Medical Studies

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.

February 2009 American Academy of Orthopaedic Surgeons

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This statement provides recommendations to supplement practitioners in their clinical judgment regarding antibiotic prophylaxis for patients with a joint prosthesis. It is not intended as the standard of care nor as a substitute for clinical judgment as it is impossible to make recommendations for all conceivable clinical situations in which bacteremias may occur. The treating clinician is ultimately responsible for making treatment recommendations for his/her patients based on the clinician’s professional judgment.

Any perceived potential benefit of antibiotic prophylaxis must be weighed against the known risks of antibiotic toxicity, allergy, and development, selection and transmission of microbial resistance. Practitioners must exercise their own clinical judgment in determining whether or not antibiotic prophylaxis is appropriate.

More than 1,000,000 total joint arthroplasties are performed annually in the United States, of which approximately 7 percent are revision procedures.1 Deep infections of total joint replacements usually result in failure of the initial operation and the need for extensive revision, treatment and cost. Due to the use of perioperative antibiotic prophylaxis and other technical advances, deep infection occurring in the immediate postoperative period resulting from intraoperative contamination has been markedly reduced in the past 20 years...

...Patients with joint replacements who are having invasive procedures or who have other infections are at increased risk of hematogenous seeding of their prosthesis. Antibiotic prophylaxis may be considered, for those patients who have had previous prosthetic joint infections, and for those with other conditions that may predispose the patient to infection. There is evidence that some immunocompromised patients with total joint replacements may be at higher risk for hematogenous infections. However, patients with pins, plates and screws, or other orthopaedic hardware that is not within a synovial joint are not at increased risk for hematogenous seeding by microorganisms...

...Given the potential adverse outcomes and cost of treating an infected joint replacement, the AAOS recommends that clinicians consider antibiotic prophylaxis for all total joint replacement patients prior to any invasive procedure that may cause bacteremia.

 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.