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MEETING OF THE HIP SOCIETY

Thirty-Fourth Open Scientific Meeting

The Twelfth Combined Open Meeting Hip Society and AAHKS

Chicago, IL

March 25, 2006

PROGRAM CHAIRMAN

William Capello, M.D.

CONTENTS:

Program

Abstracts

Hip Society Officers

AAHKS Officers

 

COURSE OBJECTIVES: The objectives of the Open Meeting of The Hip Society is to provide up-to-date information on the treatment of problems involving the young adult hip including avascular necrosis and the current thinking on bearing surfaces. Another objective is to provide a balanced view of MIS surgery and DVT prophylaxis. In addition, we will update our thinking on the treatment of femoral neck fractures including those in the pediatric age group.

COURSE DESCRIPTION: This course is divided into a series of symposia beginning with a look at the young adult hip and various treatment options as well as long-term data on the success rates of various modalities. This will be followed by a detailed look at bearing surfaces, highlighted by the presidential guest speaker. There will be other symposia giving a balanced look at DVT prophylaxis and MIS surgery. Other topics include new techniques in revision surgery as well as a look at periprosthetic bone loss. Finally, The Hip Society Awards Papers and a summarization of the proceedings of the Research Society as it applies to the adult hip will be included in the program.

 INTENDED AUDIENCE: The intended audience is orthopedic surgeons and orthopaedic residents.

Program:

7:55 a.m.

Opening Comments

James D'Antonio, M.D.

 

SYMPOSIUM I:  

YOUNG ADULT HIP

Moderator: Dennis Collis, M.D.

Eugene, OR

 

8:00 a.m.              

Osteotomy

Joel Matta, M.D.

Los Angeles, CA

 

8:07 a.m.              

Hip Joint Impingement

Robert Trousdale, M.D.

Rochester, MN

 

8:14 a.m.

Cemented Total Hips In Patients Less Than 50yrs

Graham Gie, M.D.

Exeter, UK

 

8:21 a.m.              

Outcome Of Uncemented Total Hip Arthroplasty

In Patients Aged 50 Years Or Younger

Cecil Roraback, M.D.

London, Ontario, Canada

 

8:28 a.m.

Hip Resurfacing for Patients under 50 years of age.

Results of 350 Conserve® Plus With a 2-9 Year Follow-up

Harlan C. Amstutz, M.D.

Los Angeles, CA

 

8:35 a.m.

Avascular Necrosis

David Hungerford, M.D.

Baltimore, MD

 

8:42 a.m.

Discussion

 

SYMPOSIUM II:

BEARING SURFACES

Moderator: James D'Antonio, M.D.

Moon Township, PA

 

9:00 a.m.

Presidential Guest Speaker

Wear of Hip Prostheses: Influence of Material and Head Size

John Fisher, M.D.

Leeds, UK

 

9:20 a.m.

US Experience with Alumina Ceramic-Ceramic THA

Stephen Murphy, M.D.

Brookline, MA

 

9:27 a.m.

Metal-On-Metal Bearings:

State-Of-The-Art And Science In 2006

Joshua Jacobs, M.D.

Chicago, IL

 

9:34 a.m.

Highly Crosslinked Polyethylene: Now and in the Future

William Maloney, M.D.

Stanford, CA

 

9:41 a.m.

The Future of Hip Bearings

Michael Manley, Ph.D.

Ridgewood,. NJ

 

9:48 a.m.

Discussion

 

10:10 a.m.

Break

 

SYMPOSIUM III:

PERIPROSTHETIC BONE LOSS

Moderator: Robert Barrack, M.D.

St. Louis, MO

 

10:25 a.m.

Introduction Of The Problem

John Callaghan, M.D.

Iowa City, IA

 

10:32 a.m.

Nonsurgical Management of Osteolysis:

Challenges and Opportunities

Harry Rubash, M.D.

Boston, MA

 

10:39 a.m.

Acetabular Bone Loss

Charles Engh, M.D.

Alexandria, VA

 

10:46 a.m.

New Femoral Designs - Do They Influence Stress Shielding?

Andrew H. Glassman, M.D.

Columbus, OH

 

10:53 a.m.

Discussion

 

SYMPOSIUM IV:

DVT

Moderator: Richard White-Jr., M.D.

Albuquerque, NM

 

11:15 a.m.

Who Is At Risk?

Eduardo Salvati, M.D.

New York, NY

 

11:22 a.m.

Low Molecular Weight Heparin

Clifford Colwell, M.D.

La Jolla, CA

 

11:29 a.m.

The Use of Aspirin for Prophylaxis Against Thromboembolic Disease

After Total Joint Surgery

Paul Lotke, M.D.

Vancouver, British Columbia, Canada

 

11:36 a.m.

Rationale For and Results of Mechanical Thromboembolism Prophylaxis

For Total Hip Arthroplasty

Paul Lachiewicz, M.D.

Chapel Hill, NC

 

11:43 a.m.

Warfarin After THA for VTED

Vincent Pellegrini, M.D.

Baltimore, MD

 

11:50 a.m.

Discussion

 

12:10 p.m.            

Lunch

 

SYMPOSIUM V:

HIP SOCIETY AWARDS

Moderator: William Maloney, M.D.

Stanford, CA

 

1:15 p.m.

The John Charnley Award

A Study of Implant Failure in Metal-on-Metal Surface Arthroplasties

Pat Campbell, Ph.D.

Los Angeles, CA

 

1:25 p.m.

The Frank Stinchfield Award

Grafting of Biocompatible MPC Polymer on Cross-linked Polyethylene

Liner Surface for Extending Longevity of Artificial Hip Joints

Toru Moro, M.D.

