ASEPTIC LOOSENING THA
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Transcript ASEPTIC LOOSENING THA
FIRM 1 GRANDROUND
ASEPTIC LOOSENING
OF
THA
PRESENTER: ONDARI N.J
FACILITATOR: DR. MUSEVE
03-04-2014
Incidence of hip arthritis is 3-5% in >55yrs
A good prosthesis important
Biomechanics
THA components bears atleast 3X body weight
Abductor lever arm ~2.5X body lever arm
Abductor lever arm may be dec by OA or neck
shortening
Lever arm ratios can increase to 4:1
Lenghts of lever can be surgically changed to
approach 1:1
This theoretically reduces load hip by 30%
Medialization of
acetabulum
Lateral and distal
reattachment of
osteotomized GT
Stress transfer to bone
Bone quality determines most appropriate implant
Dorr radiographic classification of proximal femur
Type A femurs
Type B femurs
Thick cortices
Narrow distal canal – ‘champaigne flute’ appearance
Found in young pts
Permits good fixation
Exhibit bone loss, shape not compromised
Implant fixation not a problem
Type C femurs
Thin cortex, wide medullary canal – ‘stovepipe’ shape
Occurs in older osteoporotic women
Less favorable for implant fixation
Dorr classification of morphology of femur
Stress transfer to bone
Stress transfer to bone desirable
Measures to decrease stress shielding
Decrease modulus of elasticity of stem eg
titanium alloy
Smaller diameter stems
Prosthetic collar
Stem shape
Tapered geometries better
Complications of THA
Intraoperative
Mortality,
nerve injuries, vascular injuries
Early postoperative
Thromboembolism,
hemartoma formation, infection,
dislocation, limb length discrepancy
Late postoperative
Heterotopic
ossification
Loosening
Most
serious long term problem
Loosening of THA components
Most serious complication
Commonly leads to revision
With Cemented THAs, the acetabulum is the
first component to fail from loosening
With cementless hips, the femoral
component loosens more often as a result
of osteolysis
Can be septic or aseptic
Zones of loosening
Femoral component
Seven Gruen zones
Acetabular component
Three Delee and Charnley zones
Gruen 7 zones
of femur
Delee and
Charnley
acetabular zones
Cemented Femoral loosening;
Radiographic features
Definite loosening
Stem failure – fracture/deformation
Cement mantle fracture esp zone 4
Radiolucency >1mm
Changes in stem position- usually varus position
Pistoning effect
Probable loosening
Continous radioluscent line at bone-cement interface
Endosteal cavitation-linear and focal osteolysis
Possible loosening
Radioluscent lines at bone-cement interface 50-100%
Are all radioluscent line due to
loosening?
Radioluscent lines btn femoral cortex and cement can
be produced by;
Cancellous bone not completely removed during sx
Normal age related expansion of femoral canal
assoc cortical thinning. Poss et al study;
Medullay canal expands at 0.33mm/yr
Cortical thickness decrease by 0.14mm/yr
NB; these radioluscet lines do not typically have the
surrounding sclerotic line noted on loose femoral stems
Medullary canal widening has not been implicated in
the process of femoral loosening
Technical problems that contribute to
stem loosening
Failure to remove adequate cancellous bone medially
Inadequate quantity of cement
Thin column cracks easily
Tip of stem should be supported by a plug of cement
Cements laminations
Presence of voids in cement
Poor mixing, injecting technique, blood or fragments of bone
Failure to pressurize cement
Failure to prevent stem motion while cement is hardening
Failure to position component in neutral or mildly valgus
position
Cementless
femoral
components
Cemented Acetabular loosening;
radiographic features
Bone-cement lucency >2mm and/or
progressive
Medial migration and protrusion of cement
and cup
Change in inclination of cup >50
Eccentric PE wear of the cup
Fracture of cup and/or cement(rare)
Technical problems during sx leading
to cup loosening
Inadequate support of the cup by bone & cement
Insufficient bone stock
Acetabullum not reamed deeply enough
Failure to remove all cartilage, loose bone fragments, fibous tissue and
blood
Failure to make sufficient no of holes in acetabulum to secure good
cement-bone bon
Failure to pressurize cement
Failure to distribute cement around entire outer surface of cup
Mvt of cup or cement mantle while cement is hardening
Malpositioning of cup – neck of femoral component impinges on margin
of socket
Pathophysiology
Generation of particulate debris
Wear
corrosion
Mechanisms of wear
Adhesion,
Wear debris sources
PE,
abrasion, microfatigue and 3rd body wear
cement, metal particles
PE bearing surfaces are the major factor
responsible for periprosthetic osteolysis
Pathophysiology cont.
Particle size important
0.5 – 10microm – pagocytosed
<0.5microm – too small to activate a response
>10microm – stimulate a giant cell response
Irregularly shaped particles more active than
spherical poarticles
Modes of wear
Is the mechanical condition under which
prosthesis was working when wear occurred
Four modes
Mode
1
Motion
Mode
10
btn two bearing surfaces as intended by designer
2
bearing surface rubbing against 20 surface
Mode
Two
Mode
Two
3
10 surfaces with interposed third-body particles
4
non-primary surfaces rubbing together
OSTEOLYSIS
Is the final pathway related to host cellular
response to debris of all types
Mechanism
Generation
of wear particles
Access of these particles to periprosthetic bone
Cellular response to particulate debris
Debris dispensed through joint fluid by
pressure gradient
Pattern of lysis depends on implant design
Osteolysis; cellular response
MQs predominant cells
Surface interaction btn MQs and wear debris
incite inflammatory response whether or not
phagocytosis occurs
Multiple cytokines/chemokines produced
Osteoclasts activated, osteoblasts inhibited
Net result – bone resorption
osteoclast osteoblast interaction
DEBRIS
MACROPHAGES
phagocytosis
cytokines/
chemokines
inhibit
Diagnosis
History
Pain on wt bearing –groin, buttock or thigh
Typically ‘start-up’ pain
Pain relieved by rest, aggravated by hip rotation
Physical exam
Antalgic gait
Limb length discrepancy
Investigations
Laboratory
R/O infection
Imaging
Progressive radiolucency
Migration of implant
Treatment
Asymptomatic patient
Radiographic loosening often appears be4
symptoms
More frequent follow-up
Revision surgery if bone destruction is
progressive
Symptomatic patient
Revision surgery
Indications for surgery
Symptomatic patient
Loose implants
Large lytic lesions
Progressive osteolysis even if no symptoms
Revision Total Hip Arthroplasty
cementless components are generally preferred in
revision settings.
The
bone sclerotic and does not provide optimal
conditions for cement interdigitation
only the loose components need to be revised
If implant remains stable despite osteolysis, bone
grafting of the defects with retention of the
implant is recommended