Shoulder Joint Replacement

Question 1

What are the most common joint replacements?

Answer 1

Hip then knee then shoulder

Question 2

What 3 categories are shoulder replacements divided into? Give an example of each

Answer 2

Unconstrained (Neer)
Semiconstrained (Gristina)
Constrained (Michael Reese)

Question 3

What is a reversed or inverted anatomy design prosthesis?

Answer 3

Do not conform to the normal joint (because humeral component is a socket instead of a ball)

Question 4

Example of reersed (inverted) anatomy prosthesis?

Answer 4

Cavendish

Question 5

What is the primary indication for elective replacement of the shoulder joint?

Answer 5

Pain relief

Question 6

With unconstrained designs generally what range of joint motion is achieved?

Answer 6

90-135 degrees of abduction

Question 7

What dictates the type of type of design chosen for a particular patient?

Answer 7

Quality of the soft tissues that surround the shoulder joint and provide joint stability

Question 8

What is involved in a preop assessment of a shoulder?

Answer 8

Range of motion
Strength
Statbility
Function

Question 9

If the rotator cuff is intact what prosthesis will usually be chosen?

Answer 9

Unconstrained

Question 10

If there is little or no stability which prosthesis will usually be chosen?

Answer 10

Constrained design

Question 11

What is the primary function of the shoulder?

Answer 11

To position the hand in space

Question 12

What are the 3 synovial joints of the shoulder?

Answer 12

Glenohumeral
Acromioclavicular
Sternoclavicular

Question 13

Which articulation of the shoulder has the largest range of motion and the most load bearing?

Answer 13

Gleno-humeral articulation

Question 14

Which joint is replaced in a total shoulder replacement?

Answer 14

Glenohumerl

Question 15

Why is the shoulder inherently unstable?

Answer 15

Shallow glenoid fossa

Question 16

Example of unconstrained shoulder prosthesis

Answer 16

Neer

Question 17

What is teh level of function of an unconstrained prosthesis dependent on?

Answer 17

Quality of the patients’ rotator cuff and deltoid muscles

Question 18

In which patients is loosening of the glenoid component an improtant factor and why?

Answer 18

Younger patients - due to the difficulty of revision operations

Question 19

What provides stability in a semiconstrained prosthesis?

Answer 19

Primarly the rotator cuff though some constraint is built into the design

Question 20

How are semiconstrained prostheses design to confer stability?

Answer 20

Glenoid component is shaped so it roofs over the superior aspect of the humeral component - resists upward shear force when arm is elevated - prevents upward sublux of humerus

Question 21

What are the disadvantages of semiconstrained designs?

Answer 21

Motion is limited compared to unconstrained

Greater forces transmitted to glenoid component bone-cement junction (more frequent loosening of glenoid component)

Question 22

How does a hooded glenoid component affect movement of the shoulder?

Answer 22

Restricts elevation

Helps to prevent upward subluxation

Question 23

What is the disadvantage of a hooded glenoid component?

Answer 23

Forces act vertically on hood - produce moments which are counteracted by additional forces at bone-cement junction - gives rise to compressive stresses superiorly and tensile stresses inferiorly

Question 24

What material is used to construct the glenoid componet of a Neer type shoulder prosthesis?

Answer 24

Polyethylene

Question 25

How can an unconstrained shoulder prosthesis be converted to a semi-constrained one?

Answer 25

Using a hooded glenoid

Question 26

What deisng are most constrained total shoulder replacements?

Answer 26

Ball-in-socket

Question 27

Why is the Stanmore total shoulder replacement unusual?

Answer 27

It is a metal-on-metal design

Question 28

How is the Stanmore prosthesis fixed?

Answer 28

Glenoid socket = 3 pegs + cement | Humeral = cement

Question 29

What are the complications of the Stanmore total shoulder replacement?

Answer 29

Unsnapping of the two components Instability Glenoid component loosening

Question 30

Briefly describe the Michael Reese total shoulder replacement

Answer 30

CoCr humeral head | Polyethylene socket which fits within a metal glenoid cup

Question 31

How is the Michael Reese designed to prevent fracture of the scapula?

Answer 31

Allows the humeral head to dislocate when a specified large moment (torque) is reached

Question 32

What is unusual about the trispherical shoulder prosthesis?

Answer 32

Has 3 balls not 1

Question 33

What material are trispherical prostheses made of?

Answer 33

Humeral metal ball Glenoid metal ball Contained within a third larger polyethylene ball encapsulated with a Vitallium shell for extra strength

Question 34

In a single ball-in-socket prosthesis what deterines the range of motion?

Answer 34

The larger the head the greater the range of motion (limited by space as need to ensure that the socket is of adequate thickness and so the ball doesn't dislocate)

Question 35

How does the trispherical shape affect the range of motion?

Answer 35

Doubles the range of motion that would be possibe with a single ball

Question 36

Which has a higher frequency of loosening, constrained or unconstrained?

Answer 36

Constrained

Question 37

Are dislocations more common in constrained or unconstrained?

Answer 37

Constrained (when they occur generally have to be treated surgically)

Question 38

What is the rationale behind reversed anatomy prostheses?

Answer 38

Increasing the radius of the ball will improve the range of motion

Question 39

What are the advantages of reversed anatomy prostheses?

Answer 39

Better lever arm for the deltoid

Question 40

What are the disadvantages of reversed anatomy prostheses?

Answer 40

Better lever arm for deltoid (causes more stress at bone-cement junction)

Question 41

What methods have been tried to fix the glenoid component?

Answer 41

``` Triagular shaped keel Extended keel Pegs A stem A wedge A large screws Flanges bolted to the base of the spine of the scapula ```

Question 42

Why do some designs have a metal backed glenoid components? (Give an example)

Answer 42

Increase fixation and aid stress distribution (e.g. Neer)

Question 43

Why are hemiarthoplasty's of the shoulder when the glenoid is in good condition popular, despite the compromise in pain relief and funciton this entails?

Answer 43

Loosening of the glenoid component