Tokyo, Japan

 

1:35 p.m.

The Otto Aufranc Award

Clinical Significance of In Vivo Degradation for Polyethylene in Total Hip Arthroplasty

Steven M. Kurtz, Ph.D.

Philadelphia, PA

 

SYMPOSIUM VI:

RESEARCH SOCIETY PROCEEDINGS

 

1:45 p.m.

Summary Of Research Society Proceedings

Richard Coutts, M.D.

San Diego, CA

 

SYMPOSIUM VII:

FEMORAL NECK FRACTURES

Moderator: Richard. Kyle, M.D.

Minneapolis, MN

 

2:00 p.m.

Medical Treatment After Femoral Neck Fracture:

Does It Make A Difference?

Kenneth Koval, M.D.

Lebanon, NH

 

2:07 p.m.

Total Hip Arthroplasty in the Treatment of Femoral Neck Fractures

William Healy, M.D.

Boston, MA

 

2:14 p.m.

Bipolar Versus Unipolar

Miguel Cabane1a, M.D.

Rochester, MN

 

2:21 p.m.

The Management of Femoral Neck Fractures in Children

John Flynn, M.D.

Philadelphia, P A

 

2:28 p.m.

Discussion

 

2:43p.m.

Break

 

SYMPOSIUM VIII:

REVISION SURGERY - ARE WE MAKING PROGRESS?

Moderator: Robert Bourne, M.D.

London, Ontario, Canada

 

3:03 p.m.

Fully Coated Stems - Is This The Gold Standard?

Daniel Berry, M.D.

Rochester, MN

 

3:10p.m.

Femoral Revision Arthroplasty With Fluted Modular Titanium Stems

Donald Garbuz, M.D.

Vancouver, British Columbia, Canada

 

3:17p.m.

Cages - The Current Role

Wayne Paprosky, M.D.

Winfield, IL

 

3:24 p.m.

Trabecular Metal In Acetabular Reconstruction

David Lewallen, M.D.

Rochester, MN

 

3:31 p.m.

Impaction Grafting Of The Socket

John Timperley, Ph.D.

Exeter, UK

 

3:38p.m.

Discussion

 

SYMPOSIUM IX:

MIS (MINIMALLY INVASIVE SURGERY)

Moderator: Arlen D. Hanssen, M.D.

Rochester, MN

 

3:53 p.m.

Patient Selection Variables for Minimally Invasive Surgery

Thomas Sculco, M.D.

New York, NY

 

SURGICAL APPROACHES:

4:00 p.m.

Direct Anterior Approach

William Hozak, M.D.

Philadelphia, P A

 

4:07 p.m.

The 2-Incision THA: Its Role in 2006

Mark Pagnano, M.D.

Rochester, MN

 

4:14 p.m.

Management of Peri-Operative Pain

Lawrence D. Dorr, M.D.

Inglewood, CA

 

4:21 p.m.

Comprehensive Approach To Rehabilitation

Benjamin Bierbaum, M.D.

Boston, MA

 

4:28 p.m.

Measurable And Clinically Relevant Outcomes

Aaron Rosenberg, M.D.

Chicago, IL

 

4:35 p.m.

Discussion

 

5:00 p.m.

Adjourn

 

Abstracts:

8:00 a.m.

Young Adult Hip: Osteotomy
Joel M. Matta, M.D.

For young adult hips, the primary causes of arthritis are acetabular dysplasia and femoral-acetabular impingement. Periacetabular Osteotomy has evolved over the past 20 years as the preferred treatment for acetabular dysplasia and is now supported by a number of follow-up studies.

Periacetabular Osteotomy was first performed in Bern Switzerland in 1984. Its impetus came from Reinhold Ganz, Chief of Orthopedics at the Inselspital, Bern and Jeffrey Mast. This osteotomy is a rotational acetabular osteotomy for correction of acetabular dysplasia. Like the preceding dial osteotomy it allows an essentially unlimited rotational correction and does not transect the posterior border of the innominate bone. As an advantage over the dial osteotomy, the periacetabular osteotomy allows a change in the center of rotation. The dysplastic hip typically has a center of rotation that is in a proximal and lateral position leading to an abnormal Shenton's line. This osteotomy tends to restore Shenton's line by bringing the center of rotation into a more medial and distal position. An advantage of the Periacetabular over the Dial besides the center of rotation change is that it is performed from the inside of the pelvis without disruption of the gluteal muscles on the external aspect of the bone. Other traditional pelvic rotational osteotomies such as the Steele, Sutherland, and Salter, do not have the same potential for rotational correction, may lead to pelvic deformity, and often retrovert the acetabulum.

Periacetabular osteotomy is indicated for patients with symptomatic acetabular dysplasia and following triradiate cartilage closure. The age range in this group is 15 to 55. The ideal indication is acetabular dysplasia patients with pain, good range of motion, a normal joint space, minimal arthritic changes, a spherical femoral head, and good congruence and coverage on the abduction internal rotation view. The majority of candidates are female and usually have a more predictably positive result than males. Older patients should meet ideal criteria where as younger patients are candidates despite less than ideal criteria. Proximal femoral osteotomy is simultaneously performed in a minority of patients to correct femoral deformity and/or enhance congruence and coverage.

