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Dr. Su
I still use the BHR, Conserve Plus, and Biomet Recap. I think
the devices are very similar, but the BHR has the longest track
record, which is very important to me. The other devices do have
the benefit of more sizes than the BHR for right now (at least
in the US), so there are some patients for whom they fit better.
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Dr. Stulberg
What is the difference between the BHR and the Cormet physically? Is the
metal alloy different, is the acetabular cup different and is the cap and stem
different?
The BHR and the Cormet Hip Resurfacing (CHS) device are both devices used for
hip resurfacing as opposed to devices that are used for total hip replacement.
Hip resurfacing with these newer devices (the BHR & CHS are FDA approved
products in the US, the ReCap (Biomet), Conserve Plus (Wright Medical), Durom (Sulzer/Zimmer)
are not FDA approved products in the US) is a rebirth of a relatively old
concept in adult reconstructive surgery in the US. Early efforts at hip
arthroplasty in the 30’s sought to “cap” the femoral head – and were considered
interpositional arthroplasties – devices to put artificial material between 2
painful bone surfaces at the hip (femoral head and acetabulum). In the 1970’s,
this concept was reborn as cemented “resurfacing total hip arthroplasty” as a
means of avoiding placing a cemented femoral component into the proximal femur.
These designs involved the use of a cemented all-polyethylene (actually – ultra
high molecular weight polyethylene – or UHMWPE) acetabular component which was
cemented into place. These were designed to avoid the devastating effects of
loosened cemented femoral components, but unfortunately resulted in devastating
problems on the acetabular side. Many femoral components survived for many years
with this approach – but most devices failed within 10-15 years following
implantation. Dr. Harlan Amstutz of Los Angeles was one of the pioneers of this
operation.
As scientists continued to study successful and unsuccessful results of hip
replacements, sometimes devices surviving up to 20+ years, metal-on-metal (MOM)
bearings (first introduced as a bearing surface in Europe in the 1960’s) emerged
as a very reasonable alternative bearing for total hip replacement. Dr. Amstutz
(US), Dr. Wagner (Germany) and Mr. McMinn (UK) were pioneers in revisiting the
resurfacing operation in the early 1990’s. The early McMinn experience with MOM
resurfacing was actually with devices manufactured for him by Corin in the early
1990’s. During this experience he had a series of hip implantations that were
unsuccessful and he believed it was directly attributable to manufacturing
processes used in making these devices. He parted ways with Corin in
approximately 1995 when he founded Midland Medical Technologies (the
manufacturer of the Birmingham device). He became a champion of that device, the
as-cast technology engendered in that device, and the technique and training
involved in implanting that device. Corin changed its manufacturing process and
developed the Cormet Hip Resurfacing device, which is the device presently
marketed in the US through a partnership with Stryker.
The reason to make this lengthy explanation is that it is important for you and
for patients to realize that the long term success of an operation is due to the
interaction of three components: the device, the surgery to implant the device,
and the patient’s use of the device. In addition, there are many similarities
between these two resurfacing devices because the initial experiences of the MOM
resurfacing operation were shared (McMinn worked with Corin).
The differences between the devices themselves are going to be subtle ones – as
both have to have the basic features of a MOM resurfacing device – a femoral
“cup” or “ball”, and a single-piece acetabular component. Both devices feature a
bearing surface of high-carbon content Chrome-Cobalt. Both components feature
geometries and clearances that allow for lubrication of the joint (synovial
fluid) in such a way as to maximize range of allowable motion with extremely low
wear rates. The BHR does this with “as-cast” Chrome-Cobalt components with
porous outer surfaces on the acetabulum to allow bone-growth fixation. The CHS
employs a double-heat treated surface (to achieve hardness, to allow
predictability of manufacture to achieve sphericity and clearance), and uses a
titanium plasma-sprayed outer surface to achieve bone attachment of the
acetabulum. Both have Hydroxylapatite (HA) coatings to assist bone attachment.
In the US, both femoral components are to be used with cement (non-cemented
devices are available outside of the US). There are slight differences in
designs as they try to optimize predictability of fixation and stress transfer.
The BHR supporters have chosen to make the “double-heat-treated” technology a
point of contention – based in large part up Mr. McMinn’s personal experience
with a device that behaved poorly. This is a bit of an injustice to a technology
that is widely used throughout the orthopaedic industry and is, in fact, the
most commonly used technology for the manufacture of MOM components (and all
other resurfacing devices). Scientifically, the issues that are important to the
metallurgy are clearance, hardness, lubrication, sphericity, and a number of
issues relating to the predictability of manufacture. Both technologies achieve
this, and patients should feel comfortable that they are receiving very highly
successful and high performing (and high performance) devices when their hip
operation is done with these materials. |
