Knee arthrosis (gonarthrosis): the various types of 'customised' prosthesis

By Cristiano Antonino On Nov 16, 2022

Let’s talk about prosthesis: knee arthrosis (or gonarthrosis) is a very common disease worldwide, second in numbers only to that involving vertebrae

It consists of the progressive degeneration of articular cartilage and most frequently affects women and people over 50.

Regardless of the causes, it leads to a loss of movement capacity and a daily pain sensation of varying intensity for the patient.

While treatment of gonarthrosis in the early stages involves the use of anti-inflammatory drugs and physical therapy, when the arthrosis progresses to a severe degree, the only solution is knee replacement surgery.

When to undergo knee replacement surgery?

Knee replacement surgery is recommended when one or both of these conditions occur and the patient

experiences severe pain when moving the joint;
complains of stiffness that limits their daily activities, including walking, climbing stairs and getting up or sitting in a chair.

The most common cause of this type of manifestation is arthrosis of the knee, the most common and widespread form of arthrosis, a chronic disease caused by degeneration of the articular cartilage.

It leads to injuries that progressively cause pain, difficulty in movement and, in more severe cases, deformation of the joint itself (valgus, varus or flexed knee).

How is a knee replacement chosen?

In the collective imagination, the surgical treatment of knee pain consists of implanting a total knee replacement.

Today, however, this image is no longer entirely correct, since in prosthetic surgery there are different types of knee implants

mono-compartmental prostheses
combined (mono + patellofemoral);
bi-monocompartmental prostheses;
total prostheses.

Within the same category of total prostheses, there are different types depending on the design, degree of invasiveness and constraint, and with a different biomechanical basis.

It is therefore up to the orthopaedic surgeon to choose the individual type of implant on the basis of

a qualitative and quantitative assessment of the type of arthrosis;
functional expectations of the individual patient.

The correct logic, in fact, should be to find the right balance between:

degree and type of arthrosis degeneration of the individual patient;
type of implant available;
patients’ needs and functional expectations.

Monocompartmental and bi-monocompartmental knee prosthesis

The mono-compartmental prosthesis may be indicated if arthrosis affects only one part of the 3 compartments of the knee joint and its cruciate ligaments are present and valid.

This type of prosthesis, in fact, has the characteristic, unlike the total prosthesis, of replacing only the damaged part of the joint.

The principle of this minimally invasive choice is to provide for the preservation of the structural integrity of the knee, with less impact perceived by patients and consequently a higher level of satisfaction.

The monocompartmental prosthesis abroad has a 30-year history, but in Italy it is in the last 15 years that its application has become more frequent: the use of high quality materials, advances in biomedical engineering and surgical techniques have enabled surgeons to obtain increasingly satisfactory results, with the result that this type of ‘third generation’ prosthesis is now widely used in minimally invasive prosthetic surgery.

The advantages of implanting this smaller prosthesis are considerable and are

less clinical impact on the patient
greater respect for surrounding tissues and muscles;
better clinical outcome;
certainly better functioning in biomechanical terms.

Today, in fact, this type of prosthesis implant is considered a safe, reliable procedure that guarantees long-term success.

In special cases, it is also possible to simultaneously implant 2 monocompartmental prostheses in the knee, to replace 2 of the 3 knee compartments damaged by arthrosis. In this case we speak of a bi-monocompartmental prosthesis.

Total knee prosthesis

If the surgeon has assessed that there is no indication for the use of the available range of compartmental prostheses due to excessive joint degeneration in all 3 compartments of the knee, he resorts to the implantation of a total knee prosthesis.

Thus, there are total knee replacements that preserve the anterior and posterior cruciate ligament or only the posterior cruciate ligament, and those that involve the replacement of both.

What is the ‘customised’ prosthesis?

It is essential that the surgeon, after analysing the degree of damage to the joint, constructs the implant to be made by customising it on the patient and choosing the type of prosthesis best suited to his or her specific case.

In this sense, the prosthesis is customised: not so much because it is moulded to the patient’s anatomical features, but because it is directly focused on solving the specific problem of the person affected by the pathology causing the joint degeneration.

What material a knee prosthesis is made of

The prostheses are made of titanium, with a surface coating of cobalt chrome.

There are versions of prostheses with a ceramicised metal coating, specially designed to reduce the risk of potential allergic reactions to the nickel present in the cobalt chrome alloy.

In its middle part, the prosthesis insert is made of highly cross-linked polyethylene, sometimes enriched with vitamin E, which makes it more resistant to wear.

How long does a prosthesis ‘last’?

A knee prosthesis lasts on average around 15 years, but it is not uncommon to see implants still in excellent condition after 20 or even 25 years.

The wear of the prosthesis materials is not only related to the wear of the prosthetic components, but is influenced by other factors related to the quality of the bone and the patient’s lifestyle.

Increasingly advanced surgical techniques and materials make it possible to increase the durability of prostheses and thus patient satisfaction.

However, if wear occurs, implant loosening occurs, resulting in the need for implant revision.

Robotic surgery: when it is needed

Robotic surgery supports knee implant operations and is used by surgeons to be as accurate and precise as possible.

The robot is set by the surgeon in the preparation phase and offers the advantage of eliminating the margin of error associated with the use of traditional instruments in performing planned bone cuts.

Also with robotic surgery, it is possible to perform combined mono- or bi-compartmental and total prosthesis operations, depending on the damage of the individual patient, allowing treatment to be customised to the individual pathology.

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