Dear Pat,

Thank you for the work you do, it helps so many.

Computer aided navigation is an
interesting concept. However, there is no evidence that it
leads to better clinical outcomes and fewer failures. On the
other hand, there is ample evidence that surgeon experience
has a dramatic effect on outcomes and complications.

One way to conceptulize this is that the experienced
surgeon’s brain is a computer with much more sophisticated
“software” than a navigation computer. When a computer is
programmed, an algorithm must be created which has certain
inherent limitations. Furthermore additional significant
sources of errors are introduced by the registration of
anatomic points for the navigation computer in surgery.

My personal opinion is that navigation that is based on a
pre-operative CT scan data, which is being pioneered by
Justin Cobb, has tremendous promise in the future to improve
the results. At this point, we are still in the early
development phase. It will probably add several thousand
dollars to the cost of each operation.

In summary, I believe the right kind of navigation surgery
based on accurate 3D CT scans holds tremendous promise for
the future. It will still require an extensive amount of
preliminary development work before it is ready for routine
use.

Interestingly, an article just published in JBJS British by
Olsen et al (91-B, 2009, pp 1281-86) confirms a low level of
repeatability in computing the most basic measure of
neck-shaft angle. There are much more important factors to
proper alignment than the stem angle, but it turns out the
navigation doesn’t even do well with this simple task. This
points out that imageless navigation needs to be validated
by CT before we give it any credibility.