There are several diseases that can affect the stifle (knee): 1) partial to full tears of the cranial cruciate ligament (rarely the caudal ligament) 2) arthritis from age 3) bone cancer above or below the actual joint and 4) patella luxation (knee cap).
Patella luxation is when the knee cap moves out the femur groove it normally slides up and down in and moves usually to the inside (medial) of the groove. This results in an inability for the leg to support weight due to the quadriceps muscle group attached from the hip to the patella to pull against no bone support. The classic sign is an animal holding its leg up and initially acting in pain. This pain results from the sudden tear from the usual location to the inside of the groove. A dog can also have a congenital (birth) defect that allows the patella to easily slip out of the groove, like a shallow groove or groove ridge that is shorter than normal. After the initial tear or congenital defect, usually the animal is not usually painful but the physics prevent the use of the leg until the patella gets back into its groove. In mild cases you can do yourself or the dog may learn to stretch its leg straight to slip it into the groove again. The severity of the luxation is measured on a 1-4 grade scale with 4 being the worse. This scale determines the likelihood that surgery is going to be needed.
A grade 1-2 is a mild luxation that usually rest or simply being aware of want is happening is all that is needed. It usually means the patella is in its groove most of the time with grade 1 requiring us to push it the inside to slip out of the groove to discover it and grade 2 occasionally slips on its own. A grade 3 is mostly out of the groove and this along with a grade 4 (always out of the groove) will require surgery to correct.
The surgical correction will depend on the grade and how long the condition has been going on. These may include 1) a simple imbrication (tightening of the outside joint capsule), 2) screwing a “ridge stop” device to inside of the groove to raise the height to prevent slippage, 3) deeping the groove (trochleoplasty) for the patella sit in a less shallow groove and 4) cutting the attachment point on the tibia and moving it more lateral (outside) of its original location (tibial tuberosity transportation). Grade 4 luxations are the most difficult and therefore may require a board certified surgeon to perform since often these are long time congenital defects with additional defects/disease.
It is important to note that even low grade luxations may require surgery if the instances are occurring frequent enough and the condition is more common in small breed dogs where there is shorter leg muscles/bones and less muscle usage (“purse”) dogs.
Courtesy – Dr. Sanjay Jain
Apple Valley Veterinary Clinic