Implant Technology Unit 5 Flashcards
when is joint replacement in the upper limb indicated
after other forms of conservative treatment have failed i.e. NSAIDs, injections
what is the primary and secondary aim of upper limb joint replacement
primary
- eliminate pain
secondary
- restore function to the particularly joint being replaced w/ a view of restoring overall functions of the hand
patients w/ RA often have several joints affected by the disease and require individual Tx plans - a problem w/ the spine or lower limb that require surgery is given priority over a problem in the upper limb, why?
- RA of the cervical spine causes instability and can be associated w/ significant or progressive neuro Sx.
- Needs to be addressed to prevent permanent damage
- successful replacement of hip and knee will lessen/eliminate need for upper limb to support BW during walking
- if these loads are not reduced/eliminated they could potentially compromise success of the surgery
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
- impairments in distal joints may compromise the critical, early physiotherapy necessary following the replacement of a more proximal joint
- arguable that more functional improvement is gained the more distal the 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
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 is unexpected about the different between a total and hemi-arthroplasty in shoulder replacements
get better pain relief and ROM w/ total arthroplasty as opposed to hemi-arthroplasty
what is proving to be the superior joint replacements in the upper limb
shoulder joint replacements are proving to be more successful in survival terms
[followed by elbow, then wrist, then fingers]
what are 6 materials used in upper limb joint replacements
stainless steel titanium titanium alloys cobalt chrome alloys polyethylene (usually UHDP) silicone elastomer
how often is shoulder replacements done
they are now the third most common arthroplastic procedure after hip and knee joint replacement
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
may also be divided according to whether or not they conform to anatomy of the normal joint
1 - reversed or inverted anatomy design
- called as such as the humeral component is a socket instead of a ball
- e.g. Cavendish prothesis
what is the aim of most shoulder joint replacements
pain relief
improvements in ROM and function
most patients have RA or OA
what is the success rates of shoulder replacements
almost 90% have no or only slight pain after a total shoulder replacement
patients generally achieve around 90 to 135 abduction w/ unconstrained designs
what will the type of shoulder replacement design used depend on
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
allow the hand to be positioned in space
what are the 3 synovial joints that make up the shoulder joint and 1 important articulation
3 joints
- glenohumeral, acromioclavicular and sternoclavicular
1 articulation
- scapulothoracic bone-on-muscle-on-bone articulation
what is the most important synovial joint in the shoulder which is the joint that is replaced in a total shoulder replacement
the glenohumeral joint
- as it has the largest ROM and most load bearing
- forces here can be as high as several times BW which a prosthetic must be able to withstand
what makes the shoulder joint very mobile but also very unstable
[what exists to make the shoulder more stable]
the shallow glenoid fossa
[the rotator cuff and other soft tissues]
what needs to be taken into consideration when the bone stock is removed during a TSR
that soft tissue attachments are preserved
[scapula is a thin bit of bone so there is only limited amount of bone stock to which a prosthetic can be attached]
what problems does the thin nature of the scapula cause
loosening of the glenoid component, especially w/ constrained design
what is the stability of an unconstrained shoulder prostheses, designed by Charles Neer, dependant on
intact, functioning rotator cuff mechanism
what are features of the design of the unconstrained shoulder prostheses
very nearly anatomical in shape and allows max potential function
achieves good pain relief
design requires only a min amount of bone to be removed [ensures soft tissue attachments are preserved]
what is the level of function in unconstrained shoulder prostheses dependant on
quality of the patients rotator cuff and deltoid muscle
the addition of a glenoid component w/ unconstrained shoulder prostheses has proved to be superior that those w/out it, w/ increased patient satisfaction, ROM and pain relief seen - but what is the disadv of this
risk of loosening of glenoid component
important factor in younger patients given the difficulty of revision operations
what is the stability of semiconstrained shoulder prostheses dependant on
rotator cuff mechanisms though some constrained is built into its design
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
called Hooded Glenoids
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
what is an example of a semiconstrained design
Gristina prosthesis
what is the disadv of semiconstrained designs
motion is limited compared to unconstrained
greater forces are transmitted to the glenoid component bone-cement junction resulting in more frequent loosening of the glenoid component
what are the biomechanical aspects of a semiconstrained shoulder replacement
- 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.
