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TOTAL HIP REPLACEMENT

Hip replacement surgery is exactly what it ‘says on the can”. It is an operation that results in the replacement of your hip joint (made of bone and cartilage), with an artificial man made hip joint (made of metal, polyethylene or ceramic).

Of all the operations performed on humans, if one looks at the effect on quality of life as an end point, two operations get the “Nobel” prize. They are eye lens replacement for cataracts and hip replacement surgery for arthritis of the hip.

The need for a hip replacement is normally due to irrevocable damage to the hip joint. This damage would usually result in major disability due to pain and / or restricted range of movement (stiffness). Some of the causes of damage to the hip leading to this outcome are as follows:

Infection of the joint, often from childhood, can result in pus in the joint which rapidly destroys cartilage. In SA one of the infectious agents can include tuberculosis, more often seen in adults. Adults, with immune system dysfunction, are also at risk of joint infection as is the case with HIV, alcoholism, old age or malnutrition.

Inflammation of the joint due to general body (systemic) disorders such as Gout, Rheumatoid Arthritis, Seronegative Arthritis and Auto-immune or Connective Tissue disorders, will eventually lead to destruction of the cartilage. There are many other rarer diseases eg Haemophilia, Sickle Cell disease etc., which lead to joint destruction with chronic inflammation as the mechanism.

Trauma due to accidents or repetitive trauma due to marathon running or impact sports, will ultimately result in cartilage destruction. Fractures of the hip joint may affect blood supply to the head (ball) resulting in collapse and joint destruction. The best functional outcome in these cases is to perform a hip replacement.

Tumours of bone and joint that affect the hip can be treated with a joint replacement if discovered early.

Avascular Necrosis (AVN) (Death of bone due to loss of blood supply and therefor oxygen) will result in collapse of the head (ball) of the hip joint, and without the bone to support the cartilage the joint will disintegrate. Causes include alcoholism especially binge drinking, chronic oral steroid use, chemotherapy and fractures of the neck of femur. Sometimes no cause is found and this is known as Idiopathic AVN.

Osteoarthritis or Wear and Tear or Degenerative or Old Age arthritis is the leading indication for hip replacements. The cause of this is a mechanical process with in some cases a genetic or familial predisposition. It is the final result or end point of many of the above mentioned causes. Femoro-acetabular Impingment is one of these causes and will lead to cartilage damage and Osteoarthritis due to mechanical forces causing cartilage damage.

Benefits and Risks of THR

This is what it is all about when deciding to have a hip replacement. The benefit is pain relief and in some cases improved range of motion while the risk is in total 1 – 2 % and includes all of the following:

  1. Infection. This is one of the complications to avoid and can be superficial or deep. Minor wound infections can be treated with antibiotics but deep infections often require aggressive management with repeat operations. This is to remove the infection mechanically with washing if caught early, or removal of all the implants, cleaning the bone and inserting a temporary spacer which is replaced with a new hip implant after 6 to 8 weeks. This is not a pleasant scenario and is one of the biggest risks in joint replacement surgery.
  2. Dislocation. Because of the mechanical nature of a hip replacement, if you try to put your ankle around your neck you will dislocate the hip. Deep bending and crossing the legs are also risky. For the first 3 months until the capsule has healed with dense scar tissue there is an increased risk of dislocation. The physiotherapists will teach you the do’s and don’ts with respect to avoiding this complication. You will be provided with access to a toilet seat raise and a ‘ helping hand’ extendable claw, to assist with daily activities.
  3. Deep Vein Thrombosis (DVT) and Pulmonary Embolism. (Blood clot in the deep veins of the leg and risk of this shooting up into the lung and heart obstructing circulation). This is a reality with any major lower limb surgery. Some people are more at risk than others but all hip replacement patients will get medication for thinning the blood, and will be kicked out of bed as soon as possible. Movement results in muscle activity and these act as pumps that cause movement of blood in the veins. The more movement the less risk of clot. Medical prophylaxis continues for 5 weeks after surgery, and despite this some people still get clots but embolization is far less.
  4. Blood loss requiring transfusion. This is, fortunately not that common because the average blood loss is only approximately 300 mL. Also there are many other methods of stimulating the bone marrow to produce New blood.
  5. Damage to nerves and blood vessels.This risk applies to any operation and great caution is taken to avoid injury to these structures.
  6. Fracture. When inserting the new hip there is a certain degree of force required and sometimes the bone can fracture. This is a rare complication, however the bone will heal to its original state and the only impact will be a delay in rehabilitation following surgery and the use of crutches for a longer period of time.
  7. Leg length discrepancy.Great care is taken to normalise the leg lengths during hip replacement surgery. The priority however always remains a stable hip with the centre of rotation in the correct position and the lever arm distance for the muscles to be recreated. Sometimes this can lead to slight lengthening of the affected leg but this should never be more than 1 cm which can easily be compensated for, and which is often not noticed by the patient.
  8. Heterotopic bone formation.(Calcific deposits in soft tissue related to scarring). This sometimes occurs after total hip replacement. It is unpredictable. Prophylactic measures to prevent its formation include localised radiotherapy and high-dose of Indomethacin anti-inflammatory for two weeks. These measures are not routinely undertaken because of the morbidity associated with this. Instead care is taken during surgery to disturb the muscles as little as possible and after the surgery is done the wound is washed with at least 3 L of sterile fluid before closure.
  9. There are many other unforeseen and very rarer complications which includes the risk of anaesthetics and the effect on the heart and lungs which in some cases can lead to death. This is the reality and the risk one takes with any operation.

