Knee replacement surgery FAQs

Over 100,000 knee replacement surgeries are carried out in the UK every year to treat knee pain, stiffness and reduced mobility. 

The most common reason for knee replacement surgery is knee osteoarthritis, that is, wear and tear of the knee joint over time that destroys the cartilage in the joint and causes the bones forming the joint to rub and grind against each other. 

Other reasons for knee replacement surgery include inflammatory conditions including rheumatoid arthritis, where your immune system mistakenly attacks the cartilage in your joints, or as a secondary problem related to trauma of the knee. 

Here, we’ll look at the different types of knee replacement surgery, how to prepare for surgery and what recovery involves. 

What are the different types of knee replacement surgery?

To understand the different types of knee replacement surgery, it first helps to understand the anatomy of the knee joint. This complex joint forms between the end of your thigh bone (femur), the top of your shinbone (tibia) and your kneecap (patella). 

The joint surfaces at the ends of these bones are all covered with cartilage, which helps the joint to move without pain. Furthermore, the lining of the joint produces synovial fluid which lubricates your knee joint to reduce friction and allow smooth movement. What type of knee replacement surgery you have will depend on exactly where the cartilage in your knee joint has worn out and your consultant will use their expertise to offer you the most suitable operation for your problem. 

There are two types of knee replacement surgery: total and partial. Both types of surgery can either be carried out manually or with robotic assistance. 

Total knee replacement surgery

This is the most common type of knee replacement surgery and involves replacing the surfaces of femur and tibia, which form the knee joint. In some cases, the underside of the patella is also replaced or resurfaced. 

Partial knee replacement

The knee joint has three compartments that comprise the bony surfaces of the joint in different regions of the knee. A partial knee replacement only replaces one specific affected compartment of the knee joint where the cartilage has worn away. 

The medial compartment refers to the bony surfaces of your femur and tibia on the inner side of your knee (ie the side closest to your other knee). The lateral compartment refers to the bony surfaces of your femur and tibia on the outer side of your knee. Finally, the patellofemoral compartment refers to where your patella rests against the front part of your femur. 

Partial knee replacements most commonly replace the bony surfaces of the medial compartment of the knee joint. 

Manual vs. robot-assisted knee replacement surgery

Manual knee replacement surgery involves your surgeon using specially designed instruments to remove the worn out ends of your bones within the knee joint. This is the traditional method of performing knee replacement surgery.

Robot-assisted knee replacement surgery is a pioneering new technique that helps patients achieve a bespoke knee replacement that is aligned and balanced based upon their individual anatomy, using planning software and a SMART robotic arm (MAKO) to make precise and accurate cuts to give the best balanced and functioning knee replacement. 

Due to the greater precision of planning that is possible with robot-assisted knee replacement surgery, there is less soft tissue injury during surgery, which means less swelling and pain, and a better range of motion after surgery. This speeds up the recovery time and reduces the amount of time you will need to spend in hospital. Robot-assisted knee replacements should also last longer and perform better as the implants can be more accurately aligned in the knee joint. 

How do you choose between a partial or total knee replacement?

The two main factors that determine whether you have a partial or total knee replacement are the wear patterns of your joint cartilage and your age. As mentioned earlier, if the cartilage in only one compartment of your knee is diseased and the rest of your knee cartilage is healthy, a partial knee replacement may be a suitable treatment option. 

If you are under 50 years old, a partial knee replacement is preferred where possible. This is because a partial knee replacement helps preserve more of the natural tissues of your knee and helps protect the rest of your knee joint cartilage. Together, this will restore the normal mechanics of your knee.

Over time, other areas of the knee may begin to wear out and revision surgery to convert a partial knee replacement to a total knee replacement may be required, but this is usually approximately 10 years later. 

Consequently, a partial knee replacement extends the time during which you can benefit from normal knee mechanics. This is because while a total knee replacement can significantly improve your range of motion and resolve your knee pain, it can’t fully replicate the natural mechanics of your knee joint and therefore it may be more appropriate to replace only the worn out areas. 

If you are over 50 years old and have more extensive cartilage damage, you may need a total knee replacement. Other reasons for having a total knee replacement instead of a partial knee replacement include poor alignment of your knee joint, any ligament injury, or inflammatory conditions including rheumatoid arthritis.

How should you prepare for knee replacement surgery?

What your care team will do

Before you are referred for assessment for knee replacement surgery, your GP will carry out some checks to ensure you are well enough to undergo surgery. You will also have a pre-operative assessment with your hospital care team. 

If, for example, you have anaemia, your iron levels and diet will need to be checked. If you have diabetes, your blood sugar levels will need to be under control. If you have a heart condition, your cardiologist will need to check that you are fit for surgery. 

What you can do

If you are a smoker, it is important to try to stop several months before your surgery. This will reduce your risk of complications during and after surgery, and improve your body’s ability to heal. 

