Dr. Gross Video & Written Interviews

Interviewed by Vicky Marlow Freelance Patient Advocate Volunteer Contributor March 2008

Dr. Gross video interview by Vicky Marlow Freelance Patient Advocate Volunteer 2008

Vicky Marlowe’s Questions:

These are my belated responses to your questions. You may post these on surface hippy. Please let me know if you need any clarification 

Thomas P. Gross M.D.   1/17/2007

I estimate that most total hip resurfacing done worldwide is done through a posterior approach ( > 90 %). There was an interesting report recently at the Annapolis MD HSR Meeting from Mr. Ronan Treacy indicating no difference in results between posterior and anterior-lateral approaches in a direct comparison looking at the rates of limp and other complications. Therefore, I do not think anyone has shown that it really matters which approach is used.

 My current personal preference is posterior minimally invasive (see my video) vascular sparing (as described by Dr. Koen DeSmet). I believe, that with this approach, I can accomplish the operation in virtually all case that are candidates ( only 2 of 1300 converted to THR intraoperatively), return patients back to activity as rapidly as possible, avoid a permanent limp, and place components in ideal position. This is personal preference, not science. Every surgeon should use the approach that he/she is most comfortable with.

How long do you feel it takes for the bone to be fully healed, grow into the prosthesis?

It is a gradual process that proceeds over 6-12 months. Dog studies have shown that the process has already begun by 6 weeks postop. At 6 months, I estimate that 90% of bone ingrowth has occurred. After 12 months bone remodeling around an implant porous surface should be back to the normal baseline with the implant well incorporated. Some impact early on will likely stimulate bone ingrowth, while too much may cause implant – bone micromotion and result in failure of ingrowth. How much then is too much?

Six months. This is not only because of bone ingrowth issues, but also because of the femoral neck fracture risk which is present for 6 months after surgery in my experience.

Although it is clear that M/M HSR is much more durable than most THRs, exactly how much impact activities can be safely tolerated over the long term is unclear. Therefore, patients should exercise caution.

Uncemented femoral resurfacing components are a new development. The acetabular components used routinely are uncemented, while the femoral components routinely have been cemented to bone.

Recently, I have developed a fully porous coated femoral component with Biomet Inc. (Uncemented ReCap). This component is FDA approved in the US for femoral resurfacing. I have been using this together with the uncemented Magnum acetabular component for uncemented total Hip Surface Replacement since April 2007. No other surgeons are yet using this device. Corin also has a device available outside the US for uncemented femoral resurfacing; it is partially porous coated plus HA coated (Corin Cormet 2000 uncemented femoral component [version 2]). Several early reports on the Corin device out of England are promising.

Mr. Richard Villar has compared the uncemented Corin Cormet 2000 version I (No porous, only HA coating) to a cemented femoral component. This study showed less bone remodeling (neck narrowing) with the uncemented component. The significance of this is completely UNKNOWN. We will watch these developments with interest.

 I also have a favorable experience (fewer patients but 8year f/u) with this original Corin version I device which I presented at the first Comprehensive US hip Resurfacing Course in Annapolis MD in November 2007. I am currently working on a manuscript for publication.

  Mr. Derek McMinn has recently added some insight into his past experience with uncemented femoral components based on the Corin McMinn component, which was made of cobalt chrome with no bone ingrowth or ongrowth surface whatsoever. Mr. McMinn tried this about 15 years ago and it predictably failed with this surface. At that point (early 1990’s) we already knew (from joint implant work done in the 1950’s) that an uncemented uncoated press-fit implant of any sort would not work reliably more than 1 – 2 years in most patients.

 At this point uncemented fixation of the femoral component in total hip resurfacing is an interesting concept. My hypothesis is that an implant that has fixation to bone by an appropriate bone ingrowth surface may result in less early complications because the thermal necrosis of bone with curing of cement is avoided. Also it may be longer lasting, if cement is subject to late fatigue failure in HSR as it is in most other joint replacement applications. But, again, I stress that this is a hypothesis which can only be validated or refuted by clinical data (That means 2+ year results in large numbers of patients).On the negative side, we need to discover how reliable the bone ingrowth process is (with these new implants and instruments) in the femoral head.

