HR Devices

A Consensus From The Advanced Hip Resurfacing Course, Ghent, June 2009 About Metal-on Metal Hip Resurfacing

K. De Smet, MD, Orthopaedic Surgeon¹; P. A. Campbell, PhD, Associate Professor²; and H. S. Gill, DPhil, University Lecturer in Orthopaedic Mechanics^{3 1} ANCA Medical Center (AMC-Ghent), Krijgslaan 181, 9000 Ghent, Belgium.
² UCLA/Orthopaedic Hospital, 2400 South Flower Street, Los Angeles, California 90007, USA.
³ Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences University of Oxford, Botnar Research Centre, Nuffield Orthopaedic Centre, Oxford OX3 7LD, UK.

Abstract

We report the consensus of surgical opinions of an international faculty of expert metal-on-metal hip resurfacing surgeons, with a combined experience of over 18,000 cases, covering required experience, indications, surgical technique, rehabilitation and the management of problematic cases.

Introduction

The last decade has seen an increased use of metal-on-metal hip resurfacing arthroplasty as an alternative to contemporary total hip replacement (THR), especially for patients who wish to participate in high-demand activities. Metal-on-metal bearings are also being used more often for THR. In June 2009, the third Advanced Resurfacing Course was held in Ghent, with a faculty that included 21 orthopaedic surgeons whose combined experience included over 18,000 metal-on-metal hip resurfacing arthroplasties. As the meeting served to bring together surgeons, highly experienced in hip resurfacing, from Australia, Europe and the Americas, the opportunity was taken to establish consensus views on issues of required experience, indications, surgical technique and rehabilitation. The aim of this annotation is to disseminate these consensus findings in order to help surgeons who are considering metal-on-metal bearings for both resurfacing and conventional THR. The findings are presented as a majority opinion, with the percentage of the faculty in agreement given in parentheses.

Required experience

The use of metal-on-metal bearings for THR and resurfacing presents a greater technical challenge than that of conventional metal-on-polyethylene bearings. The consensus (81%) was that an orthopaedic surgeon should have a minimum experience of 200 conventional THRs before starting to use a metal-on-metal hip resurfacing arthroplasty. Opinion varied on the number of these operations needed to overcome the learning curve, and ranged from 20 (36%), to 50 (28%) and more than 50 (30%).

Indications

The overall view (100%) was that the ideal candidate for an metal-on-metal hip resurfacing arthroplasty is a relatively young man with normal anatomy and primary osteoarthritis. Being female was not, by itself, a contra-indication (89%), but use of a small femoral head (< 46 mm) was contra-indicated (70%). Being female and wanting to have children was a contra-indication (66%), as was being female and having a metal allergy (70%). Grossly abnormal anatomy, regardless of gender, was also agreed to be a contra-indication (83%). There was considerable debate about bone quality, the general view being that 'good' femoral bone is a prerequisite, but no agreement was reached on a working definition of acceptable quality.

Surgical technique

The majority opinion (56%) was that the best type of femoral placement guide is that which encircles the femoral neck. There was general agreement (63%) that the current acetabular placement jigs are inadequate. The overall preference (78%) was for cementing the femoral component with a thin cement mantle with fixation holes drilled in the femoral bone, use of pulsed lavage, and reduction of the hip in less than eight minutes from the start of mixing the cement.

Rehabilitation

Full weight-bearing can be allowed on the first post-operative day (73%) and patients should use crutches for as long as needed (57%). Six weeks is the optimal time to return to normal non-sporting daily activities (44%), and six months for returning to impact sports such as running or tennis (61%).

Managing problematic cases

It was difficult to achieve a consensus on this topic, and only the broad recommendations of the discussion are reported. It was generally agreed that these patients need to be followed up and those with symptoms investigated. There was no agreement on the diagnostic value of measurements of metal ions, but it was felt that  'high' concentrations of systematic metal ions indicated a problem with the articulation. Cross-sectional imaging and plain radiographs are required for the investigation of a symptomatic metal-on-metal bearing.

It is hoped that these consensus opinions will prove useful to orthopaedic surgeons and will lead to improved outcomes after surgery for hip replacement.

Advice to patients concerning the ASR

I suggest a few points that, I think, everyone can agree to (for any hip, including an ASR):

1. If you have pain or are in any way concerned - go see your surgeon.

2. There are some screening tests. Based on current experience, if blood (or serum) ion levels of Cr and Co are <5ppb, the likelihood a problem with the implant is low. If the level of either is >10ppb, the likelihood of a problem with the implant is increased. In either event, the next step would be an imaging study (ultrasound or MRI) to look for a fluid collection, or a cystic or solid mass - as evidence of an adverse local tissue response.

