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​What to expect following knee replacement surgery

24th April 2018

There are broadly two different types of knee replacement surgery. These are known as partial (sometimes called unilateral) knee replacement, and total or full knee replacement. You may also hear knee replacement being referred to as arthroplasty. Your surgeon will decide which option is best for you depending upon the state of your knee. Partial knee replacement is less invasive and involves less downtime, so if this is a possibility for you, your surgeon will always prefer to choose this option. However, partial knee replacements run a greater risk of the need for revision surgery, so your surgeon will carefully weigh this risk against the short-term benefits.

The compartments of the knee

Your knee joint consists of three compartments. The medial compartment is the inside of your knee, the lateral compartment is the outside, and the patellofemoral compartment consists of the front part of your knee, between the patella (kneecap) and the thigh. One or two of these will be replaced during partial knee replacement surgery, and all of them will be replaced in a full arthroplasty or knee replacement operation.

What is a partial knee replacement?

A partial knee replacement is performed in hospital under general anaesthetic or a spinal block. A spinal block is also sometimes called an epidural. It is described as reduced invasive surgery, and because it certainly is less invasive than a full arthroplasty, it will result in shorter recovery time and less time on the operating table. A partial knee replacement operation will take around two hours, whereas a full replacement will take as much as three.

On the day of your surgery, you will be admitted to hospital. Your surgeon and anaesthetist will come and explain exactly what will happen during your procedure. However, most of this will already have been made clear to you by your specialist, prior to the decision being made to operate, and again at your pre-op assessment. One thing that is very important to understand about any kind of knee replacement surgery is that if your surgeon finds that your ligaments are not strong enough to support an artificial knee joint, you won't be able to have the surgery. Your surgeon will not be able to know this for certain until you are on the operating table and they are finally able to have a good look inside your knee, so you may be sent home without having the surgery. However, most people will be able to continue with the procedure with no problems.

After your anaesthesia has kicked in, the surgeon will open up your knee and replace the damaged parts of your joint with metal and plastic implants which have been measured to fit your unique knee shape. For partial knee replacement, a smaller incision is made, and less bone is removed and replaced. This means that recovery time is shorter, and the general risks associated with any surgery are lower. Around one in four knee replacements for osteoarthritis are partial rather than total. Partial replacement surgery has the advantage that because less of the knee has been removed, eventual movement range will be more natural and mobility may be better than with full knee replacement. This may mean that the patient will remain more active and for longer, and with improved knee function, quality of life will be much improved. However, as mentioned above, partial surgery does mean you are more likely to need revision of your surgery in later life.

What is a total knee replacement?

A full knee replacement may take up to three hours to perform, but equally, it can be completed in as little as an hour, depending on how extensive the damage to your knee has been, and your overall health. The procedure starts with an incision to open up your knee to reveal the kneecap or patella, which is then moved aside so the surgeon can access your joint. The damaged ends of your femur (thigh bone) and tibia (shin bone) are then carefully removed. Measurements are taken, and then the appropriate sized prosthetic implants are fixed into place. This is done using a special medical cement, or a substance which encourages your bones to fuse with the prostheses. A plastic insert will be be placed between the prosthetic bone ends, to act as cartilage, aiding smooth and painless joint movement. Depending upon the state of your knee, you may also have the back of your kneecap replaced during surgery.

After surgery is completed, the wound will be closed with stitches or clips and a dressing will be applied. Following the surgery you are likely to feel sore and tired. You may be given a switch on the ward so you can self-administer your pain medication, at safe doses. You will have tubes attached to the wound to drain blood away from the site, to stop it accumulating there. You will probably be discharged home after 2-3 days for a partial knee replacement, and 3-5 days for a total replacement. You will be encouraged by support staff to get up and start moving fairly soon after surgery, as this aids recovery. Normally you will be able to stand up within twelve to twenty-four hours. You will be encouraged to sleep with your leg elevated to boost circulation and reduce swelling, and you will also be advised to continue doing this at home for the immediate post-surgical period.

At first you will need crutches or a walking frame to assist you when you walk. In hospital, you may need assistance with certain activities, but after a week or a few days for a partial replacement, you should be able to walk unassisted on your crutches or frame. When you are discharged home, it would be helpful to have somebody stay with you for a week or two, as you are likely to feel tired and weak. You will be given lots of advice in the hospital from both your surgeon and a physiotherapist, who will give you exercises to perform which will aid your mobility. It is important that you follow these every day, as they will enhance your recovery time. Some people will be given a motion machine, which manipulates the joint in particular ways whilst you lie down. This promotes flexibility and the restoration of a full range of motion in your knee.

Most people find that they are able to start walking around without crutches again around six weeks prior to surgery. Others take a little longer, and those who have had partial knee replacement may not have to wait so long. You should find that at this time, you will be able to resume all your usual activities. However, you may still experience some knee pain until around three months post-surgery. Your leg may appear swollen for up to a year, but the good news is that, two years after surgery, your muscles should have recuperated and your scar tissue should have healed. By this point your new knee should feel like it has been there forever, although you must be realistic - your artificial joint will never attain the flexibility of your natural, healthy knee before it was damaged by osteoarthritis.

You may always feel a little discomfort upon kneeling, and you should not do rigorous activities which could damage your implant. The longevity of your prosthetic knee depends on how well you treat it. If you overdo it, you could cause serious damage which could result in further surgery. You may find that you experience stiffness and aching during and after exercise, and kneeling, running and jumping may always be difficult. This is normal, and can usually be managed using pain medication and ice packs. However, always seek medical attention if pain is severe.

Exercise will improve the adherence between the artificial joint and your bones, because each time you exert yourself, your bones compress and this will promote fusion. Exercise will improve your flexibility, muscle and bone mass, endurance and strength. All these things will mean that you will be able to participate in activities which were too painful prior to surgery. However, you will not be able to take part in very vigorous contact sports or any activity which places heavy impact upon your knees. This includes court sports, jogging and skiing. You must take care to avoid undue strain on your knee, and it is best to speak to your specialist before starting a new sport. Managing your weight to avoid too much pressure on your joints will also help your artificial knee to remain in good shape.

Having said this, bear in mind that the prognosis is good. Nine out of ten people who have experienced a knee replacement have found that it has improved their quality of life. You have a 90-95% chance of avoiding more surgery for the next ten years, and an 80-85% chance of getting twenty years out of your artificial knee. If you are older than sixty when you have your replacement, it will probably last until your old age, and even for the rest of your life.

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