What you might be thinking of:
* Patellar luxation: This is a condition where the kneecap (patella) dislocates from its normal position. It can cause pain, lameness, and clicking in the knee joint. This condition can occur in dogs of any age, but it's more common in small breeds.
* Cruciate ligament tear: The cruciate ligament is a vital part of the knee joint that helps to stabilize it. A tear in this ligament can cause significant pain and lameness. This can occur at any age but is more common in older dogs.
If you are concerned about your dog's health, it is always best to consult with a veterinarian.