Surgical Approach by Mr. McMinn
I started back in 1991 with the antero-lateral approach to the
hip for resurfacing. At that time we were worried about blood
supply to the femoral head and on theoretical grounds the antero-lateral
approach preserved the blood supply well. For many patients the
approach was satisfactory but there were some problems. The
exposure obtained in large patients was not good. This meant
that heavy retraction had to be used, and heavy retraction
caused trauma to muscle and other soft tissues which in turn led
to heterotopic ossification. The other problem was that some
patients had a permanent limp after my surgery as a result of
the surgical approach. Please understand that the instruments
were crude back then compared to today where newer designs of
instruments would cause less tissue trauma and make the antero-lateral
approach a better option. The sight of limping patients
persuaded me to change my approach to the posterior approach.
The theoretical objection to this approach was that it may cause
more damage to the femoral head blood supply. It turns out that
the problems with femoral head blood supply using the posterior
approach are very rare, as you heard at the conference. The big
advantage is that an excellent exposure can be obtained, giving
the surgeon the best opportunity for perfect component
positioning. As you heard, inaccuracy with respect to acetabular
component positioning is badly tolerated and a high acetabular
component inclination angle is the single biggest reason for
early bearing failure following a metal on metal resurfacing.
The other great advantage is that very little trauma to the soft
tissues need occur with a posterior approach resurfacing. The
other thing is that a mini-incision posterior approach can be
done by those surgeons experienced in the resurfacing operation
with good exposure and minimal tissue trauma. My unit published
our mini-incision resurfacing results a few years ago, the
average incision length was under 12 cm and measured component
position was good.
There are two other surgical approaches to be considered by
surgeons, but for different reasons these are not reasonable at
this time.
The other issue is how well an inexperienced surgeon can be
taught to reliably perform an uncomplicated resurfacing
operation. It's no use talking about Ronan Treacy's or my own
abilities in this regard as we have each performed well over
3,000 resurfacing procedures, and no matter how hard we work, we
cannot make any impact on the world demand for this procedure.
New surgeons therefore must be trained. As you heard, we tested
how good newcomers to the BHR using the posterior approach
really were and over 100 new surgeons, as well as Ronan and
myself, entered our patients on the Oswestry Outcome Centre
database. All those patients have been independently followed
up. At 9 years post-op Ronan's and my results are still
statistically significantly better, both with regard to failure
requiring revision and also with regard to hip function. Never
mind statistics, the fact is that the newcomer surgeons achieved
very creditable outcomes, which means that the whole package
with respect to training, patient selection, surgical technique
and implant durability really does work. If anything in that
mixture changes then the outcomes achieved may significantly
change. To give you one example, during 1996, one year before I
started the BHR, I carried out the Corin, double heat treated
resurfacing which I designed. All the other ingredients of the
package were the same.
Now that time has passed we can see the effect of one factor,
implant design, on the outcomes. At 5 years there is no
difference between the Corin and the BHR design on my outcomes.
At 10 years, however, the Corin series has an 86 % implant
survival whereas the BHR series has a 96 % implant survival. In
addition, in the patients who have had the Corin resurfacing and
have not been revised at 10 years, 20 % have osteolysis or early
loosening. These features bode badly for the future. Heat
treatment of the metal of the implant is not something that the
surgeon can see, and I wasn't aware that the manufacturer had
started to use this even though I was the implant designer! The
implant looks the same as the historically proven, as-cast alloy
and the early results give no cause for concern. The longer term
sadly is a different matter. I understand your interest in the
surgical approach, but it's the complete package that counts.
For a patient, therefore, the key questions for their surgeon
are: How long have you done metal on metal resurfacing? Am I a
good candidate for hip resurfacing? Is my bone good enough? Do I
have avascular necrosis which may increase the failure rate with
hip resurfacing? Do I have dysplasia or any other condition
which may seriously complicate the procedure and are you
confident you can handle any difficulties? What surgical
approach do you use and why? How were you trained and what was
the resurfacing experience of your trainer? What are your
results--- how many have you done and how many failures have you
had? What are the hip scores in your resurfacing patients? What
complications have you had with hip resurfacing? What type of
hip resurfacing do you propose using on me? What are the results
of that design used in a) the inventor’s hands and b) what are
the results of that design of implant in the hands of
independent surgeons e.g. what are that implants results on the
Australian national register? If your surgeon is using a device
with either no independent results or poor results on the
Australian register the question to be answered is: Why are you
using it e.g. are you paid to use it or is your hospital paid to
use it by the manufacturer of the device?