what movements are reduced in patients w/ semiconstrained shoulder replacements WITH a hooded glenoid component
reduction in external and internal rotation post-op
and achieve 15 degrees less flexion and abduction than patients w/ regular glenoid component
What material is used to construct the glenoid component of a Neer type shoulder prosthesis
Polyethylene
How could an unconstrained design be converted to a semi- constrained design
by using a hooded glenoid
disadv of a semiconstrained shoulder prosthesis compared to unconstrained one
restricted ROM
more freq glenoid component loosening
what are constrained total shoulder replacements mostly and what are the 3 current designs
ball in socket designs
[either normal anatomy or reversed anatomy [i.e. glenoid ball and humeral socket] ]
3 designs
- Stanmore, Michael Reese and Trispherical
what are features of the Stanmore design
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.
what are complications of the Stanmore constrained design
unsnapping of 2 components
instability
glenoid component loosening
what are features of Michael Reese constrained design
- 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 # of the scapula occurring
what is disadv of Michael Reese constrained design
As with most constrained designs, impingement of the humeral component on the glenoid component occurs which restricts ROM
what is unusual about the Trispherical constrained design
made of 3 balls not 1
the trispherical design consist of a humeral and glenoid component both with a metal ball which are both then contained within a third larger polyethylene ball - what is this encapsulated within and what does this allow
encapsulated with a vitallium shell for extra strength
design allows for a greater ROM and avoids impingement of the prosthetic component
what is the ROM of a single ball-in-socket prosthesis related to
size of the head
the larger the head the greater the ROM
however, ROM is limited by the size of the joint space, by the need to ensure that the socket is of adequate thickness and by the requirement that the ball does not dislocate [Trispherical design partially overcomes these limitations]
in practice, what causes constraint in ROM
the surrounding soft tissue rather than the prosthesis itself
what is a reversed anatomy shoulder replacement joint and what are examples of it
socket on the humeral side and ball on the glenoid side of the joint
e.g. Kessel, Fenlin, Reeves
what is the rationale behind reverse anatomy joints
increasing the radius of the ball it would improve the ROM
theoretically, these designs have a better lever arm for the deltoid
what is the disadv of reverse anatomy shoulder replacement joints
more stress at the bone-cement junction
what causes difficulty in fixing the glenoid component in the shoulder joint
the small quantity of bone in the scapula
what are methods to securing the glenoid component to the scapula
All use large amounts of bone cement
- triangular shaped keel [Neer unconstrained]
- extended keel [trispherical design]
- pegs [Stanmore ball in socket]
- stem [Liverpool and Cavendish reversed ball in socket design]
- wedge [Fenlin reversed ball in socket design]
- large screw [Kessel reversed ball in socket design]
- flanges bolted to the base of the spine of the scapula [Kolbel reversed ball in socket]
the Neer design has an optional metal backed glenoid component, what is this thought to do
increase fixation and aid stress distribution
why do constrained designs tend to have more elaborate glenoid fixation
to secure the component against the larger loads present in this type
what is the Bickel designs method of securing the glenoid component
glenoid component is cemented entirely within the glenoid to maximise the contact area
what loosens more in a shoulder joint replacement - the humeral or the glenoid component
glenoid component
- 8 times more than humeral component
what design is predominantly used for constrained total shoulder replacements
A ball-in-socket design
what is the primary indication for elective replacement of the elbow joint
pain relief , with restoration of stability as the secondary indication
[rarely is restoration of motion primary indication]
what do most elective patients suffer from in elbow joint replacements
RA
[some OA and post-traumatic arthritis]
what are the primary functions of the elbow joint
the positioning of the hand in space
to allow the forearm to act as a lever
for some, acts as a weight bearing joint e.g. those who use a walking aid
what are the 3 articulations of the elbow joint
- the humeroulnar (trochleo-ulnar)
- the humeroradial (radiocapitellar),
- the proximal radioulnar
what forces does the elbow withstand
6 times body weight during dynamic activities e.g. throwing
3 times body weight during static loading
what are the functions of the 3 articulations in the elbow joint
the humeroulnar articulation carries the majority of the load
the humeroradial and proximal radioulnar provide additional stability
what position is the elbow in in anatomical position
full extension
when the elbow is at full extension what angulation is there
10 to 15 degrees valgus angulation (outward angulation) in relation to the upper arm
