That there is a difference between hips and knees maybe shouldn’t be a surprise. They are very different joints. The hip is a ball and socket with a lot of stability coming from the bony structure, whereas the knee is a rotating hinge which in the natural state relies on the work of a number of ligaments for normal function.

In my experience, whereas a large number of patients who undergo total hip replacement would consider themselves to have a normal joint, this is much less common in those who undergo total knee replacement. Even in those who are happy with the result, most would say that they are aware that they have had surgery.

The common things that people are aware of include:

• Stiffness: a replaced knee is almost never more flexible than a normal knee and usually feels a bit stiffer.

• Lateral numbness: the area of the knee to the outer part from the scar is often numb and although the area can get smaller, some degree of altered sensation be permanent.

• Difficulty kneeling: while I am perfectly happy for patients to kneel after their surgery, only 20% do so comfortably. If you couldn’t before the operation, you are very unlikely to do so afterwards.

There are some factors that can help predict whether you are likely to benefit from knee replacement

• Length of significant symptoms: there is some evidence that those who have had clear symptoms for more than a year do better.

• Degree of arthritis on imaging: patients who have their arthritis diagnosed on MRI scanning, but where it isn’t clearly present on a plain X-ray, tend not to do as well.

• Previous surgery: patients who undergo knee replacement within six months of an arthroscopic knee procedure tend to do less well after knee replacement. Patients who have had multiple previous procedures also do less well.

• Use of anti-depressants: there has been some evidence that those needing to use anti-depressant medication are less happy with the result of their surgery.

• Age: there has been some evidence that younger patients are less happy after knee replacement surgery. This appears to be related to higher expectations in younger patients, which can’t be met.

• Gender: women may wait longer, such that the symptoms are worse. Men and women get a similar improvement in benefit, but women may do so from a lower starting point, so the result at the end isn’t as good.

Partial (Unicondylar) Knee Replacement

If the arthritic disease is principally affecting only one part of the joint and the symptoms of pain are only felt in that area, it may be possible to only replace that part of the joint. This is most common when the disease is on the inner (medial) part of the knee. Partial (Unicondylar) knee replacement (UKR) has some benefits over a total knee replacement. More patients feel that it is closer in feel to a normal knee. Recovery is generally quicker than after total knee replacement surgery. Some complications of surgery listed below are a little less frequent in partial knee replacement surgery (infection and blood clots). A downside of a partial knee replacement procedure is that it may not last quite as long as a total knee replacement. In total knee replacement surgery, 95% of joints are lasting 15 years. For partial knee replacement, that figure is just under 90%.

The quality of implants used in orthopaedic surgery is determined by an organisation called ODEP. I most commonly use the Nexgen and the Persona. 

For partial knee replacement, I use the Persona Partial Knee. 

The National Joint Registry has an online tool (Patient Decision Support Tool) that can estimate the benefit you could gain after surgery, the risk of a revision procedure and the risk of death one year after the operation, which you may find helpful. To access this, please click here.

Complications of Surgery

Although knee replacement surgery is very successful, it is still a major operation and complications do occur. The commonest complications are outlined below:

• Deep infection (around 1%). This will be higher if you are diabetic, have an inflammatory arthritis or are taking drugs that affect your immune system e.g. steroids. The figure in UKR is a little lower.

• Blood clots (about 2% in the leg and 0.5% in the lung). The risk will be higher if you have had a clot before; if you are significantly overweight; have a family history of clotting; have an inherited condition that affects your clotting or have certain cancers, even if currently controlled or in remission. Women taking some forms of HRT or oral contraception are also at higher risk and a discussion would take place about whether this should be stopped in the run-up to surgery. The risk in UKR is a little lower.

• Damage to nerves and vessels (0.1%). This is exceedingly rare in modern knee surgery. The commonest injury is to a part of the sciatic nerve, giving a weakness to the foot. Around half of these would be expected to recover fully. The risk in UKR is a little lower.