In the run-up to your surgery, it is important to stay as mobile as you can. The more you can exercise — without increasing your pain levels — the stronger your leg muscles will be. This is important because after surgery your muscle strength will deteriorate as you take the time needed to recover. If your pre-surgery muscle strength is higher, then you will have a better starting point for recovery. 

In the two weeks prior to your surgery, avoid attending large gatherings where you will be at a greater risk of contracting a viral infection, such as the flu or COVID-19, and try to eat as healthily as possible.

How long does knee replacement surgery take?

Knee replacement surgery, whether it is manual or robotic-assisted, takes between 45 and 90 minutes. 

How long is recovery in hospital after knee replacement surgery?

After knee replacement surgery, most individuals spend one to two nights in hospital, but with newer anaesthetic and surgical techniques, this procedure is becoming a day case procedure where patients are safely discharged within 12 to 23 hours of surgery. 

Before your surgery, your care team will advise you on preparations you can make at home to aid your recovery after surgery, such as removing trip hazards and arranging for a loved one to help you around the house. 

Before you are discharged from hospital, your care team will give you walking aids, such as a walking frame or crutches, as well as a prescription for any other medications you need such as painkillers.

What does recovery in hospital involve? 

Knee replacement surgery is usually performed under a spinal anaesthetic. This means the strength in your legs will return within a couple of hours after surgery. If you have a general anaesthetic, this can take longer. 

Immediately after your surgery, you will be taken to a recovery room until it is safe to transfer you back to the ward. After around an hour or so in the ward, your physiotherapist will help you to get out of bed and start walking with a walking aid. 

What does recovery at home involve? 

Pain relief

For the first four to five days at home, you will need to take strong painkillers to manage your surgical pain. After this initial period, your pain levels will decrease day by day, but if you do too much walking, this may cause increased pain and swelling; rest, ice and elevation will be helpful.

Mobility

During your recovery, it is important to keep moving your knee, ideally bending it from 0° to beyond 90° as soon as possible. By keeping your knee mobile, you will reduce the amount of scar tissue that forms — less scar tissue means less stiffness in your knee. 

For the first six weeks of your recovery, you should walk frequently for short distances. After six weeks, most people can stop using their crutches and walk longer distances. 

Your physiotherapist will provide you with a programme of exercises to perform throughout your recovery that will help mobilise your knee joint and later strengthen the muscles that support it. 

Wound care

You will need to keep your wound site dry and clean. You will be given waterproof dressings and your care team will advise you on how often to change your dressings, as well as how to perform daily hygiene routines safely, such as showering. 

Driving

You will not be able to drive for at least the first six weeks after your knee replacement surgery and will need to let your motor insurer know you have had this surgery. In most cases, you can be fully insured after six weeks if you can control your vehicle and perform an emergency stop. However, always double-check these criteria with your insurer. 

Returning to work 

In most cases, you will need to take at least six weeks off work. If you have a physically demanding job, you may need to take more time off work to give your knee the chance to get stronger. Ask your consultant for advice on how much time off you will need for your job and how best and how quickly you can safely return to work.

Sex

It is best to wait for two weeks, ie until your wound has healed, before returning to sex. After this point, you can have sex again but should be aware of positions that put your knee under strain. 

What are the risks and potential complications of knee replacement surgery? 

Every surgery comes with risks, including bleeding, blood clots, infection and nerve damage. However, all necessary steps will be taken to reduce these risks. 

Getting moving as soon as possible after surgery is part of this risk-reduction process, as it reduces the chances of stiffness developing and of blood clots forming; around one in 1,000 patients who have a knee replacement surgery will develop a blood clot that travels to their lungs (pulmonary embolism), which is life-threatening. 

For knee replacement surgery, specifically, there is a risk of numbness in the skin overlying the outside part of your knee. This numbness may be permanent but will not cause any harm; if the numbness does resolve, it can take as long as 18 months. 

In some cases, knee implants can produce unexpected noises on movement, such as a clicking or a knocking sound, this is normal and relates to the movement of the metal and plastic surfaces of the knee replacement. 

What are the warning signs of infection after surgery?

Signs that your wound site has become infected include the skin around it feeling hot and appearing red and swollen, your wound oozing yellow or green fluid (pus), your wound opening up, fever, shivers (when you aren’t cold) and/or a general feeling of being unwell. 

If you notice any of these signs, you should contact your care team immediately.

Signs of infection usually become apparent after about a week after surgery. 

How often is revision surgery needed?

Knee replacements can last anywhere from 15 to 25 years depending on your age, general health, type of knee replacement (partial or total) and activity levels. 

Around five in every 100 patients who have knee replacement surgery will require revision surgery at some stage. But the goal of your knee replacement is to improve your quality of life; relieving pain, so you can enjoy an active lifestyle.