what happens to the angulation at the elbow as it flexes and what does this mean
it reduces to a few degrees of valgus or varus angulation at full flexion
thus, the coronal plane angle between the upper arm and forearm is not fixed but varies
why are uniaxial hinge prosthesis in elbow joint replacement unsuccessful
they maintain the same coronal plane angle between the upper arm and forearm giving rise to excessive shearing forces at the bone-cement interface and subsequent loosening
what is the ROM the elbow CAN achieve and what is needed for ADL
Can achieve;
F - 140 degrees
P - 70 degrees
S - 80 degrees
ADL:
F - 30 to 130 degrees
P - 50 degrees
S - 50 degrees
what provides the stability of the elbow joint
provided equally by congruity of the joint surface
and by soft tissues [anterior capsule, medial and lateral collateral ligaments, muscles]
what position is the elbow in during most ADL
flexed
when the elbow is flexed what is providing over 50% of joint stability
the medial collateral ligament
what happens if the radial head is removed in an elbow joint replacement
reduces the joint congruity so the Medial collateral ligament must resist all VALGUS loads entirely
thus, it is important to maintain as much of the surrounding soft tissue as possible during an elbow joint replacement to minimise stresses at the bone-cement interface
what is the loading at the elbow to some degree dependant on
the stiffness of the shoulder joint
if someone w/ total elbow replacement has a stiff shoulder joint and tries to internal or external rotate the arm, the stiffness at the shoulder will increase the rotational stresses at the bone cement interface
[one reason why replacement of the shoulder may be given priority]
what is the difference between first generation and second generation elbow joint replacements
first generation
- simple, uniaxial hinges
second generation
- unconstrained design
what is the other names of first generation elbow joint replacements and what was the first success one called
constrained or hinged designs
the Dee design was first successful total elbow prosthesis
what is the construction of the Dee design
- 3 cobalt chrome parts, the humeral component, the ulnar component and the axis pin
- axis of rotation was at right angles to the long axis of the humerus and ulnar; possible ROM 0 to 150 degrees flexion
- single axis meant carrying angle of the elbow was essentially lost
- stems of humeral and ulnar components were curved to fit the medullary cavities of the humerus and ulna
- both stems were convex anteriorly and in addition the ulnar stem was curved convex laterally [meant both left and right hand ulnar components were required]
- stems retained in place with PMMA bone cement
- additional keying point provided by means of metal buttons at base of humeral stem and undersurface of ulnar platform
the Dee design gives excellent pain relief and good motion, however it is unsuccessful, why?
long term deterioration due to loosening of the prostheses
due to restricted single axis motion forces upon the elbow by the prosthesis
unnatural motion gives rise to excessive shearing forces at the bone-cement interface
also high amount of metal wear debris from the metal on metal articulations also contributed to loosening
what was another complication with the Dee design apart from loosening
required removal of large amount of bone stock causing loss of attachments of stabilising soft tissue
caused additional stress to the bone cement interface
loss of bone stock also meant that when a prosthesis failed it was extremely difficult to salvage the joint
the Dee design has been abandoned and is rarely used now, when might it be used
occasionally for revisions and for patients w/out sufficient ligament or soft tissue competence
what are the 2 main types of second generation elbow prostheses [and a recent new variation]
1 - semiconstrained metal-to-polyethylene hinge types
2 - unconstrained metal-to-polyethylene resurface types
[designs that also resurface the radial head]
what do semiconstrained elbow designs usually consist of and what are examples of some
stemmed humeral and ulnar components with a hinged-like metal-to-polyethylene articulation
e.g. Pritchard-Walker, Coonrad and Tri-Axial prostheses
what do semiconstrained elbow joints allow
varying degrees of side-to-side laxity
some times referred to as “sloppy hinged” prostheses
what is the design of a tri-axial elbow prosthesis
semiconstrained design
loose fitting metal-to-polyethylene hinged articulation with long humeral and ulnar metal stems
hinged articulation has around 5 degrees varus laxity and 6 degrees valgus laxity
what load is needed to pull apart a Tri-Axial elbow prosthesis
50N
[unlikely to happen]
what does outcomes of the Tri-Axial elbow prosthesis dependant on
the patients condition
90-95% RA patients had complete pain relief
80% for OA and post traumatic arthritis patients
what is the general design of unconstrained elbow replacements and examples of the design
resurface the lower end of the humerus and olecranon
aim being to reproduce the anatomical structure and by doing so achieve normal elbow function and contribute to joint stability
examples
- Ewald (capitellocondylar), Kudo and the Souter- Strathclyde.
