Bilateral vs. Unilateral Total Knee Replacement: Which One Do You Need?

Total knee replacement (TKR) is a highly effective surgical procedure that relieves pain and restores function in individuals with significant knee injuries or arthritis. When knee damage affects one or both knees, patients and surgeons face an important decision: Should you undergo unilateral (single knee) or bilateral (both knees) total knee replacement? You and your healthcare team can choose the best option for your needs if you are aware of the advantages, disadvantages, and risks of each strategy.

What Is Total Knee Replacement?

In a total knee replacement, the diseased bone and cartilage on the surface of the knee joint are surgically removed and replaced with artificial components, typically composed of plastic and metal. The goal is to reduce chronic pain and restore mobility.

Unilateral vs. Bilateral Total Knee Replacement: Definitions

• Unilateral TKR replaces only one knee joint during a single surgery. This is the standard approach when only one knee is significantly affected.
• Bilateral TKR can be performed either simultaneously (both knees replaced in the same surgical session) or staged (two separate surgeries with recovery time in between). The simultaneous approach saves time and consolidates recovery, while the staged approach reduces surgical stress but extends total recovery duration.

Indications: When Is Each Recommended?

• Unilateral TKR is ideal if you primarily suffer from pain and disability in just one knee. Many patients with asymmetric arthritis or injury fall into this group.
• Bilateral TKR may be recommended if both knees have advanced arthritis, causing severe pain and functional limitation, and you are a good candidate for a longer surgery. This approach is often considered for patients who want to minimise time under anaesthesia, hospital stays, and overall rehabilitation sessions.

Pain and Functional Outcomes

Recent studies suggest that simultaneous bilateral TKR provides similar pain relief and improvement in function 30 days after surgery compared to unilateral TKR. Both groups show significant pain reduction and enhanced mobility, indicating that bilateral procedures do not compromise early outcomes.

At one month after surgery, patients in the bilateral and unilateral TKR groups in an observational trial of 80 patients showed comparable decreases in pain and increases in functional capacity; there was no discernible difference in the rate of recovery or the intensity of pain. Therefore, regardless of the method used, all patients can expect an improved quality of life.

Risks and Complications

Both Procedures are relatively safe, but the risks associated with them are somewhat different.

• Unilateral TKR is associated with generally fewer risks, as it involves a relatively short procedure with fewer cardiac, pulmonary and platelet activation-related physiological stresses. The risks include infection, DVT, pulmonary embolism, anaesthesia-related complications and risk of cardiac stress, such as myocardial ischaemia in patients who had prior cardiovascular stress.
• Simultaneous bilateral TKR involves more cardiac and physiological stress, due to a longer procedure and recovery time. For some patients, this can increase the risks of cardiac complications in addition to increased risks of pulmonary embolism and/or significant blood loss from prolonged and bilateral surgery.  Fortunately, if patients are correctly selected and appropriate perioperative management protocols for blood conservation are used, any increased risks can be mitigated.

Some reviews indicate there is no significant difference in postoperative complications between simultaneous bilateral TKR and unilateral TKR. In contrast, other studies have reported that patients who undergo bilateral procedures have greater morbidity than those undergoing unilateral procedures. This is especially true for older or medically complex patients. Therefore, a complete health assessment should be performed.

Recovery and Rehabilitation

• Rehabilitating from a TKR is different for a unilateral as compared to a bilateral TKR.
• Unilateral TKR typically allows more effortless mobility initially since one leg can support more weight while the other heals. This may lead to a more straightforward early rehab process.
• Bilateral TKR demands more intensive rehab as both knees recover simultaneously. This consolidates the total rehabilitation time but requires more commitment and physical effort upfront. Some patients may experience delayed mobility initially but benefit from only one overall recovery period rather than two separate ones.

Patient Selection Criteria

Choosing between unilateral and bilateral TKR depends on:

• Severity and symmetry of disease: Bilateral TKR is suitable for patients with equivalent severity in both knees.
• Age and health status: Younger, healthier patients tolerate bilateral surgery better.
• Functional goals and lifestyle: Some prefer fewer surgeries and a consolidated rehabilitation despite a tougher initial recovery.
• Surgeon's assessment: The decision involves a personalised evaluation considering cardiovascular fitness, other medical conditions, and patient preferences.

Cost Considerations

Bilateral TKR, particularly the simultaneous approach, may reduce overall hospital stays, anaesthesia costs, and rehabilitation expenses compared to two-stage unilateral surgeries. However, these savings must be weighed against the potential increased risk of complications.

Long-term Outcomes

Studies have established that unilateral TKR and simultaneous bilateral TKR have comparable longevity and comprehensive functional results, and many patients report excellent pain relief and resuming normal activity years post-operatively. While revision rates may be slightly different, there is no evidence to suggest one is consistently superior to the other.

Summary Table: Unilateral vs Bilateral Total Knee Replacement

Final Thoughts

The choice between unilateral and bilateral total knee replacement is highly individualised. Both surgeries offer substantial pain relief and improved function. Simultaneous bilateral TKR can be a practical option for suitable candidates to undergo one operation and a rehabilitation period. However, unilateral TKR remains safer for patients with asymmetric disease or those with health concerns.

Your orthopaedic surgeon’s assessment, your overall health and lifestyle goals, and your willingness to commit to rehabilitation will guide the decision. Open dialogue with your healthcare team ensures the best approach for your knee health and quality of life.

If you are considering total knee replacement, discuss all options thoroughly to find the best solution tailored to your needs.