Unicompartmental (Partial) Knee Replacement
What is a unicompartmental knee replacement?
Unicompartmental knee replacement, also called partial knee replacement, replaces only the worn part of the knee rather than the whole joint. The knee has three compartments. When arthritis is confined to one of them, that compartment alone can be resurfaced, keeping your healthy cartilage, bone and ligaments, including the cruciate ligaments.
Dr Varun Arora performs partial knee replacement for suitable patients across Melbourne and regional Victoria, often with robotic-arm assistance. The aim is to relieve pain while keeping as much of your own knee as possible, so it feels and moves more naturally.
Different types of uncompartmental (partial) knee replacement
Which part of the knee?
Medial (inner) compartment. By far the most common site of arthritis and of partial knee replacement.
Lateral (outer) compartment. Less common, and often linked to knock knees or previous injury.
Patellofemoral (kneecap) compartment. A patellofemoral replacement resurfaces the groove behind the kneecap.
Am I suitable for a partial knee replacement?
A partial knee may be suitable when:
Arthritis is confined to one compartment on standing x-rays
The anterior cruciate ligament (ACL) is intact and the knee is stable
The knee bends well and straightens nearly fully
Any bow-leg or knock-knee deformity is mild and correctable
Pain is clearly located over the affected side
It is usually not suitable for inflammatory arthritis (such as rheumatoid arthritis), arthritis in more than one compartment, a torn or deficient ACL, or a very stiff knee. Dr Arora will assess this with an examination and standing x-rays, and occasionally an MRI or stress x-rays. If a partial knee isn't right for you, a total knee replacement or, for some younger patients, a knee osteotomy may be.
Partial or total knee replacement?
| Comparison | Partial knee | Total knee |
|---|---|---|
| Part of knee replaced | One compartment | All joint surfaces |
| Ligaments kept | Both cruciates kept | ACL removed (PCL sometimes kept) |
| Incision and tissue disturbance | Smaller | Larger |
| Early recovery | Usually quicker, shorter hospital stay | Usually slower |
| Early complications (clots, infection, medical) | Lower in large registry studies | Higher |
| Feel of the knee | Often described as more natural | Good, but more often “aware” of the knee |
| Chance of revision surgery | Higher over time | Lower |
Planning & technology
A partial knee is a precise operation. The small implant has to be positioned accurately and the ligament balance kept just right. Dr Arora offers:
Robotic-assisted partial knee replacement. A CT-based 3D plan of your knee is carried out in theatre with the help of a robotic arm. Ligament tension is measured through the range of movement before any bone is prepared, and the arm's boundaries help keep bone preparation within the planned area. Published studies show more precise implant positioning than manual techniques. The system supports Dr Arora's planning and technique, and he performs and controls every step of the operation.
3D planning and Patient-Specific Instrumentation. Your knee is planned in 3D from your own scans, so implant size and position are matched to your anatomy before surgery. The plan is delivered with cutting guides 3D-printed to fit your bone like a glove and execute the cuts to accommodate the implant unique to your anatomy.
Robotic Hip & Knee Replacement
What is involved in unicompartmental knee replacement?
Preparation of the bone
Through a smaller incision, only the damaged compartment is prepared. Less bone and cartilage are removed than in a total knee replacement.
Implantation
Metal components are fitted to the thigh bone and shin bone in that compartment, with a durable plastic bearing between them. The rest of the joint and your own ligaments are left untouched.
Alignment and testing
Alignment and ligament balance are checked carefully, and the knee is moved through its range to test stability before the incision is closed.
Your recovery
Because less tissue is disturbed, early recovery is often quicker than after a total knee replacement, though it varies between individuals. Physiotherapy and a structured rehabilitation program remain important.
Recovery at a glance.
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Day 0
Walking with a frame or crutches, often within hours
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2–3 nights
Usual hospital stay. Day surgery is possible for selected patients.
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1–3 weeks
Weaning off walking aids
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around 3-4 weeks
Driving, once cleared at review
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2-4 weeks
Return to desk-based work
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6-12 weeks
Most normal activities, including low-impact exercise
Everyone recovers differently. See Post-operative Recovery & Rehab Protocols.
