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THE 20TH ANNUAL CONGRESS OF THE INTERNATIONAL SOCIETY FOR TECHNOLOGY IN ARTHROPLASTY

ISTA 2007 OCTOBER 4-6, 2007

PARIS MARRIOTT RIVE GAUCHE HOTEL AND CONFERENCE CENTER PARIS, FRANCE Symposium Objectives:

PROCEEDINGS BOOK •

Evaluate new technologies for joint replacement, implant design and materials or biological solutions.



Interact with and learn from world-renowned orthopaedic surgeons and orthopaedic researchers.

Program Chair: Yves Catonne, M.D. (Paris)

1

ISTA 2007 The 20th Annual Congress of The International Society for Technology in Arthroplasty

October 4-6, 2007 The Paris Rive Gauche Hotel and Conference Center

PROCEEDINGS BOOK Contents Welcome Message ISTA Board of Directors ISTA 2007 Organizing Committee Layout of Exhibitors Acknowledgement of Exhibitor Support Program/Social Events Program at a Glance Agenda - Thursday, October 4 - Friday, October 5 - Saturday, October 6

Invited Lectures / Oral Presentations Poster Presentations

3 4 4 5 6 7 8-10 11-32

33-215 216-254

2

WELCOME MESSAGE Dear Colleagues: It is a privilege for me to Welcome you to Paris for the 20th Congress of the International Society for Technology in Arthroplasty (ISTA). ISTA is the only scientific orthopaedic society dedicated to the idea of providing a constructive environment for engineers and surgeons in the field of orthopaedics to come together to share their work and ideas. After two previous Congresses in France (Nice in 1990 chaired by Jean Manuel Aubaniac and Marseille in 1998 chaired by Jean-Noel Argenson), it is good to have the annual ISTA meeting back in France. The ISTA approach is different from that of conventional medical societies. Rather than presenting long-term results of recognized techniques, ISTA provides an opportunity for companies, engineers, R&D departments and surgeons to present new ideas, research and new technologies. Presentations range from fundamental (laboratory studies, biotechnology, design, etc.) to clinical (preliminary trial results, surgical techniques, CAOS, etc.) with any combination thereof. We hope every participant will enjoy their stay in Paris. We commend all of the ISTA 2007 participants and exhibitors who have come together to exchange their recent research in artificial joint technology and I thank profusely all of those organizations who have contributed in many different ways to the creation of this Congress. I am looking forward to hearing the many stimulating papers and hope that this Congress will be the most exciting and enjoyable. I also welcome the opportunity to promote international friendship and cultural exchanges in the old and historic city of Paris. Thank you for your participation. Yves Catonne Program Chair

3

INTERNATIONAL SOCIETY FOR TECHNOLOGY IN ARTHROPLASTY OCTOBER 4-6, 2007 The Marriott Paris Rive Gauche Hotel and Conference Center ISTA BOARD OF DIRECTORS, 2006-2007 President First Vice President Second Vice President First Past President Second Past President Secretary General Executive Director Treasurer Members

Yves Catonné (Paris) Won Yong Shon (Seoul) Richard D. Komistek (Knoxville) Peter Walker (New York) Takashi Nakamura (Kyoto) Nico Verdonschot (Nijmegen) Richard D. Komistek (Knoxville) Raj Sinha (Rancho Mirage) Hani Haider (Omaha), John Hollingdale (Bucks), Sam Nasser (Sterling Heights) Claude Rieker (Winterthur), Jeffrey K Taylor (Sacramento)

ISTA 20th ANNUAL CONGRESS, PARIS, FRANCE, OCTOBER 4-6, 2007 Chairman Co chairmen Organizing Committee Invited speakers

Yves Catonné (Paris) Thierry Judet (Garches), Jean Manuel Aubaniac (Marseille) Levon Doursounian (Paris), Christian Dumontier (Paris), Denis Huten (Paris), P Landreau (Paris), Jean Yves Lazennec (Paris), Remy Nizard (Paris), Philippe Piriou (Garches), Laurent Sedel (Paris) Jean Noel Argenson (Marseille), Gérard Deschamps (Dracy le Fort), Andreas Halder (Berlin), Marcel Kerboull (Paris), Jacques Yves Nordin (Paris) Dominique Saragaglia (Grenoble), Laurent Sedel (Paris), Thomas Schmalzried (Los Angeles), Marc Siguier (Paris)

PREVIOUS MEETINGS 1990 Nice, France 1991 San Francisco, USA 1992 Windsor, United Kingdom 1993 Amelia Island USA 1994 Amsterdam, Netherlands 1995 Porto Ricco 1996 Rome, Italy 1997 San Diego, USA 1998 Marseille, France 1999 Chicago, USA 2000 Berlin, Germany 2001 Hawaii, USA 2002 Oxford, United Kingdom 2003 San Francisco, USA 2004 Rome, Italy 2005 Kyoto, Japan 2006 New-York, USA

chairman: chairman: chairman : chairman : chairman : chairman : chairman : chairman : chairman : chairman : chairman : chairman : chairman : chairman : chairman : chairman : chairmen :

Internet Web

Jean-Manuel Aubaniac William Bargar Peter S. Walker Bernard Stulberg Riek Huiskes Riyaz Jinnah Giani Randelli Jeffrey Taylor Jean-Noël Argenson Rick Sumner Peter Thümler Hironobu Oonishi Peter Mac Lardy Smith Ian Clarke Giorgio Gasparini Takashi Nakamura Chit Ranawat and Peter S. Walker

www.ista.to 4

Exhibitor Layout

5

Titanium Sponsor Finsbury Orthopaedics

Exhibitors Finsbury Orthopaedics Kinamed Zimmer

Japan Medical Materials Tornier

A Special Thanks to: Depuy Orthopaedics for their support of the “Hap” Paul Award. Douglas Dennis, M.D. and Smith and Nephew for their support of the Student Biomechanics Award. .

6

Program at a Glance

……………

8-10

Agenda …………………………..

11-32

Abstracts ………………………….

33-215

Posters …………………………….. 216-254

Social Events Presidential Reception Wednesday, October 3 - 6:30 pm—7:30 pm Luxembourg Room Paris Marriott Rive Gauche Hotel & Conference Center Complimentary Spouses are welcome to attend.

Gala Awards Dinner Friday, October 5 7:00 pm-10:00 pm Automobile Club de France (Meet at the Club) Tickets required. Tickets can be obtained from the ISTA Registration desk.

7 7

ISTA 2007 PROGRAM AT A GLANCE Thursday, October 4, 2007 La Seine C Room La Seine B Room

Wednesday, October 3, 2007 6:00—

ISTA Registration (La Seine Ballroom Foyer) 6:30am - 5pm Speaker Ready Room (Le Pont de Arts Room) 6:30am - 5pm

7:00—

Exhibitors & Poster Display (La Seine Ballroom Foyer) 7am - 5pm

Welcome - Yves Catonne, M.D., Program Chair 7:45am 8:00—

A1– Hip– THR Femoral Stem

B1– Knee– TKR Kinematics 1 Chair:

Chair:

9:00—

Richard Komistek Darryl D’Lima 6 Presentations– 7 min each

Joseph Fetto Herni Migaud

10 Presentations– 7 min each

10:00—

11:00—

Coffee Break/Exhibitors/Posters

Peter S. Walker Michel Bercovy 6 Presentations– 7 min each

A2– Hip– Bearing Surfaces Chair: Ian C Clarke Aldo Toni

Coffee Break/Exhibitors/Posters B3– Knee– TKR ComputerizedAssisted Surgery 1

9 Presentations– 7 min each

12:00—

William L. Bargar

Invited: Dominique Saragaglia 4 Presentations– 7 min each

Restaurant Le Patio (Level 3) The Challenging Primary THA: Roundtable Discussion Moderator: JN Argenson 4 Speakers

