Someone asked in a comment on my last post if Border Collies get hip dysplasia when they get older. I decided to write a post about this since the answer is not, shall we say, black and white (yes-pun intended).
First of all hip dysplasia is not something your dog gets, it's something your dog has. A perfectly sound young dog can be dysplastic. The term hip dysplasia simply refers to abnormal conformation of the hip joint, not necessarily the clinical signs of the disease. Generally speaking dogs are born with dysplastic joints-largely due to the breeding of poor genetic specimens (i.e. the parents had bad hips) and in some part due to bad luck. A normal hip joint fits like a ball and socket-the head of the femur should fit deep and smooth into the hip socket. In a dysplastic dog the socket is shallow and the head of the femur not perfectly round. There are varying degrees of severity but the outcome is an unstable joint-basically the hip is permanently partly out of joint.
Over time, the normal wear and tear on the joint causes secondary arthritic changes and increased discomfort associated with the joint. These changes can include thickening of the joint capsule, bony remodeling, and decreased range of motion.
An important point to note is that the clinical signs don't always correspond to the radiographic signs. In other words a dog with radiographically severe dysplasia might not limp much but a dog with mild dysplasia might limp a lot or start limping at a younger age. This is not always true but don't be fooled into thinking your dog is normal just because you have never seen it limp.
It's also important to recognize that arthritis doesn't just occur in conformationally abnormal joints. Arthritis or degenerative joint disease generally results from normal forces on abnormal joints or abnormal forces on normal joints. So a dog with all the genetic clearances in the world may ultimately develop painful degenerative disease when we subject them unnatural forces-this may be agility, frisbee or even the overweight lab who mostly sits around the house!
Hip dysplasia is more common in medium and large breed dogs just as luxating patellas are more common in small breed dogs. However it can occur in any size, breed, or mix and even in cats. Smaller dogs are less likely to show clinical signs because they don't carry as much weight around and in many cases are also not working dogs.
This is just a brief overview of hip dysplasia but hopefully it clears up some of the common misunderstandings. Maybe one of these days I'll write about treatment options too.