How can the peroneal nerve be injured during knee replacement surgery?

Mechanisms of Peroneal Nerve Injury During Knee Replacement Surgery

The common peroneal nerve is most commonly injured during knee replacement surgery through direct compression, stretching, or traction at the level of the fibular head, where the nerve is superficial and vulnerable to injury. 1

Anatomical Considerations

The common peroneal nerve is particularly vulnerable during knee replacement surgery due to its anatomical location:

• Located just medial to the biceps femoris tendon and near the fibular head 1
• Travels in a superficial position as it wraps around the fibular neck
• Has limited soft tissue protection in this region
• Mean distance between the common peroneal nerve and the posterolateral joint capsule is only 11.9 mm (range: 4.7-22.13 mm) 2
• Located at an average angle of 42.2° (range: 25.0°-64.0°) from the anteroposterior axis 2

Specific Mechanisms of Injury

1. Direct Compression:

   • Improper positioning of retractors during posterolateral exposure
   • Pressure from knee supports or positioning devices
   • Compression from surgical assistants leaning against the knee 3
   • Tourniquet-related compression (signal loss occurs approximately 25 minutes after tourniquet application) 4

2. Stretching/Traction Injury:

   • Excessive valgus positioning during surgery
   • Forceful correction of pre-existing deformities
   • Overzealous manipulation of the knee during component placement
   • Leg positioning that places the nerve under tension

3. Anatomical Risk Factors:

   • A "danger zone" exists between 29.95° and 54.57° from the anteroposterior axis 2
   • In 58% of knees, the common peroneal nerve is in line with the popliteus muscle 2
   • Pre-existing anatomical variations (e.g., giant fabella) can increase risk 5

4. Indirect Mechanisms:

   • Postoperative hematoma formation causing compression
   • Swelling and edema leading to compartment syndrome
   • Vascular compromise affecting nerve perfusion

Clinical Presentation of Injury

When injured, the common peroneal nerve causes:

• Foot drop (inability to dorsiflex the ankle)
• Inability to extend the toes
• Steppage gait
• Decreased or absent sensation on the dorsum of the foot 5
• Progressive muscle atrophy if left untreated

Prevention Strategies

1. Intraoperative Monitoring:

   • Magnetic stimulation of the cauda equina with monitoring of extensor digitorum brevis response 4
   • Limited tourniquet time (use only during component fixation) 4

2. Surgical Technique:

   • Use Gerdy's tubercle as a landmark (safe zone has a radius of approximately 45 mm from this point) 6
   • Careful placement of retractors, especially in the posterolateral aspect
   • Avoid excessive valgus positioning during exposure

3. Postoperative Vigilance:

   • Early detection of symptoms (within hours of surgery) 5
   • Immediate neurolysis if compression is suspected
   • Physical therapy to maintain muscle tone while awaiting recovery 3

Management of Injury

If peroneal nerve injury occurs:

• Immediate removal of any potential sources of compression
• Surgical exploration if symptoms are severe or progressive
• Neurolysis for cases with identifiable compression points
• Physical therapy to maintain range of motion and muscle strength
• Recovery may take up to 3 months for complete resolution 3

Common peroneal nerve injury during knee replacement surgery represents a serious complication that can significantly impact patient mobility and quality of life. Understanding the anatomical relationships and mechanisms of injury is essential for prevention and timely management.