Today I took this picture of three thoracic vertebrae. Normal degenerative changes in the spine appear as osteophytes - little spicules of bone that protrude horizontally from the body of a vertebra. In this person's mid-back, however, there was excessive bone formation vertically, causing at least two of the vertebrae to fuse together. This condition is known as ankylosing spondylitis (or ankylosis for short). It most commonly affects the vertebral joints and the sacroiliac joint (where your hips join your sacrum in the back), and it limits the range of motion that an individual can engage in. In the case pictured, one of the vertebral discs (an area of articular cartilage) was partially or wholly destroyed during life. To cope with the loss of mobility, the body created syndesmophytes - basically, ligaments that ran vertically and originally helped stabilize the spine were converted into bone. At the top of the photo, you can see that a third vertebra has developed syndesmophytes, but these have not fused to the vertebra beneath it yet. For unknown reasons, ankylosing spondylitis appears to affect males more than females, nearly 3 to 1, and begins to affect the joints after a person reaches 30. It is a progressive disease, and there are archaeological examples that show entire spines fusing together. Unfortunately, I only had a few vertebrae from this individual, so I could not document the extent of spinal fusion for this particular person.