The Slip Felt Around the Yard
by Dr. Jain
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
4) patella luxation (kneecap).
Patella luxation is when the kneecap moves out the femur groove it normally slides up and down in and moves 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 pulling with no bone support. The classic sign is an animal holding its leg up in pain. A dog can also have a congenital (birth) defect that allows the patella to easily slip out of the groove. After the initial tear, usually the animal is not in pain, but can’t use the leg. In mild cases, you can readjust it yourself or the dog may learn to stretch its leg straight to slip it into the groove again. The severity is measured on a 1 to 4 grade scale with 4 being the worst. This determines the likelihood that surgery is going to be needed.
A grade 1 or 2 is a mild luxation and requires rest or simply being aware of what is happening. It usually means the patella is in its groove most of the time with grade 1 requiring us to push it to the inside 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), 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.
It is important to note that even low grade luxations may require surgery if the instances are occurring frequently enough and the condition is more common in small breed dogs where there is shorter leg muscles and bones and less muscle usage.