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Custom Fit Knee Systems

Can a Patient Specific Approach Make a

Difference?

Tom Minas MD MSBrigham and Women’s Hospital

Harvard Medical School

Boston MA USA

Disclosures

ConforMIS, Inc.

Stock options

Stocks

Royalties

Joint Resurfacing-Individualized prosthetic in the Young Arthritic

The clinical problemUni +Bi - compartmental OA

• Frequent wear pattern in young arthritics

• Symptoms present in both compartments + PF

• Bone stock preservation desirable over conventional TKR in 50 YO with end stage bicomp OA

• Incidence?

• Ahlback 66 YO cohort - 1966

Ahlback, S.: Osteoarthrosis of the knee: a radiographic

investigation. Acta Radiologica, Suppl 277: 7-72, 1968.

Standard Uni Implants-Femoral Fit

`AP Length

Courtesy Dr. W. Fitz, Brigham and Women’s Hospital, Boston

Medial maleLateral maleMedial femaleLateral femalePreservationZimmer High FlexBiomet OxfordS+N Oxinium

Medial male

Lateral male

Medial female

Lateral female

Preservation

Zimmer High Flex

Biomet Oxford

S+N Oxinium

Standard Uni ImplantsMedial Tibial Fit

Courtesy Dr. W. Fitz, Brigham and Women’s Hospital, Boston

ML Width

Standard Uni ImplantsLateral Tibial Fit

Courtesy Dr. W. Fitz, Brigham and Women’s Hospital, Boston

MLWidth

M/G Result Example

Incomplete Tibial CoveragePotential for Implant Subsidence & Failure

Incomplete Femoral Coverage

Limitations in Femoral and Tibial Component Alignment

Femoral Bone Cuts

Potential Notch Impingement, ACL Damage

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Technical Aspects of Lateral“Off the Shelf” Uni

Patient-Specific Image-Implant Technology

Patient Specific Resurfacing Concept

• Resurface the femur, preserve bone and ligaments

• Achieve superior fit / maximize coverage in every patient

• Restore natural function via anatomic design

• Use imaging data to “pre-navigate” instruments

– Simplifies sizing & placement challenges

– Disposable, one-time use

Partial Knee Resurfacing

iUni Unicompartmental

iDuo

Bicompartmental

Pre-Navigated InstrumentationiUni Case Study

52 YO male

Lateral iUni Case Study Medial i Uni 45 YO Female disabling B Knee OA

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Post op Medial iDuo Lateral i Duo 58 YO femalei Duo Patient

6 weeks post op , full ROM

iUni / iDuo Kit

Primary Benefits:

• Reduced steps, reduced trialing

• Reproducible technique via iJigs

• Simplified, integrated balancing

• Short learning curve

• Highly efficient OR management

Primary Drawbacks:

• Cartilage removal

OR Experience

iTotal Customized Knee

System

What has really changed in TKR since the 1980’s?

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Why iTotal?Although longterm implant survivorship is high..The Gap in Patient Satisfaction after Primary TKA

Percent of Patients Not Satisfied After Primary TKA

Symmetric CR “Off the Shelf” Implant

18 mm IC distance for Patella tracking in deep flexion

• Overhang on PCL• Uncovered MFC

Distal and Posterior Offset –Joint Surface

Distal Posterior

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Principles for surgical Technique for Symmetric Implants

• Create a symmetric rectangular extension and flexion gap from a trapezoidal assymmetric gap to accomodate the implant

• Release the tight sides and stuff the loose sides

• Use the epicondylar axis to orientate the implant and Whiteside’s line to confirm

• Ensure the tibial cut is parallel to the flexion gap at 90 degrees to have a balanced knee

• But will the implant geometry resemble the patients? or Mid-flexion instability?

• Mechanical Axis Alignment

• Patient‐Specific Fit 

•Restoration of Articulating Geometry – (J Curves, medial and lateral  joint lines and offsets)

•Restore ligaments to original state

• Bone Preservation 

• Wear Optimized Design

iTotal Design Rationale

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Preservation of the Patient’s Natural ‘J’ Curves and therefore kinematics

The patients natural ‘J’ curves(medial, lateral and trochlear) drive the femoral component geometry

iTotal Design Features• Maximize Bone Coverage;

• No implant overhang• No undersizing

• 6 Faceted Cuts• Patient individualized for

maximum bone preservation• 40 % reduction in bone

resection in a patient matched design

iTotal Design Features

•Tibial Plateau;

• Dual insert balancing capability

• Sagittal insert geometry derived from the femoral component, with increased medial conformity to promote normal motion.

• Complete proximal tibialcoverage.

• Orientation rotated for proper sagital motion

AFTERBEFORE

Virtual Alignment_CT Guided Pre-operative

The patient’s deformity is ‘Virtually Realigned’ prior to the design process starting.Correction is to mechanical alignment.

• DePuy Sigma distal femoral thickness = 9mm

• This example which is a Sz #3 equivalent implant has a 6.5mm distal femoral cut

ConforMIS “Delivery Model”Efficient, Pre-Sterilized, Disposable

Single use kit delivered a few days

before surgery

One reusable

instrument tray

Surgical Technique

• Classic Gap balancing technique

• or Measured resection

• Preserves natural joint line more accurately than traditional TKR-distal and posterior offset

• Minimal soft tissue balancing is required

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iTotal Patient Specific Surgical Plan iView 2.0 Surgical Technique iTotalPre operative x-rays

Final ComponentsPost op xray OA Valgus Knee

Postop – for Valgus OA Experience to date- iTotal

Ease for staff

Jigs accurate

Trust trials and remove all overhanging osteophytes

Minimal soft tissue balancing

Excellent intraop stability with no midflexion laxity

Minimal blood loss

Discharge home day 1-2 post op

Excellent early patient satisfaction

Must still do aggressive rehab

iTotal – 21st Century Technology

• iTotal Custom implant- joint surface –”J” curve and ligament restoration

• Prenavigation for alignment and traditional orthogonal axes bone cuts - maintains established principles of knee replacement.

• iJigs- accurate customized , disposable individualized extramedullary instruments