Unit 5a: Shoulder joint replacement

Question 1

What are the most common causes of a need for a upper limb joint replacement?

Answer 1

Rheumatoid Arthritis 
Osteoarthritis
Osteonecrosis 
Post-traumatic arthritis 
Fractures

Question 2

Which upper limb replacement patients in particular need an individual treatment plan?

Answer 2

Rheumatoid Arthritis

Question 3

Why is upper limb joint arthroplasty often not the priority with Rheumatoid patients?

Answer 3

RA of cervical spine may cause instability with neuro symptoms

Successful lower limb replacement will lessen or eliminate the need for upper limb to support body weight during walking - or could compromised upper limb replacements

Question 4

What factors should be considered when deciding which upper limb joints should be given priority for replacement if several are affected?

Answer 4

Pain is important

Functional impairment

Question 5

If all upper limb joint are equally affected by pain then what is the general rule for replacement?

Answer 5

Distally to proximally

Question 6

Why are replacements performed distally to proximally?

Answer 6

The primary pbjective of upper limb joint replacement after pain relief is to allow good restoration of hand function

Impairment of distal joints may compromise critical early physio for proximal replacements

It is arguable that more functional improvement is gained the more distal the joint

Question 7

Why do some surgeons prefer to replace the shoulder first?

Answer 7

Shoulder pain is mre troublesome at night and may radiate to the elbow

An immobile shoulder might cause increased loading on the elbow causing a replacement to fail

Rehab of other joints can be simplified with a nearly pain-free shoulder

Question 8

What flexible material has been used successfully in wrist and finger joitn replacements?

Answer 8

Silicone elastomer (rubber)

Question 9

Has total or hemi-arthroplasty been shown to have better pain relief and range of motion in the shoulder?

Answer 9

Total arthroplasty

Question 10

Give 2 potential reasons why the survival rates for upper limb replacement are not as good as those found in hip or knee joint replacements?

Answer 10

Low frequency of upper limb replacements

Highly complex nature of upper limb joints and their small dimensions

Question 11

Which of the upper limb replacements is the most successful in survival terms?

Answer 11

Shoulder then elbow

wrist and finger = worst

Question 12

What are the 3 categories of shoulder prostheses?

Answer 12

Unconstrained
Semi-constrained
Constrained

Question 13

What are reversed or inverted anatomy design prostheses?

Answer 13

Designs that do not conform to the normal joint - because the humeral component is a socket instead of a ball

Question 14

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

Answer 14

Pain relief

Question 15

What range of abduction is generally achieved wh unconstrained designs?

Answer 15

90 - 135 degrees

Question 16

How are patients assesed pre op for a shoulder replacment to determine the exact nature of their problems?

Answer 16

Range of motion
Strength
Stability
Function

Question 17

If the rotator cuff is intact and functioning which design will most likley be chosen?

Answer 17

Unconstrained

Question 18

If there is little or no stability provided by the soft tissues in the shoulder what design would be required?

Answer 18

Constrained

Question 19

What is the primary function of the shoulder?

Answer 19

To allow the hand to be positioned in space

Question 20

What are the 3 synovial joints of the shoulder?

Answer 20

Glenohumeral
Acromioclavicular
Sternoclavicular

Question 21

Other than the 3 synovial joints in the shoulder which other articulation is important?

Answer 21

Scapulothoracic bone-on-muscle-on-bone articulation

Question 22

What is the most important articulation of the shoulder and why?

Answer 22

Glenohumeral

It has the largest range of motion and most load bearing

Question 23

Which joint is replaced in a total shoulder replacement?

Answer 23

Glenohumeral joint

Question 24

Why is the shoulder joint inherently unstable?

Answer 24

Shallow nature of the glenoid fossa

Question 25

What compensates for the instability in the shoulder joint?

Answer 25

Rotator cuff and surroundnig soft tissues

Question 26

In which disease in particular is there likely to be soft tissue pathology in the shoulder?

Answer 26

Rheumatoid arthritis

Question 27

What problem exists with bone stock in shoulder replacements?

Answer 27

Scapula is a thin blade of bone and though the glenoid fossa is supported by bony buttresses there is a limited amount of bone stock to attach a prosthesis to

Question 28

With which designs in particular is loosening of the glenoid component a significant complication?

Answer 28

Constrained designs

Question 29

What is the stability of an unconstrained shoulder prosthesis dependent on?

Answer 29

An intact, functioning rotator cuff mechanism

Question 30

In a unconstrained shoulder prosthesis what is the level of function achieved dependent on?

