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

2.  Probable

 

Cement-implant radiolucent line >2mm wide

- progressive

3.  Definite

 

1.  Cement fracture

2.  Femoral stem fracture

3.  New lucency cement - implant interface

4.  Stem migration

 

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

 

II Stable fibrous ingrowth

A.  No spot welds

B.  Parallel sclerotic lines / RLL about porous coating

C.  No migration

III Unstable fibrous ingrowth

A.  Component migration

B.  Progressive increase RLL

- divergent RLL

C.  Pedestal formation (bony hypertrophy at tip)

 

 

Uncemented Acetabular Component

 

Concepts

 

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

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