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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.
¿Cuál es la duración de una prótesis?
Esta es una pregunta frecuente en la consulta. Los pacientes quieren conocer en que momento deberán realizar el recambio de prótesis. La respuesta depende de cada caso, ya que puede variar en función del nivel de actividad de la persona o sus necesidades funcionales.

En la mayoría de los casos, una prótesis puede tener una duración de entre 15 y 20 años. El trabajo realizado por el cirujano en el quirófano y el uso que haga el paciente de la prótesis son los dos factores más decisivos para determinar la duración.
¿A qué edad puede realizarse un reemplazo de rodilla?
Los pacientes que sufren artrosis viven con un dolor que a menudo les impide realizar las actividades cotidianas con normalidad. No existe una edad determinada a partir de la cuál puede hacerse un reemplazo de rodilla, si no que ese momento debe determinarse en función del grado de la lesión y el dolor del paciente.

A pesar de que en la mayoría de ocasiones, los pacientes tienen más de 60 años; ello no quiere decir que un paciente de 50 años deba sufrir un dolor continuo a la espera de cumplir los 60 y poder realizar el reemplazo. La prótesis debe ponerse en el momento en que sea necesario. Su especialista así se lo indicará.

Knee prosthesis

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