what does the Souter-Strathclyde prosthesis consist of
2 components :
- humeral component, which replaces the articulating surface of the humerus, made of Vitallium
- ulnar component, which replaces the articulating surface of the ulnar, made of high density polyethylene
what is the success rate of unconstrained designs in elbow joint replacements
90% of patients achieve good or excellent results
rates of dislocations 3-8% = slightly higher than semi constrained design
rates of aseptic loosening 1-3% = lower than semi constrained
what are elbow prostheses that resurface the radial head attempting to do and examples of this design
gain benefits of load transmission stability that are afforded by humeroradial articulation
e.g. Pritchard, Voltz and early modification of the Capitellocondylar
what are the 3 components of the Pritchard elbow replacement
1 - the metal humeral component which replaces the articulating surfaces of the trochlea and capitellum;
2 - the ulnar component, consisting of a metal stemmed base and polyethylene spacer, which replaces the articulating surface of the ulna;
3 - the radial component, consisting of a metal stemmed base and polyethylene spacer, which replaces the articulating surfaces of the radius.
what can be selected in the Pritchard elbow replacement for optimum stability
polyethylene spacers are supplied in various thickness so surgeons can select correct size for optimum joint stability
why have the results with designs that resurface the radial head in elbow joint replacements been variable
difficulties in balancing the 3 articulations at time of op
The Voltz and modified Capitellocondylar prostheses have unsatisfactory rates of loosening and dislocation and are no longer recommended for use
How do semiconstrained elbow prostheses differ from the first generation of hinged elbow prostheses
they have “sloppy” hinges with varying degrees of side-to-side laxity.
By what other name is the Ewald prosthesis also known
capitellocondylar prosthesis.
What benefit may be gained from resurfacing the radial head
additional load transmission stability
what are the 2 types of wrist joint prostheses
flexible hinge
total wrist
what is the main indication for wrist joint replacement
pain associated with RA and OA
[correction of deformity arising from these conditions is also important consideration]
when is arthrodesis in the wrist a preferred option
when only radiocarpal joint is affected
especially for younger patients and for those which exert large and regular loads on their wrists
what does the wrist joint include
extends from metaphyseal portion of the radius to the CMC joints and incorporates the 8 carpal bones
the carpal bones are interconnected by a complex network of extrinsic and intrinsic ligaments
the ligaments, particularly the extrinsic ones, are integrated into surrounding wrist capsule
how many tendons run across the wrist
24
[strong flexor tendons are positioned within the carpal tunnel formed by transverse arch arrangements of the carpals]
the distal radioulnar joint is usually considered separate from the wrist, what is its function and why is it considered in wrist joint replacements
forearm supination and pronation
most diseases that involve the wrist joint also involve this joint and must be taken into account in total wrist joint replacements
what is done if the distal radioulnar joint is diseased in a total wrist replacements
typically around 1cm of distal ulna is excised and the remaining distal ulna is carefully stabilised w/ soft tissues
where is the overall composite motion of the wrist centred
on a fixed point on the capitate through which the axes of rotation for both flexion-extension and abduction-adduction pass
essential that prostheses are precisely positioned so that the natural joint motion is reproduced, thereby assuring a better balance between the wrist extensors and flexors.