3. An aspiration of the joint may be appropriate a) to exclude infection as a cause of the joint dysfunction and b) the characteristics of the fluid may help in the differential diagnosis of a problem related to the metal-metal bearing.

I think that the first point is the most important. If you are concerned, go see your surgeon.

Thomas P. Schmalzried, M.D.

I have to start by saying that I have never had any issues with the ASR devise at all. I was very surprised about 6 months ago when the issue of ASR withdrawal first surfaced. There is no doubt that the safety margin for the ASR is lower than other resurfacing systems like the BHR due to a 'low arc of cover'- described by Dr. Desmet. This is because the rim of the cup has become 'non -articular' to accommodate the cup holder. Hence the failure rate is higher than the BHR.

The cups coming loose is certainly not true as I have implanted ASR cups in the most complex of cases. I am 100% confident that it is a technical issue.

It has proven to be an excellent tool in my hands and in dysplasia patients ( CROWE 3)- the s-rom with a ASR cup combination that is hard to beat.

The ASR reamers are very poor and not matched to the ASR cups. I have routinely used BHR or equivalent reamers for the ASR cups for 3 yrs since the time noticed the mismatch between the reamers and cup size for the ASR

The ASR has been excellent tool to provide an anatomical metal on metal articulation in small patients. I am very confident that it will work well if installed correctly. I will surely miss the ASR cup for small made patients if it is withdrawn completely.

with best regards
vijay bose
chennai

The status of DePuy Orthopaedics’ ASR platform as Feb. 2010

Last fall of 2009, DePuy decided to discontinue ASR® XL Acetabular Head System and DePuy ASR® Hip Resurfacing Platform (not available in the U.S.) worldwide. As a result of declining demand for the ASR platform and other market factors, DePuy is in the process of phasing out this platform to focus on the development of next generation hip replacement and resurfacing technologies that best meet the needs of surgeons and patients.

DePuy wants to assure patients who have been treated with a device from the ASR platform that there will be options available to them in the future should they need a revision:

· If a patient who had received the DePuy ASR® XL Acetabular Head System for total hip replacement requires a revision surgery, the acetabular component could be revised with the Pinnacle Hip Solutions platform, which would be compatible with an existing well-fixed femoral stem.

· As with any hemi-resurfacing prosthesis, including the DePuy ASR® hemi arthroplasty, a patient requiring a revision procedure would generally be treated with a total hip replacement.

· For patients outside the U.S. treated with DePuy ASR® Hip Resurfacing (not commercially available in the U.S.), DePuy intends to maintain an inventory of ASR XL heads outside the U.S. for use on compatible DePuy femoral stems. This will allow surgeons outside the U.S. the option of retaining a well-fixed ASR Cup when appropriate as part of the revision procedure.

Lorie Gawreluk
Vice President, Worldwide Communications
DePuy, Inc.

Smith & Nephew's strong profits beat expectations
February 2010

Smith & Nephew (S&N), the hips-and-knees maker, posted higher profits in the final quarter of last year after the replacement joints market stabilized.

The market suffered during the recession, but started to recover in the second half.

Traditional hip and knee ranges, like its Legion knee, did well, particularly in the US, while products designed for younger, more active patients, such as the bone-sparing Birmingham Hip Resurfacing System, were weak.

Younger patients were more likely to put off surgery than retirees because they did not want to take time off work or balked at the cost.

"Our largest business, orthopaedics, saw a good finish to a tough year," said chief executive David Illingworth. "Market conditions were a little less difficult than in the first half."

He said it’s too early to say when patients who deferred operations might have them done, and S&N is struggling to push through price increases as governments and private clients have tightened their budgets. But Illingworth was hopeful that the $12bn  global market for replacement joints would improve, with consumer confidence returning and unemployment now falling.

S&N expects revenues in orthopaedics to grow at the market rate this year after lagging in 2009.

Profits before tax rose to $175m in the fourth quarter from $162m a year earlier, with revenues 11 per cent higher at $1.07bn, helped by strong sales at the wound management division.

Analysts and investors welcomed the results, and the shares closed up 4.3 per cent at 660p.

Thomas P. Gross, M.D. Midlands Orthpaedics p.a. Current status of uncemented femoral components in hip resurfacing Midlands Orthpaedics p.a.

