What nerve is involved in a 52-year-old man with decreased sensation in the anterior medial thigh and bilateral leg weakness after robot-assisted laparoscopic prostatectomy (robot-assisted laparoscopic prostatectomy, RALP)?

Femoral Nerve Injury Following Robot-Assisted Laparoscopic Prostatectomy

The decreased sensation in the anterior medial thigh and bilateral leg weakness in this patient after robot-assisted laparoscopic prostatectomy (RALP) is most consistent with femoral nerve injury.

Anatomical Considerations

The femoral nerve is particularly vulnerable during RALP due to several factors:

• The femoral nerve passes beneath the inguinal ligament and can be compressed during prolonged lithotomy positioning
• The nerve can be stretched during pelvic procedures, especially with wide leg positioning
• The nerve may be injured during port placement or during dissection

Evidence for Femoral Nerve Involvement

The clinical presentation strongly suggests femoral nerve involvement:

• Decreased sensation in the anterior medial thigh corresponds to the cutaneous distribution of the femoral nerve
• Bilateral leg weakness suggests involvement of both femoral nerves, which innervate the quadriceps muscles

Risk Factors

Several studies have identified risk factors for nerve injuries during RALP:

• Longer operative time 1
• Higher BMI 2
• Patient positioning with excessive hip abduction 1
• Prior abdominal surgery with adhesions 3

Differential Diagnosis

While femoral nerve injury is most likely, other potential nerve injuries include:

1. Obturator nerve injury - would present with medial thigh weakness and sensory changes
2. Lateral femoral cutaneous nerve - would present with lateral thigh sensory changes (meralgia paresthetica)
3. Pudendal nerve branches - typically cause perineal symptoms 4

Management Approach

1. Immediate Recognition and Documentation:

   • Document the distribution of sensory and motor deficits
   • Assess severity using muscle strength testing

2. Conservative Management:

   • Multimodal pain control including pregabalin or gabapentin for neuropathic symptoms 4
   • Physical therapy to maintain muscle strength and prevent contractures
   • Regular neurological assessments to track recovery

3. Prognosis:

   • Most cases resolve within 2-8 weeks with conservative management 1
   • Complete recovery is common but may take up to 5 months 4

Prevention Strategies for Future Cases

The PROSPECT guidelines for prostatectomy recommend several measures that may help prevent nerve injuries 5:

• Careful patient positioning with attention to pressure points
• Limiting operative time when possible
• Avoiding excessive hip abduction and external rotation
• Adequate padding at pressure points
• Careful port placement with awareness of neurovascular structures

Conclusion

Femoral nerve injury is a recognized complication of RALP that typically presents with anterior thigh sensory changes and quadriceps weakness. Most cases resolve with conservative management, and prevention strategies should focus on careful patient positioning and operative technique.