Types of knee prostheses

23-07-2018

The knee is the most complex joint of the human body, therefore it is also the most vulnerable. When knee pain emerge, first conservative treatments are performed, but in case of a long, ineffective treatment period, the implantation should be considered. In this article, we present the types of knee prostheses and for what complaint is it recommended.

When is a knee prosthesis needed?

Knee replacement surgery is most commonly performed in people with advanced arthrosis. The wear of the joint could be primary, caused by degenerative lesions, or secondary, as a result of an earlier disease (surgery, joint lesion, inflammation, deformity).

In the case of arthrosis, the cartilage surfaces get worn, causing increased friction between the joint surfaces. Due to the torn cartilage parts, the endosteum might become inflamed, the production of the synovial fluid increases, causing the stiffness of the joint. Calcification could occur, which causes reduced range of motion and painful movement of the joint.

The typical symptom of an arthrosis is a severe pain in the joint after a longer stay, which eases after movement. It escalates with exertion and relieves only in rest. As the patient cannot use the limb intensively, the limb might shorten due to muscle atrophy, which results limping.

At first, arthrosis is treated conservatively: with anti-inflammatory and analgesic medications, and physiotherapy. If these treatments prove to be inefficient and the pain is permanently held, worsening the quality of life, knee replacement should be considered.

What is a knee prosthesis for?

By the implantation of the knee prosthesis, the worn joint surface is replaced by an artificial implant, allowing the knee its natural movement.

What type of prostheses exist?

We can differentiate the prostheses according to the replaced parts of the knee joint. If the wear takes shape only on one side of the joint, smaller implants can be used, a unicompartmental knee replacement, to resurface just that side. One-sided wear usually develops on the medial part of the joint, the prostheses replace the worn-out surface of the femoral and tibial medial condyle.

This type is used only in special cases, as 1-5 years after the surgery, the other side of the joint could deteriorate and total knee replacement will be inevitable.

Total knee implants are replacing the entire knee surface, both the femoral and tibial parts. This type of implant is used, when both, the medial and lateral parts are damaged. During the total knee replacement surgery, the worn-out surfaces are removed, the ends of the bones are accurately cut to shape and replaced by metal components, impacted onto the bone or fixed with bone cement.

A round ended metal implant is used for the femur, a flat for the tibia, and a flattened or slightly dished high-density polyethylene surface is inserted between them. This insertion is about to reproduce the anatomical cartilage surface to help to flex and stretch the knee smoothly.

These prostheses have similar geometry to a healthy knee joint, with the same range of motion. These types are called high-flex knee implants.

The rarely used, third prosthesis type is the patellofemoral replacement.  It is a type of “partial” knee replacement in which only a portion of the knee is resurfaced. During this replacement procedure, the patella is partially or completely removed and replaced by a plastic implant. It can be performed at the same time with total knee replacement or detachedly.

Choosing the right implant depends on several factors: the knee problem and the knee anatomy, as well as the age, weight, activity level, and general health of the patient. Taking into consideration all these factors, the knee specialist will suggest the most suitable type.

How long a knee replacement lasts?

The lifetime of a total knee prosthesis is about 15-20 years, depending on the accuracy of the fixation and the subsequent load. Just as wear in the natural joint contributed to the need for a replacement, wear in the implant may eventually require a second surgery. During this surgery, some parts or all of the original implant are removed and replaced with new components.

What can I expect after the surgery?

As all surgical intervention, total or partial knee replacement also involves the excavation of the surrounding tissues, which is causing pain for a few days after the surgery. Pain relief is betided with medications.

From the day after the surgery, regular exercises and conditioning physiotherapy is performed according to elaborate protocol. With no complication, the patient can leave the hospital after 3-4 days stay. The stitches are removed 10-14 days after the surgery. Medical checkups are required in 2, 6 and 12 weeks after the surgery.   In these weeks, the physiotherapist will help the patient return to normal activities, increase the range of motion, and eventually strengthen the surrounding muscles through specific exercises.

After 3 months, the patient will have almost complete knee function, but further improvement is expected within 1 year after the surgery. After the 3^rd month, the patient can walk on flat ground without any restriction.