Two different dislocations, of the patella (knee) and the atlantoaxial (neck) joint, are common in small breeds of dogs.
Patella luxation occurs when the patella leaves the natural groove of the knee when the knee is bent. It is caused by a misalignment of the knee structures. The dog will suddenly limp from a hind limb intermittently. In addition, over time, osteoarthritis will develop in his knee and cause more chronic pain.
Dislocation of the atlantoaxial - joint between the first two vertebrae of the neck where the skull attaches, will be unstable in some individuals of dwarf breeds. Dogs show pain or mild paralysis up to and including paralysis of all four limbs. Dogs are usually less than 2 years old at the time of initial diagnosis, but the disorder can occur between three and six weeks after birth.