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Thursday, 23 October 2014 00:00

Hip Dysplasia - Hip Centre

In a dysplastic hip there two approaches to restoring function. The approach taken and acetabular reconstruction of the cup placement is influenced by two factors:

1. Bone stock. High hip centres have poor bone stock (particularly if they need to be revised). Anatomical centres in severe dysplasia will require superior augmentation such as shelf auto-graft in order to obtain sufficient superior coverage.

2. Limb length discrepancy.

There are pros and cons to each approach, and each has its advocates and its critics:

	High hip centre	Anatomic centre
Pros	Technically easier Avoids the need for graft	Better biomechanically Less loosening Restoration of leg length Restoration of bone stock
Cons	Abnormal biomechanics Bone stock is not restored making revisions very difficult Higher rates of component loosening Use of smaller cups needed Potential high rate of dislocation due to impingement against acetabulum	Often needs bone grafting (shelf) to obtain superior coverage Technically more difficult

Technical options to include superior coverage include:

1. Shelf augmentation: Where the femoral head could be used as autograft. Note that cement cannot be used for superior coverage as it has shown very poor results

2. Cotyloplasty: This is a technique that involves making a perforation of the medial wall of a shallow acetabulum and then inserting an acetabular cup with the medial aspect of its dome beyond the Kohler line. This leads to medialisation of the cup by controlled medial wall fracture and bone grafting. This provides more superior coverage to the implant

The technique used is individual to each patient and their individual hip dysplasia categorisation. The approach and technique used also depends upon the surgeons preference and training. In general:

Hartofilakidis I / Crowe I – generally easy to return to anatomical centre

Hartofilakidis II / Crowe II and III – most difficult to return to anatomical centre because when the false acetabulum is in continuity with the true acetabulum the resulting superior bone stock deficiency is greatest

Hart. III / Crowe IV – Somewhat easier to return to anatomical centre (providing lengthening allows it). The true acetabulum is not eroded superiorly and although small allows for better superior coverage than in previous group

Leg length:

With a femoral reconstruction there are two considerations:

1. The leg length itself

2. The abnormal femoral anatomy

Patients generally want their leg length restored. Techniques used to restore leg length include:

Restoration of hip centre

Lengthening of the femoral component

A major limiting factor is the sciatic nerve. To protect the nerve you can safely lengthen up to 4cm or 6% of limb length (whichever is lesser).

Strategies to protect the sciatic nerve include:

Trial reduction with knee flexed and palpate the nerve assessing its tension while gently extending the knee

Somatosensory Evoked Potentials (SSEP’s) or motor electrophysiological tests

Wake-up test if nerve is under tension

Femoral shortening:

Femoral shortening is needed if soft tissue will not allow reduction or if lengthening will increase tension on sciatic nerve. Technical options include:

Sequential proximal resection: This technique involves greater trochanter osteotomy, sequential proximal resection and insertion of a cemented stem. It is technically easier but there is a risk of greater trochanteric non-union resulting in the proximal femur becoming just a straight tube (with no metaphyseal flare) and thus will only accept cemented prostheses. Very distal resection will remove the lesser trochanter with the psoas muscle insertion which leads to decreased flexion strength.

Subtrochanteric osteotomy: This technique has the benefit of maintaining the important metaphyseal anatomy and bone stock, as well as allowing for correction of antiversion abnormality by rotating the proximal segment. This is technically challenging and has a higher rate of non-union due to the fact that osteotomy is made at diaphysial bone, which has a lower potential of healing.

A posterior approach is used after preparing the femoral stem and the osteotomy is done at the subtrochanteric region. The trial stem is then inserted and the hip is reduced so the amount of definitive resection can be assessed exactly. This is followed by resection of the segment and then insertion of the definite prosthesis. The resected segment is then longitudinally split and wrapped around the osteotomy site and reinforced by two cables.

Altered femoral anatomy:

The canal can be very small and wider antero-posterior than medial-lateral with excess antiversion. Thus to overcome this stems with small diameters (5-10mm) are available to use on which the antiversion can be set independent to the anatomical antiversion such as a modular stem or cemented stem with very small metaphyseal flare (DDH stems).