2:00—

3:00—

5:00—

Chair:

Luncheon Buffet —12:15pm - 1:15pm

1:00—

4:00—

B2– Knee– TKR Kinematics 2 Chair:

ISTA Registration (La Seine Ballroom Foyer)

Speaker Ready Room (Le Pont des Arts Room)

A3– Hip– Polyethylene Bearing in THR Chair: Hironobu Oonishi Philippe Massin 10 Presentations– 7 min each

B4– Knee– TKR ComputerizedAssisted Surgery 2 Chair: S. David Stulberg Remy Nizard 9 Presentations– 7 min each Coffee Break/Exhibitors/Posters

B5 Unicompartimental Knee Chair: Jean Manuel Aubaniac Jean Yves Jenny Invited: Gerard Deschamps Jean Noel Argenson 6 Presentations– 7 min each

6:00—

7:00—

8:00—

Presidential Reception 6:30 pm—7:30 pm (Luxembourg Room- Level 3)

Exhibitor & Poster Set-Up (La Seine Ballroom Foyer)

8pm - 10pm

8

ISTA 2007 PROGRAM AT A GLANCE Friday, October 5, 2007 La Seine C Room

La Seine B Room

6:00— ISTA Registration (La Seine Ballroom Foyer) 6:30am - 5pm 7:00—

Speaker Ready Room (Le Pont de Arts Room) 6:30am - 5pm Exhibitors & Poster Display (La Seine Ballroom Foyer) 7am - 5pm

8:00—

9:00—

10:00—

11:00—

A4– Hip– THR Metal-On-Metal Chair:

Claude Rieker Christian Delaunay Invited: Thomas Schmalzried

B6– Knee– TKR Design, Mobile Bearing Chair:

8 Presentations– 7 min each

9 Presentations– 7 min each

Coffee Break/Exhibitors/Posters

Coffee Break/Exhibitors/Posters

A5– Hip– THR Alumina on Alumina Chair: Laurent Sedel Jeffrey Taylor Invited: Laurent Sedel 5 Presentations– 7 min each

12:00—

Luncheon Buffet - 12pm - 1pm

B7– Knee– TKR Technique: Approach, Ligament Balancing Chair:

Richard Cohen Peter S. Waler Invited: Dominique Saragaglia 10 Presentations– 7 min each

Restaurant Le Patio (Level 3)

1:00—

Luncheon Buffet—12:25pm - 1:15pm Restaurant Le Patio (Level 3)

A6– Hip– MIS THR Chair:

2:00—

Raj Sinha Thierry Judet Invited: Marc Siguier 4 Presentations– 7 min each

B8– Knee– TKR Deep Flexion Chair:

Coffee Break/Exhibitors/Posters

3:00—

4:00—

5:00—

Louis Lootvoet Jean-Louis Briard

A7– Hip– CAS THR Herni Judet Hani Haider 8 Presentations—7 min each “HAP” Paul Award Paper Presentation: Nico Verdonschot Yves Catonne

Samih Tarabichi Bruno Tillie

7 Presentations– 7 min each B9– Knee– TKR Various

Chair:

Chair:

Nobuo Takai Jacques Tabutin Invited: Giorgio Gasparini 8 Presentations– 7 min each

Launch of New ISTA Web Site - Hani Haider

6:00—

Gala Awards Dinner - Automobile Club de France 7:00—

7pm - 10pm—meet at the Club

9

ISTA 2007 PROGRAM AT A GLANCE Saturday, October 6, 2007 La Seine C Room

La Seine B Room

6:00— ISTA Registration (La Seine Ballroom Foyer) 6:30am - 5pm 7:00—

Speaker Ready Room (Le Pont de Arts Room) 6:30am - 5pm Exhibitors & Poster Display (La Seine Ballroom Foyer) 7am - 5pm

8:00—

A8– Hip– THR

B10– Hip and Knee: THR and TKR Coating Sam Nasser Jean Alain Epinette 5 Presentations– 7 min each Chair:

9:00—

Chair:

Young Yong Kim Marcel Kerboull

B11– Upper Limb

9 Presentations– 7 min each

10:00—

Coffee Break/Exhibitors/Posters

A9– Hip– Planning THR

11:00—

12:00—

Chair:

Chair:

Levon Doursounian Taco Gosens 5 Presentations– 7 min each Coffee Break/Exhibitors/Posters

John Hollingdale Moussa Hamadouche

9 Presentations– 7 min each

Luncheon Buffet — 12pm - 1pm

B12– Spine Chair:

Jean-Yves Lazennec Fabien Bitan 7 Presentations– 7 min each

Restaurant Le Patio (Level 3)

1:00— Chair:

2:00—

Jacques Tabutin Denis Huten Invited: Marcel Kerboull 6 Presentations– 7 min each A11– Hip Resurfacing

3:00— Chair:

4:00—

Luncheon Buffet - 12:25pm - 1:25pm Restaurant Le Patio (Level 3)

A10– Hip– THR Revision

Koen DeSmet William Macaulay Invited: Philippe Piriou 12 Presentations– 7 min each

B13– Hip and Knee– THR and TKR David Markel Vincenzo Denaro Invited: Jacques Yves Nordin 6 Presentations– 7 min each Chair:

B14– Ankle Thierry Judet Nobuo Takai 4 Presentations– 7 min each Chair:

4:15 Adjournment

5:00— 5:05 Adjournment

6:00—

7:00—

10

INTERNATIONAL SOCIETY FOR TECHNOLOGY IN ARTHROPLASTY OCTOBER 4-6, 2007 The Paris Rive Gauche Hotel and Conference Center

AGENDA Wednesday, October 3, 2007 3:00 pm – 6:00 pm 3:00 pm - 6:00 pm 6:30 pm – 7:30 pm 8:00 pm – 10:00 pm 8:00 pm – 10:00 pm

ISTA Registration Speaker Ready Room Presidential Reception Spouses invited to attend Exhibitor Set-Up Poster Set-Up

La Seine Ballroom Foyer Le Pont des Arts Room Luxembourg Room—Level 3 La Seine Ballroom Foyer La Seine Ballroom Foyer

Thursday, October 4, 2007 6:30 am – 5:00 pm 6:30 am—5:00 pm

ISTA Registration Speaker Ready Room

La Seine Ballroom Foyer Le Pont des Arts Room

7:00 am – 5:00 pm 7:00 am – 5:00 pm

Exhibitors Poster Display

La Seine Ballroom Foyer La Seine Ballroom Foyer

7:45 am

Welcome Yves Catonne, M.D., Program Chair All Attendees

La Seine Ballroom C

A1– HIP—THR FEMORAL STEM

La Seine Ballroom C

8:00 am – 10:05 am

Chairmen: Joseph Fetto (New York) Henri Migaud (Lille) 8:00 am – 8:05 am

Session overview and objectives

8:05 am – 8:15 am

A1-1—Mid to Long Term Results of a Lateral Flare Customized Uncemented Stems in Patients Younger Than 55 Years of Age Alejandro Leali, Joseph Fetto

8:15 am – 8:25 am

A1-2—Investigation of New Concept of Buffered Implant Fixation in Rat Model: Measurement of BV/TV Using Micro-CT in Comparison with Cemented Implant Fixation Choi, Donok, Park, Sukhoon, Hwang, Deuk Soo, Yoon, Yong-San

8:25 am – 8:35 am

A1-3—Two Year Results of a Short, Metaphyseal Length Femoral Stem in Prmary Total Hip Arthroplasty Mark Dolan, S David Stulberg

8:35 am – 8:45 am

A1-4—Evaluation of Tensile Strain Distribution in Loaded Proximal Femur in Relation to Lengths of Cementless Stems Nakamura, Takuya, Sumihiko, Maeno

