Custom Implants

CURRENT AND FUTURE USE OF CUSTOM IMPLANTS IN ORTHOPAEDIC SURGERY

OMTEC 2016 CHICAGO

P James Burn FRACS

Consultant Orthopaedic Surgeon Canterbury District Health Board

Christchurch

New Zealand

pjamesburn@xtra.co.nz

DISCLOSURES:

• Founding shareholder of Ossis Ltd (NZ)

• Founding shareholder of Enztec Ltd (NZ)

• Receive royalties from the Enztec Stardrill

PERSONAL PRACTICE PROFILE ( NZ POPULATION 4 MILLION) Primary THR 2,000+

Last 1,000 cases 0% dislocation for Primary THR post. approach

Revision rate 0.04 per 100 component years, with LIMA PF cup

(lowest on the NZJR)

Revision THR 300

Primary TKR 950 +

Primary UKR 400 +

Revision TKR 97+

Custom hemi-pelvic replacements 3 + 1rev

+spine, foot and ankle and general orthopaedics.

CUSTOM ACETABULAR CASES 30

DESIGNING CONSIDERATIONS

Requirement of an experienced surgeon/engineer with an engineer with clinical experience

Engineer Surgeon

“ADDITIVE MANUFACTURE 1998” BEFORE ACCESSIBLE SOFTWARE AND PRINTING

MY 3RD ITERATION TITANIUM HEMI-PELVIC

IMPLANTS WERE FABRICATED IN TITANIUM ALLOY

CUSTOM ACETABULAR CASES:

N=102

IMPLANTED IN:

NEW ZEALAND AND AUSTRALIA

MANUFACTURED BY:

OSSIS LTD, NZ In conjunction with

MED. MODELLING/3D SYSTEMS, USA

2ND CASE: THE PROBLEM

THE BIO-MODEL OF THE PELVIC DISSOCIATION AND IIIB OUTLINE OF THE PROPOSED IMPLANT

Fracture line through posterior column = 2 parts

THE NEED FOR CUSTOM IMPLANTS (HIP)

MRS MP 70 YRS SURGEONS: PCA / JB TOTAL SURGICAL TIME REVISION ALL COMPONENTS: 2.3 HRS DISCHARGED DAY 5 FULL WEIGHT BEARING

1ST GENERATION E-BEAM CUSTOM IMPLANT dealing with bone loss and the dissociation: 2008

FINAL ASSEMBLY: COMPLETE WITH HARD ON HARD BEARING

SURGICAL TIME WITH STEM REVISION 2.3 HRS

02/04/08 26/04/2010

SEVERE RHEUMATOID : FEMALE AGED 57

BILATERAL CUSTOM ACETABULAE

5 YRS POST -OP 8 MONTHS POST-OP

Cheaper overall, full weigh-bearing, therefore cost-effective

TOTAL NUMBER OF CASES USING EBM ACETABULAR IMPLANTS = 102

Ossis Ltd, NZ and Med. Modelling / 3D Systems USA

NZ AND AUSTRALIAN MARKETS OF 24 MILLION

WHAT WOULD YOU PREFER TO USE AS AN ORTHOPAEDIC SURGEON?

• Larger spherical cup

• Oblong cup

• Bone graft • Autograft (not in revision cases)

• Allograft (banked femoral head)

• Allograft (Acetabular replacement)

• Synthetic Bone substitutes, TCP, DBM

• “Metal graft” substitution

• Cages/Rings

• Triflanged implants

INVENTORY COST!

OR A ONE-PIECE SOLUTION THAT IS PATIENT PERFECT SPECIFIC!

A REAL PROBLEM AFTER 4 REVISION SURGERIES: WHAT TO DO WITH THIS CASE?

THE EBM Ti ALLOY AUGMENT: PRIMARY KNEE AND STEM (2008)

A HUGE CAVITY BUT A GOOD SOLUTION

7 YRS POST-OP : GREAT ON THE FEMORAL SIDE

INTERFACES ARE EXCELLENT

POORER INTERFACES ON TIBIAL SIDE

MED MODELLING / OSSIS MESH SEM PICTURE

THE MOST IMPORTANT “BIOLOGICAL” FEATURE

STRESS SHIELDING AND FATIGUE FAILURE

Too stiff...stress shielding

Too thin... broken stem but the bone stock was saved!!

