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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
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