what is the ROM possible at the wrist
80-90 degrees flexion
70-80 degrees extension
35 degrees adduction
15-20 degrees abduction
what is ROM needed for ADL at the wrist
10 degrees flexion
35 degrees extension
what movement is essential at the wrist for ADL
extension
reason why wrist is set at around 20 to 30 degrees of extension during arthrodesis
what joint is an important contributor to the overall motion of the wrist and why
radiocarpal joint [a condyloid joint]
it has a greater radius of curvature for abduction-adduction than for F-E which provides more stability in the abduction-adduction plane
the smaller radius for F-E provides less stability but a greater arc of motion
what is the problem will ball and socket type wrist joint designs
they have a reduced radius of curvature for abduction-adduction which makes it difficult maintaining stability in the abduction-adduction plane
the complex relationship between carpal bones and overlying tendons is poorly understood - what is particularly important consideration
how the carpal tunnel maintains the strong flexor tendons close to the axis of rotation of the wrist joint, thereby decreasing their moment about the wrist joint
what was the flexible hinge joint prosthesis introduced for
for use in combo w/ resection arthroplasty
what is the design of the flexible hinge wrist joint prosthesis
has a proximal and distal stem with a barrel - shaped midsection
1 stem is inserted into the medullary canal of the distal radius and the other is inserted into the 3rd metacarpal through the partially resected capitate
what is the flexible hinge wrist joint prosthesis composed of
high performance silicone elastomer (rubber)
the implant may be used w/ or w/out titanium bone liners (grommets)
silicone rubber spacer that helps maintain an adequate joint space and overall wrist alignment
is the flexible hinge prosthesis a total prosthesis ?
no it is a resection arthroplasty with interposition of a silicone rubber spacer
what develops around the midsection in flexible hinge prosthesis after a period of time
a new capsulo-ligamentous system
what is the success rate of the flexible hinge prosthesis
60% of patients maintain good clinical results 5 years post op
post-op ROM is not improved but arc of motion is changed to a more functional range than that preop.
what % of flexible wrist prostheses have been found to tear on the sharp bony edges of medullary canals
20%
what are the 2 types of cemented wrist prostheses called and there design
Meuli - ball and socket type
Voltz - non-spherical “ball” and shallower socket
what is the composition of the Meuli prosthesis
- distal component with eccentric prongs that are inserted into 2nd and 3rd metacarpals
- twin pronged radial component
- polyethylene ball
- ball is fitted on to the radial component and articulated with the distal component
- ball is not constrained and so permits slight distraction of the prosthesis
what are the adv and disadv of the Meuli ball and socket design
disadv
- relies on adequate and proper soft tissue balance to prevent undesirable rotatory motion
adv
- avoids possibility of rotational failures of the prosthesis
- stresses on the anchorage of the distal and radial components are reduced because impingement can occur only at extremes of motion
what is the major modification that the meuli prosthesis underwent
replacement of a single stem for the radial component with 2 prongs
and the offsetting of the “prongs” or stems of the distal component
what does the Voltz prothesis consist of
3 parts
1 - metacarpal component with a single stem that is inserted into the 3rd metacarpal
2 - single stem radial component
3 - polyethylene cup
[cup is mounted on the radial component and articulated with the metacarpal component]
what is the shape of the polyethylene cup in the Voltz prothesis
cup is not a true sphere but rather a segment of a torus with a larger radius of curvature for abduction-adduction
what does the design of the shape of the polyethylene cup in the Voltz prothesis allow for
design mirrors the normal radiocarpal joint and restricts the max range of motion to 90 degrees F-E and 50 degrees Abd-Add
what modification did the Voltz prothesis design undergo
number of stems has been reduced
what did many patients develop because of the Voltz and Meuli wrist replacement
developed ulnar deviation deformities due to the increased moment arms of the ulnar wrist tendons
caused by the sitting of the prothetic centre of rotation radial to the normal wrist’s centre of rotation
the modifications of both designs have attempted to shift the prosthetic centre of rotation so that it aligns more closely w/ normal wrist axis
what is the success rate for total wrist prostheses
similar to those for flexible prosthesis in terms of pain relief and maintenance of pre op ROM
what issues have been seen in the Meuli design and in the Voltz design
incidence of stem loosening and stress-shielding of the distal radius has found to be as high as 50% with the Meuli prosthesis
Loosening has been less frequent with the Voltz design, with incidence of around 25%, though bone resorption under the radial collar has been found in around 80%
How is wrist rotation prevented in the Meuli prosthesis?
