By Tamara Sevigny
He runs across the lawn chasing a toy when in mid-stride yelps in pain and pulls up one of his hind legs and continues limping, using only 3 legs. A few minutes later he puts his leg back down and uses it normally. This occurs about once a week and doesn’t seem to bother him that much. He cries in pain only for a second followed by a few minutes of lameness, but then he’s fine.
Affecting small and toy breeds the luxating patella, or as some call it, a “trick knee,” may be much more severe. They may hold their leg up for several days and be severely uncomfortable. Some may have it in both hind legs causing a change in posture, dropping their hindquarters, and walking with their hind legs further out from their body. Those most severely affected may not even use their hind legs, balancing their weight on their front legs as they walk, holding their hindquarters off the ground.
“I had 2 dogs with it,” says Breeder Ruth Cunningham of YankeeBelle Chihuahuas, Sidney, ME. “One had surgery on both [legs]. One I carried around most of the time.”
“It doesn’t always show up right away. Some dogs are 5 years old before it is evident,” says Ruth. Usually, the first sign occurs when the dog is running, stops, and cries in pain as his rear leg is extended or bent and he is unable to flex it back for a few minutes.
“Some say it is genetic and some say it “might” be genetic,” Ruth adds. Dogs with this condition should not be bred due to the risk of passing it onto their offspring and the extra weight pregnancy puts on the legs. “I would not breed a dog that has it,” says Ruth. “I had both of mine spayed. They were my first 2 chi’s (Chihuahuas) and I did not know what to look for in a dog back then.”
“If you put your finger on the kneecap and bend the leg you can feel the stability or lack of stability,” offers Ruth. If you are looking to get a puppy and are not sure what to look for a veterinarian can check a pup for the strength of the hind legs.
In normal knees, the patella (knee cap) glides up and down in a groove at the end of the femur when the knee joint is bent back and forth. The patella guides the action of the quadriceps muscle in the lower leg and protects the knee joint.
In some dogs the ridges that form the patellar groove are not prominent, making the groove too shallow, allowing the patella to luxate (jump out of the groove) sideways, usually towards the inside, causing the leg to lock up. When the patella luxates it cannot return to its normal position until the quadriceps muscle relaxes.
While the muscles are contracted and the patella is luxated, the joint is held in the flexed or bent position. The dog usually only feels pain while the kneecap slides across the bony ridges of the femur. Once out of place, the dog feels no pain.
Patella luxation is graded from 1 to 4 (See sidebar) based on the ease with which the patella luxates, with grade 1 being the mildest and grade 4 being the most severe. With grades 1 and 2, the dog may not even show any symptoms, while with grades 3 and 4 the dogs are usually lame.
If the condition is left uncorrected after grade 2 the patellar ridges wear down further, making the groove shallower, causing the dog to become progressively lamer. Arthritis will prematurely affect the joint causing a swollen knee and limited mobility. This is why a good evaluation needs to be done by a veterinarian early in the condition to prevent long-term arthritis and joint changes.
Surgery is the only solution for a luxating patella, although therapy is sometimes helpful in grade 1 cases. The surgery cost ranges based on each case but is usually around $1000-$1500 per leg.
There are 3 different ways a veterinarian will approach the surgery. The first will deepen the groove at the base of the femur to better contain the patella. The kneecap can also be tied down on the outside of the patellar groove to keep it from jumping to the inside. In addition, the bony protuberance at the site of the attachment of the quadriceps tendon on the tibia can be cut off and re-attached in a more lateral position. All of these procedures work well and are a permanent fix to the condition. The type of surgery performed depends on the individual case.
Recovery takes up to a month and a half after surgery. The dog is usually back to using its leg in a normal fashion within 30 days, but does need some extra TLC during this time and also requires some leg exercises during the recovery. Discussing options for a trick knee with your veterinarian is important to keep the condition from progressing and in some cases, therapy and a little care can keep your dog from needing surgery.
Occasional carrying of the leg is seen, often described as skipping or hopping, with the leg returning to normal by itself.
The frequency of luxation increases, more likely becoming a permanent condition. When palpated by the veterinarian, a dry, crackling sensation (crepitation) may occur in the joint. If not surgically treated at this point it can develop into degenerative joint changes.
The permanent dislocation that occurs through weight-bearing is possible. The dog’s stance will appear somewhat crouching or bowlegged. Surgical intervention should not be delayed.
Permanent luxation, with the affected limb, always being carried, creates a bowlegged/crouching stance. Surgery is strongly recommended as soon as possible at this stage as bone deformities of the femur and tibia can occur.