 January, 2010

Uncemented femoral components for metal on metal total hip resurfacing have shown excellent results during the initial 3 years that I have been using this new technology. The early results that I have achieved in 0ver 800 cases since March 2007 are equivalent to the early results that I achieved with the same brand cemented femoral component.

Uncemented fixation of implants to bone is a proven technology that has generally surpassed the durability of cemented fixation to bone in traditional hip replacement surgery. In the long term (at 10 years) a higher percentage of hip implants using uncemented fixation still remain attached to the bone than cemented implants, especially in younger more active patients.

Fixation of total hip implants to bone can be accomplished by cement or by porous ingrowth technology (uncemented). Cement fixation is immediate. Cement is an acrylic material (methylmethacrylate) that is very brittle and also fairly toxic to bone cells. Cemented implants gradually loosen from the bone over time by reaction to the cement itself and due to gradual fatigue failure of this material. This process is faster in more active patients and faster in implant situations where the cement is stressed by shear forces rather than by compression forces.
 
Uncemented components are initially held to the bone by a very tight press-fit which is achieved by accurately preparing the bone so that the implant can be tightly hammered-on. The implants are so tightly wedged–on that the patient can bear full weight on them immediately. They do require a period of six to twelve months of bone ingrowth before they are considered well fixed. There is usually a small chance of failure of this bone ingrowth process in uncemented implants (<1%). But if ingrowth occurs, it is much more durable than cemented fixation and rarely fails in the long term.
 
Because orthopedic surgeons in America have come to a consensus on the superiority of uncemented fixation in total hips, uncemented fixation has virtually completely replaced cemented fixation in stemmed total hip replacements, despite the fact that these implants are more expensive. 99% of acetabular (socket) components that are used today are of the uncemented type, as are about 90% of femoral stems.
 
In hip resurfacing there is universal agreement that uncemented fixation is superior for the acetabular component. However, until recently, uncemented femoral components have not been available, therefore most hip resurfacing operations in the past have employed cemented fixation of the femoral component.
 
At the time that I began hip resurfacing in 1999, there was not yet general agreement that uncemented fixation was superior to cement in hip replacements. However, the evidence was mounting that uncemented fixation was better. I therefore did not think it was logical to use cemented fixation in hip resurfacing, an operation developed specifically with the more active younger patient in mind. The only companies pursuing hip resurfacing at the time were two small English companies: Corin and Midland Medical Technology (maker of the Birmingham implant). I suspect that they did not have the financial resources to develop a more complicated uncemented femoral component with the precision instrumentation required at that time. I originally proposed an uncemented femoral component to Corin 10 years ago, but they were unable to manufacture it at that time.
 
I therefore worked with Biomet on an uncemented femoral component and the precision instrumentation required for this implant for five years. I first began implanting it in March 2007. The Biomet component has a full coating of Titanium plasma spray under the entire under-surface of the femoral component. Recently we have added an additional layer of hydroxylappatite (HA) to increase the speed and extent of bone ingrowth. This is the best implant available to maximize the chance of bone ingrowth. When I started working with Biomet to develop an uncemented femoral component, Corin also started to work on one. They were able to bring it to market in Europe first; however, their component is only partially porous-coated (less than 50%) with Titanium (but it does have complete hydroxyl appetite coating). I personally do not believe this is good enough for long-term fixation (>10 years), but nobody knows for sure yet. It is not yet available in the US.
 
Theoretically, cement is the weak link when long-term (> 10 years) fixation of the femoral component is contemplated. If uncemented femoral components can be shown to achieve reliably high rates of ingrowth in the short term, they will probably outperform cemented femoral components in the long-term.
 
At this point with nearly 2-year follow-up data on a matched group of patients, I see no difference in results whether cement or uncemented fixation is used. At this point we can be fairly certain that bone ingrowth has occurred in these components. Except for two cases where osteonecrosis occurred in the femoral head at 1 year, we have had no failures of bone ingrowth in 430 patients that have are at least one year postop, and 191 that are at least two years postop.

In summary:

• Uncemented femoral resurfacing components are now available from BIOMET for any patient who desires them.
• No other companies are yet selling these in the US
• Corin has had an uncemented femoral component available in Europe for several years.
• At 2 years of follow-up there is no difference in the failure rate between cemented or uncemented femoral component.
• Uncemented fixation of implants is more durable at 10 years than cement in hip replacement surgery especially in young active patients.
• Most clinical data on hip surface replacement to date is based on an uncemented acetabular component and a cemented femoral component. 
• I now use uncemented components on virtually all hip resurfacing operations, unless the patient specifically requests the cemented femoral device. 

Thomas P. Gross, MD