If your knee arthritis has reached the point where injections, medications, activity changes, and physical therapy are no longer giving you enough relief, the next question may be: Do I need a partial knee replacement or a total knee replacement?
The answer is not based simply on age, pain level, or how bad an X-ray looks. It depends on where the arthritis is located, how stable the knee is, how well the remaining compartments are preserved, your alignment and motion, your activity goals, and what your surgeon finds on a careful examination and imaging review.
A partial knee replacement can be an excellent option when arthritis is truly confined to one compartment. A total knee replacement is usually the better choice when arthritis involves multiple parts of the knee or when the remaining knee cannot reliably support a partial replacement.
The most important principle is simple: do not choose the smaller operation just because it is smaller, and do not choose the larger operation just because it sounds more definitive. Choose the operation that matches the actual pattern of disease.
What is a partial knee replacement?
A partial knee replacement, also called a unicompartmental knee arthroplasty, resurfaces only the worn portion of the knee rather than replacing the entire joint surface.
The knee is commonly described as having three compartments:
- The medial compartment, on the inner side of the knee
- The lateral compartment, on the outer side
- The patellofemoral compartment, where the kneecap moves against the femur
Most partial knee replacements treat isolated arthritis of the medial compartment.
Because healthy areas of the knee are preserved, a partial replacement keeps more native bone, cartilage, and ligament structures than a total knee replacement. The American Academy of Orthopaedic Surgeons notes that partial knee replacement is an alternative to total replacement when arthritis is limited to one area of the knee. Read the AAOS patient guide to partial knee replacement.
What is a total knee replacement?
A total knee replacement, or total knee arthroplasty, resurfaces the main joint surfaces of the femur and tibia across the knee rather than only one compartment.
It is generally the more appropriate operation when arthritis is widespread, when more than one compartment is significantly diseased, when deformity is substantial, or when the soft-tissue and ligament environment makes a partial replacement unreliable.
Both operations are designed to reduce arthritic pain and restore function. The difference is how much of the knee needs to be resurfaced to treat the disease effectively.
Who is a good candidate for partial knee replacement?
The best candidate usually has advanced osteoarthritis concentrated in a single compartment, most commonly the medial side of the knee.
A surgeon will look for several things:
- Pain that matches the location of the arthritis
- X-rays showing severe wear primarily in one compartment
- Reasonably preserved cartilage in the other parts of the knee
- Functional ligament stability
- Motion that is good enough to support a partial replacement
- Correctable rather than severe fixed deformity
- Symptoms that have not responded adequately to appropriate nonsurgical care
AAOS patient guidance emphasizes that arthritis should be limited to one compartment and notes that inflammatory arthritis, substantial stiffness, or ligament damage may make partial replacement inappropriate. AAOS: Unicompartmental Knee Replacement.
Candidacy is more nuanced than a checklist, however. Mild changes elsewhere on an X-ray do not automatically rule out partial replacement. What matters is whether those other areas are clinically significant enough to threaten the success of a compartment-preserving operation.
What usually makes total knee replacement the better choice?
Total knee replacement becomes more appropriate when the arthritis is not truly isolated.
Examples include:
- Advanced wear in both the medial and lateral compartments
- Significant arthritis in the patellofemoral joint plus another compartment
- Major fixed deformity
- Significant instability or ligament insufficiency
- Inflammatory arthritis affecting the joint diffusely
- Severe stiffness that is unlikely to be corrected reliably with a partial replacement
- A pain pattern that does not match one isolated compartment
The key question is not, “Can I technically put a partial implant in this knee?” It is, “Will the rest of this knee remain healthy and stable enough for the partial replacement to make sense long term?”
Partial vs total knee replacement: which feels more natural?
One reason partial knee replacement remains attractive is that it preserves more of the patient’s native knee.