Mr. McMinn’s statement that he has already tried uncemented femoral fixation and that this did not work is not completely accurate. There is no doubt that he showed that “a femoral component placed without cement and without a bone ingrowth (or ongrowth) surface will not give reliable results.” He has not published any results on a femoral component with a bone ingrowth coating, and to my knowledge, his company (MMT, which makes the Birmingham hip) has not marketed any such device.

The reference article is:

Derek McMinn; Ronan Treacy; Kyaw Lin; Paul Pynsnnt, Metal on Metal Surface Replacement of the Hip. Experience of the McMinn Prosthesis CLINICAL ORTHOPAEDICS AND RELATED RESEARCH, Number 329S, 1996,pp S89-S98

There is very little published data on the use of an uncemented femoral component.  I will need to gather data for at least three to four years before I will be able to provide any useful data on this subject.  Fixation of total joint implants to bone can be accomplished by cement or by porous ingrowth technology.  Cement fixation is immediate, while permanent fixation with uncemented components requires six to twelve months of bone ingrowth before it is considered well fixed.  Some total joint replacement components have had more success with cement fixation, while others have done better with uncemented technology. 

In hip surface replacement at eight years, approximately 95% of implants are still working in young patients with cemented femoral fixation.  Only rarely can these 5% failures be blamed directly on the cement fixation itself. 

Dr. Thomas Gross response:

Dr. Rogerson is mistaken. I suggest that he reads Mr. Richard Villar’s work. The reference is:

FEMORAL NECK RESORPTION AFTER HIP RESURFACING ARTHROPLASTY – A COMPARISON OF CEMENTED AND UNCEMENTED PROSTHESES. P Katrana; JR Crawford; S Vowler; A Lilikakis; and RN Villar. Journal of Bone and Joint Surgery - British Volume, Vol 88-B, Issue SUPP_II, 234.  
Copyright © 2006 by British Editorial Society of Bone and Joint Surgery

Mr. Richard Villar has compared the uncemented Corin Cormet 2000 version I (no porous, only HA coating) to a cemented femoral component. This study showed less bone remodeling (less neck narrowing) with the uncemented component. The significance of this is completely unknown. We will watch these developments with interest. Overall the short term results are equivalent between these two types of femoral implants.

Recently, comments have been made re: FDA status of implants. Can you clarify this issue?

Both of these statements are false.

The Birmingham  (Smith & Nephew, Richards) total HSR was the first to get FDA approval  in the US based on an unprecedented FDA decision to approve this implant on the basis of single (developing) surgeon’s foreign data. Cormet 2000 ( Corin Ltd., Stryker) total HSR was the first to be approved based on the usual mechanism of a  US run Multi-center FDA study( approval 7/2007, I was the lead investigator). Therefore, there are now 2 implants available in the US that have an FDA indication for total HSR.

The Recap/Magnum (Biomet), Conserve Plus (Wright Medical) and APR (Depuy) are all also FDA approved implants in the USA. They may be legally used by any surgeon for the purpose of total Hip Surface Replacement. (The FDA does not regulate how surgeons may use approved implants.) However, the implant companies may not promote them as total HSR devices. (The FDA does regulate how implant companies may market approved implants.)  

Approximately 20 different companies sell total HSR implants on the worldwide market, including all of those mentioned above.

 A specific use of an implant (or drug) that is approved by the FDA is termed an FDA approved indication. As soon as a company has received one indication for use of their implant (or drug), the implant (or drug) is FDA approved. The use of this same implant (or drug) for a purpose other than for the approved indication is termed an off –label use. Off-label use is legal. In fact, much of American medical practice involves off-label use of drugs and implants. It would be impossible for the FDA to regulate doctors’ practice in every situation. Actually the Supreme Court has expressly stated that this is not the FDA role (see Rehnquist opinion).

 Many insurance companies do have contract clauses that deny payment for “experimental” treatment. How to define what is experimental is very controversial. However, “experimental” is something altogether different than off-label use of implants and drugs.

 Therefore, an insurance company would be treading on thin ice if they were to use FDA indications as a basis to deny payment.