8:45 am—8:55 am

A1-5 —Alloclassic SL Offset Stem Conception Christian Delaunay, Falah Bachour, Henri Migaud

8:55 am—9:05 am

A1-6—Non-Destructive Evaluation of Damage Accumulation in Carbon Nanotube Reinforced and Unreinforced Acrylic Bone Cement Martin Browne, Polly Sinnett-Jones, Ian Sinclair

11

9:05 am—9:15 am

A1-7—Mid-Term Results of a Novel Lateral Flare Non-Cemented Hip Stem. A Clinical, Radiographic and Densitometry Study Alejandro Leali, Joseph Fetto

9:15 am—9:25 am

A1-8—Stem Fit and Thigh Pain in Uncemented Total Hip Replacement Amar Ranawat

9:25 am—9:35 am

A1-9—Rotational Stability Based on Displacements Obtained by Three-Dimensional Finite Element Analysis When Torsion Loading is Applied to Hip Prostheses Sakai R, Sato K, Sato Y, Itoman M, Mabuchi K

9:35 am—9:45 am

A1-10—Excellent Long-Term Survival (15-20 years) of Uncemented Gritblasted Straight Tapered Titanium Stems in Young and Active Patients (100 microns maximum femoral wear depth). There was a trend for more lymphocytic and macrophagic infiltration with higher wear. Immunological staining showed a mix of B and T lymphocytes. Tissues from patients whose implants were removed for suspected metal sensitivity were extensively infiltrated with diffuse and perivascular lymphocytes, often in combination with plasma cells. There was commonly abundant fibrin attached to the tissue surface which was usually eroded and necrotic. The wear of implants in these cases was generally low. Discussion: The pattern of inflammation in tissues from metal-on-metal hips has been described as lymphocytic vasculitis and the term ALVAL (aseptic lymphocytic vasculitis associated lesions) has been coined to describe these particular histopathological features [1]. Clinically, as well as histologically, patients with metal sensitivity differ from patients with failed metal-on-metal total hip replacements with wear debris. When tissue biopsies from patients with otherwise unexplained pain show abundant lymphocytes, plasma cells, extensive necrosis and fibrin deposition, and all other causes for their pain has been eliminated, a diagnosis of metal sensitivity should be considered. Timely revision should then be performed to avoid progressive local tissue damage. 1.Willert et al. J Bone Joint Surg 87:28, 2005 2.Davies et al. J Bone Joint Surg 87:18, 2005 Melbourne Orthop Gp, Australia 2ANCA Clinic Gent Belgium

1

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A4-7 THE FATE OF SLEEVED HEADS ON METAL-ON-METAL BEARING OUTCOME Christian P. Delaunay, Henri Migaud, Philippe Laffargue Clinique de l'Yvette, 67-71, route de Corbeil, 91160 Longjumeau, France Tel : 00 (331) 69 10 30 30 / Fax : 00 (331) 69 10 31 33 / [email protected] INTRODUCTION: In a previous comparative study [1], 10-year survivorship of MoM 28mm bearings from revision for any reason was 81.5% (95% CI, 57–93.5%) for the original Weber design with sleeved heads and 98.7% (81–99.9%) for the sleeveless current design. In addition, dislocation rate (5%) was partly explained by early impingement favored by head sleeve with unfavorable head-neck ratio ( 2. Using the 28mm size on a 12-14mm Morse cone without sleeve, the ratio ranged from 1.83 at the cone level to 1.75 at the prosthetic neck base level; with head sleeve of the original design (+ 2.2mm), the ratio decreased to 1.6 at any neck level. All metallic impingement between any head sleeve (CoCr alloy) and acetabular metallic bearing (CoCr) or titanium shell generated Co and Cr particles that are detectable in urine and blood. This test was useful for detection of mechanical MoM articulation dysfunction according to Archibeck mode 2 in the previous study [1,2]. In opposition, with the same 28mm size and 12-14 Morse cone configuration, but on a slimmer neck, head neck ratio became even more favorable (2.43 at the cone level). In any patient, no general toxic effect could have been detected thus far. CONCLUSIONS: Main cause of MoM failure was due to impingement favored by head sleeve and excessive cup anteversion. Co level survey showed to be a good indicator of MoM bearing behavior. According to the current knowledge, head sleeves must be avoided and head-cone compatibility is of paramount importance. REFERENCES: 1) Delaunay C. Metal-on-metal bearings in cementless primary total hip arthroplasty. J Arthroplasty, 2004, 19, 35-40. 2) Archibeck MJ, Jacobs JJ, Roebuck KA, et al. The basic science of peri-prosthetic osteolysis. J Bone Joint Surg 68 Am 2000;82:1478-1489.

A4-8 SECOND GENERATION OF METAL ON METAL CEMENTED TOTAL HIP REPLACEMENTS: 10 YEARS OF CLINICAL AND BIOLOGICAL FOLLOW-UP JY LAZENNEC *, P BOYER*, J POUPON**, MA ROUSSEAU, F LAUDE* , Y CATONNE*, G SAILLANT * Département de chirurgie orthopédique Hopital La Pitié-Salpétrière, 47-83 Boulevard de l’hôpital, 75013 Paris* Département de toxicologie, Hopital Lariboisière, 2 rue Ambroise Paré, 75010 Paris** E-Mail: [email protected] Introduction : The second generation of metal on metal prosthesis appeared at the end of the 1980s as a serious alternative to metal on polyethylene bearing couples. Short term clinical results were promising ; however certain questions persist concerning clinical, radiological and biological aspects. Release of chromium and cobalt from the bearing couple is one of these aspects. Material and Methods: The aim of this study is to analyse the results of a series of 97 cemented total hip prosthesis comprising a titanium femoral stem and the Metasul® metal-metal bearing couple.Mean follow-up is 9 years ( 7-12 ) Results: Complications were marked by 12 revisions out of which 2 were for recurrent early dislocations, 8 for clinical and radiological failure, 2 for worrying radiological alterations. During these revisions we observed a serious infiltration of metal debris 4 times, leading to an alternative strategy using an alumina-alumina bearing couple. Three more revisions are planned for rapidly evolving radiological alterations. 30 implants show radiological signs of preoccupying deterioration on the acetabular side. 8 segmentary femoral osteolysis have been observed. 12 patients suffer from recurrent subluxation. Concerning the global evolution of metal serum levels, cobalt remain stable after 5 years. The values are 3 to 4 times above those of a non exposed subject but largely below ratios considered toxic. The evolution of serum chromium levels is similar to cobalt. Implantation of two prosthesis in one same patient leads to significant increase in serum metal ratios. Discussion and Conclusion: This series raises questions concerning the reliability of the metal on metal bearing couple. Osteolysis is an unsolved problem. Today cemented fixation is debatable although this series doesn’t allow this parameter to be held directly responsible. Nothing points to any shortcomings concerning the taper fixation or the metallurgy of the femoral stem. The study of the serum metal levels seems a good indicator of the impingement situations and the functioning of the bearing couple .

