Total knee replacement vs partial knee: how surgeons decide

If you have been told you need a knee replacement, you have probably also heard the term “partial” or “unicompartmental” thrown around. The two operations are not interchangeable, and the decision between them depends on what part of the knee is worn out. This post walks through how surgeons actually decide.

The anatomy in two paragraphs

The knee has three compartments: medial (inside), lateral (outside), and patellofemoral (where the kneecap glides on the femur). Osteoarthritis can wear out any one of these, two of them, or all three.

A total knee replacement (CPT 27447) resurfaces all three compartments with metal and polyethylene components. A partial knee replacement — most often unicompartmental, sometimes called “uni” — resurfaces just one compartment (CPT 27446 for unicompartmental). A patellofemoral replacement (CPT 27437/27438) resurfaces just the kneecap compartment, and is uncommon.

The point of partial replacement is to preserve the parts of the knee that still work, including the ACL and PCL, which are removed in a typical total replacement.

When partial knee makes sense

A partial knee replacement is generally considered when:

The arthritis is confined to a single compartment, most often the medial compartment
The ACL is intact
The other compartments look healthy on imaging and at the time of surgery
The deformity is mild (modest varus, with the deformity correctable)
The range of motion is well preserved

For the right patient, partial knee replacement has real advantages:

Smaller incision, faster recovery (often weeks instead of months for return to baseline activity)
More “normal” feeling knee because the cruciate ligaments are preserved
Generally lower blood loss and shorter hospital or ASC stay
Easier revision to a total knee replacement later if needed

There are tradeoffs. Long-term registry data shows higher revision rates for partial knee replacement than for total knee — the partial may need to be converted to a total years later, especially if arthritis progresses in the other compartments. Registry data from the UK, Australia, and the US generally shows 10-year revision rates around 10-15% for partial vs 4-6% for total, though high-volume surgeons see substantially better partial-knee outcomes than the registry averages.

When total knee is the right call

Total knee replacement is the operation for:

Multi-compartment arthritis
Significant deformity (varus or valgus that does not correct passively)
ACL deficiency
Inflammatory arthritis (rheumatoid arthritis, post-infectious arthritis)
Severe stiffness or flexion contracture

Most patients who need a knee replacement get a total, because most knee arthritis is multi-compartment by the time it is symptomatic enough for surgery. Estimates vary, but in a typical orthopedic practice, around 5-15% of replacements are partial — at high-volume centers focused on partial knee, that fraction can be higher.

Total knee outcomes in 2026 are excellent for most patients. Modern implants and surgical techniques generally deliver:

90%+ patient satisfaction at 1 year
95%+ implant survival at 10 years
Same-day or next-day discharge for medically appropriate patients

The downside is that the knee will not feel completely “normal” — many patients describe it as functional but mechanically aware. Recovery is also longer than for partial knee.

What the surgeon will look at

The decision is made from imaging, exam, and intraoperative findings — in that order.

Imaging. Weight-bearing standing X-rays are essential. Non-weight-bearing X-rays can hide compartment narrowing. The standard four views (AP weight-bearing, lateral, sunrise, and a Rosenberg or 45-degree posterior view) usually tell the surgeon what compartments are involved. MRI is sometimes added for ACL evaluation, cartilage status, or unusual cases.

Exam. The surgeon will check range of motion, alignment (visible varus or valgus), ligament stability (especially the ACL), and patellar tracking. A varus deformity that corrects passively suggests an isolated medial compartment problem; one that does not correct suggests bone or capsular contracture and biases toward total.

Intraoperative findings. At the start of surgery for a planned partial knee, the surgeon usually inspects the other compartments first. If significant arthritis is found in a compartment that looked normal on X-ray, the plan typically converts to a total. Make sure the consent form covers this scenario.

Robotics and patient-specific implants

In 2026, robotic-assisted partial knee replacement (most often Mako) is widely available, and most large practices use it. The data is more favorable for robotic assistance in partial knee than in total knee — partial requires more precise positioning, and robotic systems have shown improvement in component alignment.

Patient-specific instrumentation (cutting guides based on preoperative CT or MRI) is another option, more often used for total knee. The data on improved outcomes is mixed.

These technologies are nice to have but should not be the deciding factor in choosing a surgeon. Surgeon volume and experience with the specific operation matter more.

Questions to ask before scheduling

Whether you are considering partial or total:

Based on my X-rays, am I a candidate for partial knee replacement? Why or why not?
How many partial knee replacements have you performed in the last year? Total knees?
What is your revision rate for each?
Where will the surgery happen — hospital, ASC?
What is my expected length of stay and recovery timeline?
What is the perioperative pain management plan? (Modern multimodal pathways usually include adductor canal or femoral nerve block, IV and oral pain medication, and a structured early mobilization.)
When will I be discharged with physical therapy, and at what frequency?
What is the plan if the partial converts to a total intraoperatively?
What is included in the bundled payment, and what is billed separately?

Cost considerations

Both procedures are typically covered by Medicare and commercial insurance. Cost-sharing depends on your plan, but for an elective replacement in 2026:

Out-of-network surgery should be avoided unless you understand the cost
Ambulatory surgery center facility fees are often lower than hospital outpatient fees
The implant cost is usually bundled into the facility fee, not billed separately to you
Anesthesia is billed separately and may have a separate network status

What this means for patients searching orthopedic.tel

Partial vs total knee replacement is a decision that benefits from a surgeon who does both regularly. A practice that does only total knee replacements is more likely to recommend a total knee; a practice that does both will give you a more honest assessment.

If you have been told you need a knee replacement and the conversation about partial never happened, ask. Imaging from a recent visit is usually enough to know.

The American Academy of Orthopaedic Surgeons and OrthoInfo knee replacement guide are reasonable patient-facing references.

Find a knee specialist near you and ask the question.

This post was drafted by AI and reviewed by our editorial team. Last updated 2026-05-29.