Types of knee replacements

For the sake of this topic, we divide the knee into three compartments. The patellofemoral compartment is at the front of the knee, behind the knee cap. The medial compartment is on the inner side of the knee and the lateral compartment, on the outer side.

In a partial (unicompartmental) knee replacement, only one of these compartments is replaced and resurfaced. When the entire knee joint is replaced with an implant (prosthetic), we call it a total knee replacement.

Partial knee replacements

Partial knee replacements have a success rate of 90% after 10 years. The implants last for 10 to 15 years and potentially longer, although the data to prove that isn’t available yet.

A partial knee replacement is a good option, especially for younger patients. They need to meet the following criteria to be eligible for a partial knee replacement:

• The arthritis must be restricted to only one of the three compartments.
• Any deformities of the knee need to be correctable.
• A certain range of motion needs to be maintained.
• X-rays must confirm that the patient is a candidate for a partial knee replacement.

We sometimes do knee replacements on elderly patients too if they’re very active. The recovery after a partial knee replacement is shorter (around six months) compared to nine months for a total knee replacement, which allows the patients to resume their activities sooner.

If a patient needs to have their partial knee replacement revised within the first few years, it is usually because of pain, infection or poor implant positioning. It is common for patients to need a second knee replacement in the long term, not necessarily because of the lifespan of the implant, but rather because their arthritis has progressed to other compartments.

Medial compartment replacement

The medial compartment, on the inner side of the knee, is most commonly affected by osteoarthritis. It is also the part of the knee that is predominantly affected by wear and tear due to the alignment of the joints. That is why medial unicompartmental arthroplasty is the type of knee replacement surgery that is done the most.

Patellofemoral compartment replacement

The patellofemoral compartment is at the front of the knee and replacement surgery for this compartment is rare. In my practise, we do about one or two patellofemoral unicompartmental replacements per year. When a patient has patellofemoral arthritis, we normally do an osteotomy first, to correct the patient’s joint alignment. If, after this, the arthritis continues to be a problem, we can consider a partial knee replacement.

Patellofemoral arthritis is more common in females, especially those who are slightly overweight or have patellar tracking disorder – a condition where the kneecap moves out of place when the leg is bent or straightened.

Lower success rate for patellofemoral compartment replacements

Patients with patellofemoral arthritis usually have weaker quadriceps muscles (quads) because the pain in the knee inhibits the muscle. The quads need to be strengthened after surgery, which means that the recovery can sometimes take longer than other partial knee replacements.

The success rate for patellofemoral replacements is slightly lower than for replacements of the other two compartments, at 70% after 10 years. This is usually due to the progression of arthritis or because the quads didn’t receive enough rehabilitation after surgery. Despite this, it is still a good option for young patients who are struggling with patellofemoral arthritis.

Lateral compartment replacement

Partial replacements for the lateral compartment, on the outer side of the knee, is also quite rare. As with patellofemoral arthritis, we usually do an osteotomy for patients who experience lateral compartment arthritis before considering a partial replacement.

Lateral compartment arthritis most commonly affects male and female patients under the age of 50. We usually offer older patients with lateral compartment arthritis a total knee replacement, rather than a partial replacement.

Total knee replacements

After two or three years, a total knee replacement performs as well as a partial knee replacement does. However, a patient’s age is a big consideration when deciding on a total knee replacement. We try to avoid doing a total knee replacement for patients who are younger than 65.

Knee implants last for around 20 to 25 years. This makes it an excellent option for an older patient. Let’s say a patient is 70 years old. An orthopaedic surgeon will want to make sure that the total knee replacement is done well so that it will hopefully last the patient for the rest of their life, avoiding a second operation.

Avoiding total knee replacements in young patients

In young patients, we need to keep our options open for the future and avoid burning bridges, which is why we usually start with more conservative options. Young people tend to be more active than the elderly, which means that an implant may wear out quicker, potentially causing problems for the patient. It is also inevitable that a young person will need a second knee surgery due to the progression of their arthritis.

We want to avoid doing more than one total knee replacement on the same knee. With a total knee replacement there is bone loss and ligament issues, making a second total knee replacement a longer, more complex surgery. It is much easier to revise from a partial knee replacement to a total knee replacement if the partial replacement hasn’t been successful for some reason. This also buys  younger patient some time before having to consider a total knee replacement.

An individual approach is essential

It’s important to note that each patient is unique. After doing a thorough examination of a patient and their medical and surgical history, an orthopaedic surgeon will determine which approach is best. They will discuss the pros and cons of the different options and, together with the patient, come up with an individualised approach.

Please consult your healthcare provider if you experience knee pain.