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Knee Replacement

What is a total knee replacement?

In a knee replacement, the damaged surface lining of the knee joint is replaced by metal surfaces. This helps reduce pain and improves the range of movement of the knee.

Knee Replacement

Knee replacement surgery is usually performed for arthritis. There are different types of arthritis, but in each one the beautiful smooth covering of the ends of the bone is damaged.

Over 70,000 knee replacement operations are carried out each year, and the number is increasing. The first knee replacement was performed in 1968.

Why is a knee replacement necessary?

If your knee is causing you significant problems with your life style despite doing everything you can.

The lining of the ends of the bone (articular cartilage) allows them to glide beautifully smoothly over each other like ice on ice. If this surface lining is damaged the bones can move like concrete on concrete. This can cause pain, swelling, stiffness, catching and reduced range of movement.

Arthritis can be caused by a number of different factors including age, obesity, injury, joint abnormality and hereditary factors.

Arthritis should initially be treated conservatively (non surgically).

  • Self help – Weight reduction, patient education, walking aids, exercise, shock absorbing shoes, physiotherapy.
  • Medication – Simple painkillers (paracetamol), stronger painkillers (co-codamol), opioid painkillers (Tramadol), topical painkilling creams.
  • Intra articular (into the joint) injections – Steroid and viscosupplementation injections.
  • Complementary treatments – Glucosamine and chondroitin sulphate tablets. Acupuncture.

Surgery should be considered when all these have been tried and you continue to experience symptoms that affect your quality of life. Although a knee replacement should significantly improve your quality of life, it will never be as good as your original knee.

What types of knee surgery are there?

It is possible to replace only parts or the whole of the knee depending on what parts are damaged.

The earlier you have a knee replacement the greater the chances are that you will eventually need further surgery due to wear. However, there’s some evidence that not waiting until the knee becomes too bad leads to a better surgical result.

Some people may not be able to have a knee replacement even though their arthritis is very bad:

  • If the thigh muscles (quadriceps) are very weak they may not be able to support the new knee joint.
  • If there are open sores (ulcers) on the skin especially below the knee.
  • Any active infection in the body.

Depending on a patients symptoms it may be possible perform an arthroscopy (key hole surgery) in the hope of delaying the need for a knee replacement. There are several different types of knee replacement surgery.

Total knee replacement

Most total knee replacement operations involve cutting off the damaged joint surfaces at the end of the thigh bone (femur) and top of the shin bone (tibia), and replacing these areas with pieces of metal shaped like the original bone. Between the two pieces of metal a plastic disc (made of ultra high density polyethylene) is inserted against which they articulate (move). The pieces of metal are usually fixed to the bone using special bone cement.

Some types of knee replacement have discs that move (mobile bearings) as it is thought this may reduce wear, although it isn’t yet clear whether the mobile bearing provides better long-term results.

Knee Replacement

It is common not to replace the surface of the kneecap (patella). However, where the kneecap itself is causing a lot of pain it may be necessary to replace this surface too. This involves removing the rough underside of the kneecap and replacing it with a smooth plastic dome.

Unicompartmental (partial) knee replacement

The knee is generally divided into three “compartments”: Medial (the inside part of the knee), lateral (the outside part), and patellofemoral (the joint between the kneecap and the end of the thighbone). Most patients with arthritis severe enough to consider knee replacement have significant wear in two or more of the above compartments and are best treated with total knee replacement

If the arthritis is limited to only one compartment it may be possible to replace only the affected compartment. This is sometimes called ‘unicompartmental’ or partial replacement. This is only suitable for about 1 in 4 people with osteoarthritis. It may not be known until the time of surgery whether you are suitable for a partial knee replacement or not.

It is a less extensive operation and can often be carried out through a smaller incision than a total knee replacement, which should mean a quicker recovery. The range of flexion (bending) is often better than that obtained from a total knee

For partial knee replacements the likelihood of a repeat operation is about 1 person in 10 by 10 years. It is usually easier to revise (redo) a partial knee, than a total knee.

Knee Replacement

Patellofemoral (kneecap) replacement

It is very common to develop arthritis between the back of the knee cap (patella) and end of the thigh bone it runs in (trochlea grove). If this is the only area affected by arthritis, it is possible to replace just the kneecap and its groove . This is called a patellofemoral replacement.

Knee Replacement

The operation is only suitable for about 1 in 10 people with osteoarthritis. The operation has a slightly higher rate of failure than total knee replacement – usually caused by the arthritis progressing in the other parts of the knee. However the outcome of a patellofemoral replacement can be good if the arthritis doesn’t progress and is a less major operation, offering speedier recovery times.

Complex or revision knee replacement

Some people may need a more complex type of knee replacement. The usual reasons for this are:

  • Loss of bone.
  • Major deformity of the knee.
  • Weakness or loss of the knee ligaments.

