Hip Replacement Surgery

So you have been told that you need a hip replacement.  I will preface this discussion by saying that total hip replacement surgery is very successful surgery in more than 98% of cases.  It not only relieves pain but also provides excellent function.

However, it is an elective procedure and the indication for a total hip replacement is essentially pain and disability which interferes with your lifestyle to a point that your health or your ability to maintain your general health is compromised.  Simply having an x-ray or MRI which shows that you have osteoarthritis (Joint Cartilage destruction), is not an indication for a hip replacement.  The osteoarthritis seen on the x-ray must be clinically proven to be the source of your pain firstly and secondly pain levels or a lack of movement due to stiffness, should be severe enough to warrant consideration for the operation.

A case in point relates to a patient of mine who came to see me having had a total hip replacement elsewhere. However, she was still in a lot of pain.  It transpired, that her x-rays indeed did show that she had osteoarthritis of the hip, however the actual source of her pain was in fact a prolapsed vertebral disc in her back which was pushing on a nerve, resulting in referred pain toward the hip area.  This lady underwent a total hip replacement for an osteoarthritic hip which was not generating her pain and as a consequence was quite unhappy.  Once the disc was removed with spine surgery, her pain resolved.  This story should serve as a cautionary note prior to considering surgery.

The modern hip replacement is a refinement over many decades of the original procedure described by Sir John Charnley in the early 1900s.  Over the years, through trial and error there have been many improvements not only in the materials used but also the approach used to obtain access to hip joint. This is in addition to the preoperative and post-operative care. These involve the anaesthetics, physiotherapy and the use of modern medication, which have  all lead to a safer, minimally painful and more rapid recovery process following a total hip replacement.

In brief, you will be admitted on the same day of the operation.  The operation itself takes anywhere between 45 and 90 minutes and it is very rare that there is excessive blood loss requiring transfusion.  You will be mobilised the same day as the operation and should be discharged home or to a Step-Down facility within 2  days on average following the procedure.

Hip replacements have a 98% success rate i.e. no pain and good functional outcome. This would imply a 1% to 2% risk of complications whether minor or severe.  Approximately 84% or more patient have the "forgotten Hip syndrome" at 3 months post op. This is the point at which they are mostly unaware of the hip.  Having any form of surgery requires a certain degree of trust in your surgeon. It is like flying in an airplane, your trust is placed in the hands of the pilot, i.e., you put your seatbelt on, your tray table back and enjoy the ride.  However, it is wise to know some of the details which I will describe as follows.

One of the more contentious issues in total hip replacement surgery is how to get to the hip joint.  There are essentially three main approaches: from the front, from the back or from the side.  The original approach has always been from the side, later on coming in from the back or posterior approach was popularised.  Since the 1950s, there has been a refinement of the front or anterior approach which has now to a certain degree become vogue.  Indeed, there are a number of surgeons who market themselves by way of the use of the anterior approach for total hip replacement surgery.  An example would be the so-called AMIS approach (anterior minimally invasive surgery).  Firstly, there is no such thing as minimally invasive hip replacement surgery.  The correct term would be less invasive.  This surgery still requires an incision big enough to allow the insertion of the implants, the size of which are determined by the size of your anatomy.  The crux of the matter is that the hip replacement needs to be performed with as little damage to the surrounding soft tissue as possible.  This however must be done in a safe manner. Thus the approach must be one that facilitates good visualisation and access to the bone, in order to put the implants in the correct position. This facilitates avoiding dislocation as well as providing enough vision to be able to recognize intraoperative complications, such as a fracture of the bone during insertion of the implant.  Given that the three approaches provide for this, it is then a question of which one leaves the patient with possibly the quickest recovery.  Notice, I do not emphasize cosmesis as this is truly a secondary consideration when having an operation geared towards alleviating pain and providing normalization of function.

If one adopts a scientific approach, the current evidence would show that the side (anterolateral) approach is marginally inferior to the posterior and anterior approaches. The UK and Australian Joint Registries that review more than 150000 joint replacements annually, have assessed for risk related to surgical approaches. The result is that the posterior approach has the lowest complication rate.

The differences between the anterior and the posterior approaches are still being debated, although there is a trend to slightly quicker recovery for the anterior approach in the 1st few days. In addition, the anterior approach is the only truly muscle sparing approach. However, both the posterior and the anterior approaches do not influence the gluteal muscles that are primarily required for walking and thus both approaches allow for mobilization the same day of the operation.  In my practice I perform both approaches because sometimes the posterior approach is better than the anterior approach in a particular individual and vice versa.  I firmly do not believe that there is a single approach suitable for all patients.  My technique for the anterior approach does not require a traction table as with the well marketed AMIS approach.

