases the chances significantly of suffering progressive arthritis and torn cruciate ligaments in the future. Early surgical correction is typically advised if this condition exists, however it is evaluated on a case by case basis.

Generally speaking, specialists feel that correcting all cases of patella luxation is warranted however we don’t quite agree with this. Luxation comes in four degrees of severity which we will elaborate on later. Although every individual case needs to be assessed on it’s merits, we generally recommend the following:Dog

  • Grade 1 or Grade 2: Cases that are not showing clinical signs, should be monitored rather than repaired.
  • Grade 2: Cases showing clinical signs, and all Grade 3 and 4 cases should be repaired.

Keep in mind that often Grade 2 cases will show clinical signs, but once they become Grade 3, they may no longer show signs, yet are more important to be repaired. More on that later…


The Four Grades:

Grade 1: These kneecaps can be manually pushed out of position but return to the normal position by themselves.

Grade 2:  These kneecaps sit in the normal position most of the time, but when they move out, may stay out for some time before returning.

Grade 3: These kneecaps permanently sit in the incorrect position, out of the groove. They can be moved back into the normal position but often return to the incorrect position.

Grade 4: These kneecaps are permanently in the wrong position and are difficult to get back into the correct position.


Here are some considerations when surgery is advised:

  • Generally speaking, the surgical procedure carries an excellent chance of a good long term result. However, about 5% of cases may not be successful.
  • The younger the dog the better the outcome. And the lower the grade, the better the outcome.
  • The longer you leave a surgery when recommended, the greater the chance that it either does not work, or does not work as well as it may have. A good way to think of it is – Every year surgery is delayed, there is probably about a 5% increased chance that it does not give a great result. Hence if you leave it 5 years, there may now be a 25% chance of a poor result rather than a 5% chance!
  • If your pet needs both sides done at the same time, not only is it cheaper than two separate operations, in our experience these patients recover better and faster than those that have them “staged” or done 3-6 months apart.


You may click here to view one of our advanced surgeons teaching associate veterinarians at SAH patella surgery for dogs who have slipping knee caps.

Surgical correction of sub-luxating patellas involves deepening the grove that the kneecap sits in (the femoral trochlea groove), and relocating the bone that the patella attaches to (tibial crest transposition).

Trochlea groove deepening: A wedge of bone is sawn out of the trochlea groove, re-modelled and inserted back into the groove. This allows for a deeper groove that the kneecap is less likely to slip out of, but also preserves the cartilage surface of the joint, minimising arthritis risk in the future.

Tibial crest transposition: The tibial crest is the bony prominence at the top of the tibia onto which the patella ligament attaches. The main genetic concern with sub-luxating patellas is that this crest is incorrectly positioned too far to the inside of the joint. Hence we use a bone saw to remove this from the incorrect position and replace it to the more correct front on position.

These two procedures above re align the patella to the normal position, reducing rotational forces that results in not only the luxating patella, but a much higher chance of ruptured cruciates in the future.



The recovery period is 6-12 weeks (less for two knees done at the same time).

Initially we first see you three days after surgery to remove the fentanyl patch (a morphine type transdermal pain killer that makes our patella patients feel very happy after surgery), and give the first of four Cartrophen (Pentosan) injections that help to prevent arthritis. These injections are given weekly for the first four weeks during which time we assess progress, and guide you through building up your pets exercise.

After this four week period, we see you three weekly for two more visits, by which time your pet will just about be fully healed. At Southern Animal Health, all re visits and medications are covered in the initial cost.