Hip Revision Arthroplasty

THR revision techniques

JAAOS Monograph series (Paprowsky).

Exposure

Trochanteric techniques:

1. Trochanteric slide

This is a modification of the direct lateral approach (Hardinge).

The anterior portion of the GT is osteotomised with the insertion of gluteus medius, and origin of vastus lateralis attached to it.  This is then reflected anteriorly to expose the femoral metaphysis and acetabulum.

It is reattached by circlage wires passed around the LT.

The opposing forces of the gluteus medius (pulling it superior), and vastus lateralis (pulling it distal), results in inherent stability.

Problems:
* Re-attaching such a small flake of bone – non-union.
* Any limb lengthening may make re-attachment quite difficult.

2. Vastus slide

Essentially this is a subperiosteal peel of the origin of the vastus lateralis, and anterior insertion of gluteus medius.

The incision is in the shape of a question mark.

3. Extended proximal femoral osteotomy

An osteotomy of the anterolateral 1/3 of the proximal femur, including the entire GT.

The abductors and VL remain attached to fragment.

It is carried as distal as necessary to facilitate removal of the implant.

Pre-op templating will show how far this is – the revision stem must be longer than the end of the osteotomy site by at least 4cm or 2 cortical diameters.

Technical tips:

  • Elevate the VL from the femur.
  • Use a bur to make the distal, transverse limb – round the edges to minimise stress riser.
  • Oscillating saw for the vertical limb.
  • Re-attach prior to preparation of the revision stem.
  • Prior to re-insertion of revision stem place a prophylactic circlage wire around the femur just distal to the distal extent of the osteotomy in order to prevent propagation.

Removal techniques

1. Poly exchange

Always be prepared with equipment for entire acetabular revision in-case the locking mechanism is damaged.
Techniques are;
Implant specific tools.
Drill into the polyethylene.
Split the polyethylene.

2. Cemented acetabular removal

In order to disrupt the bone-cement interface, you usually need to disrupt the implant-cement interface first.
Start superio-lateral edge of the cup.
Pass curved gouges and osteotomes to disrupt the implant-cement interface.
In removing cement be wary of possibility if intrapelvic content adhesion to cement fragments.

3. Cemented cup removal

The aim is to remove the cup with minimal bone loss.
Techniques are;
Good circumferential exposure.  This is essential.
Passage of curved gouges and osteotomes.
Be very careful of levering on the cup.
Large lever arms can be generated.  Cup removal with a large number of bone attached is dire. Titanium implants may be cut into quarters using midas-rex type device.

4. Cemented femoral stem removal

Obtain circumferential exposure of shoulder of prosthesis. This is crucial.
May require trimming of any over-hanging trochanter.
Disrupt the implant-cement interface first.
Attach an extraction device and extract the stem.
Piece-meal extraction of all cement.
Remove in a proximal to distal fashion.

Variety of tools:

  • Currettes, flexible osteotomes, gouges.
  • Use an osteotome to longitudinally split the proximal cement mantle.
  • Used curved or flexible osteotomes and gouges to remove cement further down the shaft.
  • Burs.
  • Drill and screw in tap. Particularly useful in removing the distal cement plug.
  • Sequential drilling and reverse hooks.

Supplementary techniques:

  • Osseous windows – distal to cement plug.

5. Cementing back into a cement mantle

It is essential in this situation where the cement mantle is not compromised. (For example, Revision for limb length, acetabular revision.)

6. Cementless femoral stem removal

Removal technique is dependent on the particular stem – need to know where the in growth surfaces are and disrupt these bone-prosthesis interfaces.
Proximal porous coating - proximal disruption.
Extensively porous coating - more extensive disruption (diaphyseal).
Usual principles.
Proximal exposure.
Take care and be patient – preserve bone stock.
Flexible osteotomes.
Options
“Episiotomy” – useful in proximal porous coated.
Lift the VL anteriorly at its origin to expose the metaphyseal/diaphyseal junction.
Use an oscillating saw to make a 10cm longitudinal osteotomy in this region of posterolateral proximal femur.
Attach the extractor to the stem and make sequential impaction-extraction attempts.
Extended proximal femoral osteotomy.
Take down to just distal, to the distal extent of the porous coating.
Pass a Gigli saw around the proximal stem to disrupt the bond at the calcar.
Windows at sites of spot-welding.

