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Knee prosthesis

Most knee replacements are performed in cases of advanced osteoarthritis

Most knee replacements are performed in cases of advanced osteoarthritis, when the disease has damaged the joint and performing a small exercise such as walking becomes painful and requires great effort.

In a smaller number of cases, knee replacements may be performed due to inflammatory rheumatic diseases or osteonecrosis (bone infarction).

What is osteoarthritis?
We define osteoarthritis as a degenerative joint disease in which the joint cartilage covering the bone in the contact areas is lost. Osteoarthritis is a slow and progressive disease that causes gradual wear and tear on the joint until it is practically destroyed. Osteoarthritis mainly affects people between the ages of 65 and 80, but it can vary depending on the patient's weight, activity level, and knee anatomy. In most cases, it affects more women than men.

As osteoarthritis progresses and there is a loss of joint cartilage leading to bone-on-bone contact, the patient experiences increased pain and their quality of life is diminished. In the early stages, this pain can be treated with anti-inflammatory drugs. When osteoarthritis is in advanced stages and the pain is incapacitating, it is time to perform a knee replacement.
How is the severity of the injury determined?
First, the specialist will ask you a few questions and perform a clinical examination. For a complete diagnosis, X-rays should be requested to check for cartilage loss. In certain cases, an MRI or CAT scan may also be necessary.
When should I have the operation?
Surgery is performed in cases of advanced osteoarthritis when the patient loses functional capacity and quality of life in daily activities. In any case, it will be the specialist who will recommend the prosthesis and the patient himself who will decide when to have the operation.
What type of prostheses are fitted?
The prostheses used in these replacements attempt to replicate the normal movement of the knee. There are basically two types of prostheses:
- Unicompartmental prostheses. Unicompartmental prostheses (partial knee replacement) is performed in cases where cartilage degeneration affects only one of the three compartments that make up the knee. Therefore, only the affected compartment needs to be replaced, as the rest of the joint is well preserved. The correct selection of patients is essential to achieving a good outcome. In fact, this technique is only indicated in about 10% of cases.
- Full prostheses. In total knee replacement (knee arthroplasty), the bone ends of the femur and tibia are replaced with prosthetic components. These elements are connected to each other and to the kneecap, which is sometimes also replaced, depending on the deformities, damage or the surgeon's criteria. There are different types of total prostheses, and the choice will depend on the patient's characteristics, age, bone quality and structure, ligament laxity, etc.
Most prostheses are made of plastic (high-density polyethylene) and metal (chromium-cobalt alloy) components so that the parts slide against each other like healthy cartilage, allowing the patient to perform normal knee movements. The prosthetic components are attached to the bone using a ‘cement’ (polymethyl methacrylate) that provides immediate fixation of the prosthesis.
How long will I be hospitalised?
Hospital admission is usually around six days, but this may vary depending on how the patient progresses.
Will I need to undergo rehabilitation?
It is important to follow a specific rehabilitation programme, which should be designed by a specialist and supervised by a physiotherapist. As a general rule, rehabilitation will be carried out daily for the first four weeks after the operation, and then intermittent sessions may be carried out for a further four weeks.

In most cases, six weeks after surgery you will be able to perform most everyday activities without the aid of crutches.

Recovery is not a slow process; it does not take many months, nor is it a painful process.
Will I be able to do physical exercise?
Unless contraindicated, you may engage in moderate physical exercise. High-impact sports are not recommended, as they cause greater wear and tear on the prosthesis and may necessitate replacement sooner than usual.
How long does a prosthesis last?
This is a frequently asked question in the clinic. Patients want to know when they will need to have their prosthesis replaced. The answer depends on each individual case, as it may vary depending on the person's level of activity or functional needs.

In most cases, a prosthesis can last between 15 and 20 years. The work performed by the surgeon in the operating theatre and the patient's use of the prosthesis are the two most decisive factors in determining its lifespan.
At what age can knee replacement surgery be performed?
Patients suffering from osteoarthritis live with pain that often prevents them from carrying out everyday activities normally. There is no specific age at which knee replacement surgery can be performed; rather, the timing should be determined based on the severity of the injury and the patient's level of pain.

Although in most cases patients are over 60 years of age, this does not mean that a 50-year-old patient must suffer continuous pain while waiting to turn 60 and be able to undergo replacement surgery. The prosthesis should be fitted as soon as it is needed. Your specialist will advise you accordingly.

Knee prosthesis

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