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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 study was particularly interesting because a series of MRI scans were also performed and these showed that no deterioration in the arthritis occurred in the knees injected.

COMMENT:

This is a very interesting and illuminating research paper.  We are using PRP injections as a joint preserving treatment in selected patients with knee arthritis and are monitoring our results carefully.

When arthritis of the hip becomes more advanced the articular cartilage on the ends of the bones that make up the hip joint becomes eroded so that the underlying bone is exposed.  These bones rub against each other causing pain that is felt in the groin most often, although it can be felt in the top of the outer thigh in some cases. Extra spurs of bone can also develop and in most cases the hip becomes increasingly stiff. This causes difficulty with putting on socks and shoes and with pedicure. It is often a disabling condition that can cause sleep disturbance.

What can be done to treat advanced hip arthritis?

In advanced arthritis the treatments that have been used for early arthritis often fail to control the pain and stiffness and patients become increasingly disabled and their lives are severely affected. In such cases total hip replacement needs to be considered.  This is a very successful procedure, giving affected patients a “new lease of life”.  Various types of replacement are available and the choice depends on a number of factors.  We offer all types of replacement to our patients and we carefully select the best type for each patient individually based on various factors.

Please read our patient testimonials to see what patients have to say about undergoing a hip replacement.

When the cartilage covering the ends of the bones that make up the hip joint becomes damaged and worn (thinned) the condition of wear or degeneration has started and is called early arthritis.  This can be seen as narrowing of the joint on x-rays.

What symptoms does early hip arthritis cause?

Patients describe pain in the hip that they feel in the groin.  There is often a bit of stiffness of the hip which makes putting on socks and shoes a little more difficult, but this is not always noticed in early hip arthritis.

What can be done to treat early hip arthritis?

In early arthritis, the focus of treatment is to relieve pain and to try to prevent progression of the disease to more severe arthritis which would require joint replacement.  This is called joint preservation.

Treatment options include physiotherapy with muscle strengthening, simple painkillers, viscosupplementation (“shock-absorbing”) gel injections into the joint, PRP (platelet-rich plasma) injections and in some cases, key-hole surgery of the hip to deal with any underlying cartilage tears.

This is a general term that refers to a hip that clicks or “snaps”.  The cause for the clicking can arise from inside the joint, such as a cartilage tear or loose piece of cartilage, or can arise from outside the joint due to tendons flicking over the hip joint and causing a click.  The “snapping hip” or clicking hip is not a diagnosis, but is a symptom that needs further assessment in order to determine the cause and therefore allow appropriate treatment.

What symptoms does Snapping or Clicking cause?

If caused by a psoas tendon problem, an audible snapping or popping noise as the tendon at the hip flexor crease moves from flexion (knee toward waist) to extension (knee down and hip joint straightened) can occur.  After extended exercise pain or discomfort may be present caused by inflammation of the iliopsoas bursa. Pain often decreases with rest and diminished activity. Symptoms usually last months or years without treatment and can be very painful.

The snapping sensation can also arise from a tight iliotibial band flicking over the upper, outer part of the hip.

Finally, a tear in the cartilage or labrum of the hip joint can cause a click that is often painful and can cause the hip joint to lock.

What can be done?

If the snapping or clicking is caused by the psoas tendon or iliotibial band then physiotherapy is often recommended in the first instance and can be sucessful.  Surgery for these conditions is a last resort but can be indicated in some resistant cases.

For labral tears, treatment with a hip arthroscopy can be used to repair or trim the tear and is usually successful in curing the problem.

In this condition there is abnormal contact between the ball and socket parts of the hip joint due to abnormal benign growths of bone which causes groin pain and can lead to damage to the joint.

There are two main types, although both can occur together:

Cam-type impingement – here the head and neck (“ball part”) of the joint has a prominent bump which abnormally contacts the socket in certain positions of the hip causing pain and subtle shearing movements and decentering of the axis of rotation of the hip (hence “cam” as in the cam of an engine).  When this occurs repetitively the hip and labrum  can be damaged and ultimately it is thought that this may lead to an increased risk of arthritis.

Pincer-type impingement – here abnormal extensions of bone from the edges of the socket protrude out (like the pincers of a crab) and abnormally contact the head and neck (“ball part”) of the joint causing pain and damage to the neck of the joint.

What are the symptoms?

The impingement can cause hip pain that is felt in the groin. This is often made worse by prolonged sitting or driving and with certain positions of the hip. If the impingement has caused a cartilage (labral) tear then clicking or catching can also be felt in the hip.

How is it treated?

Both types of impingement can be dealt with by open surgery, mini-open surgery or by key-hole surgery (hip arthroscopy) during which the abnormal growths are trimmed and the damage that has been caused is repaired.

The hip joint contains articular cartilage (which covers the ends of the ball and socket portions that make up the joint) as well as a more flexible cartilage, which surrounds the socket portion, called the labrum.  Both types of cartilage can develop tears.  Articular cartilage tears usually happen with wear of the hip joint, whereas labral tears can occur without wear and can be associated with femoracetabular impingement.

What symptoms can they cause?

Hip pain felt in the groin is common with both types of tear. Labral tears more commonly cause intermittent pains in the hip joint and sometimes clicking or snapping and a feeling of giving way or sudden seizing of the joint.  Specialist examination can reproduce a click that indicates a tear, but an MRI scan is usually required to confirm the problem.

How are the tears treated?

Such tears can usually be dealt with by key-hole surgery of the hip (hip arthroscopy) during which the tears are either repaired or trimmed.  Patients are usually able to return to all activities after a period of physiotherapy exercises.

Sometimes referred to as trochanteric bursitis or iliotibial band syndrome, this is a condition that  causes pain in the upper outer thigh that sometimes spreads down the outer thigh towards the knee.  It can be severe and disabling.  It is sometimes brought on by conditions that make the individual walk differently to normal, such as a foot injury or foot surgery.  Abnormal strains are put on the legs as a result and these can sometimes cause GTPS to develop.  In other cases it develops without a clear provoking cause.

Typically patients complain of being unable to lie on the affected side because this is painful.  This can wake them at night causing disturbed sleep.  It is often confused with pain arising from the hip joint, but in fact the pain originates outside the joint from the soft tissue bursa on the side of the hip, called the trochanteric bursa, and the band of tissue down the outside of the thigh called the iliotibial band.

How can it be treated?

Fortunately, in a majority of cases it can be cured.  Treatment options include physiotherapy, steroid injections, platelet-rich plasma (PRP) injections, low energy shock-wave therapy and in resistant cases surgery (often key-hole type surgery).  In our experience a vast majority of patients can be cured without the need to resort to surgery.

Provoking factors should be addressed if possible.  Appropriate physiotherapy exercises can be successful in curing the problem in many people, but unfortunately it does not work in every case.  Steroid injections are often performed as a next step, but we have found these to be variable in permanently curing the condition.  If symptoms continue, then we tend to use low energy shock-wave therapy (SWT) or PRP injections.

SWT is particularly helpful in cases that have not responded to other measures and has the advantage of requiring no needles and being a treatment that is given in the clinic setting.  It has no adverse effects and 70-80% of people with persistent symptoms are helped by this treatment.  PRP is also a useful treatment.  We tend to use it in the 20-30% of cases that do not respond to SWT.