This is an excellent overall perspective from Dr Mike:

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. They have
more frequent "skipping" episodes, may not want to jump up onto things, they
may have pain and the patella doesn't always return to normal positioning
when it is deliberately pushed out of its groove during a physical
examination.

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. That is just my best guess on
the interpretation, though. It is better to ask the vet who made it.

I think that most dogs generally get worse over time and move from
Grade 1 to Grade 2 or from Grade 2 to 3, for example. The changes may not
happen until later in life, though. A lot of dogs with Grade 1 or Grade 2
patella luxation early in life will have pretty stiff knee joints when they are
14 or 15 years old that probably are at least partially this way due to
arthritis from the years of luxating patellae. There is a lot of other
wear and tear in a long life so this is only a partial contributor but I
know that some surgeons really feel that when the whole lifetime is looked
at early surgery looks better. On the other hand, there are dogs who have
bad outcomes from the surgery, too. I lean towards leaving knees alone
until the Grade 3 stage, personally.

Mike Richards, DVM
8/18/2001
Link to this Dr Mike article and further patella questions are here: http://www.vetinfo.com/dpatella.html

This article is a detailed explanation of what luxating patellas are, why they occur, the clinical signs, and how they are treated:

http://www.dogsites.com.au/internet_..._luxation.html

Further background and treatment information on this condition, which is a known breed issue for CKCS:

http://www.veterinarypartner.com/Con...EVetID=3001459

http://www.peteducation.com/article....&articleid=457