From 1987 to 2005 the author performed 251 periacetabular osteotomies in 233 patients (18 bilateral). 19 associated femoral osteotomies were performed. The average patient age was 32 years old. Across the entire series, the median operative time was 2.5 hours and the median blood loss was 700 cc. The operative time and blood loss were compared between the first 50 surgeries and the last 50 surgeries in the series; median operative time was 3 hours in the first 50 surgeries and 1.5 hours in the last 50 surgeries. Median blood loss was 1000cc in the first 50 surgeries, and 375 cc in the last 50 surgeries. 142 patients were available with a minimum of 1-year follow-up; with an average follow-up of 4.14 years (range 1-15 years). At their most recent follow-up, 19% of patients had an excellent clinical result; 60% had a good clinical result, 14% had a fair clinical result, and 7% had a poor result. Six patients underwent subsequent total hip replacement.


8:07 a.m.

Hip Joint Impingement

 

Robert T. Trousdale, M.D.


The majority of patients who develop hip arthritis have a mechanical abnormality of the joint. The structural abnormalities range from instability (DDH) to impingement. Impingement leads to osteoarthritis by chronic damage to the acetabular labrum and adjacent cartilage.

 

In situations of endstage secondary DJD, hip arthroplasty is the most reliable treatment choice. In young patients with viable articular cartilage, joint salvage is indicated. Treatment should be directed at resolving the structural abnormalities that create the impingement.

Femoral abnormalities corrected by osteotomy or ( head-neck offset by chondro-osteoplasty creating a satisfactory head-neck offset. This can safely be done via anterior surgical dislocation. The acetabular-labral lesions can be debridement and/or repaired. Acetabular abnormalities should be corrected by "reverse" PAO in those with acetabular retroversion or anterior acetabular debridement in those with satisfactory posterior coverage and a damaged anterior rim.

Often combinations of the above are indicated.

 

8:14 a.m.

Cemented Total Hips In Patients Less Than 50yrs

 

S Lewthwaite, B Squires, G. Gie, AJ Timperley, J Howell, M Hubble, Prof. R Ling.

 

The Cemented Exeter Total Hip Replacement was introduced into clinical practice in 1970 and since that time has been used in Exeter in patients of all ages. Although cementless sockets with ceramic bearings are now used in young patients, the cemented stem remains our treatment of choice for all age groups.

In 1988 modularity was introduced into the system and since that time the Exeter Hip Research Unit has prospectively gathered data on all patients who have had total hip replacements (THR's) at the Princess Elizabeth Orthopaedic Hospital. A recent review has been conducted to determine the medium- to long-term term survivorship and function of the Exeter Universal Hip Replacement when used in younger patients, a group that is deemed to place high demands on their arthroplasties

There were 130 Exeter Hips in 107 patients who were 50 years or younger at the time of surgery and whose surgery had been performed a minimum of 10 years previously . Mean age at surgery was 42y (range 17y to 50y). 6 patients who had 7 THR's had died, leaving 123 THR's for review. Patients were reviewed at an average of 12.5 years (10 - 17 years) post-op. No patient was lost to follow up.

Results: At review, 12 hips had been revised. Of these, 9 were for aseptic loosening of the acetabular component and one cup was revised for focal lysis and pain. One hip was revised for recurrent dislocation. One femoral component required revision in 1 case of infection. Radiographs showed that a further 11 (10%) of the remaining acetabular prostheses were loose but that no femoral components were loose. Survivorship of stem and cup from all causes was 94% into the seventeenth year. With any reason for revision of the stem as the end-point, survivorship was 99% and with aseptic loosening as the end-point, survivorship was 100%.

Conclusion: The Exeter Universal Stem is shown to perform extremely well in the younger patient. No femoral component became loose and only 7.3% of acetabular components were revised for aseptic loosening at a follow-up period of 10 to 17 years.

 


8:21 a.m.

Outcome Of Uncemented Total Hip Arthroplasty

In Patients Aged 50 Years Or Younger

 

Cecil H. Rorabeck, M.D., F.R.C.S.C., SR Kearns M.D., F.R.C.S.I. (Tr & Orth), J. Bilal

 

Providing a long-lasting total hip arthroplasty (THA) for the young patient with hip arthritis remains one of greatest challenges for modern arthroplasty surgery. Between 1983 and 2000, 221 patients underwent 298 uncemented THAs at our institution. 10, 15 and 20-year survival was assessed, with any aseptic revision as the end-point. Latest radiographs were assessed for polyethylene wear, component loosening and osteolysis. Femoral stem survival was 98.9(97.7-100%)%, 96.8(92.5-100%)% and 90.7(78.5-100%)% at 10, 15 and 20 years. Acetabular component survival was 84.6(78.8-90.4%)%, 52.5(40.7-64.3%)% and 23.3(6.8-39.8%)% at 10, 15 and 20 years. Excluding polyethylene liner exchange, this increased to 90.6(85.7-95.5%)%, 65.3(52.8-77.8%)% and 55.4(38.8-72%)% at 10, 15 and 20 years. THAs performed for hip dysplasia and avascular necrosis had lower 10-year survival. 69 revisions were performed, the commonest indication being polyethylene wear (n=33). In unrevised THAs 40.3% showed asymmetric polyethylene wear. Zirconium on polyethylene articulations had significantly lower acetabular revision rates compared with cobalt-chrome on polyethylene (p=0.02). Uncemented femoral stems provided over 90% survivorship at a minimum 20-year follow-up. Contemporary bearing surfaces in association with such stems may provide long lasting THAs even in young active patients.

 

8:28 a.m.

Hip Resurfacing for Patients under 50 years of age.

