As a vet working in Hong Kong, the most common types of dogs that come through our doors these days are small breed dogs or as we call them ‘toy breed dogs’: Pomeranians, Miniature Poodles, Chihuahuas, Pugs etc.
These breeds are predisposed to knee (stifle) diseases, namely patella luxation.
The structure of the hind leg of a dog is very similar to humans, in that we both have a femur, a tibia, a fibula, and a patella in the knee joint.
The patella is a small bone that sits in front of the femur and slides up and down when we are walking.
Normally, the patella slides up and down along the deviation of the femur (as shown in upper right photo). When we have a dog (or cat, although less common) with patella luxation, we are referring to a condition where the patella is outside the normal position within the deviation of the femur.
In normal dogs and cats, the patella is contacting the femur on the surface where there are cartilage on both surfaces, and hence is a smooth sliding moment and it does not hurt. Also because cartilage has a relatively smooth surface, they don’t create resistant and wear and tear is minimal.
On the other hand, in animals with patella luxation, their patella is sliding outside of the area of the cartilage (white area in lower right photo), therefore creating more friction and hence more wear and tear to the point of contact.
Most animals do not feel pain or discomfort when they are young, however, due to the wear and tear, there will be degeneration changes on the femur and the patella and eventually osteoarthritis when they are older, this cause discomfort and pain.
Since it is structural deformity, surgery is indicated for most cases. The aim of the surgery is to correct the position of the patella, so that it is back in the normal position. Although it is one of the most common orthopedic surgery done, like other surgeries, it carries some risk, mainly like many orthopedic surgeries, there is a period of confine exercise and recovery time is usually expected to be about 4 weeks. The other major concern with this surgery is that there is a 8-10% risk for recurrence.
Dogs and cats with patella luxation usually do very well after surgery and have a very happy active life. Most surgeons recommend surgery to be done early in life rather than later to prevent arthritis from forming. If you are unsure whether your dogs and cats have this condition or whether they are fit for surgery, you should consult your vet.
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