What was going on in that strange spine? It’s likely that this poor polar bear had spondylosis (also called spondylosis deformans or ankylosing spondylosis).
Spondylosis is the formation of extra bone (osteophytes) between the vertebral bones which make up the spine. It can look like little projections from the individual vertebrae, or actually form bridges between them. When joints fuse like this, it is called ankylosis, and is thought to be the body attempting to stabilise the joint (like a bone splint) after damage to the cartilage cushions between the vertebrae.
Spondylosis is most often seen in dogs, pigs and bulls. It is particularly important in bulls kept in artificial breeding centres, where repeated mounting of a dummy-cow leads to damage to the lower back.
In some animals with spondylosis there are no symptoms. However, the bony bridges are more brittle than regular bone, and can sometimes fracture, potentially leading to bleeding and compression of the spinal cord and paralysis. In most dogs and pigs, spondylosis is often found incidentally and clinical signs can range from nothing to pain and stiffness.