69

A4-9 WEAR AND IONS IN RETRIEVED METAL-METAL TOTAL HIP REPLACEMENTS— A HIP SIMULATOR COMPARISON OF 28 MM MOM , Ian C. Clarke1, T. Sorimachi, Y. Lazennec, T. Ishida1, and H. Shirasu 1 Peterson Tribology Lab, Department Joint Research Center, Loma Linda University California, USA and 2 Department of Orthopaedic Surgery, Tokyo Medical University, Tokyo, Japan Corresponding author Ian Clarke, Ph.D. Director, Peterson Tribology Lab Department Joint Research Center Loma Linda University, School of Medicine 11406 Loma Linda Drive, Suite 606 Loma Linda, CA 92354 Phone: (909) 558-6490 Fax: (909) 558-6018 E-mail: [email protected]

The objective of this study was to correlate in-vivo, retrieval and laboratory wear studies of metal-onmetal (MOM) bearings. Twelve MOM bearings (28mm Metasul, Zimmer) with follow-ups to 10 years were retrieved for various reasons including pain, osteolysis and cup loosening. Patients averaged 55 years of age. All had the Weber Low profile cup cup design of UHMWPE ‘sandwich’ design (SULENETM). The bearings were both CoCr (PROTASULTM ; ISO 5832-12). The Alize femoral stem in Ti64 alloy was cemented in all cases. The MOM bearings were analyzed by light microscope, laser interferometry, scanning electron microscopy SEM) and contour measurements (CMM). Worn areas were described by grading system (0-6) depending on the severity of burnishing and 3rd body scratching. On the femoral heads the main central wear zone and peripheral stripe wear zones were conspicuous under the SEM and generally grades 5-6. The MOM liners featured central wear zones and in some cases rim stripes and impingement damage. Stripe inclination varied specifically from 10-30o relative to the base of the ball. Generally the liner wear ranking was one grade less severe than with femoral heads, i.e. there was more wear damage on the heads. Worn areas were also larger on the femoral heads achieving 600mm2 to the liners with 300mm2 maximum. Typical studies from our standard simulator wear studies of 32mm MOM demonstrated peak run-in wear-rates up to 15 mm3 per million cycles with an overall wear rate of 1.6 mm3/Mc and comparable to previous studies. Serum lubricants became noticeably gray with MOM wear rates > 3 mm3/Mc and darkened significantly with wear > 7mm3/Mc. Ion studiesshowed Co:Cr ratios at 2.26 as in the alloy with concentrations averaging 40ppm during run-in phase and 10ppm during steady-state phase.

70

A5-1 THE POTENTIALITIES OF ELCTROCONDUCTIVE Si3N4-TiN CERAMIC COMPOSITE FOR COMPLEX-SHAPED IMPLANTABLE DEVICES, MACHINED THROUGH ELECTRICAL DISCHARGE MACHINING (EDM) Bucciotti F., Mazzocchi M., Bellosi A. ISTEC-CNR, Via Granarolo 64, 48018 Faenza (Ra) Phone: +39 0546 699723/Fax: +39 0546 46381/E-mail: [email protected] Silicon nitride-based ceramics have been ascertained to be suitable materials for permanent biomedical devices, as articular prosthesis, reconstructive surgery, fixture systems, due to their high mechanical and tribological properties, as well as for their biocompatibility. Owing to the high hardness, the production of complex shapes from simple pieces of silicon nitride trough conventional mechanical machining, using diamond tools, is difficult and expansive. In this work we investigated the properties of electroconductive silicon nitride/titanium nitride ceramic composite and a possible processing route, that allows the net-shaping of complex components by electrical discharge machining (EDM). Fully dense pieces were obtained by hot pressing, using alumina and yttria as sintering aids. The tests on the final dense electroconductive composites evidence that the EDM can be applied as a low-cost and highly efficient route to obtain complex shapes. Bulk and surface characteristics and properties of the composite Si3N4-TiN were investigated, among which: hardness, strength, Young’s modulus, wettability against liquid including SBF, surface modification due to exposure to liquids for long term, the biochemical issues from cells in cytotoxicity tests. Microstructure and the machined surface were examined by scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS); phase composition before and after EDM was checked by XRD analyses. The thickness of the electro-machined layer and the roughness of the carved surfaces were measured by SEM and profilometer respectively. The most relevant results are the following: the composite is constituted by β-Si3N4 and TiN grains, these ones connected each other to form a through electrical conductive network. The grain boundary phases consist of silicates and oxinitrides of the cations contained in the sintering aids, located in the triple points and the interfaces in between the Si3N4 grains. As for the mechanical properties, the hardness approaches 15 GPa, the Young’s Modulus is 354 GPa, the room temperature flexural strength is about 850 MPa. The in-vitro test results stress the nontoxicity of the materials both of the dense hot pressed composite and of the βSi3N4-sintering aids powder mixtures and of the TiN powders. Melting and evaporation are the mechanism to be invoked for the ablation of Si3N4-TiN at a microscale of the EDM machining. The thickness of the altered microstructure layer and the surface roughness of the Si3N4-TiN ceramic composite is strictly correlated with EDM parameters: selected working parameters, such as low voltage (about 50-60 V) and current (about 0.5-1.5 A), yielded the best results in this sense. The microstructure of the composite EDM treated surface showed the formation of a surface layer of 10-20μm in thickness, that evidences the superpositioning of cavities and craters with a range of diameters and shapes. Results will be presented concerning either the comparison of the surface characteristics and roughness of surfaced deriving from EDM and form surfaced mechanically polished. The results of in-vitro tests depend on the surface characteristic parts. Examples of the potentialities of the experimented processing procedures in term of complexity of the final shapes for specific mini-fixtures and prostheses are presented. 71

A5-2 THE OCCURRENCE OF THE SQUEAKING PHENOMENON IN TOTAL HIP ARTHROPLASTY USING ALUMINA CERAMIC-ON-CERAMIC BEARINGS Murphy, Stephen B.; Ecker, Timo M., Tannast, Moritz Center For Computer Assisted and Reconstructive Surgery New England Baptist Bone and Joint Institute 125 Parker Hill Avenue Suite 545 Boston, MA 02120 Phone: 617-232-3040 Fax: 617-754-6436 e-mail: [email protected]

While providing superior hardness and improved wear characteristics, hard bearings such as metal-on-metal, or ceramic-on-ceramics bearings have different lubrication properties than cocr-on-poly bearing couples. Recently, a high incidence of squeaking had been reported with the use of the Stryker Trident total hip arthroplasty. In their report, the authors recommended that all patients complete a questionnaire that specifically asks about squeaking, in order to gain a proper assessment of the incidence of the problem. The purpose of this study was to assess the incidence of squeaking following alumina ceramic-ceramic total hip arthroplasty in our patient population. Since September of 2006, when the first squeaking incidences were reported, all patients returning in routine clinical followup who had undergone alumina ceramic-ceramic THA (Transcend, Wright Medical Technology, Memphis; Ceramtec, Plochingen, Germany) at any time since June of 1997 answered a questionnaire concerning squeaking. Specifically, patients have been asked the question, “Has your hip ever squeaked?” If the answer was yes, then additional questions concerning the frequency were then completed. The implant design uses an 18 degree taper between the titanium shell and the ceramic liner with the ceramic liner mounted flush with the metal rim. Questionnaires concerning 245 hips were obtained after a mean followup of 30.7 ± 29.7 months (range 0.4 – 114.2). Of 245 hips, patients stated that their hip had never squeaked in 241 (98.4 %) of these. Four patients (1.6 %) stated that the hip had squeaked at least once at some point since surgery. Squeaking had occurred once or more a year in two hips, but since disappeared. One hip squeaked once or more a month and one hip squeaked once or more a day with squatting exercises. None of these patients was able to reproduce the squeak voluntarily nor could it be elicited on examination. Further, when asked, non of the patients were limited in any given activity by the squeaking. Radiographically, there were no cases of osteolysis or loosening in any of the 245 hips. Squeaking following alumina ceramic-ceramic total hip arthroplasty using the implants described above may occur in approximately 1.6 % of patients without causing pain or dysfunction and without radiographic evidence of loosening or osteolysis.The difference in occurrence and frequency between the current study and prior reports of metal-backed, recessed ceramic liner designs suggests that the incidence of squeaking in hard bearings is affected by design considerations, surgical technique or both.

