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Copy of Shoulder Prosthesis

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Lorenzo Ferdinands

on 18 April 2010

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Transcript of Copy of Shoulder Prosthesis

Prosthesis Background on
shoulder Current Design and Technology Professional
opinion Prof VP Kumar Fixation of the
glenoid component Main
Problem Mechanical
Locking Chemical
Lock Smooth
Surface Olympia Total Shoulder System Minimized head osteotomy gap
Increases articular coverage
Decreases in-growth and tissue impingement

Pear-shaped Glenoid
Reduces impingement on the superior surface
Reduces loosening risks as edge contact is decreased

DePuy ® Global Advantage
Claims that press-fit designs are far superior to designs that rely on bone cement applications
Claims their patented design prevents “rocking horse” loosening
Cemented/Cementless Non-cemented glenoids with metaphyseal porous coatings have shown promise
Overall costs for cemented prosthesis surgery is more than for cement-less’
For cement-less application, prosthesis with metaphyseal taper is superior to usual press-fit designs
The Shoulder Maximum Range of Motion
Arm abduction/adduction/flexion/extension
Medial/lateral rotation
Present Prosthesis Low stability
Shallow glenoid socket
Decreases stability while allowing higher ROM
Connective tissue
Surrounding soft tissue
Shoulder overview
High mobility and range of motion
Relatively low load bearing
Held in place by soft tissue and capsule
Highly susceptible to dislocation Surgical Treatment In what cases?
Osteoarthritis (degenerative joint disease)
Rheumatoid arthritis
Post-traumatic arthritis
Rotator cuff tear arthropathy
Avascular necrosis (osteonecrosis)
Failed previous shoulder replacement surgery


Total replacement (2 types)

Humeral component
Glenoid component
Wear isn’t a big issue
Range of motion isn’t a big issue
Why? Little bone
Weak bone
Lot of motion
Forces unbalanced on cup causing micro-motion
Small amount of bone
38mm height/28mm lower width
Compare to hip/elbow/knee
Weak Bone
Osteoarthritic cases
Older population
High amount of motion
Forces acting
How they promote component loosening.

Glenoid Cup
To provide a good mechanical fixation to the cancellous bone.
To reduce peak micro-motions between the glenoid component and the bone.
To remove the need for bone cement as a secondary binding element.
To ensure design is sufficient to hold glenoid component in weakened bone.
Mechanical Design Requirements Properties Desired
Glenoid Cup
Good wear resistance (hard surface)
Ease of Manufacture (easy to machine into shape)
Low Corrosion in saline solution
Preliminary Ideas Limitations
Mechanical parts are too small (< 5mm)
Designs are too complex leading to high manufacturing cost
Sharp angles in design leads to stress concentration and possible corrosion prone sites.
Pear-shaped Design
Backwards protruding rims at the bottom of the stems
Snap fit nubs at the side
Allows for bone graft to be adhered onto the rims
Titanuium Alloy cup and screws
High strength
Good corrosion resistive properties
Allows the coating of bioactive hydroxy apatite.
Screws provides additional fixation on the scapula
Desirable material properties
Mimic the properties of biological articulate cartilage
Reduce contact stresses and friction Hydrogel
Poly(vinyl-alcohol)cryogel (pva-c)
Cross linked polar chains
Fabrication process : Repetitive thaw-freeze cycle
Introduce crystalline structure
Impact on contact stress on implant Hydroxyapatite
Naturally occurring mineral form of calcium apatite
Excellent bone integration
Encourage osseointegration
Highest impact strength of thermoplastic
Used as bearing surface to implants
Highly resistant to abrasion
Excellent corrosion resistance
Self lubricating
highly-crosslinked UHMWPE
Introduced in 1998
Superior than conventional UHMWPE
improved oxidation resistance
Significantly lower wear rate
Question #8
Up to --------of bones are made of modified form of the inorganic mineral hydroxyapatite, known as bone mineral
Answer: B) 50%
Question #9
What is the most commonly practiced method for HA coating in the manufacturing industry?

Answer: C) thermal spraying Question #10
Which of the following is/are propertie(s) and function(s) of articular cartilage?
A) High water content by weight (70-80%)
B) Bearing surface with low coefficient of friction
C) Distribute loads between opposing bones in a synovial joint
D) All of the above
Answer: D) All of the above
Question #1
What stabilizes the shoulder joint? Answer: B)The soft tissue: ligaments, tendons, muscles Question #2
In which cases might you have a shoulder replacement carried out? Answer: D) All of the above Question #3
What is the main problem associated with shoulder prostheses?
Answer: C) Fixation of Glenoid componet Question #4
Which factors should be considered to decide between cemented and cement-less surgery? Answer: D) All of the above Question #5
What is the most common post-operative complication? Answer: B) Humeral head subluxation and glenoid loosening Question#6
What is the biggest challenge in the fixation of the glenoid component? Answer: C) Limited amount of bone for the mechanical anchoring of the component Question #7
For a UHMWPE glenoid, which material will be the most suitable for the humeral head? Answer: A) Ceramic Osteoarthritis Question?
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