What to know about total knee replacements

A total knee replacement is one way to correct damaged bone and cartilage in the knees by implanting a prosthetic. In this article, consultant orthopaedic surgeon Mr Simon Coleridge explains why and how a knee replacement surgery is conducted.

When is a total knee replacement needed?

The knees are the joint where the end of the femur (thigh bone) meets the tibia (the shin bone). The patella (kneecap), which stabilises the joint and shields the bones, sits on top of the meniscus cartilage. Anchoring the joint are many ligaments, muscles, and tendons. The knee joint is a rotational point for the shin, but it is also used for weight distribution, balance, and stability.

The knee joint is the biggest joint in the human body, and it is fundamental for facilitating movement that is used in a wide range of activities, including but not limited to walking, jumping, crouching and sitting. 

Because of the constant strain on the knees, it is common for them to suffer from injury or gradually wear away over time. When the knee joint becomes dysfunctional, it can be quite disabling and painful. Sometimes, it is recommended that the patient rest their knees to allow for recovery, wear supportive braces, or undergo physiotherapy to strengthen and stretch the knee – but this won’t be effective for every patient.

For these cases, knee replacement surgery is explored when the knee dysfunction is severe and the pain is chronic. This includes those whose knee dysfunction has reduced their mobility, have experienced a sudden destructive injury, or who have not responded to alternative therapies. This includes conditions such as:

• Arthritis, like osteoarthritis, rheumatoid arthritis, or post-traumatic arthritis. This is when the cartilage in the joint deteriorates and the joint becomes inflamed.
• Fractures, which can happen during accidents, impacts, and falls. Fractures that heal incorrectly can later lead to post-traumatic arthritis.
• Infections of the joints, which can also deteriorate the cartilage.

Who can get a total knee replacement and how does it differ from other types of knee replacements?

Patients who are recommended to undergo knee replacement tend to be older than 60 years old. This is because knee replacements last an average of 25 years, and patients who are younger and who undergo a replacement surgery will likely need more than one replacement procedure in their lifetime – in order to avoid that, medicinal and therapeutic treatments are explored foremost.

There are two kinds of knee replacement surgery: a total knee replacement, where the lower portion of the femur and the upper portion of the tibia are removed and replaced with a prosthetic, and a uni knee replacement, also known as a partial, where only one bone portion is replaced because the damage isn’t as extensive. Suitable for patients with damage confined to one compartment of the knee (usually the medial side). It is a less invasive option whichpreserves more of the natural joint, though it’s not appropriate for all patients.

What happens during total knee replacement surgery?

Once the decision is made to proceed with a total knee replacement, several important steps are taken to ensure the patient is physically and mentally prepared for surgery. These include:

1. Pre-assessment: Patients attend a pre-assessment clinic where their general health is evaluated. This may involve blood tests, ECGs, X-rays, and a review of current medications. Any existing medical conditions—such as diabetes, high blood pressure, or heart disease—must be optimised before surgery.
2. Joint school: a group or one-on-one session to educate patients about what to expect before, during, and after surgery. This includes information about anaesthesia, recovery, rehabilitation, and lifestyle changes.
3. Prehabilitation: Patients may be referred for physiotherapy before the operation to strengthen muscles around the knee, which can aid recovery post-surgery. Guidance may also be given on assistive devices like crutches or walkers.
4. Weight loss and lifestyle adjustments: Excess weight puts additional strain on the knee and increases surgical risk. Patients who are overweight may be encouraged to lose weight before surgery. Smoking cessation is also recommended, as smoking can impair healing.
5. Fasting Instructions: On the day of the procedure, patients are typically advised not to eat or drink for several hours prior to surgery. Exact instructions vary but usually involve no solid food for six hours before the procedure and only clear fluids up to two hours beforehand.

What happens during total knee replacement surgery?

A total knee replacement can be performed as an open or a minimally invasive procedure, known as an arthroscopy. Minimally invasive techniques, as opposed to open ones which are around 10cm, use smaller incisions that range between 2cm and 4cm, and thus may be preferable for patients because they result in a faster recovery time, less visible scarring, and fewer risks for complications following the procedure.

The procedure takes only a couple of hours, and patients can be offered either spinal (regional) anaesthesia, which is commonly used because it tends to offer fewer complications, less post-operative nausea, and improved pain control immediately after surgery, or a general anaesthetic, which renders the patient completely unconcious and numb. The surgeon makes one long incision down the front of the knee (open) or a few smaller ones around the knee (minimally invasive) so that the knee cap can be moved away and the structures underneath can be accessed. The damaged portions of bone are sawn off and reshaped so that the prosthetic implant – which is made of metal, silicone, and ceramic – can be fitted on the ends. The joint is then put back into place and the kneecap reinserted on top. Finally, the wound is sealed and bandaged.

What is the recovery like after a knee replacement and what are the long term considerations?

After a knee replacement, recovery is expected to take up to a year, but this will vary depending on the kind of procedure and the patient’s condition. The patient will likely spend a night or two in the hospital to recover (although some surgeons are now offering outpatient treatment) and be prescribed painkillers to assist with the aching and soreness after surgery. They are recommended to rest and keep weight off the knee for several weeks and to abstain from strenuous activities and weight-lifting for some time, even as they return to normal activities and work/school. Patients are further recommended to participate in physiotherapy to regain stability and mobility, strengthen the muscles, and learn how to use their new joint. Full recovery may take up to 12 months. Most patients return to daily activities within 6–12 weeks, though high-impact sports and running may be discouraged.

Most patients experience a significant reduction in pain and improvement in function and mobility after knee replacement. However, realistic expectations are key:

• Activities such as walking, cycling, swimming, and golfing are typically resumed without pain.
• The prosthetic joint typically lasts 15–25 years, depending on activity level, weight, and surgical technique.
• Revision surgeryas as in some cases, the prosthetic may wear out, become loose, or cause ongoing pain, requiring revision surgery. Younger and more active patients are more likely to need a second replacement in their lifetime.