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A5-3 REVISION TOTAL HIP REPLACEMENT FOR CERAMIC HEAD FRACTURE: A LONG TERM FOLLOW-UP Vineet Sharma, MD, Amar S. Ranawat,MD, Vijay J. Rasquinha, MD, Chitranjan S. Ranawat, MD 130 East 77th St. 11th Floor, New York, NY 11355 Phone: 212-434-4700 E-Mail: [email protected] Fracture of the ceramics has and will continue to be a dreaded complication after THA with ceramic articulation. Ceramic fracture is a difficult situation as the results of revision reported in literature with various bearing surfaces are disappointing. The purpose of this study was to look at long term results of revision THA for ceramic head fractures. Methods: Out of 87 THA with ceramic on polyethylene bearing surface done by the senior author between 1990 and 1992, there were 8 cases of ceramic head fracture. All the fractures occurred while doing routine daily activities. All hips were treated with complete anterior and posterior synovectomy and exchange of bearing surface to cobaltchromium on polyethylene. All patients were followed on a regular basis after revision for wear, osteolysis and implant loosening. One patient was lost to follow up and another refused to particiapte in the study. The mean follow up after revision was 10.5 years. These patients were matched with 6 patients who had primary THA during the same period with a cobalt-chromium on polyethylene articulation. Wear rate was measured in both group of patients to see if ceramic particles lead to increased third body wear after revision. Results: There was no revision for osteolysis or aseptic loosening at a mean follow up of 10.5 years. One hip was revised for infection which occurred 12 months after the revision. The mean Harris hip score was XX at the last follow up. The linear and volumetric wear rate was the same after revision as in the control group. Conclusion: We conclude that revision THA done for ceramic head fracture has a favorable outcome provided a complete and thorough synovectomy is performed. The clinical and radiological results are the same and third body wear is not more compared to the control. Keywords: ceramic fracture, revision total hip, wear rate

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A5-4 A STANDARDIZATION PROPOSAL OF TEST METHOD FOR IMPACT RESISTANCE OF CERAMIC FEMORAL HEAD FOR HIP JOINT PROSTHESES TSUTSUMI, Sadami, MIZUNO, Mineo, TODO, Mitsugu, NISHIDA, Masaru, HATTORI, Masaaki, ASAOKA Nobuyuki Institute for Frontier Medical Sciences, Kyoto University, Shogoin, Sakyo-ku, Kyoto 606-8507 Japan Tel: +81-75-751-4130 Fax: +81-75-751-4126 E-Mail: [email protected] This research was commissioned by the Ministry of Economy, Trade and Industry, Japan, and is intended to propose an International Standard evaluating impact resistance of ceramic femoral head for hip joint prostheses. This test method should be used for material development, material comparison, quality assurance, characterization, reliability analysis and design data generation. This test method is to determine the impact resistance by observing the fracture existence or non existence after applying the impact with free falling weight to a test specimen, based on the Cone Cavity Contact Method using for measurement of compression fracture strength in guide line for ceramic femoral head for partial and total hip joint in United States FDA. An impact loading was applied with increasing a falling weight mass (M) or a falling height (H) so as increasing a suitable impact energy gradually from a low impact energy without impact fracture. In the first and second test, the same condition of impact energy shall be applied in order to ensure the fitness of a trunnion and a femoral head. The initial impact energy shall be not greater than 20J. The increment of impact energy per one impact shall be not greater than 10J. An impact energy is calculated from the following equation; E = H・M・g where E is the impact energy (J), H is the falling height (m), M is the mass of the falling weight (kg), and g is the gravity acceleration 9.8 (m/s2). A test shall be done repeatedly with increasing gradually impact energy until a fracture occurs in a test specimen. The impact energy at the test condition just before leading to a failure shall be the maximum impact resistance. Several round robin tests were conducted by three institutions for the specimens of alumina and zirconia heads. The results measured for the same specimens were not much difference among the all institutions, and it indicates the reproducible and effectiveness of this test method.

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A5-5 WEAR OF LARGE CERAMIC BEARINGS Thomas Pandorf Ceramtec, Fabrikstr. 23-29, Plochingen, Germany 73207 Phone: 49 71536 11844 Fax: 49 71536 1116844 E-Mail: [email protected]

Large diameter ceramic bearings are of increasing interest due the enlarged range of motion, enhanced stability of the artificial joints, and reduced risk of dislocations. Larger diameter hard on hard bearings may as well change the wear characteristics due to larger wear areas, different lubrication behaviour from changed diameter tolerances as known from Me-Me large bearings. But not only hard-on-hard bearings are of interest. With new low wear highly crosslinked polyethylenes, wear behavior of ceramic against XPE is of new interest. Three different wear studies were conducted: 1. Ce-Ce: Alumina matrix bearings of 36 mm, 40 mm and 44 mm with different diameter tolerances were tested according to DIN EN 14242. Roundness of ball head and insert as well as clearance of the bearing partners have been varied. 2. Ce-XPE: 36 mm bearings were compared to Me-XPE. Biological activity of the produced particles was investigated. Ce-Ce: 36 mm diameter bearings in microseparation mode with two different ceramic materials were tested, one a pure alumina, the other an alumina matrix composite. The different wear studies show:

1. Large ceramic bearings have a very low wear rate. The influenced of the clearance on wear rate is negligible. 2. Using a ceramic ball head against highly crosslinked polyethylene reduces the wear rate by 50% compared to metal ball heads. Even in microseparation mode the wear volume is very low compared to other bearing materials. The wear volume is similar to previously performed microseparation wear studies of 28 mm bearings. The wear volume depends on the used combination of the two different bearing materials. The superior wear characteristics of large ceramic bearings was proven in all tribological test setups. The use of ceramics in a hip replacement will significally reduce the risk of osteolysis leading to an increase in the durability in the human body.

