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Benefits of Partial Knee Replacement

Knee replacement surgery is recommended whenthe pain in your knee is so severe that it is having a significant impact on your day to day activities and you have tried all reasonable non-surgical treatments before making the decision to consider joint replacement

In most cases Total Knee Replacement (TKR) is performed where, as the name implies, the entire knee joint is replaced with an artificial joint (a ‘prosthesis’). In fact, 88% of all knee replacement surgeries in Australia are total knee replacements, 5% are partial knee replacements and 7% are revision surgery *.

However, not all patients have arthritis affecting all parts of the knee. For these patients there is another option with significant benefits – a Partial Knee Replacement, (sometimes also referred to as ‘unicompartmental knee replacement’, ’unicompartmental arthroplasty’ or a ‘mini knee’).

The anatomy of the knee

The knee joint comprises three separate sections or ‘compartments’…

  1. The Medial compartment (on the inside of the knee).
  2. The Lateral compartment (on the outside of the knee).
  3. The Patellofemoral compartment (the knee cap).

The most common area affected in isolation, is the medial compartment

If a partial knee replacement procedure is an option (and there are some times when it is not - see below), then there are several benefits from taking this route instead of a full replacement.

Over all, the procedure is less invasive than total knee replacement. A smaller skin incision is possible, it is not necessary to cut through the quadriceps tendon to access the joint, and all normal knee ligaments including the Anterior cruciate (ACL) are preserved. Less bone is excised, so if revision surgery is required years down the track, there is more bone stock available for fitting new prostheses onto.

As a result, the procedure results in:

  • A smaller scar on the knee, hence easier to kneel afterward.
  • Less blood loss during and after surgery.
  • less pain immediately after surgery.
  • Greater ease achieving range of movement.
  • A lower risk of major medical complications such as infection, deep vein thrombosis, and death.

All the above lead to the biggest benefits, which are:

  • A shorter hospital stay.
  • A faster return to normal activities.
  • A more natural feeling joint for the long term.

And should at some point the knee require further surgery, this is more straightforward than a revision of a total knee replacement procedure.

There are two main criticisms of partial knee replacement, revision rates, and the progression or development of arthritis in other areas of the knee.

Regarding revision rates, there is much conflicting data in the literature. Although if you look at all joint replacements done (e.g. through the Australian Joint Registry), this is the case, there are many other reports of individual surgeons and surgical centres achieving equal or better results in these terms. The reasons for these differences are complex, but include such factors as the number of each type that a surgeon regularly performs, the ease of revision of a partial compared to a total knee, and the inappropriate revision of some partial knees by surgeons that do not perform them or do not understand the intricacies of their follow-up.

With respect to the progression of the arthritis in other areas of the knee, provided the indications for the operation are carefully followed and the surgical technique impeccable, there is no reason arthritis should develop elsewhere. Medial compartment osteoarthritis is a mechanical problem and the mechanics are addressed with this technique. Even if a second operation is required later, it is certainly easier having only had a partial knee done the first time.

When partial knee replacement is not suitable:

  • Where the arthritis is present in more than the one compartment (as stated above).
  • Where there is inflammatory or rheumatoid arthritis.
  • Where there has been damage to one or more of the ligaments.
  • If there is severe deformity, stiffness, or instability associated.

Fast facts

  • Procedure takes 45 minutes.
  • Incision is only around 10cm.
  • Affected cartilage and bone is replaced with metal coverings attached to the bone.
  • A ‘spacer’ - a plastic insert is fitted between the metal components to replace the function of the cartilage.
  • 90% of patients report considerable improvement after the procedure.
  • 70% of partial knee replacements are functioning well 10 years after surgery.
  • The partial knee replacement procedure was one of the first minimally invasive types of surgery introduced in the early 1980s.

More information

Please feel free to discuss with Mr Callahan whether a Partial Knee Replacement could be right for you. We will be more than happy to discuss the pros and cons and explain in detail the points raised above.

Learn about Anatomy of the Knee and Oxford Partial Knee Replacement.

*2017 data from