Question
My 75yr-old father in law has recently been diagnosed as having some fused vertebrae in his lower back, it was diagnosed by xray. He has had no injuries or falls that we know of, nor was he born with this condition. How can vertebrae actually fuse themselves together?  

Answer
Dear Doug,

Thank you for the excellent question!  The body is an amazing thing, with so many wonders and questions to be answered.

In the lower back, we have five individual vertebra, with pads of cartilage between them that are called discs. The discs are attached to both the bone beneath and the one above.  The bones also "articulate" or approach each other at what are known as facet joints on the left posterior and right posterior of the vertebra.

When everything is functioning/moving fine, the discs are joints are lubricated by the motion that occurs at each joint. Movement is life, as I like to tell my patients.

Through life, we strain our back through bending, lifting, prolonged sitting, heavy physical work, sports injuries, etc.  Life is traumatic in general. All of these stresses on the segments of the spine take their toll. Eventually, we begin to loose a bit of the motion between the spine segments due to joint degenerative changes and/or muscular tightness and guarding.  The loss of motion results in fewer nutrients entering the joint tissues. (remember, I said that movement is life?)

The degenerative changes that occur in the joint lead to some instability within the joint. Abnormal pressures on the bones lead to bony remodeling. The cells of the bone, osteoclasts and osteoblasts start to change the shape of the joints, growing spurs. These reach out towards each other (is is the way of the body to naturally try to stabilize a damaged joint through calcium/bone growths).

After years of this, the bone spurs approximate each other as the disc space continues to decrease. Eventually there is no cartilage or disc, and bone rests upon bone. The bone spurs unify through continued bone cell activity.

This, in a nut shell, is what has likely happened with your father in law.  There are some conditions where this occurs more rapidly for unknown reasons. One in particular is called Ankylosing Spondylitis. Perhaps this is contributing to your father in laws spinal fusion. Here is a link regarding ankylosing spondylitis. http://www.mayoclinic.com/health/ankylosing-spondylitis/DS00483

The good news is that typically, fusion alone is not painful. I have several patients that have spinal fusion due to degeneration that function quite well. The bad news is that the increased bone growth sometimes causes stenosis, which is a condition where the bone growth and disc degeneration narrows the openings where the nerves pass through the spine. This can be quite painful and can cause pain that spreads into the legs.

I hope that this is helpful for you in understanding what is going on.

Sincerely,

Keith E. Biggs, DC
http://www.eastmesachiropractor.com
http://www.biggschiropractic.blogspot.com