My experience with the anterior and posterior approach has led me to the following observations:

With either approach the patients are in the same position with respect to post-operative recovery by about 2 weeks.  My physiotherapists report that the anterior approach does appear to provide for a slightly increased level of confidence with initial mobilization. The length of hospital stay is the same. My surgical experience leads me to believe that the anterior approach results in a more stable hip replacement initially,  and allows for a more confident on-table leg length assessment. However, the anterior approach is not really extensile. In other words, should there be a complication, enlarging the cut to manage the complication, such as a fracture of the femur, is somewhat more complex.  Also the anterior approach access to the hip joint results in a lot more stress placed on the tissues and is not a good idea in patients with osteoporotic bone.  The shape of the patient also can dictate the approach, for instance if a patient has a pendulous abdomen this would get in the way of the anterior approach, whereas if the patient has large buttocks, the length of the incision would be longer with the posterior approach.  Sometimes in excessively muscular patients the posterior approach is better.  It must be said that the posterior approach is the workhorse of approaches to the hip replacement and there is good evidence that it has the lowest complication rate overall.  It is the approach preferred in osteoporotic bone and is used for not only primary hip replacements, but also for all revision hip replacement surgery.  This is because it is a very versatile and extensile approach, i.e., slightly safer than the anterior approach.

From a cosmetic point of view, it must always be remembered that the length of the scar does not dictate how well the wound will heal as the wound heals from side-to-side and not from end-to-end.  What matters is what is done beneath the skin cut and that the surgeon is meticulous with his handling of the soft tissues and bone throughout the procedure.

There are many different designs of implants on the market, produced by numerous companies and these implants are designed to be versatile enough to accommodate all shapes of hip anatomy.  One of the more important aspects of hip replacements are the bearing surfaces.  Those are the bits that have to articulate upon one another and in essence are replacing the biological cartilage surfaces.  Various materials include highly cross-linked polyethylene, ceramic, ceramicised metal alloys and stainless steel metal alloys. The material that usually interfaces with the bone directly is a titanium alloy.  This material is bone friendly as it has a similar amount of bendiness or elasticity compared to that of bone.  The titanium components are usually press fitted into the prepared bone with the use of a fairly large mallet.  This provides for initial scratch fit as well as a press fit with no movement.  Less than 150 micrometers of movement is aimed for in order to allow the bone to grow onto the titanium rough surfaces.  Following insertion of the titanium components, the socket liner and the femoral head are inserted.  These are taper fit designs and are interchangeable and very modular, resulting in hopefully a perfect mechanical construct that mimics the natural anatomy of the patient.  In my practice ceramic-on-ceramic bearings are typically used for the younger active patients, i.e. those under the age of 52years. For older less active ages I often use highly cross-linked polyethylene with a ceramicised metal head.  I no longer use any metal heads. The metal heads are chrome cobalt molybdenum and nickel alloys of stainless steel.  There have been numerous concerns regarding the elution of cobalt and chrome ions at the taper fit interfaces.

The metal-on-metal resurfacing total hip replacement has largely been stopped in Europe. (The term resurfacing is a well-chosen marketing word that implies less surgery. This is NOT the case, as a Resurfacing Hip Replacement is still a Total hip replacement, just of a different design. It in fact demands larger cuts and more muscle and soft tissue release .) There are a few centers in the United Kingdom and America that still do this procedure.  In my practice it is offered to the very active, fit, large males.  Patients of small size, and this typically means most woman, have historically done very poorly with this implant.  There are no real advantages in respect of this implant other than a slightly more normal gait cycle and some studies indicate perhaps a higher level of activity possible with these implants.  However, the metal-on-metal bearing surfaces do result in metal debris that includes cobalt and chrome ions.  These can in some patients result in a biologically adverse reaction which will require early revision. Due to this, patients with resurfacings need annual follow-up with xrays (current BOA recommendation), specifically because adverse reactions to metal debris can be asymptomatic for years while causing bone and soft tissue damage. Despite this I enjoy doing Resurfacing hip replacements BUT the patient needs to be compliant wrt follow-up. Currently there are experimental versions using ceramic in terms of resurfacing, however this is not yet mainstream, and I have some serious concerns regarding future complications for this design because of the mechanical properties of the ceramic material. We shall see what the future holds in this regard.

In terms of bearing surfaces, the modern bearing surfaces each have their pros and cons.  The new cross-linked polyethylene is an excellent bearing surface and very forgiving and currently with a ceramicised metal head or ceramic head,  the wear rate is such that the hip should last 25 to 30 years.

