What is Partial Knee Replacement? A Complete Guide to Unicompartmental Knee Surgery

TLDR: Partial knee replacement (unicompartmental knee arthroplasty) is a minimally invasive surgical procedure that replaces only the damaged portion of your knee joint, preserving healthy cartilage and bone. With a smaller 3-4 inch incision, faster recovery (1-2 days hospitalization), and over 90% success rates at 10 years, it offers significant advantages over total knee replacement for patients with arthritis limited to one compartment. Ideal candidates have localized arthritis, intact ligaments, and sufficient healthy cartilage in other areas of the knee.

Understanding Your Knee Anatomy and Arthritis

Your knee joint has three main compartments: the inner (medial), outer (lateral), and kneecap (patellofemoral) areas. When I examine patients with knee pain, I often find arthritis affects just one of these compartments rather than the entire joint.

Think of your knee like a three-room house. Traditional total knee replacement renovates all three rooms, even if only one needs work. Partial knee replacement fixes just the damaged room, leaving the healthy spaces untouched.

This targeted approach makes sense when arthritis stays confined to one area. About 25% of patients with knee arthritis have this single-compartment pattern, making them potential candidates for partial knee replacement.

Signs You Might Be a Candidate

Patients who benefit most from partial knee replacement typically experience:

• Pain on one side of the knee (inner or outer)
• Stiffness that improves with movement
• Good range of motion despite pain
• Stability when walking (no giving way)
• Pain that worsens with activity

How Partial Knee Replacement Works

During partial knee replacement, I remove only the damaged cartilage and bone from the affected compartment. The procedure involves placing a metal implant on the thigh bone (femur) and a plastic and metal component on the shin bone (tibia).

The Surgical Process

The surgery typically takes 45-60 minutes and involves these key steps:

• Making a 3-4 inch incision (compared to 7-8 inches for total knee replacement)
• Accessing the damaged compartment without disrupting healthy tissue
• Removing worn cartilage and preparing the bone surfaces
• Positioning the implants for optimal alignment
• Testing the knee's movement and stability

I use minimally invasive techniques that preserve your knee's natural ligaments, including the crucial anterior cruciate ligament (ACL). This preservation helps maintain the knee's normal mechanics and stability.

Advanced Technology Options

Many surgeons now use robotic-assisted technology for partial knee replacement. This system helps achieve precise implant positioning, which can improve long-term outcomes. The robot acts like a GPS for surgery, guiding the surgeon to place implants in the exact position planned before surgery.

Benefits of Partial Knee Replacement

After treating hundreds of patients with both partial and total knee replacements, I've observed consistent advantages with the partial approach when appropriate.

Faster Recovery Timeline

Hospital stays average just 1-2 days compared to 3-5 days for total knee replacement. Most patients walk unassisted within 1-2 weeks rather than the 1-3 months typical with total replacement.

Here's what you can expect:

• Day of surgery: Walking with assistance
• 1-3 days: Hospital discharge
• 1-2 weeks: Walking without aids
• 4-6 weeks: Return to normal activities
• 3 months: Full recovery for most activities

Superior Function and Feel

Patients consistently report that partial knee replacements feel more "normal" than total replacements. Research shows that when patients have one partial and one total knee replacement, they prefer the partial knee in over 90% of cases.

The preserved ligaments and natural knee mechanics contribute to this improved feel. Your kneecap (patella) remains untouched, maintaining its normal tracking and function.

Excellent Long-term Results

Studies demonstrate that over 90% of partial knee replacements function well at 10 years post-surgery. The survival rates are comparable to total knee replacement, dispelling earlier concerns about durability.

A recent major study published in The Lancet found no significant difference in survival rates between partial and total knee replacements at 5, 10, and 15 years.

Who Makes a Good Candidate?

Careful patient selection remains crucial for success. Through years of experience, I've learned to identify the ideal candidates.

Ideal Patient Characteristics

Physical requirements:

• Arthritis limited to one compartment
• Intact ACL and other major ligaments
• Sufficient healthy cartilage in unaffected areas
• Correctable deformity (typically less than 15 degrees)
• Good bone quality

Lifestyle factors:

• Age typically over 50 (though exceptions exist)
• Realistic expectations about outcomes
• Commitment to rehabilitation
• Willingness to modify high-impact activities

When Partial Replacement Isn't Right

Certain conditions make total knee replacement more appropriate:

• Arthritis in multiple compartments
• Inflammatory arthritis (rheumatoid arthritis)
• Severe deformity or instability
• Previous knee infection
• Significant ligament damage

I always discuss both options thoroughly with patients, explaining why one approach suits their specific situation better.

