What are the pros and cons of unilateral vs bilateral knee replacement?

Unilateral vs Bilateral Knee Replacement: Clinical Decision Framework

For patients under 70 years old with ASA status 1-2, simultaneous bilateral total knee arthroplasty (TKA) is recommended as it carries no increased complication risk compared to staged procedures, while offering faster overall recovery and reduced cumulative healthcare burden. 1

Key Decision Points

Patient Selection for Bilateral TKA

Age and Medical Status:

• Patients <70 years old with ASA class 1-2 are ideal candidates for simultaneous bilateral TKA 1
• Limited evidence supports this approach specifically in this population without increased complications 1
• Older patients (≥70 years) or those with ASA class ≥3 should undergo staged unilateral procedures due to higher perioperative risk

Bilateral Disease Severity:

• Both knees must have radiographic evidence of joint damage with moderate to severe persistent pain 2
• Clinically significant functional limitation affecting quality of life in both knees 2
• Failed conservative management (physiotherapy, analgesics, anti-inflammatory drugs, intra-articular injections) 2

Advantages of Bilateral TKA (Simultaneous)

For Appropriate Candidates:

• Single anesthesia exposure rather than two separate procedures 1
• Shorter total recovery time - one rehabilitation period instead of two 1
• Reduced cumulative hospital stay compared to two staged procedures 1
• Lower overall healthcare costs from consolidated care 2
• Symmetric rehabilitation - both knees progress together without compensatory gait abnormalities 1
• Earlier return to baseline function - patients achieve full recovery sooner than with staged procedures 1

Advantages of Unilateral (Staged) TKA

For Higher-Risk Patients:

• Lower immediate physiologic stress - particularly important for patients ≥70 years or ASA ≥3 1
• Ability to use contralateral leg during initial recovery phase 3
• Opportunity to reassess medical status between procedures 2
• Lower risk of bilateral complications such as bilateral deep vein thrombosis 2
• Allows experience-based decision - patients can decide about second knee based on first outcome 4

Critical Complications to Consider

Both Approaches:

• Deep venous thrombosis (requires heparin prophylaxis and compression stockings) 2
• Infection (requires 24-hour perioperative antibiotics) 2
• Stiffness (prevented by early mobilization) 2
• Prosthesis loosening and osteolysis (long-term concern) 2

Bilateral-Specific Concerns:

• Higher immediate blood loss requiring transfusion protocols 1
• Greater initial pain burden requiring robust multimodal analgesia 1
• More challenging early mobilization without a "good leg" to rely on 3

Rehabilitation Considerations

Early Mobilization Protocol (Both Approaches):

• Rehabilitation started on day of surgery reduces hospital length of stay 1
• Supervised exercise program during first 2 months improves physical function 1, 5
• Early mobilization reduces pain and improves function compared to delayed mobilization 1

Bilateral-Specific Rehabilitation:

• Requires more intensive physical therapy support initially 1
• May need extended inpatient rehabilitation or skilled nursing facility 2
• Assistive devices (walker/wheelchair) essential during early recovery 3

Expected Outcomes

Pain Relief and Function (Both Approaches):

• Substantial improvements in pain reduction and functional improvement 2
• 85% patient satisfaction rate at 2-7 years postoperatively 3
• Little to no knee pain regardless of age, BMI, or time since surgery 3
• Effect sizes demonstrate clinically meaningful improvements (>20% improvement) 2

Revision Rates:

• 0-13% revision rates at 5+ years follow-up 2
• No significant difference between unilateral and bilateral approaches in appropriate candidates 1

Common Pitfalls to Avoid

Patient Selection Errors:

• Performing bilateral TKA in patients >70 years without careful risk stratification 1
• Ignoring ASA classification - patients with ASA ≥3 require staged approach 1
• Proceeding with bilateral surgery in patients with significant cardiac or pulmonary comorbidities 2

Perioperative Management:

• Inadequate DVT prophylaxis in bilateral cases (higher thrombotic burden) 2
• Insufficient pain control protocols for bilateral procedures 1
• Delayed mobilization - must begin on day of surgery 1, 5

Expectation Management:

• 20% of patients do not achieve excellent outcomes despite good implant survival 6
• Bilateral patients need realistic expectations about more challenging early recovery 4
• Patients should understand that bilateral surgery means no "good leg" during initial recovery 3

Clinical Algorithm

1. Assess bilateral knee disease severity - both knees must meet surgical criteria 2
2. Evaluate patient age and ASA status - if <70 years AND ASA 1-2, consider bilateral 1
3. Screen for contraindications - cardiac/pulmonary disease, coagulopathy, prior DVT 2
4. Discuss patient preferences - some prefer staged approach despite eligibility 4
5. If bilateral candidate: ensure robust perioperative protocols (DVT prophylaxis, pain control, early mobilization) 1, 2
6. If not bilateral candidate: proceed with more symptomatic knee first, stage second procedure 3-6 months later 2