Need for small components:

Cups with an outer diameter as small as 36mm are needed, as well as thickest possible poly, minimum 8mm. This may lead to the use of a very small head

Femoral stems require small diameters 5-10mm with variable metaphyseal sleeves or sizes such as modular non-cemented or DDH cemented stems

Pre-operative planning should include special technical considerations such as ensuring all components are available and performing accurate assessment of leg length.

Published in Information

Tuesday, 09 September 2014 00:00

Total Hip Revision Arthroplasty Techniques - 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.

Published in Surgical Notes

Tuesday, 09 September 2014 00:00

Total Hip Revision Arthroplasty Techniques - 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.

Published in Surgical Notes

Tuesday, 09 September 2014 00:00

Total Hip Revision Arthroplasty Techniques - 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.
Type III A - Fixation with a fully coated porous stem will be proximal to, or at, the isthmus.
Type 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.

Published in Surgical Notes

Tuesday, 09 September 2014 00:00

Total Hip Revision Arthroplasty Techniques - 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.

Published in Surgical Notes

Tuesday, 09 September 2014 00:00

Total Hip Revision Arthroplasty Techniques - 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.

Published in Surgical Notes

Tuesday, 26 November 2013 00:00

Indications and Contraindications

Indications

The most common indication for a total hip replacement is degenerative arthritis (osteoarthritis) of the hip joint. This type of arthritis is generally seen with ageing, congenital abnormality of the hip joint, or prior trauma to the hip joint. Other conditions leading to total hip replacement include bony fractures of the femoral neck at the hip joint, rheumatoid arthritis, osteonecrosis (death of the femoral head) and developmental dysplasia of the hip.

Contraindications

There are no absolute contraindications however; few relative contraindications include a skeletally immature patient and active sepsis or active infection in the joint. These patients may not be suitable for hip replacement surgery, although infected joints can be managed with a staged hip replacement surgery.

Published in Indications and contraindications

Tuesday, 26 November 2013 00:00

Implant Description

The current hip joint replacement prosthesis is composed of four major components:

A metal socket that replaces the acetabulum
A liner with highly polished inner part representing the articular surface. It is usually plastic but other materials are also used such as ceramic or metal. The liner allows the hip to move smoothly
A metal stem that is inserted in the femoral canal
A ceramic or metal ball (represents the femoral head), which articulates with the liner

There are two types of implants systems used for hip replacement:

Cemented hip replacement system, which was first designed by Sir Charnley and is still currently used with some modifications
A biological non-cemented system, which depends on the body ingrowth or ongrowth on the metal surface

Published in Implant description

Tuesday, 26 November 2013 00:00

History of Hip Replacement

Throughout the last three centuries treatment of hip arthritis has evolved from rudimentary surgery to modern Total Hip Arthroplasty (Total Hip Replacement or THR), which is considered one of the most successful surgical interventions ever developed.

Anthony White (1782-1849) of the Westminster Hospital in London is credited with the first excision arthroplasty in 1821. This procedure reduced hip pain and preserved joint movement but joint instability was a problem, which resulted from the surgery.

John Rhea Barton (1794-1871) from Philadelphia is credited with performing the first osteotomy on an ankylosed(fused) hip in 1826.

Léopold Ollier’s (1830-1900) a surgeon at the Hôtel-Dieu hospital in Lyon, France, in 1885 described the interposition of adipose tissue in uninfected joints.

Berliner Professor Themistocles Glück (1853-1942) led the way in the development of hip implant fixation. In 1891, Glück produced an ivory ball and socket joint that he fixed to bone with nickel-plated screws.

Sir John Charnley (1911-1982) pioneered hip replacement surgery during his time at Wrightington Hospital. In November 1962 the Charnley hip replacement became a practical reality and has become the gold standard for this form of treatment. Clinical and radiographic success of this procedure is now approaching 40 years of follow-up. Charnley's design consisted of two parts; a metal (originally stainless steel) femoral component and a teflon acetabular component; both were fixed to the bone using bone cement (acrylic).

Themistokles Gluck, circa 1901, performed the first documented hip replacement in 1891 with an Ivory ball and socket and fixed the bone with nickel plated screws.

Sir John Charnley (1911-1982)