A 2025 systematic review and meta-analysis including 19 studies and roughly 4,500 knees found that patients who underwent unicompartmental knee replacement reported better Forgotten Joint Scores than patients who underwent total knee replacement. In simple terms, patients with partial replacements were more likely to report less awareness of the artificial joint during daily life. The authors cautioned that the included studies were heterogeneous, but the overall direction favored partial replacement. Read the 2025 JBJS Open Access review.
That does not mean every partial knee feels natural, or that every total knee feels artificial. It means that preserving more native anatomy may provide a functional advantage for some appropriately selected patients.
Is recovery faster after partial knee replacement?
Often, yes.
Partial knee replacement generally involves less bone resection and a smaller surgical footprint than total knee replacement. AAOS notes that patients often spend little or no time in the hospital and may return to normal activities sooner after partial replacement. AAOS patient guide.
A large 2019 BMJ systematic review comparing patient-relevant outcomes found shorter hospital stays after unicompartmental knee replacement across trial, cohort, and registry data. It also found several short-term complication outcomes favoring partial replacement in large datasets. Read the BMJ systematic review.
For a patient, that can translate into advantages such as:
- Less early surgical trauma
- Earlier return of motion in many cases
- Faster progression in walking and daily activities for some patients
- Preservation of more native knee structures
Recovery still varies substantially from person to person. A partial knee replacement is still major orthopedic surgery and still requires appropriate rehabilitation.
Does partial knee replacement have a higher revision risk?
This is one of the most important tradeoffs to understand.
Large registries have consistently reported higher revision rates after partial knee replacement than after total knee replacement. A 2024 meta-analysis combining 98 clinical studies and seven national registries found higher revision rates for unicompartmental knee replacement than total knee replacement in both published studies and registry data. Read the 2024 review.
National Joint Registry data have also shown higher revision risk for partial knee replacement as a group, even though partial replacement may have lower early medical complication risks in some populations. Read the National Joint Registry analysis.
Why might a partial knee eventually need revision?
Common reasons include:
- Arthritis progressing in another compartment
- Implant loosening
- Persistent pain
- Bearing problems in certain implant designs
- Infection or fracture, although these are less common causes
A systematic review of medial partial knee failures found that progression of arthritis elsewhere in the knee and aseptic loosening were among the most common reasons for revision. Read the failure-mode review.
This does not mean a partial knee is a poor operation. It means the advantages of a smaller, more tissue-preserving procedure have to be weighed against the possibility that the knee may need further surgery later.
What did the TOPKAT randomized trial show?
One of the most useful studies for patients comparing partial and total knee replacement is the TOPKAT trial, a multicenter randomized trial of 528 patients with isolated medial compartment osteoarthritis.
At five years, both operations produced good results. The study found no statistically significant difference in the primary Oxford Knee Score between the two groups. Revision rates were also similar in the trial at five years: 10 of 245 partial knee replacements and 8 of 269 total knee replacements required revision. Partial knee replacement was more cost-effective in the study and several secondary outcomes favored partial replacement, although many differences were small. Read the Lancet TOPKAT trial.
Why can randomized-trial results look better than registry revision data?
One likely explanation is patient selection and surgeon experience. In TOPKAT, surgeons performing partial replacement were experienced with the operation. Real-world registry data include a much wider range of surgeons, hospitals, procedure volumes, and patient selection.
That difference matters. Partial knee replacement is especially dependent on getting the indication right.
Is partial knee replacement only for older patients?
No.
Age alone does not determine whether a partial or total replacement is appropriate. Younger active patients may be attracted to partial replacement because it preserves more native anatomy and may support a more natural-feeling knee. Older patients may also be excellent candidates when arthritis is isolated.
The decision should be based more heavily on:
- Arthritis pattern
- Ligament stability
- Deformity
- Bone quality
- Activity expectations
- Health status
- Long-term priorities
A younger patient also has more years during which arthritis could progress elsewhere in the knee, so revision risk becomes part of the discussion.
What about sports and higher-level activity?
