Partial Knee Replacement: Is It Right for You?

Key Takeaways

• Partial knee replacement (PKR) replaces only the damaged portion of the knee
• Best for patients with arthritis limited to one compartment of the knee
• Faster recovery and more natural knee feel compared to total replacement
• Not everyone is a candidate—specific criteria must be met
• Revision to total knee replacement may eventually be needed
• Success rates are excellent for appropriately selected patients

When osteoarthritis affects only part of your knee, replacing the entire joint may be more than necessary. Partial knee replacement offers a middle ground—addressing the damaged area while preserving healthy tissue.

This guide helps you understand whether partial knee replacement might be right for your situation.

Understanding the Knee’s Compartments

Knee Anatomy Basics

Your knee has three compartments:

Medial compartment:

• Inside of the knee (closest to other leg)
• Most commonly affected by arthritis
• Bears about 60% of body weight

Lateral compartment:

• Outside of the knee
• Less commonly affected alone
• Bears about 40% of body weight

Patellofemoral compartment:

• Between kneecap and thighbone
• Affected in “runner’s knee” and certain arthritis patterns

Why Compartments Matter

Arthritis doesn’t always affect the whole knee uniformly. If damage is isolated to one compartment, replacing only that section:

• Preserves healthy bone and cartilage
• Maintains more natural knee mechanics
• Allows faster recovery
• Provides better range of motion

What Is Partial Knee Replacement?

The Procedure

Also called unicompartmental knee arthroplasty (UKA), partial knee replacement:

• Replaces only the damaged compartment
• Uses smaller implants than total replacement
• Preserves cruciate ligaments (usually)
• Maintains natural knee anatomy in unaffected areas

Types of Partial Replacement

Medial unicompartmental:

• Most common type
• Replaces inner compartment
• Excellent long-term results

Lateral unicompartmental:

• Less common
• Replaces outer compartment
• Technically more challenging

Patellofemoral replacement:

• Replaces kneecap joint only
• Specific indications
• Less commonly performed

Are You a Candidate?

Ideal Candidates

Disease criteria:

• Arthritis limited to one compartment
• Intact anterior cruciate ligament (ACL)
• Minimal deformity (leg reasonably straight)
• Functioning posterior cruciate ligament

Patient factors:

• Age: Often 55-75 (though not absolute)
• Weight: BMI under 35-40 (varies by surgeon)
• Activity level: Moderate (not high-impact athletics)
• Good overall health

Who Is NOT a Candidate

Anatomical exclusions:

• Arthritis in multiple compartments
• ACL deficiency
• Significant deformity (bowlegged or knock-kneed)
• Inflammatory arthritis (RA, etc.)
• Fixed flexion contracture (can’t straighten knee)

Other factors:

• Very young patients (implant longevity concern)
• Very high activity demands
• Morbid obesity
• Unrealistic expectations

The 10-15% Rule

Only about 10-15% of patients needing knee replacement are candidates for partial. The rest have disease too advanced or widespread for partial replacement.

Partial vs. Total Knee Replacement

Advantages of Partial

Faster recovery:

• Hospital stay: Often same-day discharge
• Walking: Same day with walker
• Return to normal activities: 4-6 weeks
• Full recovery: 2-3 months

Better function:

• More natural feeling knee
• Better range of motion
• Preserved proprioception (joint position sense)
• Lower blood loss during surgery

Bone preservation:

• Less bone removed
• Easier revision if needed later
• Smaller incision
• Less muscle disruption

Advantages of Total Replacement

Durability:

• 15-20+ year longevity common
• Lower revision rates long-term
• Treats all compartments

Broader application:

• Works for any arthritis pattern
• Not dependent on ligament status
• More surgeons experienced with technique

Comparison Table

Factor	Partial	Total
Hospital stay	Same day-1 night	1-3 nights
Return to driving	2-3 weeks	4-6 weeks
Full recovery	2-3 months	3-6 months
Range of motion	Better	Good
Natural feel	More natural	Less natural
10-year survival	90-95%	95-98%
Revision rate	Higher	Lower

The Procedure

Before Surgery

Preoperative preparation:

• Medical clearance
• Blood tests
• Imaging (X-rays, possibly MRI)
• Physical therapy assessment
• Stop certain medications

Day of surgery:

• Arrive 1-2 hours early
• IV placement
• Anesthesia discussion
• Marking of surgical leg

During Surgery

Typical procedure:

1. Anesthesia (spinal or general)
2. Small incision (3-4 inches)
3. Damaged bone and cartilage removed
4. Metal and plastic implants placed
5. Closure and bandaging

Duration: 1-2 hours

Implant components:

• Metal cap on femur (thighbone)
• Metal tray on tibia (shinbone)
• Plastic spacer between them

Anesthesia Options

Spinal anesthesia:

• Numb from waist down
• Often with sedation
• Faster recovery from anesthesia
• May include nerve block for pain

General anesthesia:

