Information on knee replacement and some frequently asked questions

Knee replacements

The knee is the largest joint in the body and it is also one of the most complex.

The knee joint is made up of four bones, which are connected by muscles, ligaments, and tendons:

the femur, which is the large bone in the thigh
the tibia, which is the large shin bone
the fibula, which is the smaller shin bone, located next to the tibia
the patella (otherwise known as the knee cap), which is the small bone in the front of the knee.

With time, the bones may wear out. When this happens the joint becomes steadily more painful and eventually a knee replacement is the only way to get rid of the pain and improve your quality of life.

What is a knee replacement?

Joint replacements are nearly always carried out because of pain that cannot be controlled by other methods such as weight loss, muscle strengthening, painkillers, physiotherapy or other surgery. The most common cause of pain is osteoarthritis.

A total knee replacement procedure consists of replacing the diseased and painful joint surfaces of the knee with metal and plastic components shaped to allow continued motion of the knee. There are many different types of knee replacement available.

The traditional type of total knee replacement involves replacing the bone at the lower end of the femur (thigh bone) and replacing the bone at the top of the tibia.

On occasion, only part (either the inner or outer bit) of the knee joint needs replacing. This type of procedure is called a unicondylar knee replacement.

You should ask your specialist about what knee replacement they recommend and what the advantages and disadvantages of it are.

Introduction to knee implants

Almost all total knee replacements use a metal femoral component that is fixed to and curves around the bottom end of the thigh bone (femur). This moves against a hard- wearing plastic (polyethylene) liner. This liner is normally attached to a metal tibial tray at the top of the shin bone (tibia) but can be fixed directly to the shin bone. The tibial component will have a stem going into the shin bone to provide additional stability.

Implants can be cemented (fixed with bone cement) or cementless (without bone cement).

Implant types

Bicondylar or total condylar knee replacement: an implant attached to both parts of the shin bone and thigh bone. A knee cap replacement (patella) is often used as well.

Patellofemoral: a two-piece knee implant that provides a joint between the knee cap (patella) and thigh bone. The patella component is made of hard-wearing plastic.

Unicondylar: an implant attached to only one part of the shin bone and one part of the thigh bone, sometimes described as a partial knee replacement.

Implant stability levels

With knee replacement procedures, different implant types offer different levels of control over stability, or constraint, within the joint. The level of stability offered by the implant and the best option for a patient will be determined by their needs in consultation with the surgeon – instability is a reason for failure of knee implants.

The following types of constraint (stability levels) are analysed by the NJR:

Unconstrained
Posterior-stabilised
Constrained condylar or hinged / linked

The artificial components making up the knee joint are not linked to each other and have no stability built-in. It relies on the patient’s soft tissue, ligaments and muscles for stability.

Some stability is built in to these designs, the cushion of the plastic tray component fixed to the shin bone has a raised surface with an internal post that fits into a special bar (called a cam) in the femoral (thigh bone) component. The pieces work together to provide additional stability to the knee as it bends and straightens.

Where the components fitted to the thigh and shin bone are attached with a hinge type mechanism. This is used when a patient’s knee is highly unstable and the soft tissue and ligaments would not be able to support other types of replacement for example, in severely damaged knees or where a very elderly patient is undergoing a re-do (revision) replacement. This type of joint will have greater limitations on the range of movement and is not expected to last as long as other types. It requires more invasive surgery to place larger implant stems into the thigh and shin bone and also puts additional stress on the bones.

The plastic insert component fixed to the shin bone is attached firmly to the metal part beneath. The metal femoral component, attached to the thigh bone, rolls on this cushioned surface. This type of bearing may reduce the level of pain experienced following the procedure but in some cases, excessive activity or weight gain can cause a fixed bearing to wear down more quickly.

The plastic insert is less firmly fixed to the metal part beneath, it is more mobile and requires support from the soft tissues around the joint. This allows it to rotate short distances. It may allow more movement but there is a possibility of dislocation.

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, your 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?

Do I have to have a knee replacement? What are the alternatives to surgery?

The final decision to have an operation or not remains with you the patient. It will be based on the risks and benefits of having a knee replacement or choosing not to (these choices should be made clear to you). It may be that other options are available including, but not limited to, ankle supports, medication, physiotherapy, weight loss or other lifestyle changes.

What healthcare staff will be involved with my treatment?

Once it has been suggested to you (commonly by your GP) that a knee replacement may be advisable, you may well be referred to a specialist at a musculoskeletal clinic (MSK) or another GP with a speciality in the area for further assessment.