Acetabular revision

Classification systems

AAOS classification

Segmental = complete loss of bone in supporting hemispherical structure of the acetabulum.
In this classification system the rim includes the medial wall.
Cavitary = Localised volumetric loss of bone, without disruption of acetabular rim.

Type 1 – Segmental deficiency.
Peripheral – Superior, Anterior, Posterior.
Central – medial wall absent.

Type II – Cavitatory.
Peripheral – Superior, anterior, posterior.
Central – Medial wall intact.

Type III – Combined.

Type IV – Pelvic discontinuity.

Type V – Arthrodesis.

Paprosky classification

Type I – Undistorted acetabular rim.

Type II – Distorted but intact rim with adequate bone to support hemispherical cementless cup.

Type III – A non-supportive rim.
Host acetabulum is unable to support an acetabular component in the anatomical hip centre.
Will need augmentation to support a non-cemented cup which will be difficult.
Most likely to require a reconstruction ring of some kind..

Aim of revision

Restore normal centre of rotation.
Rigid construct.
Implant must be immediately stable.
Major segmental defects more problematic.
Superior and posterior deficiencies may require structural allograft.
Anterior defects not as problematic – particulate graft may suffice.
Increase bone stock.
Cavitatory defects should be filled with morsellised cancellous bone.

Crucial questions

Will stable fixation in host bone be possible (with or without morsellised graft) at the anatomic hip centre?
Are there segmental defects that require structural allograft – or can I use a high hip centre ?
Is bone loss so extensive that even with structural grafts, stability and fixation will be questionable?
Is there a pelvic discontinuity that will need reconstruction and fixation?
What is the optimal exposure to achieve my aims?

My ladder of options

The aim is to use a porous coated rim fit cup supplemented by screws. If this can achieve a stable fixation these will give the best results – places in an anatomical hip centre.
Fill any contained defects with morsellised graft.
If this results in > 50% of the cup in contact with graft it must be supplemented by a reconstruction cage and a cemented cup.
Get sufficient stability with what rim remains and the screws – what is sufficient?
No consensus.
Do not be concerned about the medial wall or small anterior defects – it is rim fit which provides fixation.
Walter – “any 3 point peripheral fixation”.
Literature criteria of minimum requirements.
2/3 rim intact.
50% contact with native host bone.
70% coverage.
May augment segmental defects with structural graft – autograft (iliac crest, fibular), or structural allograft (anatomical graft, or non-anatomical) – however these have a high rate of failure and I would be likely to move to a cage and cemented cup instead.
If this is untenable I would move to a reconstruction cage with a sup cemented into it.

Points to consider

The best results are obtained with a porous cup placed in an anatomical hip centre which is STABLE.
If stability cannot be achieved it will not work.
Use criteria for stability as above – if this criteria cannot be satisfied you must move to a ring and cemented cup.
Structural allografts don’t have good results in the literature.
Problems with revascularization-remodelling and resorption failure.
Reflects the fact that they are used in the most difficult cases – inherent bad results in this group.
Reconstruction rings/cages with a cemented cup has better results than large structural allografts.
Restore bone stock.
Graft contained defects.
Consider structural grafts even in the setting of reconstruction rings and cemented cups in order to restore bone stock.
Hip centre.
Anatomical hip centre is the best result.
May be a tradeoff between getting a good fixation with a porous cup in a slightly high hip centre (where bone stock is better) versus restoring hip centre but thus necessitating either structural bone graft or use of a ring and cemented cup to achieve it.
The best option here is not clear – there are pros and cons to both sides.

