Shoulder joint replacement

Question 1

prior to upper limb joint replacement what will most patients have been diagnosed with?

Answer 1

RA
OA
osteonecrosis
post traumatic arthritis 
fractures

Question 2

what will be given priority in RA sufferers, over upper limb joint replacement

Answer 2

spine or lower limb problems will be prioritised

Question 3

why should spine / lower limb joint replacement be prioritised over upper limb arthroplasty?

Answer 3

• RA of c-spine may cause instability & can be assoc with significant/progressive neuro symptoms&raquo_space; must prevent damage to spinal nerves or cord
• lower limb joint replacement may eliminate/lessen the need for upper limb support of body weight&raquo_space; if this isn’t addressed first it could compromise the success of an upper limb replacement

Question 4

If more than one upper limb joint is affected, how is it decided which will take priority

Answer 4

firstly pain is the determining factor

secondly, if all are equally painful, replacement is generally performed distally to proximally i.e. fingers first

Question 5

why are distal joints replaced before proximal joints, if equally painful

Answer 5

primary aim of upper limb joint replacement is restoration of hand function
distal joint impairment may compromise the important early physio to a more proximal joint in the early period following replacement
arguably more functional improvement is gained the more distal the joint

Question 6

why do some surgeons prefer to replace the shoulder before other upper limb joints

Answer 6

• shoulder pain more troublesome at night & may radiate to elbow
• immobilised shoulder may cause abnormal loadings at the elbow which may lead to early failure of an elbow prosthesis
• rehab of other upper limb joints can be simplified with pain-free (or at least less painful) shoulder

Question 7

what has been shown to provide better pain relief - total or hemi-arthroplasty

Answer 7

total

Question 8

apart from small dimensions and complexity, what added difficulty does a shoulder replacement have?

Answer 8

balancing soft-tissue and inadequate scapula bone stock

Question 9

how are shoulder prostheses divided into subcategories

Answer 9

according to constraint

• unconstrained
• semiconstrained
• constrained

Question 10

how are shoulder prosthesis described if they don’t conform to the normal joint

Answer 10

reversed or inverted anatomy designs

Question 11

primary indication for elective replacement of shoulder joint

Answer 11

pain relief

Question 12

how much abduction can an unconstrained shoulder replacement generally achieve

Answer 12

90 - 135

Question 13

what will largely influence the type of shoulder design chosen for a particular patient

Answer 13

pre op assessment of the quality of the soft tissues surrounding the shoulder joint

Question 14

if the rotator cuff is intact and functioning, what type of shoulder prosthesis would be chosen?

Answer 14

unconstrained

Question 15

what is the primary function of the shoulder

Answer 15

to allow the hand to be positioned in space

Question 16

name the 3 synovial joints of the shoulder and the other important articulation

Answer 16

glenohumeral
acromioclavicular
sternoclavicular

scapulothoracic articulation

Question 17

how high can the forces reach at the glenohumeral joint

Answer 17

up to several times body weight

Question 18

what compensates for the inherent instability of the glenohumeral joint

Answer 18

rotator cuff

• supraspinatous
• infraspinatous
• subscapularis
• teres minor

Question 19

what condition in particular is likely to involve some soft tissue pathology at the shoulder

Answer 19

RA

Question 20

what is a significant problem with shoulder replacements due to little bone stock
especially with which type of designs?

Answer 20

loosening of the glenoid component, especially with constrained designs

Question 21

what is an unconstrained shoulder prosthesis dependent upon

Answer 21

intact, functioning rotator cuff

Question 22

what has been found to be superior - shoulder replacement with glenoid component or without

Answer 22

with glenoid component replacement

- increased patient satisfaction, ROM and pain relief

Question 23

in which age group may total shoulder arthroplasty be more risky than partial

Answer 23

younger patients because total carries the risk of loosing of the glenoid component and revision operations are difficult

Question 24

what is the advantage of a hooded glenoid

Answer 24

it prevents upwards subluxation of the humeral component due to rotator cuff weakness

Question 25

what tendon will tear if there is upwards subluxation of the humerus

Answer 25

supraspinatous

Question 26

what is the disadvantage of semiconstrained designs as opposed to unconstrained designs

Answer 26

motion is limited leading to greater forces transmitted to the glenoid component bone-cement junction&raquo_space; more frequent loosening

Question 27

what do the vertically acting forces on the hood of a shoulder prosthesis tend to cause?

Answer 27

compressive stresses superiorly

tensile stresses inferiorly

Question 28

what is unusual about the Stanmore shoulder prosthesis

Answer 28

it is a metal-on-metal design

Question 29

in the Stanmore prosthesis how is the glenoid socket fixed

Answer 29

three pegs and an abundance of bone cement

Question 30

give 3 complications of the Stanmore prosthesis

Answer 30

unsnapping of the 2 components
instability
glenoid component loosening

Question 31

What is the Michael Reese replacement made of?

Answer 31

cobalt-chrome humeral head, polyethylene socket and metal glenoid cup

Question 32

does the Reese replacement allow dislocation?

Answer 32

if a specified torque is reached, the humeral head will dislocate. this prevents scapular fracture

Question 33

describe the trispherical prosthesis

Answer 33

it has 3 balls - both the humeral and glenoid components have a metal ball, both of which are contained within a third larger polyethylene ball

Question 34

what provides extra strength to the polyethylene ball in the trispherical prosthesis

Answer 34

the ball is encapsulated in a Vitallium shell

Question 35

advantage of the trispherical prosthesis

Answer 35

greater ROM and avoids impingement

Question 36

what limitations does the trispherical design overcome?

Answer 36

usually the ROM is limited by: 
- the size of the joint space
- ensuring the socket is thick enough 
- ensuring the ball doesn't dislocate 
the trispherical design overcomes these by basically doubling the ROM

Question 37

which have a higher frequency of loosening - unconstrained or constrained designs? and which are more prone to dislocation?

Answer 37

constrained for both!!!

when dislocations occur they generally have to be treated surgically

Question 38

what problem partly explains why hemiarthroplasty of the shoulder is popular

Answer 38

the problem of glenoid component loosening being much more common than humeral component loosening

Question 39

why do constrained replacements tend to have more elaborate glenoid fixation

Answer 39

they are more prone to loosening bc subjected to larger loads