Partial Knee Replacement (UKR/UNI)

The management options for knee pain include non-surgical and surgical treatments. Ideally the non-surgical treatments should be exhausted before surgical treatments become necessary.

Partial knee replacement involves replacing only the worn compartment of your knee (most commonly the medial/inner part). It’s a less invasive option than total knee replacement, providing a quicker recovery and a more natural feeling knee joint because the healthy parts of the knee have been preserved.

Who is a good candidate?

A partial knee replacement (UKR/UNI) works best when arthritis is truly limited to one compartment and the rest of the knee is in good condition.

Ideal candidates for Partial Knee Replacement :

arthritis mainly in one compartment (often medial)
the other compartments show minimal change
the knee is stable (ligaments functioning well)
Any bowing of the leg is correctable and not severe
symptoms match the involved compartment on imaging and examination

If there is more widespread arthritis, significant instability, or inflammatory arthritis, a total knee replacement is usually the better option.

Partial vs Total Knee Replacement: benefits and trade-offs

In correctly selected patients, a partial knee replacement often has important advantages:

quicker early recovery and shorter hospital stay
often a more natural feeling knee (because we preserve healthy structures)
typically less post-operative pain and blood loss
generally lower early medical complication rates than total knee replacement. In large studies the early risk of heart attack or stroke is lower for UKR than TKR (but very small risk of these in both procedures – 0.2-0.5% after UKR Vs 0.4-0.8% after TKR)
Superior day to day function and outcome scores

The concern with partial knee replacements is longevity, and not typically of the partial knee wearing out, but more that the remaining parts of the knee that were preserved begin to fail or cause pain.

partial knee replacements have a higher risk of revision surgery than total knee replacements over the long term (see registry data below)
A total knee replacement is an excellent operation and is very durable, but it is not automatically the best choice for everyone.

In well selected patients, partial knee replacement can be a long-lasting and highly successful procedure, and many patients do extremely well for many years [Joint registry data suggests survivorship of 90-93% at 15 years for UKR vs 94-96% for TKR at 15 years]

The Procedure

Including the anaesthetic and recovery time, the procedure typically takes 1.5 to 2 hours. Most patients receive a spinal anaesthetic along with sedation to ensure they are not aware of the procedure. Additional regional sensory nerve blocks will be utilised to ensure you are as pain free as possible.

The surgical incision is made along the front of the knee. The remaining healthy areas of the knee are then assessed. It is important to note that during your surgery the remainder of the knee is carefully assessed, once the knee is open, to ensure the remaining compartments look healthy enough to last a minimum of 10 years. If this is not the case then the surgeon will convert to doing a total knee replacement. Pre-operatively you will be counselled about this and asked to complete a consent form for both procedures.

The arthritic bone is removed, and metal and plastic components are used to replace the affected surfaces of the knee. The incision is closed and a dressing is applied. A bandage and ice are used to manage any swelling and bruising.

Recovery & Rehabilitation — What to Expect

Most patients find they are relatively comfortable upon returning to the ward and are encouraged to start mobilising on their new knee immediately. The physiotherapy team will guide you on how to do this safely. You can continue to use ice to manage the swelling.

The typical hospital stay is now only 1 night due to improvements in anaesthetic techniques and strong evidence of improved outcomes in patients who are mobilising normally as quickly as possible. Some patients may be suitable for this to be done as a day procedure.

Recovery varies from person to person, but most people progress through these phases:

Early recovery (0–3 weeks)

Pain and swelling gradually improve.
Begin walking with assistance (crutches or frame) soon after surgery.
Physiotherapy starts early to restore movement and strength.
Key focus in these early weeks is achieving full extension of the knee

Medium phase (3–6 weeks)

Most patients can walk more confidently without aids.
Daily activities return gradually.
Continued physiotherapy helps build strength and flexibility.

Long-term recovery (3–6 months)

Some recovery of strength and function may continue up to 6 months.
Continued improvement in comfort and activity levels.
Swelling and bruising are a common and normal part of the healing process, but significantly less than total knee replacements.

Pain management is key to ensure adequate pain relief to be able to carry out range of movement exercise throughout the day. Please see Knee Replacement Rehabilitation Videos for advice on how to best recover following Partial or Total Knee Replacement.

Frequently Asked Questions?

How is a partial knee replacement different from a total knee replacement?
A partial knee replacement resurfaces only the damaged compartment. A total knee replacement resurfaces the whole joint. In suitable patients, a partial can feel more natural and recover faster, but does have a slightly higher long-term revision risk overall at 15 years.

Is a partial knee replacement less risky than a total knee replacement?
For correctly selected patients, large studies show lower rates of early medical complications and lower early mortality compared with total knee replacement, although the absolute risk is low with both operations. In some data set the risk of venous thromboembolism is lower in partial knee replacements than in total knee replacements.

How long does a partial knee replacement last?
National Joint Registry (NJR) data shows the best performing partial knee replacements have around 5% revision at 10 years (and have survivorship of 90-93% at 15 years ), while total knee replacements are under 3% at 10 years (and have survivorship of 94-96% for TKR at 15 years.)

Can a partial knee replacement be converted to a total knee replacement later?
Yes. If arthritis progresses elsewhere or the implant fails, conversion to a total knee replacement is commonly performed.