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I-Assist guided Verilast Knee replacement
Durable knee replacement for young patients
Dr.A.K.VenkatachalamFRCS, M.Ch Orth, DNB Orth, MS Orth
www.kneeindia.com
Patient details• Ms. PM from Gujarat• 32 years • Suffering from Avascular necrosis
of Right knee• Had consulted several surgeons
elsewhere.• Had advanced damage to the
knee with bone loss from the lower end of the thigh bone
• Was unable to walk without support for few preceding years.
• Underwent I Assist guided Verilast Knee replacement in September 2014.
Key concepts in this presentation
• I –Assist • Verilast knee– What is it? How does it reduce
wear?• How I-Assist and Verilast combine to lower
wear and increase durability in young patients?
1. What is the I-Assist?
• It is a Personalized guidance system designed to assist the surgeon in positioning a total knee arthroplasty implant components intra operatively.
• It uses surgical instruments and position sensors to determine alignment axes in relation to anatomical landmarks
• To thus precisely position alignment instruments & implant components relative to these axes.
What is inside it?
• It consists of 4 half palm sized pods with electronic apps like
• Wi-Fi found in smart phones. • Gyroscope found in air planes. • The electronic sensors inside calculate the
alignment. The blinking lights on the display face indicate the correct position.
• Red light means improper position and Green light means proper position.
How does it work?
• After connecting it to the knee the surgeon moves the femur (thigh bone) in 13 different positions and the tibia ( leg bone) in 4 positions.
• It calculates the position by the electronic devices inside it.• The surgeon makes fine adjustments so that red lights turn to green. • Blinking green lights indicate zero percent error. • The surgeon can proceed to cut the bone confident that his
cuts will be perfectly aligned. • He can then finally place the implant components in the
correct alignment achieved and validated in the previous steps.
Advantages
• It guides the surgeon to get perfectly aligned cuts intra operatively.
• It gives zero error cuts and again validates it in the next step.
• Thus the surgeon gets the right fit during the surgery itself.• This ensures that the implant components are positioned
perfectly in correct alignment. • Surgeon focusses his eyes in the operating field itself and
not take his eyes away.• It thus saves time.
What does it differ from?
• Patient specific instrumentation• Computer assisted knee replacement
Alignment in Knee replacement• It is one of the factors that
ensures long life of the implant.
• A proper alignment means the implant is perpendicular to the ground.
• Mal aligned knee replacements tend to wear out sooner than normal.
• Even experienced surgeons can make errors in placement of the components.
Mal-aligned car tyre
Wear on the inside
Why do young patients need a knee replacement ?
• Rheumatoid arthritis (common) • Post traumatic arthritis (common in India and
developing countries• Avascular necrosis (rare)
Less than 65 years 12 %
65 – 75 years 10 %
75 years 4 %
Total knees fail more often in young patients
Age and failure rates
Robertsson, Thesis Lund 2000 , Swedish arthroplasty registerE [email protected]
Why ? Young patients wear away their total joints more
• than their older colleagues• Wear is proportional to
usage.• Young patients walk on
average up to 50% more than older patients.
• Usage leads to increased poly wear
• Poly wear leads to aseptic loosening
Patient age Average of steps/year
< 60 years 1200,00
> 60 years 800,00
Age & activity after THR/TKR
Problems of knee replacement in young
• Previous two slides indicates that there is a higher risk of failure in young patients and they may require a revision within 10 years
• We also know that the Redo operation will be technically a difficult operation than the primary. Result also will be inferior.
How to prolong the life of a knee replacement in a young patient ?
• The surgeon can do a TKR with a prosthesis that wears out slowly.
• Use of materials, techniques, activity modification can lead to better implant survivorship.
Prosthetic life prolongation
Wear is an issue. Steps to reduce wear • Bearings- alternate bearings like oxidized zirconium.
• Poly ethylene – X LP poly, anti oxidants, thickness.• Accuracy of component placement- ? Navigated
surgery
Options for change
• Change femoral counter-face ( Oxidized zirconium instead of routine Cobalt Chrome )
• Change Poly insert ( XLPE)
Combination is known as Verilast knee.
Oxidised Zirconium
• Meets requirements for ideal TKR• Smoother• ↓ Coefficient of friction• More scratch resistant• Less wear against both conventional and
highly cross linked poly ethylene.
What is it?• Zirconium- metallic element• Zirconia- ceramic• Zr-2.5 Nb Metallic alloy• Super heating zirconium to
500+°C in Oxygen presence• Surface transformation into
zirconia ( ceramic oxide) • Chemically bonded ceramic oxide
surface 5μ thick
Ceramic Oxide
Original Surface
Air
500oCOxygenDiffusion
Oxygen Enriched Metal
Metal Substrate
Oxidized Zirconium properties• It is a metal component• Thin layer of ceramic like material that is part of its innate
structure. This is not a coating. • Ceramic oxide is 5 μ thick• Biocompatibility is excellent, matches titanium• Very low coefficient of friction vs Cobalt chrome.• Extremely abrasion resistant. • Hard like ceramic• Equivalent strength properties to Cobalt chrome.• Adverse to chipping that can occur at insertion and over time.• Lack of Nickel allergy.
Wear properties of Oxidized zirconium
• Oxidized zirconium reduces volumetric wear by upto 89% in an abraded environment when compared to Cobalt Chrome
Oxidized Zirconium- Best of both worlds (Ceramic & Metal)
• Strength of Cobalt chrome• Low coefficient and scratch resistance of
ceramic• Non brittle as the ceramic layer is part of the
innate structure. • Decrease wear is the main advantage.4900
less volumetric wear.• 160 times smoother.
Verilast CR knee
• Femoral component made of Oxidized Zirconium
• Plastic insert made of Cross linked poly ethylene (XLPE)
• Cruciate retaining or CR knee removes less bone than other knee.
Verilast knee has the potential to last 35 years
• Potential has to be harnessed by perfect alignment.
I Assist + Verilast knee
• Gives perfect alignment during surgery itself.
• Alignment along with durable materials like Zirconium and Cross linked poly-etheylene increases life of a knee replacement to 35 years.
• No need for future revision surgery in young patients.
What is innovative in my procedure?
• Earlier Verilast knee was implanted with an earlier smart tool called “ Visionaire” patient specific instruments from the same company.
• Patient specific instruments manufacturing take time.• Technique is operator dependent.• Also used with Computer navigation – Surgeon has to keep shifting
his gaze from the operating field to the computer and back.
• This is the first time that it is used with a user friendly I –Assist smart tool.
• I-Assist and Verilast belong to different companies.• This is the first time that high end products from different companies
have been combined to hopefully give a high end durable product.
