Hip Resurfacing News - Medical Studies

Sports Activity After Total Hip Resurfacing Study 2010

nospam@example.com (Patricia Walter) — Fri, 19 Mar 2010 08:45:01 -0700

Sports Activity After Total Hip Resurfacing Study 2010

Original Link http://www.ncbi.nlm.nih.gov/pubmed/20223940?dopt=Abstract

March 11, 2010

Banerjee M, Bouillon B, Banerjee C, Bäthis H, Lefering R, Nardini M, Schmidt J.
Dreifaltigkeits-Krankenhaus and Cologne Merheim Medical Center.

BACKGROUND: Little is known about sports activity after total hip resurfacing.

HYPOTHESIS: Patients undergoing total hip resurfacing can have a high level of sports activity. STUDY DESIGN: Case series; Level of evidence, 4.

METHODS: The authors evaluated the level of sports activities with a standardized questionnaire in 138 consecutive patients (152 hips) 2 years after total hip resurfacing. Range of motion, Harris hip score, and Oxford score were assessed, and radiological analysis was performed.

RESULTS: Preoperatively, 98% of all patients participated in sports activities. Two years postoperatively, 98% of the patients participated in at least 1 sports activity. The level of sports activity decreased after surgery. The number of sports activities per patient decreased from 3.6 preoperatively to 3.2 postoperatively. Intermediate- and high-impact sports, especially tennis, soccer, jogging, squash, and volleyball, showed a significant decrease while the low-impact sports (stationary cycling, Nordic walking, and fitness/weight training) showed a significant increase. Physical activity level at the time of follow-up as measured by the Grimby scale was significantly higher than in the year before surgery. Duration of sports participation per week increased significantly after surgery. Men had a significantly higher sport level than women before and after surgery. Eighty-two percent felt no restriction while performing sports. One-third missed certain sports activities such as jogging, soccer, tennis, and downhill skiing. The Harris hip and Oxford scores showed a significant increase postoperatively.

CONCLUSION: The results of this short-term follow-up study show that sports activity after total hip resurfacing surgery is still possible. Physical activity level increased with a shift toward low-impact sports. Duration of sports participation increased. High-impact sports activities decreased. These findings can be important for the decision-making process for hip surgery and should be communicated to the patient.

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

nospam@example.com (Patricia Walter) — Wed, 17 Mar 2010 09:36:02 -0700

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 Mechanics³ 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.

Hospitals more specialized in orthopedic surgery show better outcomes for hip and knee replacement

nospam@example.com (Patricia Walter) — Tue, 02 Mar 2010 11:42:08 -0700

Hospitals more specialized in orthopedic surgery show better outcomes for hip and knee replacement

February 17, 2010 Click Here to read full article

A recent study of Medicare data by University of Iowa investigators indicates that hospitals with a higher degree of orthopedic specialization provide better outcomes for patients undergoing hip or knee replacement surgery.

The findings, which appear in the online version of the British Medical Journal, were based on a retrospective study of nearly 1.3 million Medicare beneficiaries aged 65 years and older who had hip or knee replacement procedures between 2001 and 2005 at 3,818 U.S. hospitals. The investigators grouped the hospitals into five categories according to their degree of orthopedic specialization. Orthopedic procedures accounted for 10.5% of admissions at the average hospital, while they represented 14.5% or more of the admissions in the most specialized group...

..."The findings suggest that more specialized hospitals have better outcomes even after we account for the type of patients each hospital cares for and the number of hip and knee replacement surgeries that each hospital performs," Tyson Hagen, MD, the lead author of the study, stated in the release...

Reference: Hagen TP, Vaughan-Sarrazin MS, Cram P. Relation between hospital orthopaedic specialisation and outcomes in patients aged 65 and older: retrospective analysis of US Medicare data. BMJ. Published online 2010 Feb 11.

Antibiotic Prophylaxis for Bacteremia in Patients with Joint Replacements by AAOS

nospam@example.com (Patricia Walter) — Sun, 07 Feb 2010 11:47:58 -0700

Antibiotic Prophylaxis for Bacteremia in Patients with Joint Replacements by AAOS

February 2009 American Academy of Orthopaedic Surgeons

READ COMPLETE ARTICLE BY CLICKING HERE

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.

