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Have you noticed your small breed dog running with a skipping or hopping step? Or running on three legs, holding one back leg up? This could be a sign of a subluxating patella.
The patella or kneecap should sit in a groove in the bone (the trochlea groove) in the centre of the knee joint. It is held in place by the patellar ligament, and when the knee bends it slides along this groove. Subluxation or dislocation occurs when the kneecap pops out of this groove.
A subluxating patella can occur from an injury, but most cases are related to genetics. Many small breeds such as Poodles, Yorkshire Terriers, Chihuahuas and Maltese terriers are commonly found to have subluxating patellas. The patella most commonly dislocates to the middle of the knee (medial subluxation). This occurs because of the conformation of the back legs – the trochlea groove is too shallow, and/or the leg is slightly bowed. Male and female dogs are equally affected, and approximately 50% of dogs have both knees involved
Dogs with the condition are graded on a scale of 1 to 4:
Grade 1: Often the dog shows no signs, though the vet can feel the kneecap is not stable
Grade 2: The dog will show intermittent hind leg lameness, often skipping or hopping on the back legs, and sometimes stretching the leg out to pop the kneecap back in place
Grade 3: The kneecap is dislocated most of the time. The dog will be frequently lame, though weight bearing may still be possible
Grade 4: The patella is permanently dislocated, with the affected limb carried, creating a bowlegged/crouched stance
Signs of subluxation may appear in young puppies, or may go undetected until later in life. Patella subluxation is not considered a painful condition, but dogs with more severe grades can develop arthritis as they age, and this is very painful.
Corrective surgery is advisable for dogs with severe signs, and involves deepening the patellar groove to stop the kneecap from popping out as easily. Sometimes in severe cases other bone correction may be necessary.
If your pet has been diagnosed with a subluxating patella, your vet will monitor the condition and advise on the best action.