Partial knee replacement may have advantages for patients hoping to return to a higher level of recreational activity.
A 2026 systematic review and meta-analysis found a greater rate of return to high-impact sports after unicompartmental knee replacement compared with total knee replacement in the available literature. Read the 2026 review.
That does not mean high-impact sports are automatically recommended after joint replacement. Activity advice should still be individualized based on implant type, bone quality, previous injuries, sport demands, and the surgeon’s assessment.
What role does robotic assistance play?
Robotic assistance can be particularly useful in partial knee replacement because the operation depends on accurate localization of the diseased compartment, implant positioning, alignment, and balance while preserving the unaffected knee.
At Pacific Bone & Joint, robotic technology is used as a surgical planning and execution tool, not as an autonomous surgeon. Dr. Morton controls the operation, while the robotic platform helps map anatomy and guide planned bone preparation and implant positioning.
The specific system depends on the procedure and surgical location. You can learn more about the practice’s approach to robotic hip and knee replacement in Hawai‘i.
Robotics does not turn a poor partial-knee candidate into a good one. Technology can improve execution, but it cannot fix the wrong indication.
Do I need an MRI to decide between partial and total knee replacement?
Not always.
For many patients, standing X-rays provide the most important information because they show how the knee behaves under load. Your surgeon may use several views to assess each compartment, alignment, bone loss, and joint-space narrowing.
MRI can sometimes be useful when symptoms and X-rays do not match, or when there is uncertainty about cartilage, ligament, meniscus, or other pathology. But an MRI is not automatically required before every partial knee replacement.
The decision should come from the combined clinical picture, not a single image.
What if my MRI shows arthritis in more than one area?
MRI is extremely sensitive and can show cartilage changes that may not be clinically important.
That is why the presence of an abnormality somewhere else in the knee does not automatically mean total knee replacement is required. Surgeons weigh the severity and location of those findings against standing X-rays, symptoms, examination, alignment, and function.
In other words, the question is not whether another compartment is perfectly pristine. It is whether that compartment is healthy enough to preserve.
Can a partial knee replacement later be converted to a total knee replacement?
Yes.
If a partial replacement fails because arthritis progresses, the implant loosens, pain persists, or another mechanical problem develops, conversion to a total knee replacement may be possible.
However, patients should not think of a partial replacement as simply a temporary “starter knee” with an easy guaranteed conversion later. Revision surgery can be more complex than a primary total knee replacement, especially when there is bone loss, implant loosening, or other structural damage.
That is another reason to use partial knee replacement when it is the right definitive operation for the current disease pattern, not merely as a way to postpone total replacement at all costs.
Does kneecap arthritis rule out a partial knee replacement?
Not necessarily.
This is an area where simplistic rules can be misleading. Some patients with radiographic patellofemoral changes can still do well with a medial partial knee replacement, especially when those changes are not the dominant source of symptoms.
Severe symptomatic patellofemoral disease, however, may push the decision toward a different operation.
Your surgeon should determine whether the kneecap compartment is merely showing age-related changes or whether it is an important contributor to your pain.
What if only the inside of my knee hurts?
Pain concentrated on the inside of the knee is a clue, but it is not enough by itself to establish candidacy.
Medial knee pain can also come from:
- Meniscus pathology
- Pes anserine irritation
- Medial collateral ligament problems
- Bone marrow lesions
- Referred pain
- More diffuse arthritis that happens to hurt medially
The location of the pain should agree with the imaging and examination before a partial replacement is chosen.
Should I keep trying injections and therapy before choosing surgery?
If nonsurgical treatment is still providing acceptable relief and function, there is usually no reason to rush into joint replacement simply because arthritis appears on an X-ray.
Appropriate nonsurgical care can include weight management, strengthening, activity modification, medications when medically appropriate, bracing, physical therapy, and selected injections.
