In plain language
What is unicompartmental knee replacement?
A unicompartmental—or partial—knee replacement resurfaces only the arthritic compartment of the knee, most commonly the inner medial side. The healthier cartilage, bone and major ligaments in the remaining compartments are preserved. It is a smaller operation than total knee replacement, but it is suitable only when symptoms, examination and weight-bearing X-rays confirm that the arthritis is genuinely limited to one compartment.Who it may help
When might it be considered?
- Pain and joint-space loss confined mainly to one knee compartment, usually the medial side
- A stable knee with functional ligaments and a deformity that can be corrected
- Preserved cartilage in the other load-bearing compartment and no major inflammatory arthritis
- Persistent symptoms despite appropriate exercise, medication, activity changes and other nonsurgical care
Before surgery
What may be considered first?
- Exercise-based rehabilitation, strength work and weight optimisation
- Medication, bracing, walking aids and selected injections where appropriate
- Joint-preserving realignment surgery in selected younger patients
- Total knee replacement when arthritis, deformity or instability involves more than one compartment
Inside the operating theatre
What actually happens during the operation?
Confirming isolated disease
The pain pattern, ligament stability and weight-bearing X-rays are assessed together. The surgeon checks the other compartments because a partial replacement cannot reliably treat widespread arthritis.
Inspecting the whole knee
Through a smaller incision at the front of the knee, the surgeon inspects the joint and confirms that the remaining cartilage and ligaments are suitable before committing to a partial replacement.
Resurfacing one compartment
A thin layer of worn bone and cartilage is removed only from the affected femoral condyle and matching tibial surface. The healthy opposite compartment is left intact.
Fitting the smaller implants
A small metal femoral component and tibial tray are positioned in the treated compartment, with a medical-grade plastic bearing between them. Implant alignment, stability and movement are checked carefully.
Final assessment and closure
The surgeon checks that the knee straightens, bends and remains balanced before washing and closing the wound. If the arthritis or ligament findings are unsuitable, conversion to a total replacement may sometimes be necessary.
After the operation
What does recovery involve?
Early priorities are swelling control, full knee straightening, progressive bending and safe walking.
Because less bone and soft tissue are disturbed, recovery often feels quicker than after total knee replacement, although pain, bruising and temporary weakness are still expected.
Driving, work and sport resume progressively. The preserved knee may feel more natural to some patients, but the implant still requires protection from repetitive high-impact loading.
Informed consent
Important risks to understand
- Infection
- Blood clots
- Stiffness
- Persistent pain
- Bearing dislocation or wear
- Fracture
- Implant loosening
- Progression of arthritis in the unreplaced compartments
- Conversion to total knee replacement in the future
This is a general guide, not a complete consent discussion. Your surgeon will explain risks specific to your diagnosis, health, anatomy and proposed technique.
Common patient questions
Questions people often ask
Is partial knee replacement better than total knee replacement?+
Neither operation is universally better. In a properly selected patient, partial replacement preserves more of the native knee and often allows a quicker recovery. Total replacement is more appropriate when arthritis is widespread, the knee is unstable or deformity cannot be corrected.
Can arthritis develop in the rest of the knee?+
Yes. The untreated compartments remain natural and may develop arthritis over time. This is one reason patient selection and long-term follow-up matter.
Can robotic assistance be used?+
Robotic assistance may be used to map the knee and help the surgeon plan implant position and balance. The surgeon remains in control, and technology does not replace the need for the correct diagnosis and indication.
Clinical references
These independent patient resources informed the general explanation above.