BHR vs. THR, that is the question

[Vicky]

One other thing Kaiser girl to keep in mind is that all Hip resurfacing surgeons also do THR's, but most THR surgeons do NOT do hip resurfacing.  So the ONLY docs that will ever be able to give you a true unbiased opinion are the ones that do both and a lot of both.  You are listening to docs that ONLY do THR's, now you tell me whether or not their opinions are biased?

Vicky

[John C]

There was one comment in Dr McMinn's piece that is worth taking a closer look at. He said

It is just coming to light that with nonMoM hips as we try to extend bearing life through improved materials and as we increase the bearing diameter in order to reduce dislocations, metal can leech from the (taper) joint connecting the stem and the head or the cup and the insert and cause the same problems as seen with bad resurfacings.

I had read a study from England that showed high levels of metal debris from large head MoM THRs due to these junctions in the modular femoral components. This holds some good news and bad news for resurfacing. The good news is that resurfacing is one of the few prosthetic options today that does not involve some sort of junction between the modular portions of most THR femoral components. This advantage of resurfacing eliminates a potential source of metal ions that is present in most THRs. The bad news is that if a resurfacing needs to be revised, it is usually planned to be converted to a large head MoM. I do not know of any of these that are not modular systems with one or even two MoM junctions in the femoral component.
This leaves two big takeaways. Anyone concerned with metal wear debris must look at any modular THR system as potentially being a source of metal wear problems. Secondly, anyone looking at a revision from a HR needs to inquire into this issue, since to my knowledge, all large head MoM femoral components are modular, and will have this issues of metal wear at the junctions.
It will be interesting to see if the manufacturers will go back to making non-modular femoral systems, since I believe that many of these were the source of the good long term results that were achieved with the older MoM systems.

[Tin Soldier]

John - can you explain the dif between modular and non-modular.  Maybe it's late, but I don't recall ever hearing that terminology.  I'm just trying to absorb as much as possible out of this debate and I bet there are some others that would benefit also, thanks.

[John C]

Hi Tin Soldier,
I think that the reason you have never heard the term, is that it does not apply to resurfacing. However, it is a common term used by manufacturers to describe a common category of THRs. For example, Smith and Nephew (the distributor of the BHR in this country) describes its "Modular Plus" THR model as being "the most frequently implanted artificial joint in primary care in Europe". To my knowledge, all the major brands offer modular systems as the basis of their THR lines.
The word "modular" refers to the characteristic of having more than one part to either the femoral or the actetabular component. For example, in the Biomet brand, we find the "Arcos Modular Femoral Revision System". In this model, the femoral component has three parts; the stem that goes down into the femur, a short angled section that goes on top of that and replaces the femoral neck, and whatever type of head (metal, or ceramic) that goes on top of that. On the acetabular side, Biomet makes the "Ringloc+ Modular Acetabular System" for THRs, which is the common cup with a metal back and a plastic liner. Smith and Nephew's R3 acetabular system has three parts to its ceramic acetabular component. When a surgeon installs some of these modular systems, a patient could have five or six separate parts to his THR; the ultimate modular system.
The big advantage to modular systems is that surgeons can match up parts with differing sizes, angles, and materials to customize a solution for the patient. This has been seen as a huge advantage to the surgeon and the patient, and is considered to be cutting edge technology.
If you read my quote from Mr. McMinn again, you will see where he refers to the " (taper) joint connecting" these various parts as being a new potential cause for concern. Some studies are showing that each of these connecting points may be a source of wear debris, and since most of the connections are MoM, you can understand his cause for concern. Please note that I have not read any studies specifying either the Biomet or the Smith and Nephew models as being a source of problems; I used those brands only as examples of top of the line, leading edge, "modular" systems.
So to get back to my original two takeaways: one of the advantages of resurfacing is that it is one of the few non-modular systems in that each side of the joint has only one part, so there is only one interface to create wear particles. My second takeaway is that many revision systems are modular, so a resurfacing patient going in for a revision may want to discuss this issue with his surgeon.
Sorry for the long response, but if more studies like this come out, modularity may become a controversial topic. It is way too early to tell if it will, or what brands and models may be at issue. I brought it up largely because it was an important, though easily overlooked, part of Mr. McMinn's commentary.

[Anniee]

John,

Thank you for that explanation!  I was confused about this subject before I read it, and I'm sure many others learned a lot too!

[gary2010]

http://www.gentili.net/thr/material.htm

As I understand it, the stem is titanium but the bearing surface is always Co-Cr-Mo; I am now wondering what the electrochemical potential difference is between these materials. Are we in effect making a 'battery' across the junction with the body fluids as electolyte? That would certainly contribute to leaching of metal ions.

[Lopsided]

As I understand it, the stem is titanium but the bearing surface is always Co-Cr-Mo; I am now wondering what the electrochemical potential difference is between these materials. Are we in effect making a 'battery' across the junction with the body fluids as electolyte? That would certainly contribute to leaching of metal ions.

I have considered this as well. Two different metals, or two alloys together, one of them will corrode. I doubt there would be enough current to affect the nerves, but one of the metals would remain pristine and the other would rust.

I am concerned enough about this that when I have my other hip done, I want a similar device of the same brand so that both sides have the same composition.

[B.I.L.L.]

Sooo... Kaiser girl, you still on the fence on which to get ?  Just wondering.... 8)

[Jeremy76761]

Hi Vicky,

Another respected doctor, Dr. Sculco who is Chief at the Hospital for Special Surgery (where Dr. Su works), puts THR longevity at 95-97% at 10 years, and 90% lasting to 20 years. The discrepancy with Mr. McMinn's data is interesting, if not confusing. 

http://www.hss.edu/condition-list_hip-replacement.asp

[zendy]

i had my left hip resurfaced 2 years ago in India with Dr Bose.  It is the best. I am 55 female.  i do not have a limp and have about 85% range of motion.  no pain.  I need my right hip done and i want resurfacing but my density is a bit low. I am hoping i can have HR.

[Anniee]

Zendy,

Are you taking any medication to improve your bone density? 

[Vicky]

Hi Jeremy,
You said
"Hi Vicky,
Another respected doctor, Dr. Sculco who is Chief at the Hospital for Special Surgery (where Dr. Su works), puts THR longevity at 95-97% at 10 years, and 90% lasting to 20 years. The discrepancy with Mr. McMinn's data is interesting, if not confusing."

Actually Jeremy on that link it says 80% at 20 years for THR's.  Here's an excerpt below:

Longevity

A total hip replacement has a lifespan much like anything with mechanical parts. Its longevity depends upon a variety of factors, including:

    * Patient weight
    * Patient activity
    * The mechanical properties of the prosthesis

The question of how long a prosthesis will last has been studied in detail over the years. Current studies indicated that about 80% of prostheses will function well for 20 years.
http://www.hss.edu/conditions_hip-replacement-for-arthritis-of-hip.asp

Then he goes on to talk about NEWER THR devices that have absolutely NO solid data to back it, so any of the NEWER THR devices are only speculation. 

Vicky