Results of 350 Conserve® Plus With a 2-9 Year Follow-up

 

Harlan C. Amstutz, M.D., Scott T. Ball, M.D.,

Michel J. Le Duff, M.A. and Frederick J. Dorey, Ph.D

 

Introduction:  Patients under 50 years of age with degenerative diseases of the hip pose a difficult treatment challenge.  Historically, total hip replacement in this high demand patient population has demonstrated diminished survivorship. Because it saves the femoral head and is easily revisable resurfacing arthroplasty of the hip is an attractive treatment option for young, active patients. The purpose of the present study was to determine the effectiveness of metal-on-metal hip resurfacing for the treatment of patients under 50 years of age.

Materials and Methods: From a consecutive series of over 900 Conserve® Plus metal-on metal hybrid resurfacings, 350 hips  were resurfaced in 295 patients less than 50 years old. The average age of the patients was 41.2 years (range, 14 to 49) 75% were male. ”Idiopathic” OA was the etiology in 50%, DDH in 16%, trauma in 11%, ON in 11%, LCP and SCFE 7%, Inflammatory diseases 4%, and others (PVNS and melorheostosis) less than 1%.  All femoral components were cemented with an approximate 1mm cement mantle.  The femoral metaphyseal stem was cemented in 105 hips and press-fit in the remaining 245.  All acetabular components were pressfit.

Results:  Average follow-up was 5.3 years (range, 1.6 to 9.1).  UCLA hip scores improved significantly from before surgery to most recent follow-up (pain: 3.4 to 9.4; walking: 6.0 to 9.6; function: 5.6 to 9.5; activity: 4.5 to 7.6.)  There have been no cases of acetabular component loosening. There has been a 2.8% rate of revision for femoral aseptic loosening (10 hips) and one femoral neck fracture.  An additional eight hips (2.3%) have radiolucencies about the femoral stem. All are asymptomatic but one who was lost to follow-up. Lastly, there has also been one revision for late hematogenous sepsis and 1 for recurrent subluxation from impingement. Of these failures, the average surface arthroplasty risk index (SARI) was significantly higher than the average of the entire cohort (4.3 compared to 2.6, p=0.0001). There has been no femoral component loosening when the femoral stems were cemented in.

Conclusions:  Metal-on-metal resurfacing arthroplasty of the hip is performing well at short to mid-term follow-up in young, active adults despite their high activity levels. Cementing the stem of the femoral component appears to be important, particularly in patients with risk factors. Patient selection and surgical technique are essential in improving outcomes in hips with risk factors.

 

8:35 a.m.

Osteonecrosis: A New Era

 

David S. Hungerford, M.D.

 

Osteonecrosis (ON) of the femoral head has been a significant orthopedic problem for the last 100 years. At first it was a problem of diagnosis and separation from severe OA of the hip. Since it has been separated diagnostically, it has been a therapeutic problem. The significant improvement in outcome that came to suffers of OA of the hip in the 1970's turned out to be fools gold for most patients with osteonecrosis. Although high failure rates were experienced in most categories of THR in young active patients, THR in ON patients turned out to be particularly problematic. Conservative (non-operative) management appeared to offer virtually no hope, and preservative therapy, didn't work for most patients, and often involved surgery associated with marginal success rates and exposure to significant morbidity and complications. That was the unhappy truth for ON. This lead to a nihilistic approach, of widespread advice to patients to 'hold on for as long as you can and when you can't stand it any more we will do a total hip replacement'.

It appears to me that the new bearing surfaces offer a much brighter future for patients with ON. The majority of patients present with advanced large lesions. In the past, surgeons could be justified in doing large complex operations with success rates in the 70% range because of the miserable success rate of THR and the specter of multiple revisions with increasing complication rates and dwindling success. With the new bearing surfaces and the high success of current cementless offerings, this posture can no longer be justified. Proximal femoral osteotomies, and free vascularized bone grafts are procedures that are associatd with significant morbidity and alter the proximal femur, complicating subsequent THR. These and limited femoral head resurfacing were often justified to 'buy time' until THR technology could catch up with patient need. That time has now come!

There still are some cases that present with moderate sized lesions that have not yet collapsed. Core decompression and bone grafting can still be justified because of the limited nature of the procedure, the low complication rate and the lack of consequence on subsequent THR. With some of the newer bone graft substitutes and bone stimulating biologics, the success rate of these procedures may be further enhanced. However with three long lasting highly durable bearing surfaces to choose from; metal-metal, ceramic-ceramic and metal on highly crosslinked Polyethylene, fear of Total hip replacement is not the driving factor that it was as recently as five years ago.

 

9:00 a.m.

Wear of Hip Prostheses:

Influence of Material and Head Size

 

John Fisher, M.D.

 

Younger and more active patients are now demanding reduced wear and increased osteolysis free lifetimes, as well improved function, range of motion and stability, in the choice of their hip prostheses With more active patients undertaking up to five million steps per year and life expectancies in excess of 30 years, this can deliver in excess of a ten fold increase in the functional tribological demand of the wear life of the bearing, in comparison to a lower demand elderly patient. The more active patients also demand improved biomechanical functional associated with larger head sizes. However this can lead to an intrinsic design contradiction with polyethylene acetabular cups, where larger head sizes can lead to increased sliding distances and increased wear rates. In conventional polyethylene acetabular cups, wear rates of 30 mm3/million cycles with size 28mm femoral heads, may provide up to twenty years osteolysis free lifetimes for low activity patients, but the osteolysis free lifetime is markedly reduced if patient activity or head size is increased. Alternative material combinations now have to be considered for these high demand patients.
Highly cross linked polyethylene has shown a four fold reduction in wear rates compared to conventional polyethylene, but the wear particles have been shown to be smaller and twice as reactive, resulting in only a two fold reduction in functional osteolytic potential. Consideration has to be given as to whether this improvement in the biomaterial wear performance is sufficient to recommend use with large diameter heads or with patients with up to a ten fold increase in functional tribological demand.

