In short
Not every arthritic knee needs the whole joint replaced. If only one compartment is worn, a partial replacement may preserve more of your natural knee — but only some patients qualify.
The knee is not a single joint surface. It has three compartments: the inner (medial), the outer (lateral) and the one behind the kneecap. Arthritis does not always attack all three equally, and that is the basis of the choice between a partial and a total knee replacement.
What a partial knee replacement is
A partial, or unicompartmental, knee replacement resurfaces only the worn compartment and leaves the rest of the joint — including healthy cartilage and both cruciate ligaments — untouched. In the majority of cases it is the inner compartment that wears first, which is why medial partial replacements are the most common.
Who qualifies
- Arthritis confined to one compartment on X-ray and examination
- Intact ligaments, particularly the anterior cruciate ligament
- Reasonable range of movement, without severe fixed stiffness
- Deformity that is not severe and can be corrected passively
Inflammatory arthritis such as rheumatoid arthritis usually affects the whole joint, so a total replacement is generally the appropriate choice in those patients.
How they compare
A partial replacement involves a smaller incision, less bone removal and typically a quicker early recovery. Because both cruciate ligaments are preserved, many patients report that the knee feels closer to natural.
A total replacement addresses the entire joint, which means arthritis cannot progress elsewhere in the knee and require further surgery. It is the more predictable operation across a wider range of patients, which is why it remains far more common.
What decides it in practice
Standing X-rays showing the joint under load, sometimes supported by an MRI, tell your surgeon which compartments are worn. Examination assesses ligament stability and whether deformity corrects. In some cases the final decision is confirmed once the joint is directly visualised during surgery, and you should consent for both possibilities.
If you have been told you need a knee replacement, it is entirely reasonable to ask whether a partial is an option for you and why or why not.
Frequently asked questions
Does a partial knee replacement last as long as a total?+
Partial replacements have a slightly higher rate of revision over time, partly because arthritis can progress in the compartments that were left alone. In exchange, they preserve more natural knee structure and usually feel more like your own knee.
Can a partial be converted to a total later?+
Yes. If arthritis progresses in the other compartments, a partial replacement can generally be converted to a total knee replacement, which is one reason it is an attractive option for suitable younger patients.
How do I know which one I need?+
It depends on which compartments are worn, the condition of your ligaments, your alignment and your range of movement. X-rays and clinical examination decide it, and the final call is sometimes confirmed during surgery.
This article is general health information, not medical advice, and it cannot account for your individual circumstances. Please consult a qualified orthopaedic specialist about your own symptoms before making treatment decisions.
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