Joint - Knee & Upper Limb Arthroplasty Flashcards
What is the aim of an anatomical approach to TKA?
To preserve as much soft tissue as possible
Only joint surfaces are replaced/resurfaced
What is the aim of a functional approach to TKA?
Resection of condyles and cruciate ligament
Issues with the anatomical approach
The knee has complex geometries that are hard to manufacture
Difficult surgery
Benefits of a congruent surface
Greater contact area between articulating surfaces which reduces contact stresses and thus wear
Downside of congruent surface
There is a limited range of motion –> Constraint forces are high –> Leads to loosening
What is a mobile bearing?
There is a mobile polyethylene insert between femoral and tibial components
This is able to move relative to both femoral and tibial components simultaneously
This reduces contact stress due to high contact area (low wear)
Has a greater ranger of movement so has lower constraint forces (less chance of loosening)
Materials used in modern TKA
Femoral component: Cobalt-chromium
Tibial tray: Cobalt-chromium/Titanium/UHMWPE
Patellar component: UHMWPE
When to do Total v Partial TKA
Total: When both lateral & medial components are compromised
When to use Total Shoulder Arthroplasty
When the glenoid socket is compromised
What materials are used in Total Shoulder Arthroplasty
Metal stem and metal ball
UHWMPE Glenoid socket
When to use Shoulder hemiarthroplasty
When the glenoid socket is intact (e.g. proximal humerus fracture)
What is an issue with TSA?
Rocky Horse effect: due to diameter mismatch between humeral head and glenoid surface, when loaded eccentrically (off-centre) the glenoid component rocks which leads to loosening
Pros and cons of Resurfacing Arthroplasty
Pros:
Minimal damage to bone
Able to be revised later
Greater pain relief
Cons:
Loosening due to short stem
Commonly used in younger/healthier people who place higher loads on the implant
What is reverse TSA and when is it indicated?
When the ball is placed on the glenoid socket and the flat component is placed on the humeral head
Indicated in:
Rotator cuff damage
Last resort
What effect does reverse TSA have on joint centre
Moves the joint centre of rotation INFEROMEDIALLY
Increases moment arm for deltoid muscle so less force is required to achieve the same moment. –> better able to stabilise joint
Most common reasons for Total Elbow Arthroplasty (4)
Rheumatoid Arthritis
Primary Osteoarthritis
Distal humerus fracture
Distal humerus non-union
Pros and Cons of Linked TEA
Linked TEA: Mechanical connection between humeral and ulnar components
Pros:
Less chance of dislocation as more stable
Cons:
Constrained
Increases stress on bearing surfaces and bone-implant surfaces
Pros and Cons of Unlinked TEA
Unlinked: No mechanical coupling, used in people with preserved ligaments
Pros:
o Less stress on implant/cement/bone interface(s)
o More leniency in movement
o Closer resemblance to a hinge joint
Cons:
o UNSTABLE
o High rates of dislocation
What are linkable TEAs?
TEAs that can be linked or unlinked via surgeries