If you are then referred to hospital you will see an orthopaedic surgeon or a member of his or her team. This is usually followed by a pre-surgery assessment clinic(s) where you may be seen by nurse practitioners. Either at this clinic, or on the day of your surgery, you will also see an anaesthetist to discuss options for anaesthesia and pain relief.

These appointments are also the times when you are most likely to receive information about the registry and be asked whether you would like to consent to have your personal details recorded. Your hospital should ask you to consent to your details being entered into registry , and we recommend that you do. You can see our page about patient consent on this website for more details about why. Please ask for the NJR consent form if it is not offered to you.

During your hospital stay, you might also see an occupational therapist or physiotherapist who will advise you on your aftercare and help you prepare for your recovery after the hospital stay.Together, these healthcare staff make up what is commonly called your healthcare or clinical team.

Can I get a second opinion?

The appointments you have prior to the operation (referrals to a musculoskeletal clinic and/or hospital-based assessments) are designed to further analyse and discuss your GP’s initial diagnosis. If you are unsatisfied having met with your surgeon, you can return to your GP and ask to see a different surgeon.

You could also use services like NJR Surgeon and Hospital Profile at https://surgeonprofile.njrcentre.org.uk/ to find out more about the hospitals and surgeons that provide services in your area. The service currently covers England but may extend to Wales and Northern Ireland in the future.

Can I choose which hospital and surgeon perform the operation?

In principle, yes —you do have the option in England to be referred to a specific hospital or surgical team (options may be more limited elsewhere). Of course each individual case is unique, as are the reasons for requesting a specific hospital and will need to be justified, as do any costs and other implications associated with a request to be treated at a non-local hospital. The NHS is not able to provide a commitment that a specific surgeon will carry out your operation.

What are the risks involved with having a joint replacement procedure?

The overall risk involved in joint replacement is very low. With any surgical procedure there is a small risk of medical complications such as heart attack, stroke and developing blood clots (thrombosis). Infection is rare, typically less than 1%. Other surgical problems are also rare, but include stiffness, instability, fracture, nerve damage, and persistent pain and stiffness. Your surgeon will go through all of the risks before you sign a surgery consent form.

The NJR patient decision support tool

The NJR patient decision support tool (for hips and knees) has been designed for the patient to use alone, or with their clinician, to explore more understanding about their own particular risks. (Link)

Patients should discuss with their surgeon any specific information they may want to know with regard to of the duration of an implant device.

What kind of implant (artificial joint) will be used? Are there options?

There are several types of implant largely described by how they are put together and the materials that they are made out of. As part of your hospital-based assessments, the most suitable device for your individual situation will be established and you will be able to discuss this choice with your surgeon. The most regularly used implants and options are outlined above Evidence on the revision rates for different types of implant and for different brands of implant can be found in the full NJR Annual Report at https://reports.njrcentre.org.uk/

With time, some implants wear out or become loose and occasionally break, leading to the need for further replacement (revision) surgery. The latest NJR data now shows that most knee replacement patients have less than a 5% chance of needing revision replacement surgery within 13 years of having the original operation. In the great majority of patients the implant will last well in excess of 20 years.

How can I find out how many joint replacement procedures my local hospital carries out?

The NJR has published hospital-level information for hip and knee replacements as part of its full NJR Annual Report. It includes for example, information on the number of procedures reported to the NJR as well as the number of consultants at the hospital and average patient age. This section also includes analysis of hospital data and reports which hospitals were identified as having higher than expected revision or mortality rates.

My local hospital seems to have higher than expected rates for procedures such as revisions, should I be concerned?

Your GP and/or your clinical team should also be able to provide information as to the numbers and results of procedures carried out locally. Statistics such as the numbers of revisions carried out should not on their own be taken as a guide to the standards of a hospital.

Additionally, the fact that your local organisation carries out significant numbers of revisions could be due to a number of reasons, for example, it could be a specialist centre in performing such surgery. If you have any doubts or questions though, speak with your GP or your healthcare/clinical team.

How can I find out how many joint replacement procedures my surgeon carries out?

The NJR publishes surgeon information along with information about the hospitals where those surgeons work. This can be found online at https://surgeonprofile.njrcentre.org.uk/

For each surgeon listed, it is possible to access information about their practice including how many procedures they carried out of each type, and information about mortality rates.

Further information about knee 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

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