Total knee replacement (TKR) resurfaces all three compartments of the knee — medial, lateral, and patellofemoral — and suits arthritis that has spread across the joint, offering reliable, long-studied pain relief. Partial, or unicompartmental, knee replacement (UKR/PKR) resurfaces only one worn compartment — usually the inner (medial) side — while preserving healthy bone, both cruciate ligaments, and the natural feel of the rest of the joint. Partial replacement is only appropriate when damage is genuinely confined to one compartment, the ligaments are intact, and there is no significant deformity; when arthritis involves more than one compartment or the whole joint, total replacement is generally the more durable, appropriate choice. Neither operation is a "lesser" or "bigger" version of the other — they are matched to different patterns of wear, and the right one for you is confirmed by X-rays and examination, not preference alone.
What is total knee replacement?
Total knee replacement resurfaces the ends of the thigh bone (femur) and shin bone (tibia), and usually the kneecap (patella) surface, with metal and high-grade plastic components. It addresses arthritis affecting the medial, lateral, and patellofemoral compartments together — which is the pattern seen in most advanced osteoarthritis. Both cruciate ligaments are typically removed as part of the standard technique, and the implant's own mechanism substitutes for their stabilising role.
What is partial (unicompartmental) knee replacement?
Partial knee replacement resurfaces only the damaged compartment — most commonly the medial compartment, since medial-sided wear is the most frequent isolated pattern of knee osteoarthritis in clinical practice. The lateral compartment, patellofemoral joint, and both the anterior and posterior cruciate ligaments are left untouched. Because less bone is removed and the knee's own ligaments continue to guide movement, many patients describe the replaced knee as feeling closer to natural.
Who is typically suited to partial knee replacement?
- Arthritis confirmed on examination and weight-bearing X-rays to be confined to one compartment, usually medial.
- Intact anterior cruciate ligament and no significant deformity beyond what the single-compartment wear explains.
- A reasonably preserved range of motion, without severe fixed stiffness.
- Patients who value a faster early recovery and a more natural-feeling knee, and who understand the trade-offs involved.
Who is typically suited to total knee replacement?
- Arthritis involving more than one compartment, or the whole joint.
- Significant deformity, ligament laxity, or fixed stiffness that a partial replacement would not adequately correct.
- Patients prioritising the most reliable, long-term pain relief over preserving native structures.
- Cases where previous surgery or anatomy make a partial replacement technically unsuitable.
Comparing recovery, longevity, and activity, honestly
Partial knee replacement generally involves a smaller incision, less disruption to the surrounding soft tissue, and — for the right candidate — a somewhat quicker return to walking and daily activity in the early weeks. Total knee replacement involves a larger dissection and a rehabilitation course that, while well-established and predictable, typically takes a bit longer to reach the same milestones. On durability, joint registries have generally recorded a higher revision rate for partial replacement than for total, driven partly by arthritis progressing in compartments that were not replaced, and partly by how carefully patients were selected in the first place. This is exactly why patient selection — not surgeon preference — drives the choice.
| Factor | Partial (UKR) | Total (TKR) |
|---|---|---|
| Compartments treated | One | All three |
| Bone & ligament preserved | More — ACL kept | Less — ACL/PCL removed |
| Incision & early recovery | Smaller, often quicker | Larger, well-established course |
| Suitable arthritis pattern | Single compartment only | Multi-compartment or whole joint |
| Revision risk (registry data) | Somewhat higher | Somewhat lower |
| Feel of the knee | Often described as more natural | Reliable, well-studied outcome |
General patterns from published literature and registry data, not individual guarantees. Your surgeon's clinical assessment and imaging determine which pattern applies to you.
Common myths, corrected
"Partial is the safer, easier option." Not necessarily — it is a more selective option, appropriate for a narrower set of patients. Choosing it for the wrong knee can mean a second operation sooner. "Total knee replacement is only for older or less active patients." Total replacement is offered based on the extent of joint damage, not age alone, and modern implants and rehabilitation support a good range of post-operative activity for suitable patients.
How the decision is actually made
Standing, weight-bearing X-rays of the whole leg, an examination of ligament stability and range of motion, and a conversation about your activity goals together determine which operation fits your knee. This is not a preference call made in advance — it is confirmed at assessment. See the knee replacement page for the broader overview, or read about osteotomy vs knee replacement if your arthritis is earlier-stage and joint preservation may still be an option. Book a consultation to have your knee assessed directly.