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Whats New in Hip Op Surgery?

Confused about the wide choices of hip replacement available? Orthopaedic surgeon Manoj Sood offers a useful guide to existing types and new developments.

Since Sir John Charnley developed the first successful design in the 1960’s, total hip replacement (THR) has rapidly become recognised as one of the most successful and cost-effective forms of treatment in medicine.  Charnley’s prosthesis consisted of a stainless steel femoral component (stem), with a metal head and a plastic (polyethylene) acetabular component (socket), which were both cemented into place.  This combination of a metal head articulating with a plastic socket (metal on plastic bearing surface) has been a popular choice for hip replacement.

In the early days Charnley didn’t advocate performing hip replacement in patients below the age of 70 years because he was concerned about the phenomenon of wear causing failure (see below).  The concept of a patient, in severe pain and not sleeping at night being “too young for a hip replacement”, however, is one that is difficult to accept, both for the patient and for the surgeon.  THR has since been performed in younger, more active patients.  Advances in technology have been aimed at producing higher performance prostheses.

There is no doubt, however, that the younger the patient at the time of THR surgery the greater the likelihood that the replaced hip will require a revision (“re-do”) procedure during the lifetime of the patient.  Patients below the age of 65 are likely to require at least one revision procedure, based on average UK life expectancy

Advances in hip replacement have, therefore, been aimed at both increasing the longevity of the implant and at making any subsequent revision procedure easier to perform.  This has led to a bewildering array of new prostheses and new terms and it is sometimes difficult for the non-specialist to understand the concepts behind the developments.

Failure of hip replacement due to loosening

The aim, when planning a hip replacement operation, is to implant a prosthesis that will last the patient for the remainder of their life.  Over the years, implanted metal-on-plastic THR’s wear and generate millions of tiny plastic (polyethylene) particles from the bearing surface during normal activities.  Particles can also be generated from the interface between the cement and the bone that it is locked into (cement-bone interface).  Some of these particles are very similar in size to bacteria, so the body’s defence mechanisms are confused and try to eliminate these particles.  They are taken up by defence cells (macrophages) and these cells produce various enzymes in an attempt to “digest” and destroy the particles.  The macrophages are messy eaters and leak the enzymes onto the bone surrounding the implants resulting in bony destruction or osteolysis.  This can cause loosening of the stem or socket and can result in failure of the replacement. The significant bone loss that is created by the enzymes also creates reconstructive challenges for the hip surgeon during revision surgery.

Uncemented hip replacement

Attempts to eliminate cement debris have resulted in the development of uncemented stems and sockets.  The aim is to create a permanent bond between the implant and skeleton without the need for cement.  This bond can be very successfully achieved in practice, and uncemented components work extremely well once bone grows onto them.   The weak link has been the metal-on-plastic bearing surface.  Most, therefore, use alternative bearing surfaces (see below) with such uncemented components to reduce harmful particle production and hence osteolysis and loosening.  Uncemented THR’s also tend to be used in younger patients.

Alternative bearings

In an attempt to eliminate production of these plastic particles, and so to extend the life of hip replacements, alternatives to a metal-on-plastic bearing surface have been developed.  Such alternative bearings utilise different materials, such as ceramic.  The combination of a ceramic head on a ceramic lined socket is commonly used, and offers a very low friction-bearing surface, and so, importantly, generates only very small volumes of non-plastic particles that do not elicit a reaction.   Metal-on-metal bearings have also been used, with varying degrees of success.

New polyethylene

In addition highly cross-linked polyethylene (a type of plastic that generates fewer particles) has been developed as a more durable alternative to conventional polyethylene.

The latest development is polyethylene which has vitamin E incorporated into it to improve its wear properties.

Ceramic-on-cross-linked polyethylene is also a commonly used bearing surface, which seems to generate fewer particles than conventional metal-on-plastic bearings.

Hip resurfacing

The metal on metal (MoM) bearing surface had a resurgence as hip resurfacing having first been used in the 1960’s.  Inadequate engineering tolerances led to frequent failure of this combination in the past, but modern engineering techniques have overcome the technical problems of tolerances.  This has led to a bearing that, when lubricated by joint fluid, is very low friction and produces negligible particles.  These bearing surfaces reduce the chance of aseptic loosening.  Resurfacing femoral components are very different in design to conventional components.  They have large head sizes, preserve the femoral neck and lack a stem, so that the femoral canal is not breached.  This, in theory, means that subsequent revision surgery may be easier.

