Patellar luxation is also commonly referred to as kneecap luxation, slipping patellas, slipped stifles or dislocation of the knee cap. Patella Luxation may be congenital (existing from birth) or acquired.
The patella normally moves up and down in a groove in the lower femur bone called the trochlear groove. The patella slides up and down in the groove as the leg bends and straightens. When the patella is in its normal position, its cartilage surface glides smoothly and painlessly along the cartilage surface of the trochlear groove with little or no discomfort. Patellar luxation is when the kneecap slips out of the groove. Sometimes, the groove is too shallow and thus prevents the patella from seating deep enough therefore predisposes it to dislocation. There may be other reasons as well. When there is a luxating patella, the kneecap luxates or pops out of place either in a medial position (to the inside of the knee) or lateral position (to the outside of the knee) position. This dislocation causes friction in the area, inhibits movement, can damage the joint tissues, and may cause discomfort, pain and lameness.
The congenital form of medial luxation (kneecap dislocated to the inside of the knee) is most common in toy breeds, not excluding Havanese, and is considered inherited although the exact mode of inheritance is not known. Laterally luxating patellas can be congenital but are generally the result of trauma. In Havanese, signs of congenital luxation may appear when a Havanese is quite young (less than 1 year of age) especially if the luxation is severe; lower grade luxations may appear later in life. Patellar luxation may affect one or both knees. Where both knees are affected, the degree of luxation in each may be different, where one may be affected more or less so than the other. To diagnose a patella problem your veterinarian will do a physical examination and palpation on your Havanese and it can be confirmed by x-rays.
Patellar certification is done by OFA (Orthopedic Foundation For Animails) and is also one of the tests required for a Havanese CHIC number. Testing may be done at any time, however only tests done after 12 months of age are elligible for certification. One reason to get the testing done prior to 12 months of age would be if a breeder wanted to be assured that their puppy had no apparent underlying patella problems. This can be especially important where performance events requiring jumping are planned for the future (such as agility) or if a puppy is being evaluated for potential for a show or breeding career. An early normal exam does not preclude the development of a future problem but it can identify an existing weakness. Havanese with a rating of 0 have normal patellas that do not luxate during the physical examination. OFA grading for luxation is from 1 to 4 with 1 being the most mild and 4 being the most serious. With grades of 3 or 4, your Havanese will generally show signs of lameness and surgical correction may be required. Luxation may be unilateral or bilateral. The OFA statistics as of May 2009 are 2278 dogs tested 2.9% affected and 97.1 % normal.
Should your Havanese have a luxating patella it may show signs of lameness or refuse to bear weight on his/her knee.This may happen only occasionally or frequenetly depending on the severity of the patella luxation and also the activity(ies) your Havanese is doing at the time. Your Havanese may cry out and try and staighten the leg to pop it back in or may hold up the leg until the muscle has relaxed which allows the kneecap to reposition itself.
If your Havanese shows signs of patellar luxation early in life, the major muscle groups of the thigh pull toward the inside of the leg, putting abnormal pressure on the knee joint cartilage. The result is a bowlegged stance and an abnormal pull on the patella. Over time your Havanese may develop other degenerative joint changes such as osteoarthritis. This may occur whether or not corrective surgery is undertaken.
Depending on the severity of the problem, your Havanese may require surgical correction. Surgical correction is based on the degree of luxation, the age of your Havanese and how frequently the knee luxates. Surgical correction consists of deepening the groove in which the patella sits to better contain the knee cap. The tibia may also require repositioning and generally the bone is cut and pins are used to secure position. The surgery site needs to be shaved to the skin but your Havanese does not need to be trimmed or shaved all over. The coat grows back faster than you think and will start blending in within a short time.
Following surgery, physical therapy may be recommended to facilitate use of the leg. There may be exercise limitations for 10-12 weeks after surgery, which can sometimes be a challenge with an active little breed like the Havanese. Should your Havanese require surgery on both patella's the veterinarian will generally wait approximately 6 weeks in-between surgeries, though occasionally surgery may be done on both knees at the same time. Post-surgery, most Havanese are able to return to all their previous activities.
Affected Havanese and any Havanese that has had corrective surgery should not be bred; and extreme caution should be used before considering breeding parents or littermates.
Penny Will (condensed version previously published in Dogs in Canada breedlines Fall 2009)