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A6-1 IN-VIVO COMPARISON OF HIP MECHANICS FOR SUBJECTS IMPLANTED WITH A MIS OR TRADITIONAL SURGICAL TECHNIQUE- EXTENDED STUDY Glaser Diana a, Miner TMb, Komistek RD a, Mahfouz MRa, Dennis DAb, Lui Fa a University of Tennessee, Knoxville, TN, USA a Rocky Mountain Musculoskeletal Research Laboratory, Denver, Colorado Diana Glaser, 301 Perkins Hall, University of Tennessee, Knoxville, TN 37917 Email: [email protected], Phone: 865-974-1936, Fax: 865-946-1787 The minimally invasive surgery (MIS) becomes popular because of the potentially reduced soft tissue damage and the complimentary benefits, but its superiority over the traditional technique is a subject of continuing controversy. Most often reported advantages of MIS include shorter hospitalization and rehabilitation, improved cosmetic appearance, less pain and risk of complications, decreased surgical time and blood loss. However, a comparison of separation as well as contact and muscle forces among different surgical approaches has not been examined yet but is useful in understanding THA performance. The present study is an extension to previously reported comparison of 3D in vivo kinetics of traditional and MIS THAs.1 This extended study includes additional subjects, subdivides MIS into different categories, controls for various parameters to reduce influence of marginal factors, and evaluates hip separation besides the kinetics. Fifteen subjects were evaluated under in vivo conditions using fluoroscopy while performing gait on a treadmill. Five subjects were implanted using a MIS anterolateral (AL), five using a MIS posterolateral (PL), and five with a traditional approach. All subjects received a cemented THA with similar femoral head diameter. Surgery was performed by a single incision, and subjects were matched for age, body mass index, and diagnosis to control for variables possibly influencing performance and gait characteristics. The average post-operative follow-up duration at the time of analysis was 6.4 months (3-12), 4.7 months (3.5-4.5) and 3.7 months (2.3-6.5) for patients implanted using a standard, AL MIS and PL MIS approach, respectively and was not significant different (p>0.05). The procedure for obtaining the kinematics and kinetics is identical to the previous report1. In vivo translational and rotational kinematics, derived from 3D-to-2D image registration technique, were input as temporal functions in a 3D inverse dynamics mathematical model to determine contact mechanics. The traditional subjects experienced significantly higher magnitude and incidence of hip separation than any of the MIS groups (p 12 cm) in the same period by the same experienced surgeon. In all cases a specialized dedicated surgical instrumentation was used. Inclusion criteria to enter the study group ( A-B-C Groups) were: BMI< 30, diagnosis of primary osteoarthritis, age< 75 years. The following parameters were evaluated: intra and post operative complications, total blood loss ( calculated according to Rosencher method ), time of surgery, component placement, length of hospital stay and functional outcomes (HHS, WOMAC) at six weeks. Results: No dislocations, infections and early aseptic loosening were detected in groups A, B and C. No significant differences were detected regarding the length of hospital stay in all groups . In group B the time of surgery was significantly higher than in group D. The total blood loss of group A, B and C was statistically lower than group D. Clinical outcomes at six weeks in groups B and C were significantly better that in group A and D. The following complications were detected: Group A: two sciatic nerve palsy (one transient and one permanent), one greater trochanter fracture, one femoral stem malposition. Group B: one greater trochanter fracture, one proximal femoral fracture (crack) , one rupture of tensor fasciae latae , two haematomas. Group C: no complications were detected. In control group D (149 patients) the following complications were observed: one proximal femoral fracture, one case of cup malposition ( in a severe case of dysplasia) and one infection. Conclusions: The main advantages of all MIS approaches seem to be the reduced total blood loss, even in the learning curve. However during learning curve the minimally invasive approaches seem to have a higher rate of complications than the standard procedures even in selected patients. In muscle sparing approaches (anterior and antero lateral ) the early functional outcomes are better than other approaches ( standard and mini incision). Among the evaluated minimally invasive procedures, the antero lateral approach seems to be safer and less demanding than others. 79

A7-1 VALIDATION OF AN IMAGELESS COMPUTER NAVIGATION SYSTEM FOR ACETABULAR CUP PLACEMENT IN THA Author: William L. Bargar, M.D. Sutter Institute for Medical Research 1020 29th St. #450, Sacramento, CA 95816 Phone: 916-453-5844 Fax: 916-733-8259 E-Mail: [email protected] Imageless computer-assisted navigation systems have emerged in an effort to more accurately position the acetabular component in total hip arthoplasty. These systems, with real-time adjustments for pelvic position changes, have been speculated to improve cup position and reduce positional outliers. The accuracy of these systems has not fully been validated. Purpose: The current study compares values of operative inclination and operative anteversion of acetabular cup position acquired by an imageless navigation system to post-operative pelvic CT scan measurements of inclination and anteversion in an attempt to identify the error of an imageless navigation system and validate its accuracy. Methods: Twenty-five patients (26 hips) with a mean BMI of 26.1 underwent total hip arthroplasty with the use of an imageless computer navigation system for the placement of the acetabular cup. Post-operative CT scans were obtained for all patients. 3D models of each patient’s pelvis and acetabular component were created and operative inclination and anteversion determined. Results: Intra-operative computer navigation values for operative inclination and operative anteversion were 38.8º±3.5º and 32.2º±6.8º, respectively. CT scan values for operative inclination and operative anteversion were 39.4º±4.0º and 32.6º±7.0º, respectively. The mean absolute value difference between the intra-operative computer navigation values and CT scan values for each patient for operative inclination and operative anteversion were 1.8º±1.2º and 2.0º±2.0º, respectively. Bland-Altman and standard deviation analysis indicate comparable values given by each measurement technique. With 95% confidence, the CT scan values are no greater than 2.3º and 2.7º of the observed CAS values of inclination and anteversion, respectively. Conclusions: An imageless computer navigation system can provide real-time determination of the acetabular cup position with good accuracy in a non-obese patient population undergoing primary total hip arthroplasty.

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A7-2 VALIDATION WITH ROBOTICS OF DOCUMENTATION AND ANALYSIS OF SURGICAL SKILLS THROUGH REAL-TIME MOTION RECORDING OF NAVIGATED ARTHROPLASTY INSTRUMENTS Barrera O. Andres; Garvin, Kevin. L.; Gilmore, Alisa N and Haider, Hani Department of Orthopaedic Surgery and Rehabilitation, University of Nebraska Medical Center, 985360 Nebraska Medical Center - Scott Technology Center, Omaha, NE 68198-5360, USA Phone : (402) 559 5607 – Fax : (402) 559 2575 – E-mail : [email protected] Formal assessment of surgical skills and analysis of critical-paths are not widely used in orthopaedics partly due to the lack of objective quantification, reliability, and sensitivity of existing methods. Current surgical skill assessment methods also require additional instrumentation, cost and time. Such problems can be overcome by a novel method recently introduced to record the motion of arthroplasty surgical instrumentation for documentation, surgical-skill assessment, and safety analysis. This method uses an existing computer-aided-orthopedic-surgery (CAOS) navigation system without compromising its functions of real-time tracking, rendering, or simulations. The stored data allow playback to view realistic 3D simulations of the complete bone cutting/refining process. This study aimed at validating the system/methodology and its sensitivity using an articulated robotic arm as a reliable actuator of a surgical instrument with controlled paths, to see how well its motion characteristics are captured and analysed. Software was incorporated into a customized CAOS-navigation system to log dynamic position/orientation of instruments and bones. An oscillating saw (equipped with reference-frames for infrared-tracking) was fixed at the end-effector of a Kuka-KR-15 robot. Well-defined sequences of movements were programmed for the robot, simulating the starting of a TKR femoral distal cut. Known errors were deliberately programmed-in; the saw was placed +/-100mm away from the intended plane to be cut, and tilted +/-30º in roll and pitch. The sequence was repeated at different speeds while the CAOS system logged data. Simultaneously the robot recorded the coordinates from its encoders. The data was used to compute errors in distance from the cutting instrument to the plane to be cut D(mm), and to compute pitch P(º) and roll R(º). Linear/angular speeds and accelerations of the saw, and length (L) of the whole path were also computed. Different sampling rates for the robot (T=48.0ms) and CAOS (T=66.7ms) necessitated data synchronization before cross-correlation and statistical analysis were carried out (using MatLab). Signal correlation (robot vs. CAOS) for linear positional offset (D), Pitch (P), and Roll (R) was >0.96 for all cases. Average offset (c) and gain (m) values for D were m=1.01, c=0.35mm, for Pitch m=0.99, c=0.01º and for Roll m=0.99, c=0.08º. Trajectory (L) was 5% longer for CAOS with average L=491mm. Noisier signals resulted from CAOS than the robot, and its fluctuations caused the extra length. Low-pass filtering of the CAOS signal did not significantly improve the D correlation, but those of speed and acceleration increased by one and two orders of magnitude respectively, while the L difference dropped to 0.07%. The very high correlations (≈1), very low offsets (≈0), and almost unitary gain throughout validated the acquisition and analysis system as a measurement device. The 0.35mm offset for D signals pointed to registration errors in either the CAOS or the robot, and indeed these were later traced to the former. Beyond documentation and analysis of surgical skills, such data can be used for training and optimization of surgical plans, bone-cutting approaches, and as teaching input for robotics in orthopaedics. Experimental trials on different surgeons are the next step to characterize bone-cutting skills for arthroplasty.

