A Osteolysis and Loosening

DefinitionRevision THR Osteolysis


Biological response to particulate matter

- characterised by periprosthetic osteolysis

- stimulated by wear debris

- debris gains access to any area accessible by fluid


Sources of particulate debris


1.  Wear


Mechanisms of wear

A.  Adhesion

B.  Abrasion

C.  Fatigue


Modes of wear


1.  Motion between 2 surfaces designed for motion

2.  Primary bearing surface against an non intended bearing surface

- i.e. femoral head against acetabular shell when liner has worn out

3.  Interposed third body particles i.e. bone or cement

4.  Two non bearing surfaces together i.e. back sided fretting, morse taper fretting, screws


2.  Corrosion


Electrochemical process releasing metal ions

- modular interfaces i.e. head neck

- metal on metal bearings


Types of wear particles




Cobalt alloy

Titanium alloy


Morphology of wear particles


Usually less than 1um in size


Biological response to wear particles


Small particles phagocytosed by macrophages

- unable to digest

- stimulate release of cytotoxic factors


- aggregates more macrophages

- release TNF, IL1, IL6, PGE2

- stimulated osteoclastic bone resorption


Poly wear


THR Poly WearTHR Eccentric Poly Wear


Lucent Zones


Gruen Zones


Femur:  Gruen Zones


AP 1-7

Zone 1:   Greater trochanter

Zone 4:   Tip

Zone 7:   Lesser trochanter


Lateral 8-14

Zone 8:   Anterior-superior

Zone 11: Tip

Zone 14: Posterior-superior


Charnley Zones


Acetabulum: Charnley Zones


Zone 1:  Superior 1/3

Zone 2:  Middle 1/3

Zone 3:  Inferior 1/3






1.  Easier to identify loosening in femur than acetabulum

- femur 90% accuracy

- acetabulum 65% accuracy


2.  More difficult to identify in uncemented prosthesis


3.  Lucent lines don't necessarily represent problem

- may be present in well-fixed prosthesis (retrieval studies)

- often due to remodelling 


Cemented Femur


Signs of cemented femoral component loosening

O'Neil & Harris JBJS Am'84


1.  Possible


Bone-cement lucency < 50% total

- may be due to poor cementing technique

- loosening if progressive


Cemented Femur Possible Loose


2.  Probable


Cement-implant radiolucent line >2mm wide

- progressive


Cemented Femur Probably Loose


3.  Definite


1.  Cement fracture

2.  Femoral stem fracture

3.  New lucency cement - implant interface

4.  Stem migration 


THR Probably LooseTHR Exeter Stem Fracture


A.  Subsidence

- 1-2 mm normal in first year

- > 5 mm abnormal

- measure from tip GT to head neck junction


B.  Medial midstem pivot

- pivots about midstem

- proximal medial, distal lateral

- poor cement superomedial or inferolateral


C.  Calcar pivot / bending cantilever

- distal fix strong, but proximally loose

- breakdown of proximal cement

- bone destruction


Uncemented femur


Engh classification


Types based on presence of radiolucent lines (RLL)


I.  Stable bony ingrowth


Take one year to see

A.  Spot welds at end of porous coating

B.  Absence of RLL next to porous coating

- may have RLL next to non porous coated areas

C.  Calcar atrophy secondary to stress shielding


THR Uncemented Proximal Stress ShieldingTHR Uncemented Stem Spot Weld APTHR Uncemented Stem Spot Weld Lateral


II Stable fibrous ingrowth

A.  No spot welds

B.  Parallel sclerotic lines / RLL about porous coating

C.  No migration


THR Uncemented Stem Stable sclerotic lines


III Unstable fibrous ingrowth

A.  Component migration

B.  Progressive increase RLL

- divergent RLL

C.  Pedestal formation (bony hypertrophy at tip)


THR Uncemented Subsidence


Uncemented Acetabular Component




Bone ingrowth into component averages only 12% 

- even with 84% bone contact


Non continuous radiolucent lines 

- commonly found in press fit acetabular components 

- are often not progressive


Radiographic signs of ingrowth fixation


Moore et al CORR 2006

- 3 or more 97% stable

- 2 or less, 83% unstable


Five signs

- absence of radiolucent lines

- presence of a superolateral buttress

- medial bone stress-shielding

- radial trabeculae

- inferomedial buttress


THR Uncemented Cup Superolateral Buttress 2


Radiographic signs of loosening


5 signs

- radiolucent lines that appear after two years

- progression of radiolucent lines after two years

- radiolucent lines in all three zones

- radiolucent lines 2 mm or wider in any zone

- migration > 2mm


Loose Uncemented CupLoose Uncemented Cup 2


Engh Classification


I  Osse-ointegration



B  One RLL zone 1 or 2

C  RLL zones 1 & 2


THR Uncemented Cup Stable RLL Zone 1Uncemented Cup No RLL


II Stable fibrous ingrowth

- <2mm zone 3


Uncemented Cup Stable Fibrous Ingrowth


III Unstable fibrous ingrowth

- >2mm RLL in zone 3