Alumina ceramic on ceramic bearings, have between a twenty five to 1000 fold reduction in wear volume compared to polyethylene bearings and the wear particles show a two fold reduction in biological activity. So even with the highest wear rates found under conditions of microseperation, the ceramic on ceramic bearings show a fifty fold reduction in functional osteolytic potential, and allow larger size 36mm diameter heads to be used, providing improved biomechanical function as well as extended wear life.

Metal on metal bearings have a twenty five to 500 fold reduction in wear rate compared to conventional polyethylene bearings. Wear rates are critically dependent on design and radial clearance with lower radial clearance giving lower wear). For these lubrication sensitive bearings, wear is predicted to reduce with larger head sizes. There are concerns that the nanometre size metal wear particles can cause hypersensitivity and elevated ion levels, and there is considerable interest in use of larger diameter bearings such as surface replacements that have even lower wear rates.
Recent experimental studies have shown a further reduction to metal on metal wear with novel differential hardness ceramic on metal bearings and with surface modified metal on metal bearings. Future clinical studies will reveal whether these will also lead to reduced metal ion levels in vivo.
As the functional and tribological demands of patients increase, alternative hard on hard bearings are required to provide low wear and extended osteolysis free life times, when coupled with larger head diameters.

 

9:20 a.m.

US Experience with Alumina Ceramic-Ceramic THA

 

Stephen Murphy, Timo Ecker, Moritz Tannast, Benjamin Bierbaum,

Jonathan Garino, Eric Hume, Richard Jones, Robert Zann, Kristaps Keggi and Kenneth Kress

 

Bearing wear and associated osteolysis are the most common problems affecting the long-term results of total hip arthroplasty. Alumina ceramic-ceramic bearings have been introduced as one method of addressing these problems. The current study reviews the clinical outcome of the use of alumina ceramic-ceramic bearings in the United States and specifically reports on the 2 to 8 year results of 22 surgeons who participated in an FDA-IDE study.

1687 THA were performed in 1466 patients using alumina ceramic-ceramic bearings (Transcend(r) and Lineage(r) acetabular components, Wright Medical Technology, Inc.) by 22 surgeons in the US from April, 1997 to February, 2003 and studied prospectively. Of these, 1031 hips were followed for a minimum of 24 months (range 24 to 101 months), mean 47.91 months. Patients were aged 52.08 +/- 10.77 years (range 18-81 years).

Results. Of the 1687 THA's, aseptic revisions included femoral component revision for loosening or failure of osseointegration in 11 hips and of the acetabular component in 2. Three hips were revised for acetabular liner fracture and one was revised for femoral head fracture. Other revisions included three hips with mis-matched head-liner bearing diameters and one hip where the liner was not properly seated. Two hips were converted to a non-ceramic bearing during the index operation for use of a lipped-liner or extended head. One hip was revised for recurrent instability. 7 hips were revised for infection. 3 hips were revised in association with periprosthetic fracture. There have been no other cases of wear and no cases with osteolysis in any unrevised hip as visible on plain radiographs. 8 year Kaplan-Meier Survivorship for revision of any component for loosening or bearing failure is 97.3 % (Standard Error 0.008).

Results of data from this prospective FDA/IDE demonstrate that the alumina ceramic-ceramic bearings are reliable and show very few early problems. Ceramic fractures do occur rarely and may be similar in incidence to reports of fractures of polyethylene components. The incidence of instability is extremely low despite the absence of lipped liners and fewer head-length options. The bearings continue to demonstrate the absence of osteolysis in this series of more than 8 years maximum follow-up.

 

9:27 a.m.

Metal-On-Metal Bearings: State-Of-The-Art And Science In 2006

 

Joshua J. Jacobs, M.D., Nadim Hallab, PhD, Robert Urban,

Anastasia Skipor, M.S. and Marcus Wimmer, PhD.

 

There continues to be keen interest in the application of metal-on-metal bearings in total hip and hip resurfacing arthroplasty. The advantages of metal-on-metal bearings include a substantially lower volumetric wear rate in comparison to conventional metal-on-polyethylene bearings, easy fabricability, high fracture toughness, and the ability to use large femoral heads thereby improving the range of motion and lessening the risk of postoperative instability. The major disadvantage of metal-on-metal bearings relates to the potential intermediate- and long-term biological effects of chronic elevations in local and systemic cobalt and chromium levels. Even though volumetric wear rates are substantially reduced compared to conventional bearing couples, metal-on-metal bearings actually produce a greater number of particles since the debris generated is in the nanometer size range, likely as a consequence of wear-induced metallurgical transformations (recrystallization and martensite formation) at or near the surface. While the bioreactivity of nanometer-sized cobalt-alloy debris is not well-characterized, large numbers of such minute particles yields a relatively high specific surface area (surface area/mass) available for dissolution (corrosion) of these particles. This may account, at least in part, for the substantial elevations in serum and urine cobalt and chromium concentration that have been documented by numerous investigators.

As more experience is gained with the so-called second-generation metal-on-metal bearings, intermediate-term clinical results are now becoming available. While these studies are generally favorable, there have been reports of early osteolysis, possibly related to metal hypersensitivity. In addition, histopathological studies on tissues retrieved from patients with failed metal-on-metal devices reveal a pattern of lymphocytic response that is distinct and suggestive of a delayed-type hypersensitivity response.

In the high demand patient, metal-on-metal bearings remain a viable option for total hip arthroplasty and the only currently available option for surface arthroplasty. Continued surveillance of populations with metal-on-metal devices is warranted to determine whether there is a demonstrable long-term survivorship advantage associated with the use of these bearings and to determine whether chronic elevations in systemic metal content are tolerated in the long term.

