How does a total knee arthroplasty (TKA) work after anterior cruciate ligament (ACL) resection?

Total Knee Arthroplasty After ACL Resection: Functional Mechanisms and Considerations

Total knee arthroplasty (TKA) after anterior cruciate ligament (ACL) resection requires specialized surgical planning and rehabilitation approaches to address the unique biomechanical challenges, with instability being the most common complication requiring revision.

Biomechanical Challenges in Post-ACL Resection TKA

Stability Considerations

• Post-ACL resection knees present unique stability challenges during TKA due to altered knee biomechanics and soft tissue adaptations 1
• Instability is the most common reason for revision in these patients, with a 10-year survivorship of 92% (lower than standard TKA) 1
• Both global instability (6 cases) and flexion instability (1 case) were identified as primary causes of revision in a large study of 165 knees 1

Prosthesis Selection

• Posterior-stabilized (PS) designs are most commonly used (90% of cases) in post-ACL resection patients 1
• PS designs compensate for the absent ACL function through the cam-post mechanism, which provides anteroposterior stability 2
• Despite PS designs, the goal of replicating ACL function is only partially achieved, with 72% of knees still exhibiting a positive pivot shift test 2

Surgical Considerations

Soft Tissue Balancing

• Achieving proper soft tissue balance is the primary challenge in post-ACL resection TKA 1
• The absence of the ACL creates anteroposterior instability that must be addressed through:
  • Careful ligament balancing
  • Appropriate prosthesis selection (typically PS designs)
  • Proper component positioning to optimize stability

Bone Stock and Component Positioning

• Prior ACL reconstruction may have created bone tunnels or altered bone stock
• Evaluation of bone quality is necessary as poor bone stock may require specialized implants or techniques 3
• Proper alignment of the prosthesis is critical for long-term success 3

Rehabilitation Protocol

Early Phase (0-6 weeks)

• Immediate knee mobilization is critical to increase joint range of motion and reduce pain 4
• Early full weight-bearing exercises are encouraged but should progress as tolerated 4
• Cryotherapy is recommended immediately after surgery to reduce knee pain 4
• Isometric quadriceps strengthening should begin from the first postoperative week (if not causing pain) 4

Intermediate Phase (6-12 weeks)

• Progress to concentric and eccentric exercises in closed kinetic chain 4
• Neuromuscular electrostimulation can be added to isometric strengthening in the initial 6–8 weeks 4
• Closed kinetic chain exercises should be prioritized in the first postoperative month 4
• Open kinetic chain exercises (90–45°) can be added as early as 4 weeks 4

Advanced Phase (12+ weeks)

• Strength and motor control training should be combined in the rehabilitation protocol 4
• Plyometric and agility training may further improve subjective function and functional activities 4
• Core stability exercises can improve functional outcomes and subjective knee function 4

Pain Management

The evidence supports a multimodal approach to pain management following TKA 4:

• General anesthesia combined with a femoral nerve block for surgery and postoperative analgesia, or alternatively spinal anesthesia with local anesthetic plus spinal morphine
• Supplementation with paracetamol and conventional non-steroidal anti-inflammatory drugs or COX-2-selective inhibitors
• Intravenous strong opioids for high-intensity pain or weak opioids for moderate- to low-intensity pain
• Cooling and compression techniques

Monitoring and Follow-up

Return to Activity Criteria

• No pain or swelling
• Full range of motion
• Stable knee (pivot shift, Lachman, instrumented laxity evaluation)
• Normalized subjective knee function and psychological readiness
• Isokinetic quadriceps and hamstring peak torque at 60°/s should display 100% symmetry for return to high demand activities 4

Potential Complications

• Instability (most common complication requiring revision) 1
• Flexion instability and stiffness requiring manipulations under anesthesia 1
• Infection (second most common cause of revision) 1
• Arthrofibrosis (may require arthroscopic lysis of adhesions) 5

Conclusion

TKA after ACL resection presents unique challenges centered primarily on achieving proper stability. Posterior-stabilized designs are typically used, but achieving optimal soft tissue balance remains difficult. A structured rehabilitation protocol focusing on early mobilization, progressive strengthening, and neuromuscular training is essential for optimal outcomes. Careful monitoring for instability is crucial as it represents the most common cause of revision in these patients.