A detailed guide to unicompartmental knee replacement, including suitability, benefits, alternatives, risks and rehabilitation.
01
Why might this treatment be considered?
Partial knee replacement may be considered when osteoarthritis is confined to one compartment of the knee—most often the inner side—and the remaining compartments and key ligaments are suitable. Symptoms, examination, alignment and weight-bearing X-rays are considered together. If arthritis is more widespread, total knee replacement may be the more reliable option.
02
What does the procedure involve?
Only the damaged compartment is resurfaced, using a metal femoral component, a metal tibial component and a polyethylene bearing. More of the patient’s own bone, ligaments and unaffected joint surfaces are retained than in a total knee replacement. Final inspection during surgery may occasionally show that a total knee replacement is more appropriate, and this possibility is discussed beforehand.
Understanding your knee
Partial and total knee replacement
Partial replacement
Total replacement
BoneCartilageMetal implantPlastic bearing
A unicompartmental replacement resurfaces one affected side, retaining the other suitable joint surfaces. Total replacement resurfaces both sides of the femur–tibia joint. The kneecap compartment and ligaments are not shown.Original simplified educational diagram. Not to scale; not an operative plan. Soft tissues are omitted for clarity.
03
Potential benefits
Relief of pain arising from the affected compartment
Preservation of more natural bone and knee ligaments
A smaller operation with less blood loss and often a faster early recovery than total knee replacement
Movement that may feel more natural for some patients
A shorter hospital stay may be possible in suitable patients
04
Reasonable alternatives
Physiotherapy and an individual exercise programme
Activity modification, weight optimisation and medication when appropriate
A walking aid, brace or knee injection in selected circumstances
Total knee replacement
Delaying or deciding not to have surgery
05
Important risks and limitations
Every procedure carries risk. The likelihood and importance of each risk vary between individuals.
The general surgical risks of bleeding, infection, blood clots, wound problems and medical or anaesthetic complications
Ongoing pain, stiffness or less improvement than hoped
Progression of arthritis in the other knee compartments, which may require conversion to a total knee replacement
Wear, loosening or fracture around the implant
Instability or bearing problems; a mobile bearing can rarely dislocate
Nerve or blood-vessel injury, which is rare
A higher likelihood of later revision than with total knee replacement when all implants and patient groups are considered
The need to change to a total knee replacement during surgery if the arthritis or ligament condition is less suitable than expected
06
Recovery and expectations
Mobilisation and exercises begin soon after surgery, with walking aids used as required.
Early pain, swelling and bruising are expected but initial recovery is often quicker than after total knee replacement.
Physiotherapy and regular exercises restore movement, strength and confidence.
Blood-clot prevention, wound care and discharge arrangements are tailored to the individual.
Recovery continues over several months, and return to driving, work and sport depends on progress and clinical advice.
Shared decision-making
The relative advantages of partial and total knee replacement depend on the pattern of arthritis, ligament function, age, activity and priorities. These trade-offs, the possibility of conversion to total replacement and the option not to proceed are discussed through shared decision-making.
National Joint Registry evidence
Outcomes and revision surgery
The National Joint Registry (NJR) records joint replacement outcomes across the UK. Partial knee replacement is also described as unicompartmental knee replacement.
Measure
Published NJR evidence
What this means
Best-performing fixed-bearing brands
1.88% revised at 5 years
The best-performing fixed-bearing unicompartmental brands in the 2025 report were below 2% at five years.
Best-performing fixed-bearing brands
5.03% revised at 10 years
Selected modern partial knee implants can have good registry longevity when used in suitable patients.
Comparison with total knee replacement
Patient groups differ
Partial knee patients are typically younger, and age, case selection, implant choice and surgical experience influence revision risk.
Important context
These are population and implant-level figures, not a prediction for one person. Partial and total knee replacement are not interchangeable for every pattern of arthritis. Suitability and the trade-off between faster early recovery and later revision risk should be discussed individually.
Your diagnosis, expected benefit, material risks, alternatives and recovery plan will be discussed individually. You can take time to ask questions and may delay or decline treatment.