Resurfacing has yielded variable results depending on the type of prosthesis used and the type of patient that it is used in.  The metal-on-metal bearing surface does not generate significant particles, but does produce metal ions.  Some patients (especially patients with smaller components in place, such as women) develop adverse reactions to metal, resulting in failure of the hip resurfacing, and the need for revision surgery.  This seems also to be influenced by the design of some types of resurfacing.  Whilst the Birmingham hip resurfacing, for example, has good published results, the ASR hip resurfacing had much poorer results and was subsequently withdrawn.  The numbers of hip resurfacing procedures has declined over the last couple of years, because of these problems.  Resurfacing using a well-designed prosthesis with good clinical results remains an option in very carefully selected young and very active patients in whom the potential benefits of a more stable low-wearing metal-on-metal bearing outweigh the possible disadvantages.

MoM heads and sockets have also been used with normal stems (as opposed to resurfacing components).  The outcome of this combination may offer poorer results, but, further research on the outcomes and risks of MoM hip resurfacing and replacements is necessary.  Most surgeons are currently not using MoM devices and are awaiting the outcome of the numerous studies that are underway.

Mini-incision hip replacement

It is possible to perform a hip replacement through a small (10cm or less) incision. This is something that some patients find an attractive proposition and surgeons find an exciting challenge.  Mini-incision operations are routine for some surgeons. This technique is more cosmetically acceptable and the reduced tissue damage that is possible can result in a more rapid rehabilitation initially and reduced length of stay.  The important thing is that, whatever the incision size, the components must be implanted and positioned properly, and compromises must not be made in order to keep the incision small.  Specially designed instruments have made mini-incision replacements technically easier to perform.

Mini-stems

A number of so called “mini-stems” have been designed that are smaller than conventional stems and so preserve more bone when implanted.  These THR’s are therefore theoretically easier to revise should this become necessary.  Some of these stems are simply shorter versions of existing designs, whilst others are radically different in design and are truly bone-preserving.  Long-term results are not yet available as most of these designs have been on the market for only a few years.

The anterior supine approach

This is a relatively new surgical approach that aims to implant a THR through the front of the hip joint in an operation that involves minimising muscle damage.  The operation is performed with the patient on their back instead of the more usual position where the patient is on their side.  The smaller amount of tissue damage is said to allow more rapid mobilisation after THR.  It has been adopted by some surgeons, but is not in widespread use, and has some disadvantages, such as an increased risk of nerve injury.  Further studies will determine its place.

Navigation in hip replacement surgery

Accurate positioning of THR components is essential for a number of reasons, such as reducing the rate of dislocation of the THR, a feared complication, and optimising the longevity of the THR. Techniques, akin to a miniature form of the satellite navigation systems used by many motorists, have been developed to help ensure this.  This technology is available and is being used and evaluated by some surgeons.  It is clear that experienced surgeons have a smaller error rate in positioning components and such surgeons do not uniformly believe that navigation offers them significant benefits.  As the technology becomes easier and quicker to use, more accurate and more widely available, however, it may well be increasingly adopted.

The future

Further developments will occur in bearing surfaces with new materials being tested.  Research into the use of diamond, the hardest substance known to man, in bearing surfaces (as it is used in certain drills) has already begun.  Long-term studies of mini-stems will determine if these will take over from conventional stem designs.  Components made of new, improved materials may also appear.

The history of THR shows us that successful implants and techniques inevitably become part of mainstream practice and are available to patients who might benefit.   The most important aspects for success in THR surgery, and joint replacement surgery in general, however, are that an appropriately investigated and informed patient should have an appropriately selected THR implant with a good track record implanted by an appropriately qualified and experienced surgeon using techniques that minimise potential complications and that allow rapid return to activity.

Manoj Sood is a consultant trauma and orthopaedic surgeon and

hip and  knee specialist practising in London, Hertfordshire and Bedfordshire.  For further details go to hipandkneesurgery.co.uk or call 020 71274202.

The article addresses common questions that patients ask about revision hip replacement including reasons for revision, a brief outline of what is done at revision hip surgery and outcomes from revision hip surgery.  The full-text of the article appears below.

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The challenge of revision hip replacement surgery

Total hip replacements (THRs) are performed when hip joints become arthritic and significantly painful.  They are very successful procedures, however, they will eventually wear out and in some cases complications may develop, requiring a further operation, called a revision (or re-do) hip replacement.  Orthopaedic surgeon Manoj Sood gives an overview of this procedure.

A revision or “re-do” total hip replacement procedure involves the removal of the existing THR and its replacement with new components.  A hip replacement consists of a stem, a head and a socket.  Sometimes only the socket or stem requires replacement, but at other times the whole THR is removed and replaced.  This is complex surgery, but is required in certain situations where the existing THR is not functioning satisfactorily or has become painful or infected.

How common is this type of surgery?