These knee replacements usually have a longer post (stem) down the inside of the bone which allows the component to be more securely fixed. The components are designed to form a hinge joint locked together to create increased stability. Extra pieces of metal and/or plastic may be used to compensate for any missing bone.

If you have severe arthritis where the bone has been worn away or undergoing revision (redo) surgery, it is usual for one of these special replacements to be used.

Computer assisted surgery

Computer assisted surgery (CAS) is a technique where surgery is performed with the aid of computer producing images.

The knee is “mapped” and the computer compares it to a normal knee. Sensors are attached to the cutting blocks “making sure” that the bone is cut in exactly the correct place and at the correct angle. It was hoped that this would improve the results of total knee replacement surgery, but has as yet not been proved.

What is done in preparation for a total knee replacement?

It is important that you understand what is involved in a TKR and that you are both physically and mentally prepared.

I will explain the operation to you when you first decide to proceed with the operation. On the morning of the operation we will discuss the operation again and we will complete a consent form. This confirms that you understand the risks, benefits and possible alternatives to the procedure and have given your permission for it to go ahead. It is important that you understand what is involved.

It is usual to be seen in a pre operative assessment clinic. Bloods will be taken, a heart tracing performed, a water sample will be checked for infection and a swap taken to make sure you do not have MRSA. Any pre-existing medical problems such as diabetes and high blood pressure should be optimized before the operation. Patients who are on anticoagulants (blood thinners) will probable need to stop these before the operation. Please inform me of any medication you take when we first meet and bring them with you when you come to hospital.

You will be asked if you are willing for the details of your operation to be entered into the National Joint Registry (NJR) database. The NJR collects data on hip and knee replacements in order to monitor the performance of joint implants throughout the UK.

Any sign of infection in the body (including colds) usually requires the operation to be postponed.

The fitter you and your knee are prior to surgery the better. As part of your conservative (non surgical) treatment you may have had physiotherapy to improve the muscle strength and range of movement. You will be using crutches or sticks immediately following your knee replacement and it easier to learn how to use them before the operation.

Bring loose fitting clothes with you to hospital as they are easier to get on and off after the operation.

How is total knee replacement performed?

The operation can be performed using a general anaesthetic. Spinal and epidural anaesthetics are also used; these numb the body from the waist down allowing you to remain awake throughout the operation.

The leg is painted in a dark brown antiseptic solution to reduce the risk of infection. It is best to wear old, dark coloured underwear as the solution stains clothes. A tourniquet (a tight bandage) is placed around your thigh and inflated when you are asleep to reduce bleeding and so improve visualization. If the procedure takes a long time this can cause discomfort in the thigh muscles and some numbness in the leg for a few days after the operation.

A 6-8 inch incision (cut) is made over the front of the knee. The patella (knee cap) is moved out of the way. The damaged ends of the thigh bone and shin bone are accurately cut to shape using special cutting jigs. Trial implants are used and once I am happy with the correct size, alignment and movement of the artificial joint, the definitive implants are cemented in place using “bone cement”. Different thicknesses of plastic spacers are tried between the metal bone ends to ensure the knee is moving properly before the definitive one is locked in place.

Operating theatres can be surprisingly noisy. If you have a spinal anaesthetic you will hear the sound of the drill and saw and feel the impact as the prostheses are hammered into place. You will hear the sound of the anaesthetic machine and feel the cuff on your arm as it measures your blood pressure. I have music playing in theatre and you can choose to bring in music of your own choice.

Local anaesthetic is often injected in and around the knee to help reduce post operative pain. Drains may or may not be inserted into the knee cavity before the knee is sewn up. Surgical clips are normally used to close the skin.

What happens after the operation?

You will be transferred to a bed in the operating room and taken out to the recovery room were you will begin to wake up from the anaesthetic. Once the recovery nurse is satisfied you are sufficiently awake you will be taken back to the ward.

You will have a drip in your arm and may have a catheter ( a tube into your bladder). The anaesthetist may have organised for you to have a special pump connected to your drip – patient controlled analgesia (PCA). This allows you to control the amount of pain killer you are receiving by pressing a control button. It is easier to suppress pain than to treat pain. Use and ask for pain killers a soon as you feel any discomfort.

You will be closely monitored on the ward with the nurse regularly observing your temperature, pulse and blood pressure.

The day after the operation the drip will be removed as soon as you are eating and drinking. It is sometimes kept in place while you continue to use the PCA. Your haemoglobin (red blood count) will be checked and the drains and catheter removed. An x-ray will be taken. The physiotherapist will help you out of bed and begin your rehabilitation exercises.

It is common to become constipated due to the pain killing drugs and relative inactivity. Medication will be given to “help you on your way”.

