Partial Knee Replacement

A partial knee replacement, also called a unicompartmental knee replacement (UKR or UKA), replaces only the part of the knee affected by arthritis rather than replacing the entire joint.

The knee can be divided into three main compartments:

• the medial compartment on the inside of the knee
• the lateral compartment on the outside
• the patellofemoral compartment between the kneecap and thigh bone

Most partial knee replacements are performed for arthritis affecting only the medial compartment.

Unlike a total knee replacement, the healthy parts of the knee are preserved. The aim is to reduce pain while retaining as much of the patient's natural knee anatomy, ligaments and movement as possible.

A partial knee replacement can be considered when advanced arthritis is limited predominantly to one part of the knee and the remaining compartments are sufficiently healthy.

It may be appropriate when:

• pain comes predominantly from one side of the knee
• X-rays show advanced arthritis isolated to one compartment
• the other parts of the knee remain reasonably well preserved
• the knee has suitable ligament stability
• deformity and stiffness remain within a range that can be corrected

A partial knee replacement is not suitable for every patient with knee arthritis.

If arthritis is widespread throughout the knee, there is major deformity or instability, or other parts of the knee are significantly damaged, a total knee replacement may be more appropriate.

Choosing between partial and total knee replacement therefore requires careful assessment of your symptoms, examination and imaging.

The operation has similarities to a total knee replacement, but considerably less of the knee is replaced.

A spinal or general anaesthetic may be used, together with additional pain relief around the knee.

An incision is made at the front of the knee. Because only one compartment is being replaced, the operation can generally be performed through a smaller surgical exposure than a total knee replacement.

The affected compartment and the remainder of the knee are carefully assessed.

Occasionally, surgery may need to be changed to a total knee replacement if the arthritis is found to be more extensive than expected.

A small amount of damaged bone and cartilage is removed from the affected side of the femur and tibia.

The healthy cartilage, bone and important ligaments in the remainder of the knee are preserved.

Small metal components cover the worn surfaces of the femur and tibia.

A strong plastic bearing sits between these components, creating a new smooth surface for that part of the knee.

The implants may be fixed using bone cement or a cementless technique depending on the implant and individual circumstances.

The deeper tissues are repaired using strong sutures and the incision is closed in several layers with absorbable sutures.

I generally close the skin with a fine absorbable suture underneath the skin and use a glued mesh over the incision. This provides additional support while the skin heals.

Although partial knee replacement is generally a smaller operation than total knee replacement, preparation remains important.

Before surgery:

• stop smoking or vaping if possible
• optimise diabetes and other medical conditions
• maintain good nutrition
• improve general fitness where possible
• tell the team about previous blood clots, heart or lung problems and sleep apnoea
• provide a complete medication and supplement list

Maintaining knee movement and muscle strength can assist early recovery.

Exercises commonly focus on the quadriceps, hamstrings, hip muscles and knee range of movement.

Arrange help with transport, shopping and other activities during early recovery. Remove trip hazards and prepare somewhere comfortable to rest, elevate the leg and perform exercises.

Your treating team will advise which medications should be continued or stopped before surgery.

As Brisbane has a warm and humid climate, particularly during the summer months, consider making sure you have access to a cool, comfortable and preferably air-conditioned environment during your early recovery. Apart from making recovery more comfortable, published research has found an association between warmer weather and higher rates of surgical-site infection, including research specifically examining infection following knee and hip replacement surgery. Keeping yourself comfortable and your surgical dressing clean and dry is therefore particularly important during Brisbane's warmer months.

Partial knee replacement can often have a faster early recovery than total knee replacement.

Patients generally begin walking soon after surgery with assistance from a physiotherapist. Hospital stay varies and some suitable patients may be able to leave hospital the following day.

Walking commonly progresses from crutches or a frame to a stick and then independent walking.

Swelling and bruising are normal but may settle more quickly than after a total knee replacement.

Physiotherapy focuses on:

• restoring knee movement
• improving quadriceps strength
• normalising walking
• gradually returning to everyday activities

Driving should only resume when you can safely and confidently control the vehicle and are no longer affected by medications that impair driving.

Most patients have made substantial progress with walking and everyday activities.

Strength and endurance continue to improve and exercise can gradually become more demanding.

Further improvement in strength, confidence and knee function can continue for many months.

Some patients report that a partial knee replacement feels more like their natural knee than a total knee replacement. A 2025 systematic review and meta-analysis comparing joint awareness after partial and total knee replacement found lower joint awareness after partial knee replacement, although there was considerable variation between the studies and this outcome cannot be guaranteed for an individual patient.

For appropriately selected patients, both partial and total knee replacement can provide substantial improvement in pain and function.

The TOPKAT randomised controlled trial comparing partial and total knee replacement found that both procedures produced good clinical outcomes at five years for patients with isolated medial compartment osteoarthritis.

More recently, 10-year follow-up of the TOPKAT trial has provided further long-term evidence comparing these two approaches.

There are advantages and disadvantages to each procedure.

A large systematic review and meta-analysis published in the BMJ found that partial knee replacement was associated with shorter hospital stays and favourable results in several patient-relevant outcomes. However, revision surgery was more common after partial knee replacement than after total knee replacement.

This trade-off is important when deciding which operation is appropriate.

Partial knee replacements can function well for many years, but their revision rate is generally higher than that of total knee replacement.

A major systematic review of long-term knee replacement survival found that national registry data suggested approximately 70% of unicompartmental knee replacements remained unrevised at 25 years, compared with approximately 82% of total knee replacements.

These are population-level estimates and cannot predict how long an individual knee replacement will last.

Because a partial knee replacement leaves the other compartments intact, arthritis can sometimes progress elsewhere in the knee over time.

If the implant fails or arthritis progresses significantly, the partial knee replacement can often be revised to a total knee replacement. Revision surgery, however, can be more complex than a first-time knee replacement.

Contact our office, your GP, or seek urgent medical attention if you notice:

• increasing redness, warmth or swelling
• increasing pain after initial improvement
• wound leakage or pus
• fever or feeling significantly unwell

Infection is uncommon but potentially serious after any joint replacement.

Seek assessment for:

• new calf pain or tenderness
• significant one-sided leg swelling
• sudden shortness of breath or chest pain

Sudden breathing symptoms require emergency assessment.

Persistent leakage, opening of the incision or rapidly increasing swelling should be reviewed.

Difficulty regaining movement despite exercises and physiotherapy should be discussed with your treating team.

Ongoing pain does not necessarily mean that the implant has failed. However, new pain after initially doing well, increasing swelling, or pain developing in another part of the knee should be assessed.