Answer 30

The quality of the patients' rotator cuff and deltoid muscles

Question 31

In which patients in particular is loosening of the glenoid component an issue?

Answer 31

Younger patients

Question 32

How is stability achieved in semi-constrained shoulder prostheses?

Answer 32

Still primarily dependent on the rotator cuff mechanism although some constraint is vuilt in to its design

Question 33

Why is the glenoid component of constrained prostheses shaped so that it roofs over the superior aspect of the humeral component?

Answer 33

To resist the upward shear force produced when the arm is elevated - preventing the upward subluxation of the humerus that can occur when there is rotator cuff weakness or abscence

Question 34

What occurs as a consequence of upwards subluxation of the humerus?

Answer 34

Tearing of the supraspinatus tendon

Question 35

What are the disadvantages of semi-constrained designs?

Answer 35

Motion is limited compared to unconstrained Greater forces are transmitted to the glenoid component bone-cement junction resulting in more freuent loosening of the glenoid component

Question 36

Explain what causes stresses at the bone-cement junction with hooded glenoid components?

Answer 36

A arm elevates mucle forces pull the humerus upward but is prevented by hood Range of motion is restricted by hood and prothesis/bone/tissues come into contact with hood Forces act vertically on the hood producing moments Moments must be counteracted by additional forces at the bone-cement junction - causing stresses

Question 37

What design are most constrained total shoulder replacements?

Answer 37

Ball-in-socket designs (some the same as normal anatomy and some reversed)

Question 38

What is unusual about the Stanmore total shoulder replacement?

Answer 38

It is a metal-on-metal design

Question 39

What are the complications of the Stanmore metal-on-metal design?

Answer 39

Unsnapping of the 2 components Instability Glenoid component loosening

Question 40

What materials is the Michael Reese total shoulder replacement made from?

Answer 40

Cobalt-chromium humeral head and polyethylene socket which fits within a metal glenoid cup

Question 41

What is the specific design feature of the Michael Reese prosthesis put in place to prevent scapula from fracturing?

Answer 41

Allows humeral head to dislocate when a specified large moment is reached

Question 42

How is a trispherical total shoulder replacement structured?

Answer 42

Humeral and glenoid components have a metal ball, both of which are contained within a third larger polyethylene ball (which is encapsulated within a vitallium shell for extra strength)

Question 43

In a single ball-in-socket prosthesis how does head size affect the range of motion?

Answer 43

Larger the the head the greater the range of motion

Question 44

In reality what is range of motion restricted by?

Answer 44

Size of the joint space Need to ensure socket is of adequate thickness Requirement that the ball does not dislocate

Question 45

What are the advantages of the trispherical design?

Answer 45

Larger overall range of motion than would be possible with a single large ball - surrounding soft tissues acts as the constraint to motion Maintains good stability

Question 46

Do constrained or unconstrained designs have a higher frequency of loosening?

Answer 46

Constrained have a higher frequency of loosening

Question 47

Are dislocations more common in constrained or unconstrained designs?

Answer 47

Dislocations more common in constrained design (when they occur generally have to be treated surgically

Question 48

What are common causes of failure of constrained designs?

Answer 48

Loosening Dislocation Mechanical failure of components Disassembly of components

Question 49

What is the rationale behind reversing the normal anatomy in prosthesis design?

Answer 49

By increasing the radius of the ball it would be possible to improve the range of motion Provide a better lever arm for the deltoid

Question 50

In anatomically reversed designs, what is the consequence of providing a better lever arm for the deltoid?

Answer 50

Much more stress at the bone-cement junction

Question 51

What methods have been tried for fixation of the glenoid component?

Answer 51

``` Triangular shaped keel Extended keel Pegs Stem Wedge Large screw Flanges bolted to the base of the spine of the scapula ```

Question 52

What are the benefits of metal backed glenoid components?

Answer 52

Increase fixation | Aid stress distribution

Question 53

In which design is there larger loads on the glenoid component and therefore a need for this to be extra secure?

Answer 53

Constrained designs

Question 54

What approach was taken to secure the glenoid component in the Bickel prosthesis?

Answer 54

Glenoid component cemented entirely within the glenoid to maximise the contact area

Question 55

How common is loosening of the glenoid component compared to the humeral component?

Answer 55

8 times more common

Question 56

Why might some surgeons elect for hemiarthroplasty when the glenoid is in good condition despite the compromise in pain relief and function?

Answer 56

Due to concerns of glenoid components loosening

Question 57

Overall what is the preferred shoulder prosthesis?

Answer 57

Unconstrained (provided good condition of surrounding soft tissues)