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A7-3 ESTIMATION OF SOFT TISSUE THICKNESS IN IMAGELESS NAVIGATION OF CUP ORIENTATION IN THA Ko, Byung-Hoon., Park, Suk-Hoon., *Hwang, Deuk Soo., Yoon, Yong-San Department of Mechanical Engineering, KAIST, South Korea Daejeon, 305-701 * Medical School Orthopedic Department, Chungnam National University, South Korea. Daejeon, 301-721 TEL :+82-42-869-3022, FAX :+82-42-869-3210, E-mail:[email protected] When using an imageless navigation system for THA, it is difficult to accurately measure the anatomical landmarks of the pelvis for determining the anterior pelvic plane (APP). The measured APP is commonly used to define the acetabular cup orientation. However, there is difference between the measured and actual APP due to the measurement error by the unknown thickness of soft tissue at the anatomical landmarks, especially at the pubic symphysis. The misinterpretation in cup angles when using wrong pelvic reference plane can be substantial, particularly for anteversion. The object of this work is to establish the estimation formula for the unknown soft tissue from the statistical analysis of the patients’ B.M.I. and indentation depth. In our study, the linear relation between the soft tissue thickness and patient’s physical parameters (BMI, indentation displacement) was found. The proposed method was applied to the shape of probe tip for measuring anatomical landmarks using imageless navigation systems. The actual thickness of soft tissue was measured using a portable ultrasound imaging system (SONOACE PICO®, Medison) and linear probe (HL5-9ED®, MEDISON) for 25 volunteers in supine positions. In order to obtain the indentation depth of the soft tissue on the pubic bone, 3D position measurement device (MicroScribe, IMMERSION Inc.) was used. The diameter of the flat ended tip was 6mm. Simultaneously, the compressive force was measured with a S-beam load cell (BONGSHIN LOADCELL®) during sounding. In addition, the positions of both ASIS and the center of the pubic bone were measured to obtain the distances between both ASIS points and the pubic bone. A multiple regression analysis was used to estimate the thickness the soft tissue (p< 0.05). The estimation Equation for the unknown soft tissue thickness can be expressed in terms of BMI and displacement:

− 4.87 + 1.03x1 + 0.59 x 2

1 2 Y= Y(mm): soft tissue thickness under minimum force (0 ~ 0.5N)

x1

: body mass index

x2

(mm): displacement under maximal force (20 ~ 25N)

The mean error between the thickness, as estimated by the linear equation, and by the ultrasound image was less than 0.2 ± 4 mm. When the cup inclination is 40° and anteversion is 15°, before correcting the soft tissue thickness, the rotational error of APP results in -7.85° ± 3.2° in the cup anteversion. By using the estimation formula, the cup orientation error was significantly decreased to -0.09° ± 1.96° in anteversion and -0.05° ± 0.49° in abduction (p < 0.05). The misinterpretation of acetabular cup angles increases with the rotational error of the pelvic reference frame. The difference between the ideal and measured plane affect the rotational error of the reference frame. With the proposed estimation equation, it is possible to reduce the error in the anteversion that occurs as a result of the difference between the actual and measured pelvic plane.

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A7-4 NAVIGATION IN HIP RESURFACING: REPORT OF INITIAL RESULTS Author: Michael L. Swank, Leslie L. Korbee Cincinnati Orthopaedic Research Institute E-Mail: [email protected] Introduction: Use of the Birmingham Hip Resurfacing implant system was approved in the United States by the FDA in May of 2006. A computer assisted surgery (CAS) software program has been developed to enable navigation of the hip resurfacing procedure, primarily the placement of the pin which secures the hip resurfacing implant into the femoral head. That software is the BrainLAB Vector Vision Hip SR package. The goal of navigation in hip resurfacing is to overcome some of the challenges associated with conventional hip resurfacing and improve patient outcomes by preventing femoral neck notching. With the BrainLAB Vector Vision Hip SR software package, the surgeon uses a pre-calibrated CAS drill guide to navigate the central pin directly to the planned position with millimeter precision. The software provides the surgeon with real-time risk information, warning the surgeon if the implant position does not correspond to the treatment plan. The optimal position of the head implant can be easily defined by controlling in varus/valgus position and depth of the femur component in real-time. The purpose of this study is to use the BrainLAB Vector Vision Hip SR software in conjunction with the Birmingham Hip Resurfacing implant and to then evaluate the final position of the implant post operatively along with patient outcomes. Method: All patients undergoing hip resurfacing procedure with the Birmingham Hip Resurfacing implant system were enrolled prospectively. To date twenty one resurfacing patients have been evaluated. Data has been collected on preoperative planning of the stem shaft angles, and the intro-operative report of these angles along with the post operative data from navigation and from post operative imaging. The preliminary outcome of the patients enrolled in the trial has been recorded and analyzed including skin to skin time, anesthesia time, blood loss, post operative complications, length of stay and mortality and morbidity. These measures were compared to thirty-seven age matched controls undergoing navigated total hip replacement surgery. Subjects were excluded from the study if they failed to meet any of these criteria: poor quality of bone stock to support the implant; age greater than 60; anatmic abnormalities of the femoral head that would inhibit placement of the femoral resurfacing component; any routine contraindication to total hip replacement surgery, including but not limited to active infection, heart failure, lung failure, or severe untreated bleeding abnormalities, untreated anemia, or pregnancy. Data was collected from the subject’s hospital medical record concerning blood loss, operative time, operative mortality, length of stay and morbidity. Results: The results revealed that the resurfacing group and the primary total hip replacement groups had identical lengths of stay with 2.0 days. Both groups also had 100% discharge to home, had no transfusions, and no major complications. Analysis of the stem shaft angles comparing the data from computer screenshot to the post operative film revealed that there was a mean difference of 6 degrees from final computer screenshot to post operative x-rays. The variability of measurement error on film images is approximately 5 degrees. A summary of the other clinical results are: mean skin to skin time for resurfacing cases = 110 minutes vs. 77 minutes for primary total hips in this initial series; mean anesthesia time for resurfacing cases = 155 minutes vs. 115 minutes for primary total hips; mean surgical blood loss for resurfacing cases was 438 cc’s vs. 284 cc’s for primary total hips. Discussion: The comparison of the neck shaft angles from the intra-operative measurements vs the post-operative films confirmed that the final verification from the navigation software corresponded well to the radiographic data. The variance between the planned neck shaft angle and the final date from x-ray was only 1-2 degrees with all components in valgus placement with no femoral notching. With these results, it appears that there is a tendency to increase the post operative valgus of the stem component which could reflect a deficiency on post operative femoral rotation capture on radiographs compared to intra-operative nevigation data from computer screenshots. Of note is that there was no increased varus observed in the component placement. Component placements for all cases are within safe parameters and variances from plan are within the error inherent with radiographic measurements. Preliminary clinical outcomes were comparable to those for age-matched primary total hip patients. However, there was increased skin to skin and anesthesia time of 30-40 minutes, which may be due to the learning curve for this initial series of cases. From this preliminary data, it appears that navigation in hip resurfacing offers the surgeon necessary information for optimizing placement of the resurfacing stem. In this initial series the early clinical outcomes were compared to those observed with primary total hip replacement. References: 1. Barrett AR, Davies BL, Gomes MP, Harris SJ, Henckel J, Jakopec M, Rodriquez v Baena FM, Cobb JP. Preoperative planning and intraoperative guidance for accurate computer-assisted minimally invasive hip resurfacing surgery. Proc Inst Mech Eng {H} 2006; 220 (7): 759-73. 2. Hess T, Gampe T, Kottgen C, Szawlowski B, Intraoperative navigation for hip resurfacing. Methods and first results. Orthopade. 2004 Oct;33(10):1183-93. 83 3. Allison C. Minimally invasive hip resurfacing. Issues Emerg Health Technol.2005 Mar;(65):1-4.

