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
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
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

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


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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


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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

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Cements laminations
Presence of voids in cement
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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


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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