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Implant Design and Technology ENG3052M

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Colin Grant

on 24 January 2018

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Transcript of Implant Design and Technology ENG3052M

Learning Outcomes

Critically evaluate design methodology and associated considerations for implants

Apply advanced design methodology and procedures to medical implants

Apply scientific methodology, systematically solve problems
Implant Design and Technology


Dr Colin Grant WG26

2 hour closed-book examination

Reading List
Basic Orthopaedic Biomechanics,
VC Mow and WC Hayes, 1997
Basic Biomechanics of the Musculoskeletal System, M Nordin and VH Frankel, 2001

Keywords: Orthopaedics, Bio-mechanics, Arthroplasty, Medical Implant, Joint Replacement

- the branch of medicine dealing with the correction of deformities of bones or muscles (musco-skeletal), originally in children in 1741
: correct or straight (Greek)
: child (Greek)

Early advances in Orthopaedics surgery came out of World War I
Mortality of femoral fracture was reduced from 87% to 8% use of a simple splint
This module will concentrate on the use of implants to correct bone and joint problems

Characteristics of Physicians and Engineers
-Engineering approach to problem solving
Design of Implants
-Background, scope & types
-Functions and design constraints
-Manufacturing and production
-Regulatory requirements
Orthopaedic products
UK (NHS) Statistics

Physician (Characteristics):
-Evidence-based approach: base decisions on clinical data alone
-Acquiring and applying a vast array of information: invaluable, but largely qualitative and unstructured, non-specific representations of biological systems
-Dealing with urgent problems in human health
-Taking responsibility well-being of individual patients

Engineer (Characteristics):
-Scientific approach: develop theories to explain existing data and predict future results, then test these theories
-Simplified, reductionist view of problems
-Structured approach: searching out information, choosing and defining problems carefully
-Appreciation, understanding, application and extension to new situations
-Works to a pre-planned time-scale (or budget....)

Broad spectrum of collaboration
-Interaction between medical/surgical and engineering contributions such as in joint prosthesis & implant technology
-Engineering-based metrology instruments such as blood pressure devices
-Biology-based designs such as genetic engineering, biophysics/biomechanics of biological matter, tissue engineering

-Engineering specifications (Qualitative and quantitative)
-Iterative approach to design:
Engineering Design Approach
Idealised Medical Design Procedure
Designing an implant is a complex issue
First recorded successful hip replacement surgery took place in 1940 in Carolina, US made from cobalt-chrome alloy
The majority of material development used in medical devices has occurred in the last 50 years and has been accompanied by growing research field of biomaterials science

Limited understanding of natural joints
-Natural joints are too complex to accurately copy (for a singular use)
-Mimic the structure and properties of natural tissues?
-Minimal invasiveness and damage
General goals of implant design
Relief of pain
Restoration of function
Environmental conditions
Surgical requirements

Arthritis - progressive auto-immune disease

Treatment (UK) usually very conservative; mild drugs with increasing strength on demand when patient suffers

Replacement of all articulating surfaces (total joint replacements, TJR)

Range of angular movements:
Internal/external rotation

Articulating speed (faster/slower ?)
Loads acting on the joint (progressive load bearing)
Soft tissue: muscles, ligaments, bursae

Small contact stresses
(how do we measure contact stress for a ball & socket joint ?)

Does not fracture
Minimal wear
Does not loosen

Insensitive to misalignment - surgeons are

Insensitive to size mismatch - implants are seldom made to measure

Insensitive to different kinetics of patients

Space limitations
Fixation requirements
Proximity of nerves, arteries, etc

Different surgeon favour different techniques
Space limitations

” or “i
Aseptic infection
Instrumentation/surgical tools
-Revision procedure

Materials consideration:
-Effects of the host:
tissue reaction and immunological response
-Effects of the implant:
mechanical compatibility, degradation, corrosion

Limited choice of materials

What do we generally use?

Ultra high molecular weight polyethylene (UHMWPE)
Silicone (e.g. polydimethylsiloxane, PDMS)

Stainless steel (316L)
Cobalt chrome alloy (Co-Cr-Mo): cast or wrought
Titanium alloys (e.g. Ti6Al4V)

Alumina (Al2O3)
Zirconia (ZrO2)


Anticipated total market
Range of sizes/options required
Batch sizes
Manufacturing processes (wasteage high)
Maximum acceptable cost

MDD (Medical Device Directive - Europe)
Class II b: high risk - includes most joint replacement implants
Class III: very high risk - includes implants that undergo chemical change, such as bone cement

FDA (Food, Drug Administration - USA)
Class I: General Controls
Class II: Performance Standards - includes common orthopaedic implants
Class III: Pre-market Approval

Joint replacements
-Hip, Knee, Ankle, Toe
-Shoulder, Elbow, Wrist, Finger
Spinal implant
-Fusion, Artificial Discs
Fracture fixation
-Intramedullary nail: long bone
-Plates: range of bones
-Screws, rods and wires: small bones
-External fixator: complex fractures

(Hemi) arthroplasty (cup or head)
Resurfacing hip prosthesis
Total hip prostheses

Total knee joint replacement (Arthritis)
Visco-supplementation using hyaluronic acid
Anatomy of the knee

Module Information
Lecture 1
What to expect from me?
Entrance in to lecture room early (provided no-one else in before)
Will try to make the lectures as stimulating as possible
Ask anything, at anytime, by any means.... there's no such thing as a silly question
I'll have the power point loaded on to Blackboard by the Friday before lectures
If you want the '
' presentation, send me an email request
When you talking to me - I'm listening giving you my entire attention
Any other suggestions..??
What I expect from you
Be on time - late students cause disruption
Mobile phones switched off (or on silent, as you may need to use it as a calculator)
Interact - I'll be asking questions, please contribute to discussions
Keep non-topical discussions to a minimum
When I'm talking, please listen, giving me your full attention
Any other suggestions..??
Hip - 63,571
Knee - 64, 667
Shoulder - 4225
Ankle - 464
Elbow - 505
Full transcript