 

9:34 a.m.

Highly Crosslinked Polyethylene:

Now and in the Future

 

William J. Maloney, M.D.

 

Highly crosslinked polyethylene was introduced more than five years ago to address the most common long term complication in total hip replacement, osteolysis associated with the biologic reaction to polyethylene wear debris. The hypothesis was that enhanced crosslinking would decrease the wear volume and thus decrease the incidence of osteolysis. Prospective clinical trials have been performed evaluating many of the currently available products. In general the results have been excellent demonstrating a significant reduction in wear even at two years. Follow-up is too short to conclude that there will be a corresponding reduction in osteolysis.

Two potential problems have been identified with the first generation products. The first relates to in vivo oxidation. One product is manufactured is such a way so that the implant has a relatively high oxidation potential. Early retrievals have shown oxidation and the formation of a white band primarily in the non-weightbearing regions of the component. However, to date, this has not correlated with accelerated wear in prospective studies. The second problem relates to decreased mechanical properties of highly crosslinked polyethylenes compared to conventional material. Polyethylene fracture has been reported in a limited number of cases. Factors unique to these cases include the use of large femoral heads and elevated rim liners with malpositioned sockets. The net effect is loading of unsupported polyethylene and subsequent fracture. Both issues are currently being addressed with the next generation of crosslinked polyethylenes which are currently undergoing laboratory and early clinical evaluation.

 

9:41 a.m.

The Future of Hip Bearings

 

Michael T. Manley, Ph.D.

 

Contemporary bearing technologies continue to decrease wear debris in the hip and reduce the potential for osteolysis in young patients in the medium term. However, an overlooked consequence of present acetabular designs is the abnormal stress distribution in acetabular bony structures caused by stiff, well-fixed acetabular shells. Stress analysis of the normal acetabulum and the acetabulum with hemispherical shells of different material properties demonstrates the adverse remodeling potential associated with all contemporary designs in the young pelvis. Concomitant reduction in bone density may make acetabular structures less resistant to wear debris intrusion.

Comparison of hemispherical acetabular shells with more geometrically flexible designs shows an improvement in acetabular stress state with the geometrically flexible devices. It is likely that the future of acetabular bearings and acetabular reconstruction is a hard head/flexible socket bearing couple that can address current concerns, such as wear and bearing noise, while at the same time prevent long-term stress related deterioration of bony structures.

 

10:25 a.m.

Periprosthetic Bone Loss: Introduction of the Problem

 

John J. Callaghan, M.D.

 

In 1968 Charnley reported a pattern of non-linear endosteal erosion of bone in association with cemented total hip arthroplasty. Since that time, numerous authors have demonstrated the phenomenon of "osteolysis" around both cemented and cementless femoral and acetabular components. Over the years, surgeons and basic science investigators have come to understand the importance of nanometer size wear generated particles in the development of "osteolysis" type periprosthetic bone loss. In addition, the understanding of the contribution of access channels for wear particle transport has been recognized. More recent work has centered around the contribution of fluid pressures generated in the total hip arthroplasty construct.

In addition to the "osteolytic" pattern of bone loss, bone loss associated with "stress shielding" around implants has been described and investigated. The phenomenon has been reported around both cemented and cementless implants. The contribution of the initial bone quality at the time of hip replacement has been suggested as a major factor in the extent of bone loss related to stress shielding. Investigators have demonstrated the difficulty in differentiating bone loss related to stress shielding versus that related to wear particle generation, and the potential additive effect of these two phenomenon. A better understanding of the factors contributing to bone loss should enable surgeons and implant designers provide total hip arthroplasty constructs for our patients which limit the bone loss associated with the long term function of these constructs.

 

10:32 a.m.

Nonsurgical Management of Osteolysis: Challenges and Opportunities

 

Harry E. Rubash, M.D., Carl Talmo, M.D. and Arun Shanbhag, Ph.D., M.B.A.

 

Recent technological advances in bearing surfaces have resulted in significant reductions in wear and potential improvements in implant longevity, however, osteolysis currently remains a major source of failure in total hip arthroplasty In vitro and animal models have been instrumental in determining the pathophysiology of this disease and also carefully dissecting the biochemical pathways by which particulate wear debris leads to peri-implant bone loss. Numerous cytokines and inflammatory mediators, including TNF-?, and IL-1 are critical participants in this cascade and may represent prime targets for pharmacologic intervention. Osteoclasts, the end effector cells involved in the osteolytic process, also represent potential targets. Cell surface receptors on osteoclast precursors such as RANK on osteoclasts and RANK-ligand on stromal cells provide opportunities to arrest osteoclast maturation. Enhancing the naturally occurring osteoprotegrin represents another recent attempt at modulating osteoclast behavior and a possible target for pharmacologic therapies.

In this presentation, we will succinctly summarize the various strategies attempted by investigators: from intercepting TNF-? activity, interfering with the RANK-RANKL interaction necessary for osteoclast development and maturation, bisphosphonate therapy, to using viral vectors to deliver genes. The challenges of each of these approaches as well as their opportunities will be summarized. Until there is convincing evidence of efficacy in human clinical trials, the recommended management of osteolysis around THA remains vigilant screening and appropriate surgical intervention when there is the presence or potential for component loosening, periprosthetic fracture or major bone loss.

 

10:39 a.m.

Acetabular Bone Loss

 

Charles A. Engh, Sr., M.D.