General risks overview
IMPORTANT TO KNOW
As with any surgical procedure, partial knee replacement carries risks. Potential risks and complications include:
Infection
Blood clots (deep vein thrombosis or pulmonary embolism)
Stiffness or ongoing pain
Progression of arthritis in other parts of the knee, which may require conversion to a total knee replacement
Implant wear or loosening
Fracture of the shin bone near the implant
Dislocation of the plastic bearing (with mobile-bearing designs).
Nerve or blood vessel injury
Risks associated with anaesthesia
This is a general overview and not a complete list. Dr Arora will discuss the risks and benefits relevant to you in detail before surgery.
Partial Knee Replacement Frequently Asked Questions
Am I suitable?
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You may be if your arthritis is limited to one compartment, your ACL is intact, and your knee moves well with only mild deformity. Dr Arora will assess this through examination and standing x-rays. See "Am I suitable?" above.
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There's no strict age limit. Younger, active patients appreciate the more natural feel. Older patients often benefit from the quicker recovery and lower rate of early complications.
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Not necessarily. Higher body weight is no longer considered an automatic barrier for many modern implants, but it increases surgical risk overall. It is assessed individually.
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A partial knee relies on your own ligaments for stability. If the ACL is torn or worn out, the knee may be unstable and the implant may wear faster, so a total knee is usually recommended.
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Often yes. Mild kneecap wear without kneecap symptoms doesn't usually rule out a medial partial knee. Significant kneecap pain or damage may favour a total knee.
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Yes. When both hips need replacing, the anterior approach can be used on each side, either together or a few months apart.
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Yes, if both are suitable. Depending on your health, they may be done together or a few weeks to months apart.
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Both treat arthritis on one side of the knee. An osteotomy realigns your own bone and suits selected younger, very active patients with malalignment. A partial knee resurfaces the worn area and gives more predictable pain relief in established arthritis. See Knee Osteotomy.
The operation
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Dr Arora uses robotic-arm assistance for most partial knee replacements. It helps position the small implant precisely and balance the ligaments. See Robotic Hip & Knee Replacement.
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Usually around 8–10 cm, smaller than for a total knee replacement.
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Metal components (usually cobalt-chrome or titanium) on the thigh bone and shin bone, with a durable plastic bearing between them. Some designs are cemented and others press-fit (cementless), and the bearing may be fixed or mobile.
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Usually a spinal anaesthetic with sedation, often with local anaesthetic around the knee for pain relief. Your anaesthetist will discuss the options.
Recovery
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Most people find early recovery quicker and more comfortable, with less swelling and an easier return of bend. Rehabilitation exercises are still important.
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Driving is often possible from around three to four weeks, once cleared at review. Desk-based work is often possible from two to four weeks, and physical work takes longer.
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Because your own ligaments are kept, many people say a partial knee feels more natural than a total knee. Some awareness of the knee is still common, especially in the first year.
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Kneeling is safe for the implant. It can be uncomfortable at first because of the scar, but many people kneel more easily after a partial knee than after a total.
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Walking, cycling, swimming, golf, gym work, hiking and doubles tennis are commonly enjoyed. Running and high-impact sport place more load on the implant and should be discussed with Dr Arora.
The long term
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Many partial knees last 15 years or more. However, registry data show they are revised more often than total knee replacements over time, so the long-term picture is part of the decision.
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The main reasons are arthritis developing in another part of the knee, loosening of the implant, and unexplained pain. Careful patient selection and accurate implant positioning help reduce these risks. The threshold to convert a partial knee to a total is also lower than for revising a total knee, which partly explains the higher figure.
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Some patients eventually need conversion to a total knee, usually because arthritis progresses elsewhere in the knee. Many never do. Your knee will be monitored at regular reviews.
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Because a partial knee removes relatively little bone, conversion to a total knee is usually less complex than revising a total knee. Results may not be quite as good as a first-time total knee, and occasionally extra implant components are needed.
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Typically at two weeks, six weeks and around three months, then at one year and periodically after that with x-rays.
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Contact us promptly if you have fever, increasing wound redness or discharge, a sudden increase in pain or calf swelling. If you have chest pain or shortness of breath, call 000.
Trusted resources
These independent sources give more information about partial knee replacement.
External links are provided for general information. Dr Arora is not responsible for the content of external websites. Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an appropriately qualified health practitioner.
Knee Surgery in Melbourne
If you would like to discuss your symptoms or treatment options, contact Dr Varun Arora to schedule a consultation.