2 Year Study Uncemented Femoral Components by Dr. Gross 2010

nospam@example.com (Patricia Walter) — Fri, 15 Jan 2010 10:22:49 -0700

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

The Influence of Head Size and Sex on the Outcome of Birmingham Hip Resurfacing

nospam@example.com (Patricia Walter) — Tue, 05 Jan 2010 11:27:15 -0700

The Influence of Head Size and Sex on the Outcome of Birmingham Hip Resurfacing

READ ORIGINAL STUDY BY CLICKING HERE

The Journal of Bone and Joint Surgery (American). 2010
Callum W. McBryde, MD, FRCS(Tr&Orth)1, Kanthan Theivendran, MRCS1, Andrew M.C. Thomas, FRCS1, Ronan B.C. Treacy, FRCS(Tr&Orth)1 and Paul B. Pynsent, PhD1

1 Research and Teaching Centre, Royal Orthopaedic Hospital, Bristol Road South, Northfield, Birmingham B31 2AP, United Kingdom. E-mail address for C.W. McBryde: cwmcbryde@hotmail.com

Investigation performed at the Royal Orthopaedic Hospital, Birmingham, United Kingdom

Background Hip resurfacing has gained popularity for the treatment of youngand active patients who have arthritis. Recent literature has demonstrated an increased rate of revision among female patients as compared with male patients who have undergone hip resurfacing. The aim of the present study was to identify any differences in survival or functional outcome between male and female patients with osteoarthritis who were managed with metal-on-metal hip resurfacing.

Methods A prospective collection of data on all patients undergoing Birmingham Hip Resurfacing at a single institution was commenced in July 1997. On the basis of the inclusion and exclusion criteria,1826 patients (2123 hips, including 799 hips in female patients and 1324 hips in male patients) with a diagnosis of osteoarthritis who had undergone the procedure between July 1997 and December2008 were identified. The variables of age, sex, preoperative Oxford Hip Score, component size used, surgical approach, lead surgeon, and surgeon experience were analyzed. A multivariate Cox proportional hazard survival model was used to identify which variables were most influential for determining revision.

Results The mean duration of follow-up was 3.46 years (range, 0.03 to10.9 years). The five-year cumulative survival rate for the655 hips that were followed for a minimum of five years was97.5% (95% confidence interval, 96.3% to 98.3%). There were forty-eight revisions. Revision was significantly associated with female sex (hazard rate, 2.03 [95% confidence interval,1.15 to 3.58]; p = 0.014) and decreasing femoral component size hazard rate per 4-mm decrease in size, 4.68 [95% confidence interval, 4.36 to 5.05]; p < 0.001). Revision was not associated with age (p = 0.88), surgeon (p = 0.41), surgeon experience (p = 0.30), or surgical approach (p = 0.21). A multivariate analysis including the covariates of sex, age, surgeon, surgeon experience, surgical approach, and femoral component size demonstrated that sex was no longer significantly associated with revision when femoral component size was included in the model (p = 0.37).Femoral component size alone was the best predictor of revision when all covariates were analyzed (hazard rate per 4-mm decrease in size, 4.87 [95% confidence interval, 4.37 to 5.42]; p <0.001).

Conclusions The present study demonstrates that although female patients initially may appear to have a greater risk of revision, this increased risk is related to differences in the femoral component size and thus is only indirectly related to sex. Patient selection for hip resurfacing is best made on the basis of femoral head size rather than sex.

1 in 12 Hip & Knee Surgeries Need Corrective Operations

nospam@example.com (Patricia Walter) — Mon, 04 Jan 2010 08:43:29 -0700

Surgery hits hip pocket

Click Here to Read Complete Article

By Sue Dunlevy From: The Daily Telegraph January 04, 2010

ONE in every 12 hip and knee replacements need corrective operations and new surgical techniques are more susceptible to problems, according to Australia's largest health insurer. Medibank Private has reviewed its data on the 3990 hip replacements and 4860 knee replacements it paid for in 2008 and found "on average surgeons perform revisions on 8.3 per cent of their total procedures"...

...The National Joint Replacement Registry, which is studying the reliability of hip and knee replacements, has found newer joint replacements that are cementless or hybrid are more likely to need further surgery than the older cemented replacements...

...And research found the more reliable cement joint replacements are used in just 23 per cent of hip replacement operations...