 

Bone loss following total hip arthroplasty falls into two categories, bone loss that occurs due to stress-induced bone remodeling and bone loss from osteolysis. Although both types of bone loss can begin immediately after implantation, stress induced bone loss, or stress shielding, can be detected on radiographs approximately 1 to 2 years postoperatively while bone loss caused by osteolysis can be detected at 6 or more years postoperatively.

Bone loss by both etiologies is easier to visualize and quantify in the femur than in the pelvis for two reasons. First, the simpler cylindrical geometry of the femur and the ability to rotate a patient's leg make it possible to view the stem inside the femur at multiple projection angles. The complex geometry of the pelvis also makes it difficult to obtain more than a few reproducible x-ray projections. Second, the bone loss that occurs in the femur is predominately cortical rather than cancellous, which is easier to detect on radiographs and DEXA. Plain radiographs and DEXA are less effective for identifying and quantifying bone loss behind an acetabular shell since the bone loss is predominately cancellous.

We have found the most reliable method to assess pelvic bone loss to be quantitative CT of hemipelves obtained from patients at autopsy. The ideal patient is one who has had a unilateral hip total hip arthroplasty. Both the implanted and non-implanted hemipelves, devoid of soft tissue and the femoral component, can be scanned by CT in identical orientation. Using high kV settings that are not safe for living patients, any beam scatter from the thin titanium shell can be eliminated. The resulting images from each side can then be compared for changes in cancellous bone density behind the acetabular shell.

The pattern of bone loss of a hip implanted with an acetabular shell is dependent on whether the porous coating on the shell has become osseointegrated, meaning that it has become fixed by bone growth inside the sintered beaded or fibermesh surface. When bone ingrowth has occurred, a characteristic pattern of bone remodeling can be clearly identified on the CT images. Any residual subchondral plate is resorbed and replaced by the more rigid titanium shell. If the shell was positioned at surgery to have maximum cortical contact with the acetabular rim, and the acetabular fossa remains intact, cancellous bone atrophy occurs behind the dome of the shell and cortical hypertrophy occurs at the rim at the areas of localized cortical contact. These changes are usually not visible on serial plain radiographs because radiographs are so sensitive to slight alterations in technique. Additionally, since DEXA predominantly records cortical bone loss, and this stress-induced bone remodeling consists mostly of cortical bone atrophy, the changes are difficult to detect by DEXA.

Despite having over 25 years of experience, the authors have not been able to document either a cup loosening or stem loosening resulting from stress induced bone remodeling. In fact, if these changes are not visible in the femur, the authors believe that the femoral component is probably not osseointegrated and that late failure is more likely to occur than if the changes are present.

Pelvic osteolysis represents a very different pathologic process than stress shielding. Soft unstressed bone near the joint is resorbed when it comes in contact with joint fluid under increased pressure, particularly if the joint fluid contains particulate debris. The radiographic definition of osteolysis is quite different than that of stress shielding and includes 1) a localized expansile area devoid of cancellous bone, 2) a sclerotic border, and 3) a clear communication pathway between the lytic area and the joint space. CT is much more accurate for diagnosing pelvic osteolysis than plain radiographs and with modern CT technology, the 3 distinguishing radiographic features are always visible. CT is particularly valuable for detecting small lesions hidden on plain radiographs behind the cup and for confirming the connection to the joint space, which often can not be defined on radiographs. Finally, CT also is advantageous since it allows for accurate measurement of lesion volume.

In contrast to stress-induced bone remodeling, which seems to stabilize after a few years, pelvic osteolytic lesions almost always progressively enlarge in a linear manner. Although the authors have visualized many extremely large lesions in the pelvis at late follow-up, very few resulting complications, such as cup loosening or pelvic fracture, have been observed. As a result, the best method of surgical treatment of this condition is unknown.

 

10:46 a.m.

New Femoral Designs --- Do They Influence Stress Shielding?

 

Andrew H. Glassman, M.D., M.S. and J. Dennis Bobyn Ph.D.

 

Stress mediated bone resorption -"stress shielding"- is influenced by host factors (e.g. pre-operative bone mineral density), implant factors (stem stiffness, extent of ingrowth surface), and by the rigidity of implant fixation to host bone. The role of femoral component design has been long recognized and is the focus of this presentation.

Stem stiffness is the product of stem geometry and modulus of elasticity of the alloy or composite from which the implant is fabricated. Implant stiffness can therefore be manipulated by changes in materials, stem shape, or both. Early attempts at reducing stem stiffness focused upon stem materials, employing various polymer-metal composites. Many such designs suffered mechanical failure attributable to poor fatigue strength of the surface polymers. Titanium alloy was recognized as suitably strong with a lower modulus than cobalt chromium alloys. Within certain size ranges, the use of titanium versus cobalt alloy stems results in reduced stress shielding.

A subsequent strategy was the limitation of the ingrowth surface to the proximal implant. It has been clearly demonstrated that in so doing, for similarly shaped implants of identical composition, the distal extent of stress shielding is significantly reduced. However, in concentrating the area of load sharing to the most proximal femur, the severity of bone loss per unit of bone is actually increased.

Recent attempts to reduce implant stiffness have centered largely upon changes in stem geometry; specifically, the removal of implant material to reduce the cross-sectional moment-area and hence, the bending stiffness of the stem. Medial "cut-outs", "clothespin" designs, and flutes are examples of efforts to reduce the mid- and distal stem stiffness. However, the geometric contribution to stem stiffness is most pronounced in the bulkier proximal aspect of the stem. There is a paucity of data in the form of controlled studies using DEXA analysis to demonstrate that such design changes reduce stress shielding. Previously, some advocated maximum proximal "fit-and-fill" with bulky metaphyseal-filling implants. Such designs, despite being proximally coated, were associated with significant stress shielding. Wedge-shaped stems that are flatter in the anterior-posterior dimension demonstrate less stress shielding than canal-filling stems that fill the femur more completely.