• Completely asleep
• May be combined with nerve block

Recovery Timeline

Hospital Stay

Many patients go home same day. Criteria for discharge:

• Pain controlled with oral medication
• Able to walk with walker or crutches
• Able to use bathroom
• Have help at home

Week 1

What to expect:

• Pain and swelling (improving daily)
• Walking with walker or crutches
• Bending knee to about 90 degrees
• PT exercises at home
• Ice and elevation important

Typically can:

• Bear weight as tolerated
• Shower (after waterproof dressing or staple removal)
• Do simple self-care

Weeks 2-4

Progress:

• Transition from walker to cane
• Increased range of motion
• Decreased swelling
• Regular PT sessions

Milestones:

• Staple/suture removal (2 weeks)
• Driving (often 2-3 weeks)
• Return to desk work (2-3 weeks)

Weeks 4-8

Progress:

• Walking without assistive devices
• Nearly full range of motion
• Decreased pain
• Building strength

Typical activities:

• Light household tasks
• Short walks outside
• Stationary bike
• Swimming (once incision healed)

3 Months and Beyond

Full recovery:

• Most patients feel back to normal
• Continue strengthening exercises
• Return to golf, hiking, biking
• Full activity by 3-6 months

Outcomes and Success Rates

What Research Shows

Survivorship:

• 10-year implant survival: 90-95%
• 15-year survival: 80-90%
• 20-year survival: 70-85%

Patient satisfaction:

• 90%+ report significant improvement
• Most rate knee as “good” or “excellent”
• Higher satisfaction than total knee in some studies

Factors Affecting Success

Better outcomes:

• Appropriate patient selection
• Experienced surgeon (volume matters)
• Good rehabilitation
• Normal weight
• Realistic expectations

Risk factors for revision:

• Younger age at surgery
• Higher BMI
• Progression of arthritis
• ACL problems
• Technical issues

Revision Rates

• ~1-2% per year need revision
• Higher than total knee replacement
• Revision to total knee is usually straightforward
• Good outcomes after revision

Potential Complications

Early Complications

Blood clots:

• Risk: 1-2%
• Prevented with blood thinners, compression
• Symptoms: Calf pain, swelling

Infection:

• Risk: Less than 1%
• Treated with antibiotics, sometimes surgery
• Symptoms: Fever, redness, drainage

Stiffness:

• Risk: 2-5%
• Managed with PT, sometimes manipulation

Later Complications

Implant loosening:

• Risk: Main long-term concern
• May require revision
• Usually develops gradually

Bearing dislocation:

• Risk: 1-2% with mobile bearing designs
• May need revision

Progression of arthritis:

• Other compartments can develop arthritis
• May eventually need total knee replacement

Cost and Insurance

Typical Costs

• Hospital and surgery: $15,000-$40,000
• Often less than total knee due to shorter stay
• Physical therapy: $1,500-$3,000

Insurance Coverage

• Medicare and most insurance cover when medically necessary
• May require prior authorization
• Deductibles and copays apply
• Outpatient surgery may have different coverage

Choosing a Surgeon

What to Look For

Experience matters:

• Ask how many partial knees they do yearly
• Higher volume associated with better outcomes
• Minimum: 12-25 per year recommended

Questions to ask:

• What percentage of your knee replacements are partial?
• What are your outcomes and revision rates?
• Am I a good candidate based on my X-rays/MRI?
• What approach/implant do you use?

Robotic-Assisted Surgery

Many surgeons now use robotic assistance:

Potential benefits:

• More precise bone cuts
• Better implant positioning
• May improve longevity

Considerations:

• Not proven superior in all studies
• Surgeon experience still most important
• May increase cost

Frequently Asked Questions

How long will a partial knee replacement last?

Average is 15-20 years, but ranges from 10-25+ years. Your activity level, weight, and how well the surgery was done all matter. Some patients never need revision.

Can I kneel after partial knee replacement?

Most patients can kneel, though it may feel different or uncomfortable. It’s generally easier than after total knee replacement due to less tissue disruption.

What activities can I do after recovery?

Most low-impact activities are fine: walking, hiking, cycling, swimming, golf, doubles tennis. High-impact activities (running, jumping) are generally discouraged to protect the implant.

Why would I need revision to a total knee?

Common reasons include: loosening of the implant, progression of arthritis to other compartments, persistent pain, or bearing problems. Revision to total knee typically has good outcomes.

Is partial knee replacement newer and less proven?

Actually, it’s been performed since the 1970s. Modern implants and surgical techniques have significantly improved outcomes. For appropriate candidates, it’s a well-established option.

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Exploring treatment options? Learn about when knee replacement is necessary or read about hyaluronic acid injections as a non-surgical option.

Last medically reviewed: February 2025

Medical Disclaimer: This article is for informational purposes only and is not a substitute for professional medical advice. Discuss surgical options with your orthopedic surgeon to understand if you’re a candidate for partial knee replacement.