Last year over 80,000 THRs were performed in the UK.  More than 1 in 10 of these (approximately 8,600) were revision THRs.  There is evidence that the number of revision THR procedures performed in the UK is increasing.

What are the reasons for needing a revision THR?

A revision THR may be required for a number of different reasons.  Common reasons include:

The THR may have become painful because it has been in place for many years and the components have begun to wear and loosen, moving a little in the bone. This type of loosening usually causes some bone loss and damage, and this bone loss needs to be dealt with at the time of revision surgery.

• THRs can dislocate on repeated occasions and revision surgery may be needed to stop this distressing complication from happening.

• Patients may fall and sustain a fracture of the bone around the THR, called a peri-prosthetic fracture, and this can require a revision THR.

• A deep infection may develop in a THR, and, if this occurs, revision surgery will frequently be required to eradicate the infection and to implant new non-infected components. A single operation may be performed to eradicate the infection (single stage revision), but often surgeons prefer to do a two-stage revision involving two separate operations (see below).

How long does a revision THR operation take to do?

The exact time taken depends on the complexity of the individual case, as all cases are different; however it takes at least twice as long to do a revision THR as it does to do a first time THR.  This means that it takes a minimum of 2-3 hours and significantly longer in more complex cases.  It is specialist surgery requiring the use of specialist techniques and specialist equipment.

What preparations are necessary before revision THR surgery?

Preparations start some time before the day of surgery as it is essential that the surgeon plans the surgery very carefully.  I plan all my revision THR procedures some weeks in advance and this includes computerised templating of every case.  Sometimes specialist equipment is required and this is arranged in advance.  My anaesthetist carefully assesses and prepares the patient for what will be major surgery.

What happens during revision THR surgery?

Usually a larger incision and specialised approaches to the hip joint are required to gain adequate access to perform the surgery.  The Revision THR operation then involves three phases.  The first phase involves the careful removal of the appropriate THR components whilst causing minimal damage to the bone that contains them.  This requires special equipment.  If the cement needs to be removed I commonly use an ultrasonic machine that “melts” the cement so that it can be safely removed.  The second phase involves replacing any bone lost (see above) either with bone graft or using special porous metal augments (specialised building blocks) to create a solid foundation for the new THR.  The third and last phase involves placing the new THR.

If a deeply infected THR is being revised, this is commonly done as a two-stage process.  The first stage operation involves removing the infected THR and placing a temporary hip replacement called a spacer.  This spacer often contains antibiotics within it to help fight the infection.  Once the infection has been cleared, a second operation is performed to place a new non-infected THR.  Using this approach, it is possible to eradicate the infection in 80-90% of cases.

Both uncemented and cemented implants can be used for revision THR’s although my preference, in the majority of cases, is to use uncemented components.

What are the outcomes after revision THR?

A vast majority of my patients can put full weight on the revised THR, with crutches for support, within 48 hours of surgery.  A very small number need to put partial weight only on the operated leg for 6 weeks.  A number are given a brace to wear for six weeks, usually if the revision THR was performed because the hip was recurrently dislocating.

A successful revision THR offers relief from the symptoms that necessitated the procedure.  Revision THR is a more complicated procedure than a first time THR, and so the risks of the procedure are higher.  However, when performed by a surgeon who is specially trained to perform this type of surgery, and who does it regularly, the outcomes should be good in a vast majority of patients.  The pain of a loosened THR, the unpredictability of an unstable THR that dislocates repeatedly and the painful deep infection of a THR can be cured in a vast majority of patients.

How many times can a THR be redone?

The truth is that there is no limit to the number of times a THR can be revised.  Clearly, however, multiple revision procedures are not desirable as the more times a hip is revised, the more scar tissue is created in muscle and this can cause limping and loss of function.  In addition, the risk of infection after the procedure increases the more times a hip is operated upon.

With modern THR techniques, we expect well performed THRs using proven prostheses to last a minimum of 10-15 years, even in active individuals, before revision THR is required.  The younger the patient is at the time of their first THR, the more likely they are to wear out their THR and require revision surgery.  Hence the drive to use harder wearing THRs and to implant THRs that are smaller so that they are theoretically easier to remove if a revision THR is needed.

How can the number of revision THR procedures needed be reduced?

The key to this is to make THR’s last as long as possible, mainly by improving the “bearing surface” which is the part that wears and generates debris that causes loosening, which I discussed in more detail in the article in Arthritis Today 157.  It is also vital that poorly performing THR prostheses (those that fail early) are identified as soon as possible so that their use can be curtailed.  It is also important that high standards are practised during THR surgery to minimise the risks of complications such as dislocation, due to poorly-placed components, and infection.