Clinical trials with a contemporary composite stem began in the United States and abroad in 1994. The stem features a solid cobalt chromium core covered with a polymeric layer enclosed by an extensive porous coating of titanium fiber metal. DEXA studies demonstrate a significant reduction in stress shielding as compared to similarly sized and shaped implants fabricated of solid metal.

Clinically, stress shielding is usually associated with bone ingrowth and a favorable clinical result. To date, no data suggests a correlation between stress shielding and a risk of adverse events such as femoral shaft or trochanteric fracture, or osteolysis. However, in the event that a well-fixed stem requires removal for late infection or other cause, significant stress shielding complicates removal and compromises the bone stock remaining for reconstruction.

 

11:15 a.m.

Who is at risk?

 

Eduardo A. Salvati M.D., Burak Beksac M.D.

and Alejandro Gonzalez Della Valle, M.D.

 

The activation of the clotting cascade that occurs during total hip arthroplasty (THA) places patients at risk for venous thromboembolism (VTE). A thorough review of the current literature recognizes the following predisposing factors, outlined in order of importance: hip fracture, malignancy, particularly if associated with chemotherapy, antiphospholipid syndrome, history of VTE, immobility, administration of tamoxifen, raloxifene, oral contraceptives or estrogen; morbid obesity, stroke, atherosclerosis and American Society of Anesthesiologists (ASA) Physical Status Classification of 3 or greater. The following risk factors are considered weak or controversial: advanced age, diabetes mellitus, certain cardiovascular conditions, such as congestive heart disease and atrial fibrillation, varicose veins, and smoking.1, 2

However, 50 % of patients who develop thromboembolism after THA have no clinical predisposing factors. 3 Since the late 1990s, there has been an increased awareness of the role of heritable thrombophilia and hypofibrinolysis in the development of VTE. Combinations of these genetic factors with one another or with the recognized clinical risk factors previously mentioned multiply rather than add to the risk of VTE.4

We have defined in a matched controlled study the major genetic predispositions which increase the risk of VTE after THA: deficiency of antithrombin III (<75%) and of protein C (<70%), and homo-heterozygosity for the prothrombin gene mutation.5 Pre-operative genetic screening for these factors, in conjunction with the recognized clinical risk factors previously mentioned, can identify postoperative VTE risk and differentiate patients who could be protected with milder and safer forms of prophylaxis (aspirin, intermittent pneumatic compression), with those at higher risk who need to be anticoagulated. Preoperative genetic screening is cost effective. 5

  1. Heit JA, O'Fallon WM, Petterson TM, Lohse CM, Silverstein MD, Mohr DN, Melton III LJ: Relative Impact of Risk Factors for Deep Vein Thrombosis and Pulmonary Embolism: A Population-Based Study. Arch Intern Med 162:1245-1248, 2002.

  2. Salvati EA, Pellegrini VD, Jr., Sharrock NE, Lotke PA, Murray DW, Potter H, Westrich GH: Recent advances in venous thromboembolic prophylaxis during and after total hip replacement. J Bone Joint Surg Am 82:252-270, 2000.

  3. Gonzalez Della Valle A, Serota A, Go G, Sorriaux G. Sculco T, Sharrock N, Salvati E: Venous thromboembolism is rare after THR with a multimodal prophylaxis protocol. In press, Clin.Orthop 444, March 2006.

  4. Lane DA, Grant PJ: Role of haemostatic gene polymorphisms in venous and arterial thrombotic disease. Blood 95:1517-1532, 2000.

  5. Salvati EA, González Della Valle A, Westrich GH, Rana AJ, Specht L, Weksler BB, Wang P, Glueck CJ. Heritable thrombophilia and development of thromboembolic disease after total hip arthroplasty. THE CHARNLEY HIP SOCIETY AWARD. Clin.Orthop 441:40-55, 2005.

 

11:22 a.m.

Low Molecular Weight Heparin for DVT Prophylaxis

 

Clifford W. Colwell Jr., M.D.

 

Low molecular weight heparins (LMWH) have been studied extensively in total hip arthroplasty (THA) and provide both highly effective and safe DVT prophylaxis. Low molecular weight heparin received the highest rating, A1, in the American College of Chest Physicians (ACCP) recommendations for use in DVT prophylaxis after elective total hip arthroplasty. The prevalence of DVT with LMWH prophylaxis was 16% in a combination of THA studies involving over 6,000 patients, with a relative rate reduction of 70% compared to placebo. In these same studies, the prevalence of proximal DVT was 6%. LMWH is given by subcutaneous injection and can be started 12 hours before surgery, or 12 to 24 hours after surgery, or 4 to 6 hours after surgery at half the usual dose. Major bleeding rate reported for low molecular weight heparin is about 5% compared with about 4% in placebo trials. According to the GLORY data, surgeons in the USA report using LMWH prophylaxis on 43% of THA cases compared with a reported 90% in other countries. Also available is a synthetic pentasaccharide, fondaparinux, which also received an A1 rating in the ACCP recommendations. Combining two studies with over 1,600 patients, the overall DVT rate was 5% with a proximal DVT rate of approximately 2%. No major bleeding was reported, but overall bleeding was 3%. As with all interventions, the benefit has to be considered against the risk in use of these anticoagulants.

 

11:29 a.m.

The Use of Aspirin for Prophylaxis Against

Thromboembolic Disease After Total Joint Surgery