Hip replacements

SUMMARY

  • arthritis in the hip is very common

  • hip arthritis causes pain, stiffness and difficulty walking

  • the pain can be felt deep in the hip, in the groin, in the thigh or even in the knee

  • early arthritis can be helped by anti-inflammatories, physiotherapy or injections into the joint

  • severe arthritis requires hip replacement surgery

  • there are many different options for different types of hip replacement and these should be discussed with your surgeon

  • about 95% of hip replacement patients report excellent results, with loss of pain and significant improvement in function

  • about 95% of hip replacements are still working fine after 10 years, with about 80% still working well after 20 years


The procedure of total hip replacement (THR) has been practiced for many years now, with excellent reported results. Modern hip replacements should be expected to last many many years, with in excess of 95% of the hips that we put in lasting more than 10 years.

THR involves removing the arthritic bone around a hip and replacing the joint with a new artificial bearing. The hip is a ball and socket joint, with the ball being at the top of the thigh bone (femur) and the socket (acetabulum) being in the side of the pelvis.

 

 The various steps in performing a total hip replacement:-  A, The femoral head is removed. B, the acetabulum is reamed. C, the femur is reamed. D, a plastic cup is cemented into the socket of the hip, a metal stem is inserted down the centre of the femur and a metal ball is placed onto the top of the metal stem. E, the hip is 'reduced' - the new head is relocated into the new socket.

With a traditional hip replacement, the ball of bone (the femoral head) is cut away, and a metal stem is fixed inside the bone of the top of the femur. The metal is fixed into the bone with a special bone 'cement', made of an artificial substance called polymethylmethacrylate, which sets solid. A metal ball is then placed onto the top of the metal stem. The bone of the socket in the pelvis is then scraped out (reamed), and a polyethylene cup is cemented into the pelvis. The metal ball is then located into the new plastic cup, giving a good strong artificial ball and socket joint.




 

 

 A polished double-taper femoral stem with a metal head that sits in a plastic cup. Both the stem and the cup are cemented onto the bone.

A post-op X-ray showing an Exeter total hip replacement cemented into the femur and the pelvis, with a metal ball in a plastic socket.

The results of hip replacements are generally excellent, with in excess of 95% of hip replacements still in place and working well after 10 years.

However, the operation itself should not be underestimated. It requires either a general or a spinal anaesthetic, and the surgery itself can last 1 hours. Patients can, not infrequently, require blood transfusions after the surgery, due to the blood loss that inevitably occurs during the procedure. Patients are generally kept in hospital for something in the region of 5 - 10 days postoperatively, depending on their general fitness.


 Different Types of Hip Replacement
Most traditional THRs use a special type of bone cement to fix the prostheses into the bone of the femur and the pelvis. However, there are many THRs available now that do not rely on cement, and which instead are press-fit into the bone. They are normally textured and/or coated with chemicals (hydroxyapatite) that encourage the bone to grow onto the surface of the prosthesis.

Some companies have developed hip replacements with harder bearing surfaces, such as ceramics or metal-on-metal. These each have their potential merits and potential problems. In the past there have been some concerns with the use of ceramic balls and sockets, where there were cases where the ceramics were too brittle and therefore cracked and broke. Modern ceramics, however, are more reliable and the wear rate with a ceramic-on-ceramic hip can be as much as 1000 times less than is seen in a traditional metal-on-plastic hip.

 

 An uncemented hip replacement. A ceramic socket sits inside the metal acetabular shell, and a ceramic head sits at the top of the uncemented stem. The acetabular shell and the femoral stem are coated in a layer of hydroxyapetite, so that the bone grows onto the surface of the metal.


Other companies have focused on the development of hip replacements using metal balls in metal sockets. However, concerns have been raised about these metal-on-metal bearings, which have now been shown to be associated with various significant potential problems - CLICK HERE for further information.

The very best top-of-the range option currently available for hip replacement surgery is to have pre-operative computerised 3-D imaging performed, to allow detailed pre-operative planning, with the use of uncemented prostheses with ceramic-on-ceramic bearings, with modular necks (to allow detailed positioning) or with custom-made stems (for those patients whose anatomy is 'outside of the norm'). CLICK HERE for further information.