B Assessment Bone Loss

IndicationsRevision THR CT scan Bone Defects

 

1.  Loosening
2.  Infection
3.  Instability
4.  Periprosthetic fracture


Objective


1.  Exclude infection
2.  Re-establish the structural integrity & bone stock
3.  Establish normal Joint mechanics
- restore the centre of rotation of the hip
4.  Initial rigid fixation of bone graft
5.  Adequate containment of the new prosthesis

 

Aetiology Bone Loss


1.  Osteolysis
2.  Surgical / iatrogenic (with implant removal)
3.  Acetabular dysplasia
4.  Fracture
5.  Infection

 

Preoperative Assessment


1.  Exclude infection
2.  Quantify bone loss

 

Classifications

 

Femoral

- Paprosky

- AAOS

 

Acetabular

- AAOS
- Paprosky

 

Femoral Bone Loss

 

Paprosky Classification
 

I Minimal metaphyseal cancellous bone loss / intact diaphysis
- i.e. seen after removal of uncemented component without biological ingrowth on surface
 

II Extensive metaphyseal cancellous bone loss / intact diaphysis
- often seen after removal of cemented prosthesis

 

Revision THR Paprosky II FemurRevision THR Paprosky II


IIIA Metaphysis severely damaged / > 4cm diaphyseal bone for distal fixation
- grossly loose femoral component
- first generation cementing techniques

 

Revision THR Paprosky IIIA FemurRevision THR Paprosky IIIA 3


IIIB Metaphysis severely damaged / < 4cm diaphyseal bone for distal fixation
- cemented with cement restrictor
- uncemented with substantial distal osteolysis

 

Infected THR Paprosky Type IIIA


IV Extensive metaphyseal and diaphyseal bone loss / isthmus non supportive

 

AAOS Classification


I Segmental
- proximal (partial or complete)           
- intercalary
- greater trochanter


II Cavitary
- cancellous
- cortical
- ectasia (dilatation)


III Combined segmental and cavity


IV Malalignment
- rotational
- angular


V Femoral Stenosis


VI Femoral Discontinuity

 

Acetabular Bone Loss
 

AAOS Classification


Type I    Segmental deficiencies

Peripheral -  superior / anterior / posterior

Central - medial wall absent

 

Revision THR Anterior wall segmental defect


Type II    Cavitary deficiencies


Peripheral  -  superior / anterior / posterior
Central - medial wall intact

 

Revision THR Cavitatory Deficiency CupRevision THR Contained Defect Cup CTRevision THR Cemented Cup Anterior Wall Intact


Type III    Combined deficiencies


Type IV     Pelvic discontinuity

 

Separation of anterior and posterior columns


Type V    Arthrodesis

 

Paprosky Classification


Based on ability of the remaining host bone

- to provide initial stability to a hemispherical cementless acetabular component

- until ingrowth occurs


Type 1    

 

Undistorted rim
- anterior and posterior columns intact
- no superior migration

- may have some contained deformities
- ishium, teardrop and Kohlers line intact


Type 2

 

Distorted but intact rim
- can support a hemispherical cementless implant

 

Revision THR Paprosky Type 2 Cup

 

Some distortion, minimal superior migration
- at least 50% good support by host bone
- anterior and posterior columns intact
- no substantial osteolysis of ischium or teardrop

 

2A

- superomedial migration but superior rim intact

 

Revision Acetabulum Paprosky Type IIA

 

2B

- < 1/3 superior deficit

- remainder is still supportive

- replace with allograft for bone stock

 

2C

- medial migration to Kohlers, but wall intact

- rim is supportive

- manage as for protrusio

 

Revision Acetabulum Paprosky Type IICRevision THR Superior Migration Cup but Rim intact


Type 3

 

Non supportive rim
- columns not supportive, superior migration> 3 cm

- require structural allograft for support

 

Revision THR Type 3 Acetabulum


4 radiographic criteria


1.  Superior migration of the hip centre
- indicates damage to anterior and posterior columns
- supero-medial indicates greater damage to anterior column
- supero-lateral indicates greater damage to posterior column


2.  Ischial osteolysis
- bone loss inferior posterior column


3.  Teardrop osteolysis
- inferior anterior column and medial wall


4.  Position of the implant relative to Kohler’s line
- deficiency of anterior column

 

3A

-  > 40% host bone contact

-  < 50% rim missing

 

3B

- < 40% host bone contact

- > 50% rim missing