If you have done any research on hip replacement, you will realise that there are lots of choices about which implants to use and how they are put in your body. Use this short guide to develop your understanding of the implant that your surgeon may recommend for you.
There are five main areas when it comes to making a choice on the best implant for a hip replacement:
- how the implants are fixed in place
- what material the bearing surfaces are made of (bearing surfaces are the bits that actually make contact with each other)
- the surgical approach used to put the implants in
- whether the implants are “off the shelf” or custom made, and
- whether you use a patient specific guide or robot to help with the surgery.
How are implants fixed in place?
Hip replacements have a stem that is placed in the femur (thigh bone) with a ball on the top and a socket that is put into the pelvis. These implants can either be fixed in place with bone cement, or wedged into the bone with a coating on them allowing the bone to grow onto the implant surface (this technique is called “cementless”).
Both techniques are effective. Many surgeons opt for cementless fixation in younger patients as they seem to do at least as well as cemented stems. Also, if the hip replacement ever needs replacing (which is more likely if you are young), they are easier to take out and replace.
With cementless fixation there is a slightly higher risk of breaking the bone whilst putting them in, consequently cement is often the fixation of choice in those patients who are older and likely to have weaker bone.
Many surgeons will cement the stem in the femur and put a cementless socket in the pelvis (a “hybrid” hip replacement). This option gives maximum flexibility in terms of positioning the implants and the choice of bearing surface.
As a patient of Grosvenor Orthopaedic Partners we will discuss this in more detail as part of the consultation process and can answer any questions you may have.
What bearing surface should I have?
The bearing surfaces are the parts of the hip replacement that are in contact with each other. The ball at the top of the femur can be made of metal or ceramic. The lining of the socket can be plastic, ceramic or metal.
In most cases a hip replacement will have one of the following:
- a metal head in a plastic liner
- a ceramic head in a plastic liner
- a ceramic head in a ceramic liner.
All of these work well. Ceramic is harder wearing than metal or plastic so should last longer, but there is a small chance of squeaking with ceramic on ceramic bearings. Ceramic heads with a modern plastic liner have similar outcomes to ceramic on ceramic bearings without the risk of squeaking, consequently the number of hip replacements with this combination is increasing.
We no longer put metal heads on standard hip replacements with metal liners of the socket, as they are not considered effective.
However, resurfacing operations, as undergone by Sir Andy Murray, are still available for men with large hips.
If you do have a hip resurfacing it is recommended that you have regular blood tests, x-rays and potentially MRI scans to ensure the implant is functioning properly.
What is a surgical approach and which should I have?
A surgical approach basically determines where the surgeon makes their incision and which muscles they divide, or move, to get to your hip.
There are three main hip approaches:
The anterior approach to hip replacement
The anterior approach goes through the front of the hip. It has the advantage that no muscle needs to be cut, so you tend to recover faster and need less painkillers, though by 6 weeks after the operation there is no difference between this approach and the posterior approach.
The downside to the anterior approach is a slightly higher complication rate than with the other approaches. Not everyone is suitable for an anterior approach.
The lateral approach to hip replacement
The lateral approach goes through the side of the hip. This involves detaching some of your abductor muscles.
The advantage to this approach is that there is a very low risk of the hip popping out of joint, but the downside is that if the abductor muscles do not heal properly you can be left with a permanent limp. This approach is becoming rare amongst hip surgeons.
The posterior approach to hip replacement
The posterior approach goes through the back of the hip. During this approach the big gluteus maximus muscle is split and some small muscles are detached from the back of the hip, these are all repaired at the end of the operation.
This is the standard approach for most hip surgeons in the UK. The advantage is that it offers the best view of the femur and the socket, the downside is that the split/detached muscles have to heal so it can ache for a bit longer than the anterior approach.
As a patient of Grosvenor Orthopaedic Partners we will discuss with you the most appropriate approach based on a number of factors, including your overall health and age.
Should I have a custom made hip replacement?
Custom made implants are produced exactly to your bone specifications and are a desired option for some patients.
These implants can be very useful if you have extreme anatomy, but there is no evidence that they function better than standard “off the shelf” implants.
Robots and patient-specific instruments
There is plenty of technology available to help the surgeon place the implants exactly where they want them.
At the moment there is not much evidence to say that this technology produces better results than standard surgical techniques, however research is ongoing.
“We are currently involved in a research trial looking at the Corin OPS system. Unlike all the other systems, this product not only helps the surgeon accurately place the implants using patient specific instruments, but also analyses the optimum place to position the implants according to how your spine and pelvis moves.”
Simon Newman, Consultant Orthopaedic Hip Surgeon at Grosvenor Orthopaedic Partners
Choosing your hip surgeon
Ultimately, your choice of surgeon probably has the biggest impact on how your hip replacement operation goes. Find someone you trust and let them use the techniques and implants they are familiar with as that is most likely to produce an excellent result.
Choosing an orthopaedic surgeon that specialises in hip surgery is essential. The National Joint Registry (www.njrcentre.org.uk) publishes the number of joint replacements each surgeon performs. A specialist hip surgeon is likely to be doing at least 80-100 per year.