Revision of THR

Question 1

What are the indications of revision THR?

Answer 1

• Osteolysis
• Loosening
• instability
• infection
• Mal-alignment
• Polyethylene wear

Question 2

What is the classification of loosening in acetabular component in THR?

Answer 2

• Charnley zones
• 1 superior 1/3
• 2 middle 1/3
• 3 inferior 1/3

Question 3

What is the classification of loosening in femur component in THR?

Answer 3

• Gruer zones
• 1-7
• 1-GT
• 4 tip
• 7 lesser trochanter

Question 4

What are the presentation of acetabular and femoral components?

Answer 4

• Groin pain-> acetabulum
• Thigh pain-> femoral stem
• start up pain-> component loosening
• Night pain-> infection

Question 5

What is the classification of acetabular bone loss?

Answer 5

AAOS

• Type 1= Segmental
  
  • loss of acetbular rim or medial wall loss
• Type 2 = Cavitary
  
  • volumetric loss of acetabular cavity
• type 3- combined
  
  • segmental and cavitary
• type 4 - pelvic discontinuity
  
  • complete seperation between superior and inferior acetabulum
• Type 5
  
  • arthrodesis

Question 6

Name another classificatio system of the femoral bone loss?

Answer 6

• Paprosky
• type 1- Minimal metaphyseal bone loss
• type 2-excessive metaphyseal bone loss with intact diaphyseal
• type 3a- excessive metadiaphyseal bone loss, minimum of 4cm of intact cortical bone in diaphysis
• type 3b- excessive metadiaphyseal bone loss,
• type 4 excessive metadiaphyseal bone loss,& a non supportive diaphysis

Question 7

Describe the classification of femoral bone loss?

Answer 7

• AAOS
• type 1= segmental
  
  • loss of bone of the supporting shell of femur
• type 2= cavitary
  
  • loss of endosteal bone with intact cortical shell
• type 3= combined
  
  • combo of segmental and cavitatry
• type 4= malalignment
  
  • loss of normal femoral geometry due to prior surgery/trauma or disease
• type 5= Stenosis
  
  • obliteratio of canal due to trauma/bony hypertrophy or fixation device
• type 6= femoral discontinuity
  
  • loss of femoral integrity from fx or non union

Question 8

What investigations would you do to confirm loosening?

Answer 8

• xrays
  
  • AP, full length femur
• CT scan
  
  • useful to determine extent of osteolysis
  • radiographs frequently underestimate osteolysis
  • component position
• Labs
  
  • ESR/CRP/HB- infection
• aspiration - if infection suscepted

Question 9

What is the tx for femoral loosening?

Answer 9

Femoral revision

1. Primary THR components
   
   • for minimal metaphyseal bone loss
2. femoral impaction bone graft
   
   • morselized Fresh frozen allograft packed into canal. smooth tapered stem cemented into allograft. paprosky 3b-4
   • disadv= stem subsidence
3. uncemented stems extensively porous coated long stem prothesis - 95% at 10 years- paprosky 2-3a
   
   • must bypass most distal defect by 2 cortical diameters- prevents bending moment thru cortical bone
4. cemented stems- historically high failure rate but Haydon et al 2004 JBJS Am in their experience cemented femoral revision had 91% survivorship when the cause was aseptic loosening. They found early generation cementing techniques, poor cement mantle, poor bone quality, age of less than 60, and male gender to be risk factors for failure in cemented revisions.
5. modulated oncology components- proximal femoral replacement- type 4 paprosky

Question 10

What is the tx for acetabular loosening?

Answer 10

• Porous coated hemisphere cup with secured screws
  
  • if rim competent >2/3 of rim remaining
  • cup placement inferior and medial - lowers joint reaction force
• Reconstruction cage with structural bone allograft
  
  • if rim incompetent (<2/3 rim remaining)
  • graft placed behind cage.
  • PE cup cemented into cage
  • allograft failure is most common complx
  • high failure rate 40-60% without recon cage due to component migration after graft resorption
• In cases of minor, contained, acetabular defects, morcellized allograft and/or autograft bone, combined with a cemented or cementless acetabular component can lead to successful reconstruction. However, these constructs do not confer enough stability when the loss of bone stock is more extensive and encroaches on the acetabular columns, or compromises >50% of the weight-bearing surface. so then a cage with graft is used- ilioischial ring cage

Question 11

What are the indications and outcomes for conversion from a hip arthrodesis to a THR?

Answer 11

• Low back and knee pain
• Outcomes
  
  • Implant survival > 95% at 10 yrs
  • competence of gluteal musculature is predictive of ambulatory success- by EMG study

Question 12

What is more common to fail the cemented acetubular component or the femur?

Answer 12

• Acetabulum
• Failure of the acetabular component was the most common reason for revision at thirty-years for the Charnley “low-friction” total hip arthroplasty.