Information on hip replacement and some frequently asked questions
Hip replacements
The natural hip joint is a ball and socket joint which, with time, may wear out. When this happens the joint becomes steadily more painful and eventually a hip replacement is the only way to get rid of the pain and improve your quality of life.
What is an hip replacement?
A hip replacement, often referred to as a hip implant or implant device is, in more basic terminology, an artificial implant that replaces a hip joint that is damaged.
Joint replacements are nearly always carried out because of pain that cannot be controlled by other methods such as painkillers, physiotherapy or other surgery. The most common cause of pain is osteoarthritis or inflammatory arthritis.
The aim of a hip replacement is to replace the worn out joint surfaces with new artificial surfaces. There are many different types of hip replacement available.
The traditional type of replacement, which has been in use for many years, is a metal ball on a stem cemented into the femur (thigh) and a plastic socket cemented into the pelvis. This is still the most commonly used type of hip. In the older patient it is highly unlikely that it would wear out and need to be replaced again within their lifetime.
If you are a younger, more active patient your specialist may have advised you that a hip replacement without using cement or with harder bearing surfaces, such ceramic-on-ceramic may be more appropriate.
Alternatively, your specialist may have advised a type of replacement known as hip resurfacing. In this operation, instead of the ball part of the hip joint being removed (as in a standard hip replacement), it is cut to shape and a new metal surface cemented on. The socket also has a metal surface and is fixed into the pelvis without using cement.
Ask your specialist about what type of hip replacement they recommend and what the advantages and disadvantages of it are.
Introduction to hip implants
Hip replacements are made up of a number of parts (components) which can be made of different materials. As a result, the surgeon can select a number of different combinations to help meet a patient’s needs.
The main implant components are described below:
- Femoral head
- Bearing surfaces
- Femoral stem
- Acetabular component
- Metal-on-plastic
- Ceramic-on-plastic
- Ceramic-on-ceramic
In a continued effort to prevent the loosening of artificial hip implants, after years of wear, top alternative bearing surfaces have been used including metal-on-metal and ceramic-on-ceramic. Here, the head and cup are made of the same material.
The movement between the femoral head (ball) and acetabular cup (socket) is known as the bearing surface. As with any two surfaces, repeatedly rubbing them together will cause the surfaces to wear and over time this produces minute particles of debris. These particles can spread into the tissues around the hip joint and this has been shown to have a role in artificial hip joints becoming loose over time.
This part of the joint replacement is seated in the thigh bone (femur) after removal of the ball at the top of the bone (the patient’s existing femoral head). It may be cemented in place using bone cement. Alternatively, it may be held by press-fit without use of cement. This tends to rely on a tight fit into the space in the centre of the thigh bone (known as the shaft of the femur) and in some cases, subsequent bone growth onto the surface of the implant itself.
Sometimes a special coating is applied to encourage this.
This is the cup or socket of the hip and there are two basic types. Cementless cups generally have a metal shell with a back that encourages bone growth into it. They are fitted tightly into the prepared hip socket and the fixation may be reinforced with screws. A liner is then fixed into the shell. The liner may be plastic, ceramic or metal.
Cemented cups are made of a type of hard-wearing plastic (known as ultra-high molecular weight polyethylene). This type has only undergone minor modification since the 1960s. They are fixed into the prepared hip socket (acetabular) with bone cement.
The original hip replacement had a metal head articulating with a plastic cup. This produces minute plastic debris but is still in widespread use and long-term studies suggest that it is suitable for older patients. Efforts to reduce the amount of debris released and make hip replacements last longer have led to efforts to make changes to the bearing surfaces.
A new form of highly cross- linked polyethylene has better wear properties than standard polyethylene in testing. Studies to look at the wear rates of this modified plastic cup in patients are encouraging, and now show that over 20 years or more this type of material results in a longer lasting metal-on-plastic hip replacement.
The use of a ceramic head, as opposed to a metal one, has also been shown to reduce wear rates when used with plastic cups in testing and clinical studies. The ceramic surface is smoother and more resistant to scratching.
Early results from the NJR are very encouraging and at 10 years this is the bearing with the best reported outcomes.
In a continued effort to prevent the loosening of artificial hip implants, after years of wear, top alternative bearing surfaces have been used including metal-on-metal and ceramic-on-ceramic. Here, the head and cup are made of the same material.
Special note on resurfacing
Resurfacing procedures use a cementless hip acetabular cup, but instead of the femoral head being removed, it is reshaped and a metal cap placed over it. Both components are made of metal. NJR data has confirmed other reports that in most patient groups they have an inferior performance to conventional hip replacement and they are now not recommended in older patients, women or smaller men because of high failure rates.
Special note on metal-on-metal procedures
Metal-on-metal hip replacements became popular in the mid-2000s, but the NJR identified very poor results for this type of implant. Their use has now largely been abandoned.
Thinking about your treatment options
Joint replacement is a highly successful operation that can bring relief from pain and improve mobility. Joint replacements are very hard wearing and most patients will never need further surgery. However, going through the process can be baffling and many patients do not always understand their options or the detail of their treatment plan. It is important you feel supported by your surgeon when discussing your available options.
Working together with your practitioner is known as shared decision-making.
Shared decision-making recognises all the different factors in your life that will lead to better quality decisions, from your own research, surgeon’s advice, through to the support from your family and friends.
Sources such as this National Joint Registry information should make you feel confident in asking questions about your surgery, your implant and your recovery. There are some commonly-asked questions below. You may wish to write these out and make some notes. Whatever the reason for your joint replacement, there are many others going through the same process, and it may help to know you are not alone. There is additional support out there for you on shared decision-making as well as advice on looking after yourself before and after surgery.
FAQs
As you make plans for your joint replacement surgery it may be helpful for you to make a note of any questions or queries you may have either for your surgeon or clinical team at the hospital. Some commonly asked questions are:
- Do I need joint replacement surgery? Are there other options available to me?
- If I do, how should I prepare for surgery?
- What type of implant are you recommending? What are the pros and cons?..
- What surgical technique would be used? What are the pros and cons?
- What should I know about my aftercare?
- What do I need to think about when I return home after my operation?
Further information about hip replacement
There are many organisations that provide additional general information about joint replacement, including specific guidance before and after surgery as well as online discussion forums. Please see links here for some of these, such as: patient groups including Versus Arthritis; and The British Hip Society (BHS) who all have further useful advice.
The National Institute for Health and Care Excellence (NICE) recently published Quality Standard Guidelines for Joint Replacement (hip, knee and shoulder). This quality standard covers care for adults before, during and after primary elective hip, knee or shoulder joint replacement and is another useful source of reference. You can find this document here