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 – it is difficult to demonstrate an
advantage to him with a navigation system.  Further, the
registration process takes a little time – 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.