• Severe stiffness (1%). Some people find it difficult to get the knee moving after the operation, despite the help of the physios. In this case it may be necessary, after a few weeks, for them to be readmitted and have a procedure called a manipulation under a general anaesthetic (essentially the surgeon forcefully bends the knee to try and improve the range of movement) . Despite this procedure the long term outcome of the surgery is often poorer in terms of pain and function. The risk in UKR is a little lower.

• Intraoperative fracture (0.5%). Bone is hard, and saws and hammers are used as part of the surgical technique. Occasionally there is a crack in the bone. This is often noted at the time of surgery and dealt with immediately, with the replacement then proceeding as planned. Rarely it is noted after the surgery and may need a return to theatre to fix the problem.

• Residual pain. Some 5-10% of patients will have some residual symptoms of pain after a total knee replacement. Although usually at a lesser level than before the surgery, it can still be distressing and limit day to day function.

• Blood Transfusion (less than 5%): Blood transfusion is uncommon after joint replacement, and in my hands the rate runs at less than 5%. We take steps to optimise your blood count before surgery, as the risk of transfusion is higher in those patients with low haemoglobin levels. A few patients with some chronic conditions  (e.g. kidney disease or rheumatoid arthritis) can’t have their blood count normalised and that would be discussed with you before your surgery.

  If you don’t want to receive blood, that wish would be respected and documented when you consent for the surgery.

Consent form

While the above sections cover the commonest risks associated with the surgery, there are more. Different organisations produce consent forms to cover as much as possible. It is very difficult for any patient to retain and recall all of this information in the time available during a consultation. I have included here a link to the Ramsay Healthcare Knee Replacement consent form. If you are considering total knee replacement surgery, please read this through as it may help you identify any questions to bring to your consultation or your pre-op review appointment.

Mortality after knee replacement surgery: Patients often ask about the risk of death after a big operation. This is often very difficult to be precise about, but the NCEPOD in the UK had a tool that uses age and general health to give an estimate. The general health is described using something called the ASA score. ASA1 is fit and healthy, ASA2 means you have some other condition e.g. diabetes, but it is well controlled, ASA3 means your general health has a greater effect on your quality of life e.g. COPD limiting your mobility or angina and ASA4 means your health is very poor. It would not be possible to perform surgery at Fulwood Hall if you fall into the ASA4 category. The estimate of your ASA status wouldn’t be finalised until you have your pre-op assessment.

The table below gives an estimated mortality at 30 days for patients undergoing knee replacement.

Patients with other medical problems: Many patients will have mild medical problems such as high blood pressure, well controlled on medication. This doesn’t add a significant risk to having major surgery. Some however, will have more serious underlying heart, lung or kidney problems that may increase the risk of complications. This would apply to any major surgery requiring an anaesthetic and are not specifically linked to hip replacement. This can be discussed at your orthopaedic appointment, but if significant would also need to be discussed with the anaesthetist at your pre-op check. Sometimes your surgery would be postponed while further tests or specialist consultations occur. In some circumstances it would not be possible to perform surgery at Fulwood Hall and your care would need to be transferred to the local NHS Trust.

Medication: Some tablets that you take may need to be temporarily stopped in the run-up to your operation. This will be discussed and confirmed with you at your pre-operative check.

Anaesthetic: The operation is usually carried out under spinal anaesthetic, with sedation as needed - you do not have to be awake. This will be discussed in more detail, as well any risks involved with the anaesthetist.

A video explaining the process of Knee Replacement Surgery can be found here.

Surgery in the time of Covid-19: The pandemic has caused some changes to be made around planning major surgery. Surgery is safe in fully vaccinated people who test negative. There is no longer a need to isolate or have a routine test prior to your surgery. However if you do contract Covid then you still cannot have surgery for a period of seven weeks from the positive test (accurate as of September 2023).