Sam Rajaratnam unpacks the differences between partial and total knee replacement to help patients ask their surgeons the right questions.

Partial knee replacement (also known as unicompartmental or unicondylar) is a surgical procedure in which only one compartment of the knee is replaced with a prosthetic implant. It is also increasingly fashionable to describe it as a knee resurfacing.

By contrast, a total knee replacement (or a total knee resurfacing) - involves replacing the worn surface of all three compartments of the knee with an implant (the medial compartment, the lateral compartment on the outside of the knee, and the patellofemoral compartment).

Total and partial knee replacement in the treatment of osteoarthritis of the knee

Both procedures are used to treat knee osteoarthritis - due to worn away cartilage and bone on bone interaction - when pain and increased loss of function are affecting daily life to a significant degree.

The vast majority of patients in the UK requiring surgery for knee osteoarthritis (OA) are likely to need and have a total knee replacement. It is the gold standard of care once osteoarthritis of the knee is deemed to require surgical intervention, as most people develop significant degeneration in more than one compartment of the knee.

However, for certain patients whose arthritis is confined to one compartment of the knee, a partial knee remains an excellent option.

Who is a good candidate for a partial knee replacement?

There are clear guidelines for appropriate use of partial knee replacement, meaning it is not a case of which procedure is better, but rather, which is most appropriate for a patient. It is rather like a dentist choosing carefully between a filling and a crown when treating a worn out tooth.

Careful patient selection is important when considering which procedure one should have. Alongside short and longer term goals, each patient’s age and unique circumstances must be carefully considered in the decision-making process.

A unicompartmental (partial) knee replacement requires a stable knee and undamaged ligaments support the knee. It is also extremely wise to avoid a partial knee replacement when the patient has an inflammatory arthritis affecting their joint, as a systemic inflammation will eventually damage the rest of the knee that has not been addressed with surgery.

One of the main advantages of a partial knee replacement is that it allows for the preservation of healthy bone and tissue, as only the damaged portion of the joint is removed. This can result in a more natural feeling knee, greater range of motion and a quicker return to everyday activities.

Partial knee replacement can be less invasive with a faster recovery 

Partial knee replacement can be less invasive than total knee replacement, which usually means a smaller incision and lower pain levels in the short term - and a faster rehabilitation and recovery. 

Furthermore, there are lower costs associated with partial knee replacement due to implants and a shorter hospital stay.

Reservations regarding partial knee replacement

Partial knee replacement is not suitable for patients with arthritis in more than one compartment of the knee. Otherwise, the patient may be left requiring a further operation/revision, having gone through the process once, only to remain in pain as the other compartments start failing.

The prosthetic implant used in partial knee replacement has a shorter lifespan than that used in total knee replacement, which means that patients are more likely to undergo revision surgery.

The most common reasons for failure of a partial knee are wrong decision making: ignoring pre-existing wear in the other two compartments of the knee), getting the technical alignment of the partial knee wrong - which then leads to wear in the remaining compartment; loosening/bony collapse underneath the partial implant, or inflammation which can wear out other compartments.

Indeed, data from large national joint registries and multi-centre databases showed that “at five years the revision rate after partial knee replacement (at 8.8%) was around 2.5 times more likely than after total knee replacement”. 

Typically, osteoarthritis progresses, so there is an increased likelihood of needing more surgery at a later date after a partial knee replacement

Typically, osteoarthritis progresses, so there is an increased likelihood of needing more surgery at a later date after a partial knee replacement - depending on age and rate of disease progression.

If further surgery or revision after a partial knee replacement is required at a later date, a subsequent knee replacement is often more complicated than having it done the first time around (often necessitating the use of stems and augments, which are more invasive implants). What’s more, further surgery can be more complex due to scar tissue - thus resulting in potentially inferior results.

Total knee replacement or a total knee resurfacing can be performed on patients with arthritis in any compartment of the knee, making it a suitable option for a wide range of patients.

With modern knee replacement advances, the recovery from a total knee resurfacing can be very fast, with the majority of patients driving and returning to reasonable function within about 3 weeks.

Ultimately, total knee replacement patients are less likely to need to undergo revision surgery as soon, or at all. And with total knee replacement implants lasting between 25 and 30 years nowadays, revision rates are extremely low. Given success rates of between 85% and 99%, total knee replacement can be a strong long term solution.

Both total and partial knee replacement procedures have pros and cons so, in terms of deciding between them, the most important factor to consider is the extent of damage to the knee joint.

The most important factor to consider is the extent of damage to the knee joint

If only one compartment of the joint is damaged, a partial knee replacement may be a good option. However, if more than one compartment is damaged, a total knee replacement will be necessary to provide adequate pain relief and improve function.

Ultimately, the decision should be made in consultation with an experienced knee replacement surgeon, who can evaluate the specific needs and goals of the patient and recommend the most appropriate treatment option.

The best chance of a patient achieving a good result is to “get the decision and operation right the first time”.

is one of the the highest volume knee replacement surgeons in the country. A knee replacement revision specialist recently stated:

“Narrowing a surgeon’s practice to a finite number of procedures, makes for a better surgeon. Sam Rajaratnam is a true super-specialist in knee replacement surgery and at the top of his field.”

Mr. Sam Rajaratnam FRCS (Tr. & Orth.) is an internationally renowned Consultant Orthopaedic Surgeon particularly specialising in knee replacement surgery and also sporting injuries of the knee. He is one of the most experienced surgeons in the field of knee surgery, achieving some of the best outcomes in the country, with his patients experiencing complications 3 times less often than the national average.

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