Osteolytic defects around stable porous cups

Osteolysis around porous cups tends to be an isolated, expansile lesion, in contrast to the osteolysis seen around cemented cups which tends to be linear.
Removal of the well-fixed cup will likely result in further loss of bone stock, thus treatment is either:
Liner exchange
After removal of the liner the granuloma in the defect can be debrided through any screw holes, and the defect packed with morsellised bone graft.
If locking mechanism is intact simply insert a new liner.
Superior window
This is useful where the granuloma is inaccessible through the cup (either due to its location, or lack of holes in the cup).
Cement a new liner directly into the cup.
If locking mechanism is not intact the poly liner must be moved, debride and graft through the holes, roughen the floor of the cup, and cement in a new cup.

It is contentious whether success depends upon:
* Debriding the granuloma that forms in the osteolytic defect, OR
* Removing the poly load that is driving the lysis.
This is thought to be the most important step.
Supported by the Maloney study – in cases of just liner exchange (no debridement), no lesions progressed after exchange, and 1/3 completely resolved.

Pelvic dissociation

General points

Involves complete dissociation of the acetabulum from the ilium.
Generally look at the posterior column.
If the posterior column is gone, there is a dissociation.
If the posterior column is intact there is no dissociation.

Treatment (Walter) - Young patients

Aim here is for a ‘biological solution’ ie reconstruction of bone loss, and no cement.
It involves 2 stage surgery with a long period (many months) of TWB in interim.

Technique:
1st stage – to stabilise the dissociation and fill the bone defects.
Posterior approach to hip and acetabulum.
Reduce and fix the posterior column.
Use pelvic reconstruction plate from ilium to ischium.
The anterior column does not need to be fixed – combination of stabilisation of the posterior column and impaction grafting will help it heal.
Impaction grafting of defects with NON-IRRADIATED allograft and mesh.
Leave all other prostheses out.
No spacers as they will load the acetabulum and slow or prevent union of the posterior column and incorporation of the bone graft.
6 weeks bed rest followed by several months TWB.

2nd stage – Re-implantation of prostheses.
Posterior approach.
Remove mesh.
Ream acetabulum as per normal.
Re-insert.

Treatment – Elderly patients

Approach here is more traditional.
Single stage procedure.
Elderly patients are less tolerable of prolonged immobilisation
Cons of non-biological solution (cement) less problematic in the elderly.                             Posterior approach to hip and acetabulum.
Reduce and fix the posterior column.
Screw in a reconstruction cage.
Some reconstruction cages may simultaneously fix the posterior column.
Cement a cup into the cage.

Femoral revision

Goals

  • To extract prosthesis with minimal damage
  • To implant a new stem which will be STABLE
  • To manage and augment bone loss

Classification of femoral bone loss

AAOS classification.
Type I – Segmental loss.
Any loss of cortical shell.
Type II – Cavitary loss (cancellous or endosteal cortical loss without violation of the outer shell).
IIA – Cavitary loss.
IIB – Ectasia (femoral expansion with cortical thinning and complete loss of cancellous stock).
Type III – Combined.
Type IV – Malalignment.
Type V – Stenosis.
Type VI – Femoral discontinuity.

Paprosky classification

This is useful in decision making where an uncemented revision stem is to be used.

Type I - Minimal defects with intact metaphysis and diaphysis, and partial loss of calcar or AP bone stock.
Type II - Metaphyseal defect with normal diaphsyis, calcar completely absent and major AP bone loss.
Type III - Defects of metaphysis and diaphyseal junction.
III A - Fixation with a fully coated porous stem will be proximal to, or at, the isthmus.
III B - More distal defect, but fixation will still be achieved (just distal to the isthmus) – need minimum 6cm bone contact (assess stability intra-op).
Type IV - Extensive metaphyseal and diaphyseal bone loss and a canal which will not support even a long stem.

