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Dr. Kurtz had an article online
that had concerns about the head neck rations of hip
resurfacing compared to total hip replacement. We wanted
to provide potential hip resurfacing patients with
opinions of other top resurfacing surgeons to explain
their views.
Vicky,
I
read over the discussion of the head-neck ratios and
impingement that you forwarded which was very thorough.
There is no question that the head to neck ratios of a
total hip arthroplasty with a small diameter neck are
larger than with resurfacing arthroplasty, especially a
metal on metal big femoral head construct. This would
translate into less impingement and greater stability
which increases as the head size increases. If
biomechanics were the only factor involved in the choice
of a prosthesis then I would opt for the MoM Big Femoral
head type every time. However, there are many other
factors to consider including the technique used in the
procedure.
As you can see from the discussion even small
traditional heads with small necks have a better
head-neck ratio than resurfacing and yet in clinical
practice traditional hips have a dislocation rate in
most series of 3-4% in primary replacement which
increases up to about 20% in revisions. This compares
with a dislocation rate around 0.3-0.4% in resurfacing
series. Factors that explain this dichotomy are the more
natural soft tissue balance and more accurate leg length
and offset that are associated with resurfacing and the
decreased "jump distance" of a small head prosthesis
when compared to large head prostheses (the actual
distance the head has to move before it dislocates is
much less for a small head than a large even though the
head-neck ratios may be greater in the small head).
In our series and especially in McMinn's and Treacy's 10
year series, late neck fracture has not been a clinical
problem so if impingement with a resurfacing was such a
detriment we would expect to see 1) impingement pain, 2)
decreased range of motion, or 3) late neck fracture.
This does not appear to be the case if care is taken
technically to not notch the superior neck of the femur
during the procedure. Of the late neck fractures
reported, the biggest factor seems to be avascular
necrosis rather than impingement. Obviously, this is
very rare also since the 10 year survivorship for
osteoarthritis is 99.6%!
In summary, I agree with the statements presented
regarding head-neck ratio and feel it particularly
supports using a large head vs. a small head traditional
prosthesis. However, clinical results and other
biomechanical factors would seem minimize its importance
as regards to resurfacing arthroplasty as noted above.
The other major advantages of resurfacing in a young,
active patient population ( bone sparing, high activity
friendly, diminished proximal femur osteopenia, and ease
of later revision) far outweigh the theortical
considerations presented.
Thanks for the opportunity to respond.
Sincerely,
John Rogerson, MD
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