You will receive a blood thinning injection (into your tummy or leg) every day. When you go home you will be given blood thinning tablets to take for approximately 20 days. Check with your insurance company if they will pay for them, or if your GP will prescribe them otherwise you may be charged.

It is usual to be in hospital no more than 5 days. Patients are discharged when the wound is clean and dry and the physiotherapist and patient are happy. You should be able to fully extend (straighten) and flex (bend) the knee to 90°.By this stage you will be able to walk (at least 10 meters with sticks) and use the stairs. The physiotherapist will give you a home exercise program (HEP).

What are the possible complications?

Total knee replacement surgery is a very common operation and is very safe. Most knee replacements are problem free but serious complications can arise in 2% of cases. Most of these complications are minor and can be successfully treated.

However, in order to make an informed decision and give your consent, you need to be aware of the possible side-effects and possible complications of this procedure. Despite all the potential side effects and complications listed below, 90% of patients are happy with their new knee.


These are the unwanted but mostly temporary effects you may get after having the procedure.

You should expect some pain, stiffness, swelling and bruising around the knee. This is likely to last for some weeks and will gradually improve as the knee heals and you get back to your normal day-to-day activities.

Your new knee will not bend as far as your original one and often clicks and clunks due to the hard metal and plastic surfaces.

It is possible to kneel after a replacement but most people choose not to.

Initially there will be some numbness to the side of the scar. It’s unlikely that the feeling will return completely to normal but it usually improves over about two years.


Complications are problems that may occur during or after the operation. Most people aren’t affected. These can be divided into those related to any operation and those related to the operation itself.

Possible complications of any operation:

  • Reaction to anaesthetic.
  • Haematomas/ bleeding.
  • Blood clots.

These can form in the legs and travel to the lungs (pulmonary embolus 0.3%) which can be fatal. If they stay in the legs (deep vein thrombosis 2-3%) you will need to be treated with blood thinners for about 3-6months.

Possible complications of the operation

  • Infection in the joint – On average this happens in about 1 in 50 cases. Usually the infection can be treated with antibiotics. About 1 in 150 patients develop a deep infection which may mean removing the new joint until the infection clears up. In extreme cases, where the infection cannot be cured, the knee replacement has to be removed permanently and the bones fused together so the leg no longer bends at the knee.
  • Wear – The metal ends move against the plastic spacer which in time will wear out or the metal ends will work loose. The younger you are when the knee is put in and the more active you are, the quicker it will wear. The likelihood of needing another operation is increased if you are overweight or involved in heavy manual work.It is possible to redo (revise) the replacement, but each time the result is not quite as good or lasts as long. It is hoped that 90% of knees will still be working well 10-15 years after they are put in.
  • Stiffness – The normal knee bends from straight to about 135°, a replaced knee bends to about 110°. If it does not bend as much as this it can be difficult to use stairs and deep chairs. If the movement does not improve with physiotherapy, an operation to bend the knee when you are asleep may be needed.
  • Continued symptoms – Although some people are disappointed with the outcome of their surgery, or are unsure whether there has been an improvement, about 90% of people who have had the operation say they are happy with their new knee.
  • Neurovascular damage – About 1 in 1,000 suffer damage to arteries that usually requires further surgery to repair the damage
  • Bone fracture – The bone around the artificial knee joint can sometimes break after a minor fall – usually after some months or years especially in people with weak bone (osteoporosis). If this occurs surgery is usually needed to fix the fracture and/or replace the joint components.

Looking after your new knee

The physiotherapist or an occupational therapist will tell you what to do , amd what not to do after your knee surgery. It is important that you to follow their advice.

Following discharge from hospital you need to pay attention to the following potential problems:

  • Wound care – Keep the wound area clean and dry. A dressing will be applied in the hospital and should be changed as necessary. Ask for instructions on how to change the dressing before you leave the hospital. You may be allowed to shower but not bath until the sutures or staples are removed, usually a week to 10 days after surgery. Please let me know if the wound appears red or begins to leak.
  • Blood clots – Calf pain, chest pain, or shortness of breath are signs of a possible blood clot. Notify me immediately if you notice any of these symptoms. Keep using your compression stockings and taking the tablets you have been given until they are finished.
  • Stiffness – The knee can become very stiff in the weeks after the operation for no obvious reason. You will have been shown exercises by the physiotherapist whilst in hospital and it is usual to have some physiotherapy once you leave hospital.
  • Pain – Pain should reduce after about four weeks although some pain is likely for as long as six months. Make sure you take regular pain killers and anti-inflammatories (if allowed). Using them before the pain builds up.
  • Swelling – cooling the knee helps reduce swelling and helps with pain control. I encourage the use of a cryocuff which can be used continuously throughout the day, taking it off at night. If you are using ice instead of a cryocuff, always cover the ice with either a towel or pillowcase. You can “ice” for 10 minutes at a time during the day approximately every 1-2 hours. This helps to reduce pain and inflammation. An double tubigrip (elasticated stocking) should be used during the day and taken off at night. Whenever possible take the tubigrip off and use the cryocuff. Raising the foot off the floor (on a footstool or similar) is another good way of reducing swelling. Get up and walk around for at least five minutes every hour so as not to increase the risk of a blood clot.
  • Infection – If you notice any infection or sores on your leg you should seek early advice from your GP. You should also look after your feet to reduce the risk of infection.