I will end this section by saying that the benefit of pain relief and in many cases improved range of motion following a hip replacement, can be guaranteed up to 99% of cases. It is an excellent operation in the right patient with the right indications. It is however in most cases an elective procedure.

Types Of Hip Replacement Implants (The Hardware)

Broadly speaking there are two types of hip replacement.

    1. Total hip replacement and these are subdivided into 3 types.
      1. Cemented
      2. Hybrid
      3. Uncemented

These types will incorporate different materials with respect to the ball and socket otherwise known as the bearing surfaces. These bearing surfaces have a defined Wear rate. The following is a list in order of the least wear rate to the most:

      1. ceramic on ceramic
      2. metal on metal
      3. ceramic in highly cross-linked polyethylene
      4. Oxinium in highly cross linked polyethelene
      5. Metal in in highly cross linked polyethelene

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  1. Resurfacing total hip replacement of which there are various designs.
    The original hip resurfacing design is the Birmingham Hip Resurfacing and a more recent advance on this design is the Birmingham Mid-Head Resection Resurfacing.
    Resurfacings are all metal on metal bearings and in the future there may be ceramic on metal or Oxinium on Oxinium but the latter is still in the research stage.

The type of implant to be used in your hip replacement will depend on a number of factors:

  1. Age
  2. Activity level
  3. Sex
  4. Underlying cause for the Hip joint destruction
  5. Quality of bone
  6. Allergies
  7. Geometry of bone
  8. General physical condition and organ function

Generally the metal on metal resurfacing procedures are best for young, large and active males.

Ceramic on ceramic bearings are for young active individuals especially women and the ceramic or Oxinium on highly cross linked polyethelene is good for the older active age groups.

If the bone stock is good then uncemented stems are used and if there is osteoporosis then cemented stems are used. Cemented polyethelene sockets are very rarely used nowadays. Most sockets are uncemented metal sockets with either ceramic or highly crosslinked polyethelene liners.

There are some other varieties of hip replacements known as Bipolar or Tripolar hip replacements which are mostly used in fractures of the neck of femur (thigh bone) of the hip joint. Other indications are for tumour surgery and in the elderly patient who is not that mobile of if there is an increased risk of dislocation due to dementia for example.

Adressing some misconceptions in hip replacement surgery

    1. Surgical approaches
      There are numerous surgical approaches to the hip for the purposes of hip replacement surgery and some of these have been popularized in the lay press and used by some surgeons to market themselves. Suffice it to say that there is no level one evidence to say that one approach is better than the other and none of these approaches are new as they have all been described more than 2 decades ago. Minimally invasive surgery was all the vogue a few years ago but these small cuts resulted in malorientated implants and complications resulting in revision surgery. All modern surgical approaches apply a less invasive principle with an emphasis on protection of soft tissue. Remember that wounds heal from side to side and not from one end to the other, so the length of the scar is only a cosmetic issue and does not have a bearing on the outcome of the surgery. There is only evidence to show a trend to a shorter hospital stay for the pure anterior(front) approach and the posterior(back) approach to the hip.
    2. Resurfacing total hip replacement versus ordinary total hip replacement
      Resurfacing hip replacements main advantage is that it is bone conserving because the neck of the femur is preserved. Because of this however the surgical approach is larger and the recovery slightly longer initially, but at 3 months all patients are at the same level even if they had a less invasive ordinary hip or total hip replacement. Total hip replacements require the neck to be removed which allows more space to operate and therefore the incision is shorter.

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  1. One size fits all
    Hip placements are not all the same in the same way that patients are not the same. As time has gone by and medicine has advanced and as evidence has been gathered, the individualization of hip replacements has become more refined. As a patient you should be assessed holistically taking all parameters into consideration before a decision is made regarding the correct implant for you.
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