Thomas E. Menke, M.D.
The unquestionable success of hip and knee replacement
surgery has understandably triggered an effort to find a similar
procedure for the spine. Several different types of disc replacement
prostheses have been implanted in Europe for over ten years. The
potential benefits of such surgery—preservation of spinal motion
and minimization of adjacent level stress—are also unquestionable.
In the spine, however, there are a few more major obstacles to overcome.
Because the vertebra of the spine are much smaller bones than the
femur, tibia, and pelvis, there is less space and fewer options
available to obtain a bone-prosthesis interface. Also, the vertebra
articulate with one another, not only through the disc, but also
through two facet joints at each level. Replacing only the disc
leaves the native facet joints as possible sources of pain and/or
future degeneration. Additionally, we are attempting to couple artificial
surface motion with native joint surface motion which may actually
increase facet joint pain and degeneration. Finally, even when short-term
success can be achieved, prosthesis wear is a major concern. Prosthesis
wear has been a significant problem for the intermediate and long-term
success of hip and knee replacement, even though this surgery is
generally performed on the elderly. Disc replacement candidates
are young, active patients in whom prosthesis wear is almost certain
to be a major problem.
Successful artificial disc replacement is a lofty goal worthy of
further investigation. Current techniques and biomaterials have
not shown the ability to achieve long-term success. Therefore, we
must temper our enthusiasm for this evolving treatment option.