For patients with knee arthritis and excess weight, even modest weight loss may reduce symptoms and joint load. We recently reviewed that evidence in our guide to weight loss and knee arthritis.
Once pain and loss of function remain unacceptable despite reasonable nonsurgical care, the discussion changes from “How do we avoid surgery?” to “Which operation best fits this knee?”
Partial knee versus total knee: the tradeoff in plain language
For a properly selected patient, a partial knee replacement may offer:
- More native knee preserved
- Smaller surgical footprint
- Often faster early recovery
- Better range of motion in many series
- A more natural-feeling knee for some patients
- Potentially lower early medical complication burden
The tradeoffs include:
- It only works when disease is sufficiently localized
- Arthritis can progress elsewhere
- Registry data show a higher long-term revision rate than total knee replacement
- Surgeon experience and proper patient selection matter substantially
A total knee replacement may offer:
- Treatment of more widespread arthritis
- Greater applicability when multiple compartments are involved
- Lower revision rates in many national registries
- A more definitive solution for diffuse disease
Its tradeoffs include:
- More bone and joint surface are resurfaced
- Early recovery may be more demanding
- Some patients perceive the knee as less natural than a successful partial replacement
Neither operation is automatically “better.” The better operation is the one that matches the knee you actually have.
Questions to ask your surgeon
If you have been told you need knee replacement, useful questions include:
- Is my arthritis truly limited to one compartment?
- Which compartment is causing my pain?
- Are the other compartments healthy enough to preserve?
- Are my ligaments stable enough for a partial replacement?
- Is my deformity correctable?
- What are the reasons you recommend partial or total replacement in my specific knee?
- What is the revision tradeoff in my situation?
- Would robotic assistance be useful for my operation?
- What would make you change from a planned partial replacement to a total replacement?
- What should I expect from rehabilitation and return to activity?
A good joint-replacement decision should make sense when the surgeon shows you the X-rays and explains the anatomy. You should understand why your knee qualifies for one operation rather than simply being told which implant you are getting.
When should you consider an evaluation?
Consider an orthopedic evaluation if knee arthritis is causing persistent pain, limiting walking or work, disturbing sleep, preventing activities you value, or no longer responding adequately to nonsurgical treatment.
At Pacific Bone & Joint, the goal is not to push every patient toward the same procedure. The goal is to determine whether your knee is best treated with continued nonsurgical care, a joint-preserving strategy, partial knee replacement, or total knee replacement.
If you have been told you need a knee replacement and want to understand whether partial or total knee replacement fits your arthritis pattern, request an appointment with Pacific Bone & Joint for an individualized review of your symptoms, examination, and imaging.
Sources and further reading
- American Academy of Orthopaedic Surgeons. Unicompartmental (Partial) Knee Replacement. OrthoInfo.
- National Institute for Health and Care Excellence. Joint replacement (primary): hip, knee and shoulder. NG157. Recommendation 1.7.1, 2020; quality standard updated 2022.
- Beard DJ, et al. The clinical and cost-effectiveness of total versus partial knee replacement in patients with medial compartment osteoarthritis (TOPKAT): 5-year outcomes of a randomised controlled trial. The Lancet. 2019.
- Wilson HA, et al. Patient relevant outcomes of unicompartmental versus total knee replacement: systematic review and meta-analysis. BMJ. 2019.
- Poursalehian M, et al. Unicompartmental Knee Arthroplasty Offers More Natural Feeling Joints Compared with Total Knee Arthroplasty: A Systematic Review and Meta-Analysis. JBJS Open Access. 2025.
- Migliorini F, et al. Revision of unicompartmental knee arthroplasty: a systematic review. BMC Musculoskeletal Disorders. 2024.
- Vossen RJM, et al. A Greater Rate of Return to High-Impact Sports Favoring Unicompartmental Knee Arthroplasty Compared with Total Knee Arthroplasty: A Systematic Review with Meta-Analysis. Journal of Knee Surgery. 2026.