Treatment

Paprosky protocol

Type I – As for primary.
Type II - IIIB – Fully coated stem with variable degrees of calcar replacement.
Type IV – Impaction grafting or allograft-prosthetic composite.

Points to consider

Primary aim is a stable prosthesis.
Uncemented stems have better results than cemented stems in the literature.
Must obtain axial and rotational stability – micormotion of > 40um will result in fibrous ingrowth.
Meticulous femoral bone preparation is crucial - the cancellous bed will be poor (studies show fixation strengths of 70% less than in the primary setting).
Meticulous removal of all previous cement or pseudomembrane.
All sclerotic areas need to be burred down to “fresh” bleeding or cancellous bone – take care not to perforate though.
Rigorous cementing technique if you are going to cement – need good pressurisation
A stem longer than 7 inches requires an anterior bow.
The apex of the anatomical femoral bow is 7 inches below the LT.

Uncemented revision options

Proximally porous coated
Be wary as:
These obtain fixation by “fit and fill” in the metaphysis and in revision setting it is often the metaphysis which is deficient.
The cylindrical stem often provides little torsional stability unless they have deep cutting flutes (such as the SROM).
The stems are often straight and in the revision setting a long stem is frequently needed – be aware of the anatomic bow of the femur, and that the long straight stem can be accommodated.
Bridging of bony defects with long, proximally coated stems will provide limited distal stability.
Fully porous coated – Best results (approaching primary stems – 3-7% failure at 13 years).
Often a better option due to the following:
They obtain their fixation in the diaphysis (where the bone is generally good) – bypassing the deficient metaphyseal bone.
Less anatomic variation in the diaphysis as compared to the metaphysis allows for more reliable fill.
Success is correlated with:
Canal fill > 90%.
Diaphyseal support of > 4-6cm.
Satisfy these criteria and the success approaches primary stems.
Problems with this technique (both relate to difficulty of any further surgery) and proximal stress shielding.
This is made worse by the fact that thus far these stems are only available in Co Cr.  Due to its stiff modulus, Co Cr stems bigger than 13.5mm and are associated with stress shielding.
There is difficulty in removing an ingrown fully porous stem.

Techniques to restore bone stock

Impaction grafting
This is used in order to create a femoral bone bed which will support a cemented long stem.
Technique:
Fully expose the femur.
Any segmental defects must be converted to contained defects – mesh or strut grafts with circlage fixation.
Prophylactically circlage wire the femur.  It must be able to withstand the significant hoop stresses which need to be generated for this technique to work successfully.
Insert a thick intramedullary plug at least 2m pass the most distal lytic defect – hold it there by interference fit, and by passing a K-wire transversely beneath it.
Pass an IM guide-wire down and into the centre of the plug – confirm its central location.
Use a cannulated system to systematically impact morsellised bone graft chips into the femur, creating a solid endosteal canal.
Chips should be 3-5mm in size – too small will allow poor fixation.
Pack the bone in a distal to proximal fashion.
Final tamp will be 1-2 sizes larger than the stem to be used.
Remove the IM guide wire.
Broach in normal fashion.
Cement the stem in routine fashion – insert cement slightly more liquid than normal.
Insert a highly polished, collarless, double-tapered stem (Exeter).
Protected weight bear for 3 months and results are encouraging.
Main problem is with excessive subsidence.

APC (allograft prosthesis composites) and strut grafts
Indications:
Calcar defect > 5cm – if it is < 5cm use a calcar replacing prosthesis.
Large intra-medullary defect with a thin cortical shell.
This generally involves applying strut grafts using circlage wires.
How much load these grafts can then support is controversial; Some advocate loading them to encourage their incorporation. Others bypass them (distally fit stems) suggesting that you can’t expect them be true structural supports – most apply this approach.
Create a step cut at site of junction with the native diaphysis.