Ceramic-on-ceramic bearings however still have the lowest wear rate of all bearings.  This is what we call a hard-on-hard bearing.  Historically there have been issues with brittleness and therefore potential for these bearings to break.  The implant I use has a patented titanium band integrated with the ceramic liner and there are no reported breakages of this design.  Further issues as it relates to ceramic bearings are that on occasion these can result in a squeaking noise.  The incidence of this varies but generally it is approximately 1% to 3% of cases and usually only when the patient is moving the hip into extremes of position.  The beauty of ceramic is that there is no reported biological response to the little bit of wear debris that is created.  That is opposed to any other materials such as the metal implants and/or the polyethylene implants. This lack of response to ceramic debris leads to the lowest rate of aseptic lysis (loosening of bone attachment to the implant), which is often a reason for revision.

The details of the materials we use for hip replacements are a textbook’s worth of discussion and any of these concerns can be directly discussed at consultation.

The possible surgical complications associated with hip replacement generally equate to between 1% and 2% and these can vary from minor to severe.

The top two surgical risks are infection and dislocation. See below.

Infection is the number one reason for re-operation after a joint replacement. My infection rate for primary hip replacements is below 0.5%. I am completely OCD when it comes to perioperative preventative measures, as are most surgeons. See Infection prevention Protocol. Did you know that up to 70% by weight of the DNA that constitutes you as an individual actually belongs to the bacteria and viruses that live symbiotically in and on you? It is these same organisms that can result in an infected joint replacement. There is growing evidence that all implants are in fact already colonised by bacteria by the end of the operation. The development of infection is dependent on the volume of colonization, this is controlled by the surgeon and the patient’s health or immune status or ability to fight or control these organisms. Food for thought!

Further risks are the concerns regarding anaesthesia and the reaction to medication.  This is a separate risk factor which will be influenced by the general physiological status of the patient, for example a patient with heart disease will have more anaesthetic risk.  Most chronic medical conditions are normally stabilised prior to any form of a hip replacement surgery.  From my side, one of the main concerns is whether or not you are on any form of blood thinner as we will need manage this perioperatively.  Typically if you are on a form of cardiac aspirin this will need to be stopped 4-5 days prior to surgery. If you are on any form of low molecular weight heparin, again this will need to be stopped prior to surgery with conversion to a shorter acting heparin and reinstitution of your usual medication following surgery.  Prior to surgery the shorter acting heparin is stopped for 24 hours. Other modern blood thinners in tablet form, like Xarelto or Pradaxa must be stopped 48hrs before.

There is quite substantial evidence that initial outcomes perioperatively are negatively affected with any form of anaemia.  Routine blood tests are always done to check for this at least two weeks prior.  I would suggest that prior to surgery you should supplement with iron and basic vitamins in terms of general nutrition. Other chronic conditions such as Diabetes, immune related disorders, chronic use of steroids etc. all increase the risk of infection. It is paramount that these conditions are well controlled.

Generally with the modern technique there is not too much bleeding intraoperatively.  For the patients where we have concerns such as Jehovah’s Witnesses and and/or the revision cases we normally use a cell saver technique where the blood lost is placed through a closed system of filters and re-infused into the patient; approximately half the volume lost.  Again, preoperative anaemia must be corrected.

There is a lot of evidence regarding the insidious effects of smoking. Certainly, when it comes to having surgery, smokers have higher complications from heart and lung problems to surgical wound healing and infection. So do yourself a favour and stop smoking at least one month before surgery and preferably for life.

Obviously all other general risks associated with surgery do apply.  These include accidental injury to nerves and vessels surrounding the area as well as major anaphylactic reactions to medication.  These are fortunately very rare.  We have mentioned already the risk of fractures during the insertion of the implant.  Any fractures that occur can be managed immediately at the time of surgery, bone is the only organ in the body which heals to its original state and therefore the outcomes are normally good.  It is only the mobilization postoperatively which will be limited for a period of time in order to optimize the fracture union.

The second most common risk factor peculiar to hip replacement surgery is an unstable hip after surgery and resultant dislocation.  If your hip does dislocate we normally relocate the hip and reassess, but generally three strikes and you are out, i.e. if you have three dislocations within a short period of time, then revision is indicated.  This is often a difficult scenario to deal with, and is avoidable by means of appropriate positioning of the limbs perioperatively. All of this will be taught to you by the physiotherapists both before your surgery (if you go to a hip replacement “antenatal class” as I call it) and after the surgery while in the wards. It is up to me as the surgeon to place the implants in the correct position and with the least amount of muscle damage, thus minimizing the risk.  Sometimes we find that later on in life when you have perhaps had spinal surgery with fusions it can change the inclination of the pelvis which can then result in dislocations, however, this is a rarity.  Other causes of late onset dislocation are historically the wearing of the bearing surfaces and/or loosening of the implants as time goes by.  Again the modern implants tend to have a lower rate in respect of these problems. The modern hip replacement also uses larger head sizes. This too results in lower dislocation rates. In the older less steady patient I use a dual mobility head and cup design which is even more stable but there is a small compromise on wear rate.