A7-5 IS LEWINNEK’S PLANE A RELIABLE REFERENCE FOR HIP NAVIGATION? TABUTIN Jacques, PINOIT Yannick, MIGAUD Henri, LAFFARGUE Philippe, PUGET Jean CH Cannes – 15 avenue des Broussailles – 06401 CANNES Cedex 01 0033 4 93 69 71 30 / 0033 4 92 18 67 30 / [email protected] The anterior pelvic plane (APP : defined by the antero superior iliac spines and the pubic symphysis) is generally considered as the vertical plane. Is this true? Does its orientation vary between upright and recumbent position ? Does it vary after THA? Is there a relation with pelvic version? Materiel and Methods: Strict lateral X-Rays views were done in 106 standing patients : 82 THA without hip or knee flexion contracture (40 having sustained a dislocation), 24 without any joint pathology : these last patients have had there radiographs done first standing then lying flat. Moreover 19 stable prostheses had X-Rays before and after the THA. Were measured: the angle between vertical and anterior pelvic planes (positive if cranially open), the angle between the vertical axis and the pelvic axis (from center of S1 to center of femoral heads) : pelvic version. Results: Neither sex (1.7° +/- 6 for men 1.5° +/- 5.9 for women) nor age had any influence on the orientation of Lewinnek’s plane or on the pelvic version. The anterior pelvic plane was not vertical in 38% of cases (+/- 5°). There was no significant difference between the groups of patients as for the orientation of the APP : 2.9 +/- 5.7° for the THA, 1.2 +/- 5.2° for healthy patients and the same was observed in the total hip groups : 3.5 +/- 5.8° in the dislocation group 2.3 +/- 5.5° in the stable group. In standing patients pelvic version varied more widely (14 +/- 9.2 ; -9 to + 31) than orientation of APP (2.3 +/- 5.8° ; - 18 to + 18) refering to vertical. In the 24 healthy subjects the change from standing to lying significantly (p = 0,0002) influenced APP orientation : from 1.2 to 2.25°, with wide variations (-10 to + 12). In the 19 patients with pre and post X- Rays the THA did not significantly influence APP orientation (-1° +/- 7) but it varied by more than 5° for 7 patients. Discussion: Orientation of the APP is not dependent on sex or age. APP orientation varies less than pelvic version but it does not reflect well modifications induced by pelvic morphology. Navigation systems seem to improve the control of cup inclination but the same is not true for anteversion, especially when guidance relies on the APP. In 38% of cases this reference is not reliable, and even transcutaneous palpation of the bony landmarks is an added source of error. Considering the APP as vertical in upright position may induce an error of about 10° (half the anatomical anteversion). Moreover the APP orientation varies from orthostatism to clinostatism. This is generally not taken into account and may lead to impingement or dislocation. Conclusion: The APP does not seem quite reliable as a reference plan in the upright position. Lateral decubitus and draping for the operation alter considerably the precision. A more functional, kinematics based navigation might be a solution.

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A7-6 REDUCTION OF ROBOT MILLING TIME EXPLOITING INHOMOGENEOS BONE PROPERTY IN THA Park, Suk-Hoon., Kim, Nam-Jung., Shin, Hyun-Joon., Yoon, Yong-San. Department of Mechanical Engineering, KAIST, Daejeon, 305-701, South Korea TEL : +82-42-869-3022, FAX : +82-42-869-3210, E-mail : [email protected] Total hip arthroplasty is one of the most successful operations in orthopedic surgery. However, post-surgical results depend largely on the surgeon’s skill. For the more accurate shaping of the femur as well as the alignment of the inserted stem, many surgical robots for THA have been developed and commercialized. The most popular robot system for THA is ROBODOC. This surgery robot showed improved results in terms of the error in the orientation and in the fit of the implant. However, additional surgical procedures are required with the systems, as it uses a CT image for the registration. Moreover, the surgical system needs a large exposure to fix the femur. To alleviate this problem, we developed a compact robot system known as ARTHROBOT. This system uses a blockgage-based registration; therefore, CT/MRI images are not needed. However, this robot is fixed to the femur with specially designed bone clamp and needs a large incision for the bone clamp. Thus we developed a second version to reduce the incision size; a robot system that is fixed into the femoral cavity was designed. The performance was acceptable with the plastic model bones. However, the time required for the milling with this system is a little bit too long. In this study, an adaptive control method is suggested to reduce the time that is needed for shaping the femur with the milling robot. The femur is composed of different property bone, cortical bone and cancellous bone. If the robot cut hard part of the bone with high speed, the shaped canal became inaccurate because of the tool vibration. However, when the robot cut relatively soft bone with high velocity, accurate cut is possible. In the suggested adaptive control method, the force at the milling tool tip is measured to monitor the bone hardness and the tool transfer rate is changed accordingly, a single axis force sensor was attached between the milling tool and the robot. The suggested method was incorporated into our robot and validated. The machining time were compared between the constant tool feed rate and actively controlled tool feed rate using plastic model bones(SAWBONES®, USA) and fresh bovine bones. Average shaping time was decreased from 760±20 seconds to 250±20 seconds with the plastic bones and from 450±20 seconds to 170±40 seconds with the bovine femurs. It was possible to reduce the machining time to one third using the robot in THA by the adaptive control using the force measurement at the tool. We are further studying on the more efficient control algorithm considering the heat damage by the high speed milling tool.

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A7-7 NAVIGATED CONTROL OF THE CUP ORIENTATION DURING TOTAL HIP REPLACEMENT JENNY Jean-Yves, DOSCH Jean-Claude, BOERI Cyril, USCATU Marius Hôpitaux Universitaires de Strasbourg, Centre de Chirurgie Orthopédique et de la Main, 10 avenue Baumann, F67400 Illkirch-Graffenstaden (France) Tel +33388552145, Fax +33388552146, E-mail [email protected] INTRODUCTION: Positioning of the cup of a total hip replacement (THR) is considered critical for the short and long term results of the procedure. The precise recording of the position of the pelvis is a prerequisite during this procedure to get a confident reference for cup orientation. It has been demonstrated that the conventional, non navigated measurements are less than optimal. CT based navigation systems have been demonstrated to improve the accuracy of the recording of the pelvic position. Non image based navigation system might allow the same accuracy at lower costs. The anterior pelvic plane (Lewinnek) is an accepted reference to determine the 3D pelvic orientation. We designed this study to validate the accuracy of a non image based navigation system for cup orientation during total hip replacement according to the Lewinnek plane, with post-operative 3D CT-scan analysis. MATERIAL AND METHODS: 50 cases of navigated total hip replacement have been analysed. Navigation was performed with the OrthoPilot ® system (Aesculap, Tuttlingen, FRG), a non image based system. A localizer was implanted on a screw on the anterior iliac crest. Three relevant landmarks (both antero-superior iliac spines and pubis) were palpated with a navigated stylus, defining the anterior pelvic plane (Lewinnek plane). Acetabular preparation and cup implantation were performed under navigation control. Safe zone for acetabular implantation was defined pre-operatively : 40 to 50° of abduction, 10 to 20° of flexion in comparision to the anterior pelvic plane. The final orientation of the cup was registered intra-operatively by the navigation system, and compared to the 3D CT-scan measurement of the cup positioning with the same reference frame. RESULTS: 2 CT-scan were considered unreliable for cup orientation, and consequently 48 cases were analyzed. There was no significant difference between the intra-operative (42° ± 4°, range: 35 to 49°) and post-operative (44° ± 5°, range: 30 to 57°) measurements of the cup abduction. The mean paired difference was 2°: this difference was significant (p0.05), no statistically significant difference was found between the final intra operative vs. post operative angle (p=>0.05). No statistically significant difference was found between adjusted vs. final angles (p=>0.05).There was a statistically significant difference when pre op angles were compared with post op angles (p=

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