blackcat - the ridge on a ridgeback is not just the way the coat lies, and hair actually grows inwards, and in cases of Dermoid Sinus (which is similar to spina bifida in humans)
it is a congenital condition that they are born with, found on the midline of the neck, back, and tail along the spinal column. The hairs grow inwards and form tubes which can fill with debris and pus that cannot escape naturally as they would in outward growing tubes. An abscess can form and resultant swelling can rupture the skin, which is not only painful but can be life threatening. Although it can be operated on, it can be difficult to locate and remove, and sometimes they cannot be found and it is kinder to put the puppies to sleep. Sometimes the Dermoid Sinus can grow round the spinal cord, and cause much pain and distress to the animal.