When wear and pain in the knee do not ease with other treatments, a doctor may suggest a joint replacement. This page explains what the operation is, who it is for, how it is done, and what to expect afterwards.

What is a knee replacement?

The knee is where the thigh bone and the shin bone meet. A smooth, slippery layer called cartilage covers the surface of both bones. Cartilage lets the knee bend and straighten smoothly and without pain. Over the years, or after an injury, cartilage wears away. This is called osteoarthritis. When cartilage is thin, the bones rub on each other, and the knee becomes painful, swollen and stiff.

In a knee replacement (also called “arthroplasty”, or sometimes a “knee prosthesis”) the surgeon removes the damaged surface of the bones and puts in artificial parts made of metal and plastic. The aim is to reduce pain and let the knee move more freely again.

Sometimes only part of the knee is damaged, and the surgeon replaces only that part. This is called a “partial replacement”. Which type suits you is the doctor’s decision.

Who is it for?

A doctor may raise a joint replacement in these situations:

Severe knee pain or stiffness that makes walking, climbing stairs or getting up from a chair hard
Pain at rest or at night
Swelling that does not settle with rest and other treatments
The knee bending inwards or outwards
Non-surgical treatments that have not worked

There is no set age or weight for the operation. The decision is based mostly on how severe the pain is and how much it limits you. In medical sources most patients are between 50 and 80 years old, but each patient is assessed on their own.

To decide, the doctor takes your history, examines the knee and asks for an X-ray. Sometimes a blood test or MRI is needed too. Only a doctor, after examining you, can say whether you need the operation.

How is the operation done?

Before the operation you talk with the anaesthetic team. The anaesthetic may be general (you are asleep) or a spinal block (you are numb from the waist down and awake or lightly asleep). The anaesthetist decides the type with you.

The general steps are:

The surgeon removes the damaged cartilage and a small amount of bone beneath it from the end of the thigh bone and the top of the shin bone.
The metal parts are fitted onto the bone. They are either fixed with a special bone cement or fitted so that the bone gradually grows onto them.
Sometimes the back of the kneecap (the small bone at the front of the knee) is also covered with a plastic part. Some surgeons do not do this.
A plastic layer is placed between the metal parts so that they glide smoothly on each other.

Medical sources usually give the operating time as one to two hours. The exact method and equipment, such as the type of implant or the technique, are chosen by the surgeon based on your situation, and you should ask him directly before the operation.

After the operation

Hospital. Some patients go home the same day and some stay several days. Sources usually say “one to four days”. Physiotherapy often starts a few hours after the operation.
Preventing clots. After the operation the risk of a blood clot in the leg veins is higher. Moving the ankle, walking early, compression stockings or boots, and sometimes a blood-thinning medicine are used to prevent this. The doctor decides the type and duration.
Exercises at home. Bending and straightening the knee and strengthening the thigh muscles are the basis of recovery. The physiotherapist or surgeon will teach you the movements.
Stitches. Stitches or clips are usually taken out from about ten days to a few weeks later. Keep the wound dry until it is fully closed.
Daily life. Sources give three to six weeks for a return to most daily activities. Driving is about four to six weeks later, depending on the source, and your doctor must approve it. Going back to work depends on the type of work, and one source gives six to twelve weeks.
Full recovery. Full recovery can take several months or more. Some pain with activity and at night is normal for a few weeks. Swelling may last for months.

These times are only general ranges. Recovery speed varies from patient to patient, and you should ask your own doctor.

Risks

Most patients do not have a serious complication. Still, every operation carries risk. The most important are:

Infection. It can occur in the wound, or deeper and around the implant, even years later. One American source reports serious joint infections in under 2 percent of patients. A superficial infection gets better with good treatment. A deep infection may need another operation.
Blood clot in the leg. A clot may travel to the lung (pulmonary embolism), which is dangerous. This is why prevention and knowing the signs matter.
Stiff knee. Scar tissue can sometimes limit movement. Physiotherapy and sometimes other treatments help.
Wear or loosening of the parts. Over the years the implant may wear or become loose.
Nerve or blood vessel damage, and lasting pain. These are uncommon.

Long-term conditions such as diabetes or heart disease can increase the risk. Only a doctor, after reviewing your records, can tell you your personal risk.

When to call

Contact your doctor or treatment centre soon if:

You have a temperature of about 38 degrees or higher, chills, or alternating feelings of heat and cold
The area around the wound is red, hot, painful or more swollen, or has discharge or pus
Knee pain gets worse even at rest
You have cramp-like pain or tenderness in the calf, or new or worsening swelling in the calf, ankle or foot

If leg swelling or pain comes with sudden shortness of breath or chest pain, a clot may have reached the lung. This is an emergency. Call 115 (the emergency number in Iran) or go straight to the emergency department, and do not drive yourself.

Every patient’s treatment plan is different; ask your doctor about your own situation.

Knee replacement