Wrist rotation is prevented in the Meuli prosthesis by the correct and adequate balancing of the surrounding soft tissue
Which normal wrist articulation does the Voltz prosthesis resemble
radiocarpal joint
What are the two main problems associated with total wrist prostheses
loosening
stress-shielding of the distal radius
what is the most frequently indicated hand joint replacement
replacement of the metacarpophalangeal (MCP) joint
what are the 2 types of MCP joint replacement
flexible hinge
total MCP
what is the main indication of MCP joint replacement
pain and deformity associated w/ RA
some patients may have impaired hand function secondary to soft tissue imbalance [but w/ minimum discomfort]
what may be a preferred option for the MCP joint in younger patients requiring a strong pinch
arthrodesis of the index finger
- fused at around 40 degrees of flexion
what is the features of the MCP joint
condyloid joint formed by the ovoid head of the metacarpal and the elliptic cavity of the base of the proximal phalanx
joint is surrounded by joint capsule, collateral ligament, fibrocartilaginous palmar plate and muscle tendons [All of these contribute significantly to the stabilisation of the joint]
what is ROM of the MCP joint
3 planes of movement: F-E, Abd-Add and a small amount of Pro-Sup
major motion occurs in sagittal plane w/ around 0-90 degrees flexion
overall, the MCP contributes almost 80% of total finger flexion arc
[restricted MCP motion can therefore significantly impair hand function]
what was the flexible silicone elastomer hinge prosthesis for MCP joint replacement designed for
an adjunct to resection arthroplasty and relies on encapsulation to help maintain alignment
how is the flexible hinge MCP joint replacement inserted
inserted into the hollowed medullary canals of the metacarpal and proximal phalanx once adequate soft tissue and bone are resected to ensure that the implant functions freely
how does the flexible hinge MCP joint replacement move
stems are not fixed so the joint flexes and extends they glide within the medullary canals
piston-like motion thought to be beneficial in terms of more even force transmission and increased ROM
what may or may not be added to flexible hinge MCP protheses and why were they introduced
titanium bone liners (grommets)
introduced to shield the implant from sharp bone edges after high tear rates has been recorded
press-fitted (interference fitted) into position
what is the success rate for flexible hinge MCP prostheses
70-80% patient satisfaction
what happens if a fracture occurs with flexible hinge MCP prostheses
the prosthesis need not always be replaced as the joint often continues to have pain-free motion and remain stable
what are examples of a total MCP joint replacements and how are they designed
Steffee, Schultz, Strickland
all of these incorporate a metallic component that articulates with a polyethylene component
both components are cemented in to the medullary canals
what are the problem associated with MCP total joint replacements
implant fracture
migration
loosening
total MCP joint replacements do not yet provide consistent results compared to the flexible hinge replacements - however, when is a total MCP joint replacement preferred
younger patients who would wish to perform manual tasks that place higher demands on the MCP joints
what is the main indication for interphalangeal (IP) joint replacement
pain and deformity associated with RA, degenerative arthritis and post-traumatic arthritis
[Implant arthroplasty of the distal interphalangeal joint is rarely indicated, since this joint contributes far less to the overall finger motion]
what is preferred procedure for DIP joints
arthrodesis as more reliable procedure and results in only min functional deficit
what are the 2 types of IP joint replacement
flexible hinge
total interphalangeal
[actual protheses are same as those used for MCP joints but have smaller dimensions]
what problems does replacement IP joints face
same problems as MCP joint replacements
[implant fracture, migration and loosening]
what is the features of the proximal and distal IP joints
bicondyloid joints
formed by the 2 condyles of the more proximal phalanx and the corresponding cavities of the more distal phalanx
joints are stabilised by bony articulation itself and surrounding soft tissues (joint capsule, collateral ligaments, the fibrocartilaginous palmar plate and muscle tendons)
ROM for PIP and DIP
major plane of motion is sagittal plane for flexion-extension
PIP
- 0-110 degrees flexion
DIP
- 0-90 degrees flexion
PIP contributes 85% of interphalangeal motion
DIP 15%
[therefore, preservation of PIP joint motion is far more critical than that of DIP joint]
what is the success rate for flexible hinge prostheses in PIP joints
PIP joints have satisfactory pain relief in 98% of cases
40-60 degrees ROM expected
0.5% infection rate [rare]
5% fracture rate
what is the name of the highly successful finger joint replacement
Swanson flexible hinge prosthesis
what is the preferred shoulder joint replacement method
unconstrained prostheses, provided good condition of surrounding soft tissues, particularly the rotator cuff
why is wrist joint replacements the least established of larger upper limb joint replacements
the high rate of loosening