 The future of revision THR

Developments continue in the field of revision THR.  Some are aimed at reducing the complications that require a THR to be performed, and others are directed at improving the techniques, equipment and implants that are used in revision THR procedures.

What is clear is that although revision THR is major surgery, modern revision THR performed by specialists in this field is a predictable procedure that can give reliably excellent results, provided that complications don’t occur.  The risk of such complications is higher than in first time THR procedures and careful counselling of the patient is required before any revision THR procedure, so that the specific risks can be explained in detail.

Manoj Sood is a Consultant Orthopaedic Surgeon and a Hip & Knee Specialist.

Arthritis Research UK’s booklet on hip replacement is available at 0300 790 0400 or enquiries@arthritisresearchuk.org.

Sometimes hip joints that have been previously replaced must be replaced again.  This can be required for a number of reasons, but common reasons for re-doing the hip replacement include:

-the previous hip replacement reaching the end of its life and wearing out

-complications developing either early after the original procedure or some years later, such as, infection, the artificial joint loosening from the bone, dislocation of the joint or fractures around the stem of the hip replacement.

The three main stages of a revision hip replacement are:

–removal of the existing components and bone cement with minimal damage to the patients bone

–reconstruction of any existing bone loss using bone graft or advanced porous substances

–implanting (inserting) the new components whilst ensuring that the hip is stable (re-do hip replacements have a higher risk of dislocation, so careful attention to this issue is vital)

This sort of surgery takes about two or three times as long as the time taken to perform a  first time hip replacement.  It also carries significantly increased risks of complications compared to the original hip replacement.  These are discussed in detail with our patients prior to their revision procedure.

Re-do surgery is complex and challenging, and the best results are achieved by surgeons who specialise in the various techniques that may be needed to achieve a successful re-do surgery and therefore a well-functioning revision joint replacement.  There is also little doubt that the best results are achieved by those who perform this sort of complex surgery regularly.  Modern revision hip surgery has become a subspecialty within itself.

Mr Sood has undergone specialist training in some of the best hospitals in the world to perform complex and revision hip replacement and performs revision joint replacement procedures on average once every week.  He is one of fewer than 5% of UK surgeons who perform this number of revision procedures.  He prides himself in achieving excellent outcomes for his revision patients, a proportion of whom have already had unsuccessful revision procedures to the same joint performed elsewhere.

Please click on the link below to read an article written by Mr Sood about revision Hip Replacement:

Surgery for Failed Hip Replacements

Resurfacing is technically more difficult to perform, and so is usually best performed by specialist hip surgeons.  The decision to perform a hip resurfacing is also more complex than a THR and has to take into account a number of factors.  Not all patients are suitable for this technique.  It is also important that the resurfacing prosthesis used has a good track record and is implanted optimally.

Types of Hip replacement

Total Hip replacements can be classified in a number of ways:

-according to the attachment of the THR components (stem and cup) to bone:

• with cement (cemented)
• without cement (uncemented or press- fit).

-according to the articulating material that the ball and socket are made of:

• metal, oxinium or ceramic (ball) or metal, plastic or ceramic(socket). 

Types of THR stem:

–conventional sized stems, which are used in the majority of patients.

–mini sized stems, which are used in some younger patients with good bone quality to preserve as much bone as possible to aid future re-do procedures that are likely to be required in the lifetime of these patients.

Mini-incision surgery and rapid recovery

We routinely perform THR through a mini-incision, unless this is contraindicated for any reason, minimising muscle damage and leaving a small cosmetically very acceptable scar.  We routinely get patients standing and taking some steps on the first day post-surgery and walking by the second day to help minimise any complications that result from prolonged inactivity.  We view THR surgery as a “pit-stop” to relieve pain and increase mobility in an otherwise well individual.

Further information

Click here to view a very helpful guide to Total Hip Replacement produced by Arthritis Research UK.

Unlike the knee joint, the hip joint is a ball and socket joint with strong muscles surrounding it and has a very small joint space. Therefore, in order to perform such key-hole surgery the joint needs to be pulled apart a little (distracted).  This is done using special equipment that pulls on the leg and thus distracts the hip joint. This creates space in which the tiny fibre optic camera and instruments can be manipulated.

Procedures that can be performed during a hip arthroscopy include labral tear trimming or repair, articular cartilage injury treatment by microfracture or cartilage transplantation, femoroacetbular impingement treatment, and treatment of a clicking hip caused by a psoas tendon problem.  Hip arthroscopy can also be used to investigate the cause of hip pain where other tests have failed to diagnose this.

The surgery takes approximately 1 1/2 to 2 hours and most patients can go home the same day. Crutches are usually required for about 2 to 3 weeks and physiotherapy is important.