* The patella (commonly known as the kneecap) normally rides in a groove at the bottom of the femur at the level of the knee joint in a groove called the trochlear groove; Fig 1 and 2 show a front view of the knee joint; Fig 1 demonstrates the patella in the groove, where as Fig 2 demonstrates the knee cap dislocated out out of the groove (P=patella; F=femoropatellar ligaments which hold the patella in the groove; PL=patellar ligament; G=trochlear groove that the patella rides in). Fig 3 demonstrates a skyline view of the trochlear groove and the patella – you are looking down the thigh or femur bone toward the knee joint; take note of the deep groove that is found in a normal animal.
* Patellar luxation is caused by congenital abnormality usually at the level of the hip joint and results in abnormal forces on the kneecap, which cause it to eventually ride outside of the groove. The groove becomes very shallow and the attachment of the ligament of the patella may be malpositioned on the tibia bone. Luxating patellas are graded on a scale of 1 to 4 (some sources use 1 to 5).
Grade 1 are patella luxations that are found on physical exam by looking for them when the dog shows little to no clinical signs — the patella can be luxated manually but doesn’t do this much on its own.
Grade 2 luxations occur when there is occasional spontaneous lameness but the patella returns to normal positioning easily enough that the dog usually isn’t pained much by it. This is typically the dog that occasionally carries a rear leg for two or three steps on occasion but then puts it back down and goes as if nothing was wrong.
Grade 3 luxations is usually used to describe dogs who are beginning to have a loss of function due to the luxation of the patella. Grade 4 luxations are when the legs are painful enough that the dog tries not to use them, when the leg can not be fully straightened manually and the dog shows evidence of chronic pain or disability, including poor to no ability to jump.
Grade 5 (or severe grade 4 depending on the grading scheme) is when the dog won’t use the legs or when the gait is stiff legged due to the patella being underdeveloped or permanently dislocated and fixed in place outside its normal position.
Most veterinary orthopedic surgeons recommend repairing dogs in Grade 3+ without question and advocate fixing grade 2 dogs frequently. So a 2.5 grade is probably one in which the examining veterinarian is leaning towards thinking surgery is necessary. It is better to ask the vet who made it.
Read more: Patella Problems in Dogs
* Intermittent skipping gait
* Stiffness of the hind limb
* Some pets show only a single sign, whereas others show many signs of the condition
* Failure to treat the condition could lead progressive debilitating arthritis of the joint
* trochleoplastyIf the groove that the patella rides in is shallow or misshapen, it is surgically deepened; we usually use an advanced technique to perform this called the block osteotomy. The illustration right demonstrates elevation of the cartilage/bone plate. I now use a modified procedure in which the cartialge/bone plate is left attached to the soft tissues (periosteum) at the top of the groove, thus minimizing the risk that the cartilage/bone plate will become displaced in the joint.
* If the attachment of the patellar ligament to the tibia, called the tibial crest, is in the wrong position, it is repositioned. This is done by creating a cut in the tibial crest (see illustrations below) and reattaching the bone in a position so that the patella is realigned within the trochlear groove. Pins are used to fasten the bone in place; the pins usually do not need to be removed unless they migrate out of position or a bubble of fluid (seroma) develops over the end of the pin.