What to Expect: The Patient Journey

Before Surgery

Your preparation starts weeks before surgery. I typically recommend:

• Physical therapy to strengthen muscles
• Weight optimization if needed
• Managing other health conditions
• Understanding the recovery process

Pre-surgical imaging, including X-rays and sometimes MRI, helps me plan the exact implant size and positioning.

Recovery and Rehabilitation

The recovery process differs significantly from total knee replacement. Most patients experience:

• Less post-operative pain
• Reduced blood loss
• Earlier mobility
• Faster return to activities

Physical therapy begins within 24 hours of surgery, focusing on:

• Range of motion exercises
• Strengthening surrounding muscles
• Gait training
• Functional activities

Long-term Outcomes

After full recovery, most patients return to:

• Low-impact sports (golf, tennis, cycling)
• Hiking and recreational activities
• Work without restrictions
• Normal daily activities

High-impact activities like running or basketball aren't typically recommended, though some patients do return to these sports successfully.

Potential Risks and Limitations

Like any surgery, partial knee replacement carries risks, though they're generally lower than with total knee replacement.

Surgical Risks

Standard surgical risks include:

• Infection (less than 1%)
• Blood clots
• Anesthesia complications
• Bleeding

Specific to Partial Knee Replacement

Progression of arthritis: The most common reason for future surgery is arthritis developing in previously healthy compartments. This occurs in about 10-15% of patients over 10-15 years.

Conversion to total knee replacement: If problems develop, partial knee replacement can be converted to total replacement. This conversion surgery typically produces results similar to primary total knee replacement.

Technical challenges: The surgery requires specialized training and experience. Surgeon experience significantly impacts outcomes.

Making the Right Choice for Your Knee

Deciding between partial and total knee replacement requires careful consideration of multiple factors. During consultations, I evaluate:

• Your specific arthritis pattern
• Activity level and goals
• Age and overall health
• Bone and ligament quality
• Personal preferences

Questions to Ask Your Surgeon

When considering partial knee replacement, ask:

• Am I a good candidate based on my arthritis pattern?
• How many partial knee replacements do you perform annually?
• What are my expected outcomes and timeline?
• What happens if I need future surgery?
• How will this affect my activity level?

The Future of Partial Knee Replacement

Technology continues advancing rapidly. Robotic-assisted surgery is becoming more common, improving precision and potentially outcomes. New implant materials and designs aim to increase longevity and function.

Patient-specific instrumentation, where surgical guides are custom-made from your CT scan, represents another advancement improving accuracy.

Key Takeaways

Partial knee replacement offers significant advantages for appropriate candidates:

• Faster recovery and less invasive approach
• Preservation of healthy tissue and natural mechanics
• Excellent long-term results comparable to total knee replacement
• Option for conversion if future problems develop

Success depends heavily on proper patient selection and surgeon experience. If you have knee arthritis limited to one compartment, discussing partial knee replacement with an experienced orthopedic surgeon could open the door to faster recovery and better function.

About Dr. Cory Calendine's Practice

Dr. Cory Calendine provides advanced orthopedic care specializing in partial and total knee replacement surgery for patients throughout Franklin, Brentwood, and the Greater Nashville area. With extensive experience in both traditional and robotic-assisted knee procedures, Dr. Calendine offers personalized treatment plans tailored to each patient's specific needs and goals. His practice serves Middle Tennessee communities with comprehensive joint replacement services, from initial consultation through complete recovery, helping patients return to active lifestyles with minimal disruption. Patients from Williamson County and surrounding areas benefit from Dr. Calendine's expertise in minimally invasive techniques and commitment to optimal outcomes. To schedule a consultation about your knee replacement options, contact Dr. Calendine's office serving the Franklin and Nashville metropolitan area.

This article is for educational purposes only and should not replace professional medical advice. Always consult with a qualified orthopedic surgeon to discuss your specific condition and treatment options.