...The latest report from the National Joint Replacement Registry found that three types of hip replacements - the ASR, Durom and Recap hip replacements - had more than twice the risk of revision of other resurfacing prostheses. Hip replacements with smaller femoral head sizes are also more likely to be revised.

The Allegretto knee, one of the most common knee-replacements used in Australia, has a 10 per cent revision rate at 2.5 years, which is considerably greater than other similar prostheses.

Hip Resurfacing is Viable Alternative to Hip Replacement

nospam@example.com (Patricia Walter) — Sat, 01 Aug 2009 13:23:50 -0700

Hip Resurfacing is Viable Alternative to Hip Replacement

Patients who had hip resurfacing surgery, such as the Birmingham Hip Resurfacing technique, reported a better quality of life, less pain and greater satisfaction a year after surgery than those who had a total hip replacement.

PRLog (Press Release) - Jul 31, 2009 - Oceanside, NY – Patients who had hip resurfacing surgery, such as the Birmingham Hip Resurfacing technique, reported a better quality of life, less pain and greater satisfaction a year after surgery than those who had a total hip replacement, according to a study presented at the American Academy of Orthopedic Surgeons (AAOS) 2009 Annual Meeting.

The study was based on data on the outcomes of 214 total hip replacement patients and 132 hip resurfacing patients that was recorded in a joint registry maintained at a single surgeon’s practice from 2003-2006. Orthopedic surgeon Dr. Elizabeth Anne Lingard of Freeman Hospital in Newcastle Upon Tyne, England, was the study’s lead researcher.

Each patient enrolled in the study completed a questionnaire preoperatively and one year after surgery. The questionnaire included the Western Ontario and MacMaster Universities Osteoarthritis Index (referred to as WOMAC, it is a 24-item questionnaire that is completed by the patient and focuses on joint pain, stiffness and loss of function related to osteoarthritis of the knee and hip) and the SF-36, a self-report questionnaire completed by the patient that measures health-related quality of life (and generates 8 subscales: physical functioning, role limitations due to physical problems, bodily pain, general health perceptions, vitality, social functioning, role-limitations due to emotional problems, and mental health; and 2 summary scores: physical component and mental component). The patients also completed a questionnaire regarding satisfaction with their procedures and outcomes one year after surgery.

The study showed that one year after surgery both groups of patients experienced significant improvements in WOMAC and SF-36. Hip-resurfacing patients, however, posted significantly higher WOMAC scores for decreased pain symptoms. When asked about patient satisfaction with the surgery, a greater number of hip-resurfacing patients said they were satisfied with their ability to perform functional activities after surgery.

"The (Birmingham) hip resurfacing technique allows me to preserve more of the patient’s natural bone structures and stability," said Bradley Gerber, MD, Chief of Joint Replacement Surgery at South Nassau Communities Hospital. "I see hip resurfacing as the ideal solution for many of my younger, active patients who suffer from hip pain. As my patients are getting younger and younger, and are staying physically active much later in life, I've needed an alternative to total hip replacement that accommodates their age and lifestyle. Hip resurfacing is that alternative."

Dr. Gerber was among the first surgeons in the U.S. to perform the Birmingham Hip Resurfacing (BHR) technique. Rather than replacing the entire hip joint, as in a total hip replacement, hip resurfacing simply shaves off the damaged cartilage and bone and a metal cap is placed onto the head of the leg bone (femur).

Total hip replacement involves the removal of the entire femoral head and neck, replacing it with a metal ball, while the BHR leaves the head and neck untouched. It is the neck length and angle that determines the natural length of a patient’s leg after surgery. Since it is not removed and replaced with an artificial device during the resurfacing procedure, there is a greater likelihood of maintaining accurate leg length.

In addition, traditional hip replacements use a plastic socket compared to the BHR implant (which is a metal socket). A plastic socket wears down over time, and may need to be replaced surgically. In fact, it is a leading cause of follow-up surgeries.

The BHR is intended for patients suffering from hip pain due to osteoarthritis, hip dysplasia (a congenital disease that, in its more severe form, can eventually cause crippling damage and painful arthritis of the joints) or avascular necrosis (a disease resulting from the temporary or permanent loss of the blood supply to the bones, often leading to collapse of the joint surface), and for whom total hip replacement may not be appropriate due to an increased level of physical activity. For these reasons, Dr. Gerber feels the BHR is ideal for patients under age 60 who live non-sedentary lifestyles.