Getting back to normal

You will probably need some help at home for several weeks. If you do not have sufficient help at home, you may wish to spend some time in a rehabilitation centre.

The following tips can make the initial period more comfortable:

  • Rearrange furniture so you can manoeuvre with sticks or crutches. You may temporarily change rooms (make the living room your bedroom, for example) to avoid using the stairs.
  • Remove any throw rugs or area rugs that could cause you to slip. Securely fasten electrical cords around the perimeter of the room.
  • Use assistive devices such as a long-handled shoehorn, a long-handled sponge, and a grabbing tool or reacher to avoid bending too far over.

It will be some weeks before you recover from your operation and start to feel the benefits of your new knee joint. Make sure you have no major commitments for the first six weeks after the operation.

Keeping up your exercises will make a big difference to your recovery time. You’ll probably need painkillers as the exercise can be painful at first. Gradually you will be able to build up the exercises to strengthen your muscles so that you can move more easily.

It’s important to use crutches during the first few weeks after surgery and until the knee is strong enough to support you. Falling could damage your new joint. You will need to take care in the first few weeks when moving around and doing household jobs so that you don’t damage your new knee. Your physiotherapist should advise you on these tasks but here are a few tips:

  • Walking – Don’t twist your knee as you turn around. Take several small steps instead. It should be possible to walk outside about three weeks after your knee surgery but make sure you wear good supportive outdoor shoes. After three weeks, try to take longer strides to regain full straightening (extension) of the leg.
  • Walking aids – Crutches and sticks are useful at first. As you leg gets stronger you will begin to walk without aids. This process may take less time if you’ve had a partial knee replacement or longer if you’ve had a more complex operation. Your surgeon or physiotherapist will be able to advise you on this.
  • Going up and down stairs – When going upstairs lead with your unoperated leg, then move your operated leg up. When going downstairs, put your operated leg down first, followed by your unoperated leg. “Good leg to heaven, bad leg to hell”.
  • Sitting – Don’t sit with your legs crossed for the first six weeks.
  • Kneeling – You can try kneeling on a soft surface when the scar tissue has healed sufficiently. Kneeling may never be completely comfortable but should become easier as the scar tissue hardens up.
  • Sleeping – You don’t need to sleep in a special position after knee surgery. However, you should avoid lying with a pillow underneath your knee. Although this may feel comfortable it can affect the muscles resulting in a permanently bent knee.
  • Household jobs – You should be able to manage light household tasks, but avoid heavier jobs, or get help with them, for the first few months. Avoid standing for long periods as this could lead to your ankles swelling.
  • Driving – You should be able to drive again after about six weeks as long as you able to perform an emergency stop quickly and safely. If you have had surgery on your left knee you may return to driving when you can control the clutch as long as you’re not taking strong painkillers.
  • Travel– Your new knee may activate metal detectors at airports. If this happens, you can show them your scar and they will usually pass a hand scanner over the area. You should not fly for more than 3 hours within 3 months of your operation. If you are travelling by car, get out regularly to stretch your legs.

Activity, Exercise and Sport

Once home, you should continue to stay active. The key is not to overdo it! You can expect some good days and some bad days.

Exercise is critical for the long tem care of your knee. You should be able to resume most normal activities of daily living within 6 weeks following surgery.

Some pain with activity and at night is common for several weeks after surgery. Your activity program should include:

  • A graduated walking program to slowly increase your mobility, initially in your home and later outside.
  • Resuming other normal household activities, such as sitting and standing and climbing stairs.
  • The physiotherapist will give you a set of exercises to undertake when you are at home to restore movement and strengthen your knee.

A time goes on you should be able to return to normal exercise. The time that this will take depends on the knee surgery and your level of fitness and activity prior to your operation. Cycling is an excellent aerobic workout, swimming, low-resistance rowing, stationary skiing machines, walking, hiking, and low-resistance weight lifting all are excellent ways to maintain fitness without overstressing the implant.

Suitable activities include bowling, croquet, golf, doubles tennis, table tennis, ballroom dancing and square dancing.

Being over weight causes the knee to wear quicker than it should do.

Your new knee will continue to improve for as much as two years after your operation as the scar tissue heals, the range of movement improves and the muscle strength increases.