Treating Knee Osteoarthritis with a Joint Prosthesis

Who is it for?

The first criterion to consider when evaluating whether knee osteoarthritis should be treated with a prosthesis is to have an X-ray taken to determine the wear and tear on the joint. When the X-ray shows a complete absence of space between the two bones, it means that the cartilage is completely worn away. For the knee, special projections may be indicated to identify the defect, as wear may be limited to only a few points that are not visible on conventional X-rays.

In all cases, knee wear detected on the X-ray is not the only decision-making criterion. Indeed, major osteoarthritis that produces few or tolerable symptoms does not provide an absolute indication for the placement of a knee prosthesis. The following criteria must be met for a patient to be eligible for the placement of a knee prosthesis: total knee wear detected on X-ray, pain and limitations in daily life reducing quality of life, poor pain control with non-surgical treatments, use of anti-inflammatory drugs at doses that endanger the stomach or general health.

The Procedure

Treatment for knee osteoarthritis is initially bloodless and medical. The goal is to relieve pain: when this treatment is no longer effective, surgery may be offered.

The two most important surgical options in the treatment of knee osteoarthritis are osteotomies and knee prostheses. Knee osteotomy corrects the anatomical axis of the lower limb: thus, the patient's weight is distributed to a part of the knee with healthy cartilage. However, this operation has certain limitations, depending on the patient's age, the type of deformation, and the quality of the bone. In addition, several years (5 to 7 years on average) after such an operation, a recurrence of pain symptoms is observed.

Total knee arthroplasty or knee prosthesis surgery involves covering the surface of the knee bones with a prosthesis which, like a normal knee, will have smooth surfaces and will be able to support loads. The choice of prosthesis type is dictated by the bone conformation, the weight, and the physical activity of the patient. The materials most commonly used today are metallic alloys (femoral and tibial component) specifically designed for medical use, and highly biocompatible polymers (a special type of plastic) for the intermediate part between the two metallic surfaces. Like the normal knee, prostheses are also subject to wear and tear, depending on the loads dictated by the type of activity practiced, and it is therefore not possible to provide an unlimited functional guarantee, although the development of new materials allows for durations that seemed quite impossible ten years ago.

The Following Days and Rehabilitation

There are no fixed rules for establishing the progression of rehabilitation, considering also the type of prosthesis used.

Generally, during the first postoperative day, rehabilitation aims at active isometric strengthening and active isotonic strengthening. During the first week, the orthopedic surgeon adds lower limb stretching exercises.

It should be remembered that the day after the operation, the patient is allowed to walk normally, without the aid of crutches and/or orthopedic devices.

From day 7 to day 14, the previous exercises are intensified, running is allowed, but it must be gradual and interspersed with walking phases. Cycling and swimming are allowed from the 7th postoperative day.

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Results

The goal of a knee prosthesis is to obtain a mobile, stable, and painless knee.

The good results obtained after a knee replacement operation are confirmed by current data in the scientific literature. Indeed, this operation relieves knee pain and gradually improves the quality of life of most patients: with modern prosthetic implants, a survival rate of around 92% is observed more than 10 years after the operation.

By analyzing complex studies involving thousands of operated patients, it is observed that these results do not vary with the different prosthesis models used (prosthesis with or without preservation of the posterior cruciate ligament, fixed or rotating plateau prosthesis, presence or absence of patellar prosthesis...) and the different surgical techniques used (fixation with or without bone cement...). However, it can be seen that the results vary considerably over time. Most functional improvements occur during the first postoperative year and then stabilize.

The Type of Prosthesis

There is no single knee prosthesis. Knee osteoarthritis can be more or less advanced, and patients, all different from one another, can benefit from prostheses adapted to their specific case.

Schematically, two types of prostheses can be distinguished:

• The unicompartmental prosthesis;
• The total knee prosthesis;

In the first case, the prosthesis replaces the cartilage of only one femoro-tibial compartment of the knee. Their main advantage is that bone resection is minimal. This type of prosthesis can be offered to relatively young patients with unilateral osteoarthritis, a healthy anterior cruciate ligament, and minimal angular deformity of the lower limb. The total or bicompartmental knee prosthesis is the most common type. It consists of two metallic elements, which are anchored to the bone by "cement", and a central element in "plastic" (polyethylene) which allows them to slide. The total prosthesis, which also replaces the cartilage of the kneecap at the femoropatellar joint, is indicated in cases of global osteoarthritis, in elderly subjects, with marked alterations of the load axis or ligamentous degeneration. In these cases, the resection and bone loss may be significant, but with the advantage of functional recovery of the knee.

Tricompartmental Prostheses

Tricompartmental gonarthrosis occurs when all three compartments of the knee are affected by the symptoms of arthritis. Hence the name "tricompartmental". This condition causes degenerative changes in the knee joint. Due to its diffuse nature across multiple areas, it can be more serious than other types of osteoarthritis.

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