While the BHR implant closely matches the size of a patient’s natural femoral head (hip ball), it is substantially larger than the femoral head of a traditional total hip replacement implant. This increased size translates to greater stability in the new joint, and it decreases the risk of dislocation of the implant after surgery, which is a leading cause of implant failure after total hip replacement.

In addition to the BHR, orthopedic surgeons at South Nassau’s Long Island Joint Replacement Institute specialize in custom-fitted total joint replacement as well as minimally invasive joint replacement surgery, such as the Uni-Knee® partial knee replacement and Image-Guided Knee Replacement technique. Minimally invasive joint replacement reduces trauma to surrounding tissue, blood loss during surgery, post-operative pain, and recovery time, leading to a speedier rehabilitation and return to daily activities. According to Dr. Gerber, the average length of stay of patients treated by the institute is less than 3 days, which is well below the national average.

The Joint Replacement Institute combines image-guided medical technology with minimally invasive knee replacement instrumentation. Image-guided surgical technology is used to determine the precise alignment of the replacement parts; improves the surgeon’s view of and feel for the surgical field and reduces the size of the incisions to perform a replacement.

Other procedures offered by the Institute’s physicians include reconstruction of foot and ankle injuries, pediatric orthopedics, hand and upper extremities, and meniscus cartilage transplantation and Carticel Therapy to correct recurring knee cartilage injuries.
For more information about the Long Island Joint Replacement Institute or to schedule a consultation, call 1-877-SouthNassau. www.southnassau.org.

The Influence of Head Diameter, Clearance, Cup Position, and Head Position on Wear Rates in Metal-on-Metal Resurfacing 2008

nospam@example.com (Patricia Walter) — Fri, 10 Apr 2009 08:21:10 -0700

"The results also confirm clinical ion level measurements that steep cup angles can substantially increases wear"

Presented at the 2nd Annual Total Hip Resurfacing Arthroplasty Course in LA Oct. 2008

By: John Fisher
Co-Authors: Ian Leslie, Sophie Williams, Eileen Ingham, Graham Isaac
Institute of Medical and Biological Engineering
University of Leeds

Background: There are considerable variations in metal ion levels and metallic wear rates in patients with metal on metal resurfacing. In this in vitro study the effect of design variables of head diameter and bearing clearance and patient variables of cup and head position on metal ion levels and wear rates are were investigated. Methods: Hip joint simulator studies were carried out on size 39mm and size 55mm metal on metal resurfacing with the same design. Size 55mm diameter bearings with 110 micrometer diametrical clearance were compared to size 54mm diameter with larger >250 micrometer diametrical clearance. The wear rates of size 39mm bearings with a standard cup position of 45 degrees, were compared to a steep cup position of 60 degrees and to a steep cup position combined with micro separation associated with head offset deficiency.

Results: Initial bedding in wear rates and ion levels were higher with size 39mm bearings compared to size 55mm, but in long term after 15 million cycles there was no difference in the steady state wear rates. Bearings with the larger diametrical clearance had higher initial wear and steady state wear rates at five million cycles. Cup position and head position resulted in much greater increases in wear. For the 39 mm bearings, a 60 degree cup position resulted in a 9 fold increase in wear. A steep cup and microseparation resulted in a 17 fold increase in wear after two million cycles and a 39 fold increase in wear compared to the long term steady state wear rate.

Conclusions: The study confirmed clinical ion level studies of increased wear with larger clearance bearings. The results also confirm clinical ion level measurements that steep cup angles can substantially increases wear. The study also indicates that offset deficiency and microseparation may be responsible for extremely high wear rates and ion levels found in some retrievals and some patients. Further work is needed to investigate effect of different head sizes with steep cups and microseparation and the effect of version.

The Influence of Head Diameter, Clearance, Cup Position, and Head Position on Wear Rates in Metal-on-Metal Resurfacing 2008

nospam@example.com (Patricia Walter) — Fri, 10 Apr 2009 08:21:10 -0700

By: John Fisher
Co-Authors: Ian Leslie, Sophie Williams, Eileen Ingham, Graham Isaac
Institute of Medical and Biological Engineering
University of Leeds