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%

Lateral and distal reattachment of osteotomized GT

Medialization of acetabulum

Stress transfer to bone

Bone quality determines most appropriate implant

Dorr radiographic classification of proximal femur Type A femurs

Thick cortices Narrow distal canal – ‘champaigne flute’ appearance Found in young pts Permits good fixation

Type B femurs 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/yrCortical 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, abrasion, microfatigue and

3rd body wear Wear debris sources

PE, 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 btn two bearing surfaces as intended by designer

Mode 2 10 bearing surface rubbing against 20 surface

Mode 3 Two 10 surfaces with interposed third-body particles

Mode 4 Two 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

cytokines/ chemokines

MACROPHAGESDEBRIS

phagocytosis

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