Shoulder joint replacement Flashcards
prior to upper limb joint replacement what will most patients have been diagnosed with?
RA OA osteonecrosis post traumatic arthritis fractures
what will be given priority in RA sufferers, over upper limb joint replacement
spine or lower limb problems will be prioritised
why should spine / lower limb joint replacement be prioritised over upper limb arthroplasty?
- RA of c-spine may cause instability & can be assoc with significant/progressive neuro symptoms»_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»_space; if this isn’t addressed first it could compromise the success of an upper limb replacement
If more than one upper limb joint is affected, how is it decided which will take priority
firstly pain is the determining factor
secondly, if all are equally painful, replacement is generally performed distally to proximally i.e. fingers first
why are distal joints replaced before proximal joints, if equally painful
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
why do some surgeons prefer to replace the shoulder before other upper limb joints
- 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
what has been shown to provide better pain relief - total or hemi-arthroplasty
total
apart from small dimensions and complexity, what added difficulty does a shoulder replacement have?
balancing soft-tissue and inadequate scapula bone stock
how are shoulder prostheses divided into subcategories
according to constraint
- unconstrained
- semiconstrained
- constrained
how are shoulder prosthesis described if they don’t conform to the normal joint
reversed or inverted anatomy designs
primary indication for elective replacement of shoulder joint
pain relief
how much abduction can an unconstrained shoulder replacement generally achieve
90 - 135
what will largely influence the type of shoulder design chosen for a particular patient
pre op assessment of the quality of the soft tissues surrounding the shoulder joint
if the rotator cuff is intact and functioning, what type of shoulder prosthesis would be chosen?
unconstrained
what is the primary function of the shoulder
to allow the hand to be positioned in space
name the 3 synovial joints of the shoulder and the other important articulation
glenohumeral
acromioclavicular
sternoclavicular
scapulothoracic articulation
how high can the forces reach at the glenohumeral joint
up to several times body weight
what compensates for the inherent instability of the glenohumeral joint
rotator cuff
- supraspinatous
- infraspinatous
- subscapularis
- teres minor
what condition in particular is likely to involve some soft tissue pathology at the shoulder
RA
what is a significant problem with shoulder replacements due to little bone stock
especially with which type of designs?
loosening of the glenoid component, especially with constrained designs
what is an unconstrained shoulder prosthesis dependent upon
intact, functioning rotator cuff
what has been found to be superior - shoulder replacement with glenoid component or without
with glenoid component replacement
- increased patient satisfaction, ROM and pain relief
in which age group may total shoulder arthroplasty be more risky than partial
younger patients because total carries the risk of loosing of the glenoid component and revision operations are difficult
what is the advantage of a hooded glenoid
it prevents upwards subluxation of the humeral component due to rotator cuff weakness
what tendon will tear if there is upwards subluxation of the humerus
supraspinatous
what is the disadvantage of semiconstrained designs as opposed to unconstrained designs
motion is limited leading to greater forces transmitted to the glenoid component bone-cement junction»_space; more frequent loosening
what do the vertically acting forces on the hood of a shoulder prosthesis tend to cause?
compressive stresses superiorly
tensile stresses inferiorly
what is unusual about the Stanmore shoulder prosthesis
it is a metal-on-metal design
in the Stanmore prosthesis how is the glenoid socket fixed
three pegs and an abundance of bone cement
give 3 complications of the Stanmore prosthesis
unsnapping of the 2 components
instability
glenoid component loosening
What is the Michael Reese replacement made of?
cobalt-chrome humeral head, polyethylene socket and metal glenoid cup
does the Reese replacement allow dislocation?
if a specified torque is reached, the humeral head will dislocate. this prevents scapular fracture
describe the trispherical prosthesis
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
what provides extra strength to the polyethylene ball in the trispherical prosthesis
the ball is encapsulated in a Vitallium shell
advantage of the trispherical prosthesis
greater ROM and avoids impingement
what limitations does the trispherical design overcome?
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
which have a higher frequency of loosening - unconstrained or constrained designs? and which are more prone to dislocation?
constrained for both!!!
when dislocations occur they generally have to be treated surgically
what problem partly explains why hemiarthroplasty of the shoulder is popular
the problem of glenoid component loosening being much more common than humeral component loosening
why do constrained replacements tend to have more elaborate glenoid fixation
they are more prone to loosening bc subjected to larger loads
