WHAT THE PATELLA IS AND WHAT IT DOES

 The canine patella is equivalent to the human knee cap. It is a bony structure that sits in a groove in the femur (thigh bone) on the front of the stifle (knee joint).

 Attached to the patella are the quadriceps tendon and the patellar tendon. The quadriceps tendon runs from the patella up to the muscle mass on the front of the thigh and to a lesser extent down over the patella to the patella tendon. The patella tendon runs from the patella down to a protuberance on the front of the tibia.

 When the muscles contract, they pull the quadriceps tendon up which pulls the patella up, which, in turn pulls on the tibia via the patella tendon. The result of all this pulling is to straighten or extend the leg.

 As the leg is extended and flexed, the patella rides up and down in the trochlear groove. Ideally, the groove should be deep enough for the patella to fit snugly into it. If the tendons, muscles and bones are all aligned properly, the result is a stable, sound stifle joint. Improper alignment means instability and this not only leads to degenerative joint disease, but also places increased stress on other ligaments and supporting structures.

 Many dogs show no outward signs of this problem until they are about five our six years old when arthritis sets in. By then, who would think about stifle problems being the cause? Other show outward signs as early as eight weeks old by holding up one hind leg and skipping a step or two, holding one leg up as if injured, or by moving with the hind legs crouched under the body just slightly.

 Loose patellas can come about in several different ways. One day, suddenly, a puppy or adult is found to be carrying one of his hind legs. Later in the day, he is again on all fours. Upon examination, it is found that the puppy is affected with patella luxation and that the channel on the thigh bone of the dog in which the patella runs, is unusually shallow. The kneecap in inclined to slide out of position if the dog twists it's body around or suddenly turns on that particular leg.

 When there is little angulation between the long bones of the hind leg, when the dog is said to have little rear angulation, when the dog is straight in stifle, the band of muscle (patellar tendon) in which the patella is seated, is under reduced tension and can lead to the patella sliding out of its groove on the femur. We then have another form of the same trouble - luxation. This does not mean that all dogs who have little angulation automatically have loose patellas. Nor does it mean that a well angulated dog cannot have the problem. There are variables in this as well as other things. Dogs can have this defect in different degrees from a slight looseness to actual displacement of the patella. It can show up at any time; however, too often not until the dog is older and by then severe degenerative changes can already occured that cannot be corrected by surgery. Arthritic changes set in and the dog must be put down or live in pain for the rest of its life.

 Patellas can be checked for looseness as early as 4 to 5 weeks of age. Sometimes, even earlier. Loose patellas DO NOT tighten with age. Your vet can show you how to check, or have him check your puppies. Granted those patellas are tiny at 5 weeks and those fingers checking them are large, but it can and should be done.

Do not feel too secure in an early diagnosis of normal patellas. As the dog matures and gains weight, the stress put on the patellar tendon and shallow grooves may result in loosening patellas at a later age, especially on a stud dog. Patellas should always be rechecked before a dog is bred.

 In spotting an unangulated leg, it is helpful to note the narrow thigh and often a long hock. The dog that stands or moves somewhat bowlegged is suspect. Since unangulated rear legs can sometimes be hidden by coat or disguised by a clever handler, it is useful to watch toplines when the dog moves. Often dogs with knee problems do not seem to be able to extend the back legs out behind them or bend at the knee and hock easily when moving. These dogs seem to move as if a pencil was attached at the hip rather than a jointed, flexible leg. As a result, the dog is often higher in rear than at the shoulders when in motion.