Implant technology - unit 5 deck 1 Flashcards
when is joint replacement in the upper limb indicated
After other forms of conservative treatment, such as rest, anti-inflammatory drugs, intra- articular injection, have failed.
what is the primary and secondary aim of upper limb joint replacement
- Primary is to eliminate pain
- Secondary is to restore function to the particularly joint being replaced w/ a view of restoring overall functions of the hand
Typically, patients undergoing upper limb joint replacement will have been diagnosed with one or more of what conditions (5) ?
- RA
- OA
- osteonecrosis
- post-traumatic arthritis
- or fractures.
Sufferers of rheumatoid arthritis often have several joints affected by the disease. It is therefore usually necessary to develop an individual treatment plan for each patient.
If the patient has problems with the spine or lower limbs that require operative intervention these will be given priority over upper limb joint arthroplasty, why is this?
- RA of the cervical spine may cause instability and can be associated with significant or progressive neurological symptoms, which must be addressed in order to prevent permanent nerve damage
- Successful total joint replacement of the hip and knee will lessen or eliminate the need for the upper limb to support the body weight during walking or other activities. If these loads are not reduced or eliminated they could potentially compromise the success of an upper limb joint replacement.
When several upper limb joints what is the key factor in deciding which joint should be given priority ?
Pain
[functional impairment is only a secondary consideration]
if several upper limb joints are affected, and all joints are equally affected by pain, then as a general rule what order with joint replacements usually be performed
distally to proximally i.e. fingers first, wrist, elbow and finally the shoulder
what is the reasoning for some surgeons working distal to proximal?
- primary objective of upper limb joint replacement, after pain relief, is to allow restoration of hand function. It is arguable that more functional improvement is gained the more distal the joint
- impairments in distal joints may compromise the critical, early physiotherapy necessary following the replacement of a more proximal joint
some surgery prefer to replace the shoulder however, before other distal joints, what are the reasons for this
- Shoulder pain is more troublesome at night and may radiate to the elbows
- An immobile shoulder will cause abnormal loadings at the elbow which may lead to early failure of an elbow prosthesis
- Rehab of the other upper limb joints can be simplified with a pain free or near pain free shoulder
A patient presents with the following three problems associated with RA. List them in order of the highest priority for surgery.
- painful elbow joint
- painful hand joints
- cervical spine instability
- cervical spine instability
- painful hand joints
- painful elbow joint
what is the general criteria for upper limb joint replacements
- tolerate by human body w/ no short term and little long term risk
- relieve pain and achieve sufficient mobility for activities of daily living
- function w/out failure, ideally should last the expected life span of the individual patient
- insertion w/ predictable outcome guaranteed by competent surgeon
- cost effective
what are 6 materials used in upper limb joint replacements
- stainless steel
- titanium
- titanium alloys
- cobalt chrome alloys
- polyethylene (usually HDP)
- silicone elastomer (Rubber)
Which provides better pain relief and ROM - a total or a hemiarthroplasty of the shoulder joint ?
A total arthroplasty
Rank the joint replacements of the upper limb from longest survival rate to lowest
Shoulder > Elbow > Wrist > Finger
how often is shoulder replacements done
3rd most common after hip and knee replacements
what is 1 way designs of shoulder prostheses are divided and what are these categories
divided according to the amount of movement constraint
1 - unconstrained e.g. Neer Prosthesis
2 - semiconstrained e.g. Gristina prosthesis
3 - constrained e.g. Michael Reese prosthesis
what is another way designs of shoulder prostheses are divided
Divided according to whether or not they conform to anatomy of the normal joint:
Designs that do not conform to the normal joint, are termed reversed or inverted anatomy designs because the humeral component is a socket instead of a ball - e.g. Cavendish prothesis
What condition do most patients requiring a shoulder joint replacement suffer from ?
RA or OA
What is the primary and secondary goals of a shoulder joint replacement?
- Primary = pain relief
- Secondary = improvements in ROM and function
what is the success rate in shoulder joint replacements providing pain relief ?
Approx 90%
Good results have also been achieved in restoring ROM with shoulder joint replacements what ROM of abduction is usually achieved ?
90-135 degrees
what will the type of shoulder replacement design used for a patient depend on and what is done to determine which joint replacement is used?
- quality of the soft tissue that surround the shoulder joint and provide joint stability
- patients will undergo preoperative assessment of ROM, strength, stability and function to determine the exact nature of their problems
what shoulder replacement design will be used if the rotator cuff is intact and functioning
unconstrained prosthesis
what shoulder replacement design will be used if there is little or no stability provided by soft tissue
constrained design
what is the primary function of the shoulder joint ?
To allow the hand to be positioned in space
What compensates for the inherent instability of the shoulder joint ?
The surrounding soft-tissues, esp the rotator cuff muscles (think SITS)
Describe the design features of the unconstrained shoulder prostheses
- It has a humeral component and a polyethylene glenoid component
- The design is very nearly anatomical in shape and allows the maximum potential function and achieves good, predictable pain relief.
- design requires only a minimal amount of bone to be removed. This ensures that soft tissue attachments (including the rotator cuff attachments) are preserved.
in semiconstrained designs the glenoid component of constrained prosthesis is shaped so that it roofs over the superior aspect of the humeral component - what is this called and what does is resist and help prevent ?
- called Hooded Glenoids which resist upward shear force produced when the arm is elevated
- thus prevents upward subluxation of the humerus that can occur when there is rotator cuff weakness or absence, and avoids tearing of the supraspinatus tendon
How does the hood in an unconstrained shoulder prosthesis affect the biomechanics ?
- As the arm is elevated the muscle forces tend to pull the humerus upward, but this is prevented by the hood.
- ROM of the shoulder is restricted by the hood as during elevation the prosthesis or intact bone/soft-tissues will come into contact with hood.
- forces that act vertically on the hood produce moments about some point which must be counteracted by additional forces at the bone-cement junction.
- These forces tend to give rise to compressive stresses superiorly and tensile stresses inferiorly.
Describe the design features of the stanmore constrained shoulder replacement
- metal on metal design
- cup-shaped glenoid socket is fixed with three pegs and an abundant amount of bone cement
- The humeral component is also cemented in place.
- Once in position the two components are snapped together.
Describe the design features of the michael-reese constrained shoulder replacement
- cobalt-chromium humeral-head component and a polyethylene socket which fits within a metal glenoid cup.
- diameter of the lip is slightly smaller than that of the humeral head so that the ball is captive (i.e. it is a ball-in-socket design).
- designed to allow the humeral head to dislocate when a specified large moment (torque) is reached, so to prevent a fracture of the scapula occurring
Describe the design of the trispherical constrained shoulder replacement
Both the humeral and glenoid components of the Trispherical prostheses have a metal ball, both of which are contained within a third larger polyethylene ball (which is encapsulated with a Vitallium shell for extra strength).
How does the trispherical design partially overcome the limitations to ROM in single ball and socket designs ?
- Effectively doubling the ROM that would be possible with a single ball of the same size as the humeral and glenoid balls and giving a larger overall ROM
[In practice the surrounding soft tissues act as the constraint to motion rather than the prosthesis itself, while the prosthesis maintains good stability.]