82 yr female with worn PE liner

82 yr male with thigh pain

BIOLOGY NOT RESPECTED

CAUSES OF FAILURE OF IMPLANTS

PROBLEM

1. MODULUS MIS-MATCH

2. MAL-POSITION

3. FRICTION

4. WEAR PARTICLES

5. INFECTION

SOLUTIONS

1. MATERIALS AND STRUCTURE

2. EDUCATION and

INSTRUMENTATION

3. BETTER TRIBOLOGY

4. MATERIALS AND SURFACES

5. SURGICAL TECHNIQUE,

SURFACE COATINGS

RESPECT BIOLOGY AND ITS SOLUTIONS

DESIGN THE IMPLANT TO “BLEND IN” WITH MODULUS MATCHING RESPECT THE PRIMARY AND SECONDARY TRABECULAE UNDERSTAND THE SUBCHONDRAL BONE PLATE UNDERSTAND THE GROWTH PATTERN OF A LONG BONE

3D PRINTING OF MATERIALS

THIS IS A TOOL THAT CAN ADDRESS THE ANISOTROPIC REQUIREMENTS OF THE IMPLANT TO MATCH BONE

THE METALLURGY OF PRINTED METALS MAY NEED FURTHER IMPROVEMENT i.e. HIP TREATMENT

WHY USE CUSTOM IMPLANTS: ARE THEY FISCALLY VIABLE?

They reduce the inventory in revision and complex primary: TRUE?

The dead stock sitting in hospitals is avoided $$$$ : TRUE

The surgery is rehearsed during design:

Unexpected findings minimized: TRUE

Make primary implants more useable in revision surgery: TRUE

CUSTOM DOES NOT EQUAL CUSTOMIZABLE

(Descriptive and Legal Regulatory processes, N.Z.)

WHO PAYS CURRENTLY IN N.Z.

PUBLIC HOSPITALS WITH PRIOR APPROVAL OF SERVICE MANAGERS

PRIVATE INSURANCE COMPANIES, AGAIN PRIOR APPROVAL AND EXPLANATION

DO THE OUTCOMES OF CUSTOMISED IMPLANTS EXTRAPOLATE TO STANDARD PROVEN IMPLANTS?

The “IdentiFit Hip” experience (milled stem) ?20% per annum failure, Dr J Hart, Australia

OPEN QUESTION

WHY CUSTOM IMPLANTS? A SMALL STEP AFTER REQUIRED IMAGING ANYWAY!

The complexity is simplified: TRUE (surgeon’s pulse < patient’s!)

PRE-OP PLANNING AND CT SCANNING

• Tray size would be known

• Augment thickness planned and manufactured

• Bearing thickness still not predictable

• Saving on inventory required

Inventory required 3 thicknesses of hemi-augments X 6 trays = 18 , or full size augments = 18: Grand total could be 36 parts

REVISION: 9/6/2016, CURRENT OFF THE SHELF LCS AND AUGMENT OF IMPLANT, NOT BONE STOCK

AN INFECTED TKR REFERRED AFTER 8 MONTHS WITH A SPACER

3 YRS POST OP LEFT KNEE

OTHER USES

CUSTOMISED PRIMARY IMPLANTS RATHER THAN CUSTOM AUGMENTS

In THR: easily “do-able” due to spherical bearings

(adjustable neck lengths etc.)

In TKR: Surface geometry critical for outcomes to be

predictable (PE does not adapt as menisci!)

In knees the soft tissue elasticity and balance is

variable, needing a range of sizes

In Trauma: specialised fixation plates

AM SPINAL IMPLANTS 2011 But still a range of heights per level needed Indications: very small female.

PATIENT EXPECTATIONS:

STRESS SHEILDING

INSERTION OPTIONS FOR CUSTOM IMPLANTS

1. Standard instruments to give standard “internal” cuts

2. Customised cutting blocks but accuracy can be problematical (Oxford Knee 2/22 accurate in NZ trial, Mr R Maxwell)

3. Robotic bone shaping using data files from the implant: MAKO etc.

SILVER COATED TITANIUM IMPLANT 1999 FOR FEMORAL OSTEOMYELITIS

COURTESY PJ BURN

Enztec Ltd NZ

Yes it works!

THE FUTURE

New biocompatible materials (polyimide etc.)

“Plastic” knees

Custom implants incorporating active surfaces

(antimicrobial and osteo-inductive)

Composite structures ( AM parts and standard parts)

DESIGNS ARE INFINITE BUT A CAUTIONARY NOTE…

RULES OF BIOLOGY CANNOT BE BROKEN… Particulates, surface finishes, corrosion

THE REACTION OF LIVING TISSUES NEEDS TO CONSIDERED… Osteolysis, ALVAL, toxicity of ion release, impurities in and on implants

THE MATERIAL’S SPECIFIC ENGINEERING PARAMETERS HAVE TO BE ALLOWED FOR... Fatigue resistance, loadings, corrosion and valency, scratches

THANK YOU FROM NEW ZEALAND