Treatment
Arthritis rarely ruins a whole knee at once. It usually destroys one compartment while the others remain perfectly good — and a partial knee replacement respects that. Only the worn surface is resurfaced; the healthy cartilage and, importantly, both cruciate ligaments stay exactly where they are. The result is a smaller operation, a quicker recovery, and a knee that keeps much of its own mechanics. The catch is that not every knee qualifies — so this page is as much about who shouldn’t have one as who should.
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Your knee is really three compartments in one joint: the inner side, the outer side, and the surface behind the kneecap. In most arthritic knees the damage concentrates in one of them — usually the inner. A partial replacement resurfaces just that compartment with a small metal and plastic bearing, and leaves everything else untouched: the other compartments, the collateral ligaments, and both cruciates. Keeping the cruciates is the detail that matters most, because they are what tell your knee where it is in space — which is why so many partial replacement patients describe the knee as feeling like their own rather than like an implant. Less bone is removed, less is disturbed, and recovery reflects that.
How much of the joint is resurfaced
Figures reflect typical courses in published series for suitable patients — our specialist will give you the numbers that apply to your own knee.
Most people weighing this up have one question dominating the rest. Tap yours — the straight answer is one scroll away.
Closer than a total replacement does — and there is a mechanical reason, not a marketing one. The cruciate ligaments are the knee’s internal guidance system: they control how the joint rolls and glides through a bend, and they carry the nerve endings that tell your brain where your leg is without looking. A total replacement removes at least one of them; a partial keeps both. That is why partial replacement patients more often report a knee that simply gets on with things — stairs, kneeling, deep bends — rather than one they remain aware of. Pain relief itself is excellent with either operation when the right one is chosen. What differs is the character of the knee afterwards, and for people who are active, kneel for work or worship, or simply want the joint to feel unremarkable, that difference is the whole point.
Partial replacement is a smaller operation than a total, and the risk profile follows: less blood loss, less physiological stress, and lower rates of the medical complications that follow bigger surgery — which matters more the older or less well you are. The uncommon: infection, blood clots in the leg, stiffness, ongoing pain, and problems with the implant such as loosening or the bearing not sitting perfectly. The specific one: arthritis progressing in a compartment that was healthy on the day — the main reason a partial ever needs converting to a total later. And the honest one about technique: implant position matters enormously in a partial, which is why planning and precision — including robotic assistance where it is used — are worth taking seriously. Even so, the single biggest determinant of a good result is not the tool but the selection: the right knee, chosen properly, treated by someone who does this regularly.
Quicker than most people expect, because so little is disturbed. Most patients are up and walking on the day of surgery, home within one to two days, off walking aids within one to three weeks, managing stairs and errands by two to four weeks, and driving around three to four. Comfortable, confident function usually arrives by about three months, with quiet improvement continuing for a year. The one thing that consistently separates good recoveries from slow ones is the same as ever: doing the strengthening work rather than waiting for the knee to sort itself out. Wherever you are:
The decision starts with what your imaging shows, not with which operation sounds nicer. A consultation examines the ligaments, checks whether the deformity corrects, and reads the wear pattern across all three compartments — then lays out partial, total, and non-surgical options with honest trade-offs for each.
Go in strong — it shortens everything afterwards. Thigh strengthening in the weeks before surgery reliably speeds recovery, and sorting the practical side early helps: a plan for the first fortnight, help at home, and realistic time off. Detailed instructions come well before the day.
Movement early, strength steadily, patience with the last 10%. Walk daily, do the exercises properly, and expect swelling to come and go for some weeks — that is normal, not a setback. Report calf pain, fevers, or a wound that looks angry. The knee keeps improving well past the point most people stop noticing.
Statistically, partials are revised somewhat more often than totals — and that number deserves unpacking rather than repeating. Most revisions are not the implant failing; they are arthritis appearing in a compartment that was healthy when you had the operation. Your knee kept living, and the parts you kept kept ageing. Two things make that far less alarming than it sounds. First, converting a partial to a total is a well-established, generally straightforward operation — quite unlike revising a failed total replacement, which is a considerably bigger undertaking. Second, the threshold for revising a partial is lower: a patient with a good knee and one grumbling compartment gets offered surgery earlier than someone with a total replacement that is merely imperfect, which inflates the comparison. Set against that: the great majority of partials are still serving their owners at ten years, having delivered a more natural knee for the whole of that decade.
This is the question that decides the result. A partial in the wrong knee disappoints; in the right knee it outperforms. Check your picture:
That pattern is what partial replacement was designed for. The next step is a consultation with your imaging: confirming the other compartments really are healthy, testing the ligaments properly, and weighing a partial against a total and against carrying on as you are.
A partial may not be your operation — and forcing one would be the wrong favour. Arthritis across several compartments, a stiff knee or a torn cruciate usually point toward a total replacement, which does an excellent job in exactly those knees. An assessment tells you which you are, with the reasoning.
And remember: the operation that fits your knee beats the operation that sounds smaller.
Tap the one that sounds like you — and get the straight answer:
A partial knee replacement — also called unicompartmental replacement — resurfaces only the worn compartment of the knee, most often the inner side. The healthy cartilage in the other compartments is left alone, and crucially both cruciate ligaments stay in place. Because the knee keeps its own ligaments and most of its own surfaces, it tends to move and feel more like a natural knee than a total replacement does.
Suitability is decided by the pattern of wear rather than by preference. The knee needs arthritis confined to one compartment, intact ligaments — particularly the ACL — reasonable movement, and a deformity that corrects on examination rather than being fixed. Roughly a quarter of arthritic knees meet those criteria. Widespread arthritis, inflammatory joint disease or significant stiffness point toward a total replacement instead.
Whichever matches your knee. A partial offers a smaller operation, quicker recovery, better movement and a more natural feel, but carries a somewhat higher chance of needing revision later because the untouched compartments keep ageing. A total replacement is more comprehensive and more predictable over the very long term, with a longer recovery and a knee that feels more mechanical. The wear pattern on your imaging usually settles the argument.
Faster than after a total replacement. Most patients walk the day of surgery, go home within a day or two, manage stairs and daily activities within two to four weeks, and drive at around three to four weeks. Comfortable, confident function typically arrives around three months, with continued improvement beyond that. Recovery is quicker largely because less bone is cut and the ligaments and other compartments are undisturbed.
The large majority are still working well at ten years, and many considerably longer. The most common reason one needs revising is not the implant failing but arthritis progressing in a compartment that was healthy at the time of surgery. If that happens, converting a partial to a total replacement is a well-established operation — which is one of the reasons a partial is an attractive first step for a suitable knee.
Related: Knee osteoarthritis · Total knee replacement · Knee osteotomy · Knee surgery
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