Dr. Schmalzried Discusses Computer Assisted Navigation

[Pat Walter]

Dear Pat,

There is some data indicating that navigation can improve the accuracy of femoral component placement in hip resurfacing.  The real issue is "compared to what"?  For an inexperienced surgeon, navigation may help him avoid component positioning problems that have been associated with "the learning curve".  However, for an experienced surgeon, who has an established mechanical alignment system with a high success rate â€" it is difficult to demonstrate an advantage to him with a navigation system.  Further, the registration process takes a little time â€" so the cost-to-benefit ratio for the experienced surgeon in a busy O.R. is questionable.  The navigation systems are not hard to learn to use, even for old guys like me!

A bigger challenge is acetabular component positioning.  This is true for total hips, and even more important for resurfacing.  There are 2 parts to the acetabular positioning problem.  The first is identifying the desired position for that patient and the second is putting the cup in that position.  Keeping the pelvis in one position and finding accurate pelvic/acetabular landmarks can be challenging.  The lateral opening angle is the easier part.  Most surgeons today agree that between 40 and 50 degrees is desirable.  Version is more complicated because the desired acetabular version is dependent on femoral version.  Acceptable version is also related to the lateral opening angle and the resultant bearing contact area.  Again, the issue is experience.

If I have any doubt about component positioning, I get an intra-operative x-ray.  Admittedly, there can be some challenges to getting a good intra-operative view.   For what it’s worth, we did an x-ray review of my first 500 resurfacings (minimum 1 year follow-up).  I have never had a femoral neck fracture and all sockets are below 50 degrees lateral opening.

Best wishes.

Thomas P. Schmalzried, M.D.