It is paramount that I spend time and energy templating preoperatively and converting my planning to the surgery itself in order to facilitate correct leg lengths following surgery.  Leg length discrepancies can occur, normally they are less than 1 cm which is internationally acceptable and in most cases patients are very rarely aware of this as a problem. We aim for less than 1 mm difference. Other issues can intervene with regard apparent leg length discrepancies and these include fixed curvatures of the spine which result in pelvic tilt.  At least 80% of people naturally have a slight difference in their leg lengths, this is a normal phenomenon.  My aim as a surgeon is to recreate the center of rotation of your hip and the correct tensioning of the soft tissues around the hip in order to prevent dislocation primarily and optimize the function of the muscles around the hip.  If this is done, in most cases the leg lengths will be within a few millimeters. ( see section on robotic or computer enhanced techniques)

Further concerns are deep-vein thromboses.  Some people have a familial tendency to develop this, therefore a family history is important.  There are numerous risk factors associated with the development of deep-vein thromboses and the primary one is not moving after surgery, so muscle activity facilitates blood circulation and therefore less risk of clotting in the veins. Having active COVID-19 and  Smoking are a high risk factors as well.  All my patients will be on a blood thinner, ultimately in the form of a small dosage of aspirin or similar, on a daily basis for at least one month.  Whilst in the wards and initially mobilizing you are provided with  arteriovenous foot pumps in order to massage the feet and facilitate circulation of blood.  Travelling long distances overseas is not recommended within six weeks of surgery.  If it is absolutely necessary it is essential to be on a slightly stronger blood thinner which one can obtain and we will give you the necessary prescription for this.  Usually the peak danger period for the production of blood clots in the veins is between 8 to 10 days post-surgery.  There are a few other odd possible complications peculiar to surgery around the hip and this includes the formation of calcium deposits within the muscles known as heterotopic ossification.  This is a rare event nowadays due to the better handling of soft tissues and I also use at least 3 litres of sterile fluid after surgery in order to wash out the hip which not only prevents infection, but also the incidence of calcification within the muscles. The use of postoperative non-steroidal anti-inflammatory medication which we give in any event for pain control, also assists in lowering the incidence of this complication.  Some patients, such as those with renal failure and other forms of calcium metabolism problems will also be at risk of developing heterotopic ossification and you will be made aware of this at the preoperative consultation.

Hip replacement surgery is not without risk, as with any other form of surgery and anything can happen during an operation. This may include heart attacks, strokes and even death on the odd occasion. Fortunately these are truly rare events but nonetheless as a patient you need to understand that any operation has its risks.  As always however, it is better to look at the glass which is half-full and in most cases 98% of patients having hip replacements do exceptionally well and after three months often forget that they have had the surgery.  This is a good operation and provides a good functional outcome with good pain relief.

As clinicians we like to review our patients in terms of measuring the outcome of their operations.  Obviously I would want you to have a great outcome with no pain and good function.  Internationally there are numerous scoring techniques which we use to assess these outcomes as an objective measure of the success rate of our operations.

Successful surgical outcome from a surgeon’s perspective is simple. I want you to have a pain free uncomplicated joint that is stable and provides you with realistic function. (It is an artificial joint after all). Hopefully as a patient this aligns with your expectations defining a good outcome.

You will see on my website that there is access to appropriate outcome questionnaires related to the hip and the knee which you fill in prior to having the operation and thereafter as a form of long-term follow-up in this regard.

What is interesting about outcomes however, is that other than surgery there are other factors. Subsequent results of all forms of surgery are strongly influenced by essentially the emotional state of the patient and their mental attitude and expectation prior to going in for the operation. This is independent of the surgery and surgical team. There is a direct correlation with poor outcomes in hysterical patients, overly emotive patients, patients who suffer from a great deal of anxiety and those who have secondary gain. If you are on medication, remain compliant. Take control of your health by optimizing your meds, your diet, your activity and cutting out the bad habits and stress factors as much as possible. Perioperative compliance wrt physiotherapy and medication is under your control and will influence your risk of complications and by extension your outcomes.

As a surgeon, it is not in my interest for my patients to have a poor outcome, therefore in all cases without exception, I will endeavour to perform at my very best in order to have a great result.  In life it is unfortunately true that there are some things we are unable to control and as a patient one has to place your trust in the surgeon as much as possible. Much like getting into an airplane and travelling, you would trust the pilot to get on with his or her job and do it well so you can enjoy the ride.  As the patient or “passenger”, the nurse (air hostess) and or the hospital food (airline food) may not be perfect, but please keep the bigger picture in mind, which is arriving at your destination safely.

There is no doubt that a positive and calm approach to any operation results in better outcomes following surgery.