Joint - Knee & Upper Limb Arthroplasty

Question 1

What is the aim of an anatomical approach to TKA?

Answer 1

To preserve as much soft tissue as possible

Only joint surfaces are replaced/resurfaced

Question 2

What is the aim of a functional approach to TKA?

Answer 2

Resection of condyles and cruciate ligament

Question 3

Issues with the anatomical approach

Answer 3

The knee has complex geometries that are hard to manufacture

Difficult surgery

Question 4

Benefits of a congruent surface

Answer 4

Greater contact area between articulating surfaces which reduces contact stresses and thus wear

Question 5

Downside of congruent surface

Answer 5

There is a limited range of motion –> Constraint forces are high –> Leads to loosening

Question 6

What is a mobile bearing?

Answer 6

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)

Question 7

Materials used in modern TKA

Answer 7

Femoral component: Cobalt-chromium
Tibial tray: Cobalt-chromium/Titanium/UHMWPE
Patellar component: UHMWPE

Question 8

When to do Total v Partial TKA

Answer 8

Total: When both lateral & medial components are compromised

Question 9

When to use Total Shoulder Arthroplasty

Answer 9

When the glenoid socket is compromised

Question 10

What materials are used in Total Shoulder Arthroplasty

Answer 10

Metal stem and metal ball

UHWMPE Glenoid socket

Question 11

When to use Shoulder hemiarthroplasty

Answer 11

When the glenoid socket is intact (e.g. proximal humerus fracture)

Question 12

What is an issue with TSA?

Answer 12

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

Question 13

Pros and cons of Resurfacing Arthroplasty

Answer 13

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

Question 14

What is reverse TSA and when is it indicated?

Answer 14

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

Question 15

What effect does reverse TSA have on joint centre

Answer 15

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

Question 16

Most common reasons for Total Elbow Arthroplasty (4)

Answer 16

Rheumatoid Arthritis
Primary Osteoarthritis

Distal humerus fracture
Distal humerus non-union

Question 17

Pros and Cons of Linked TEA

Answer 17

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

Question 18

Pros and Cons of Unlinked TEA

Answer 18

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

Question 19

What are linkable TEAs?

Answer 19

TEAs that can be linked or unlinked via surgeries