How to assess for femoral nerve injury in an adult patient with no significant medical history after femoral surgery presenting with numbness?

Assessment of Femoral Nerve Injury After Femoral Surgery

Assess for femoral nerve injury by testing quadriceps strength (knee extension), sensory loss over the anterior and medial thigh, and checking for an absent patellar reflex—these three findings together confirm femoral nerve dysfunction.

Motor Examination

• Test knee extension strength as the primary motor indicator, since the femoral nerve innervates the quadriceps muscle group, and weakness here is the hallmark motor finding 1
• Document the degree of quadriceps weakness using a standardized grading scale (0-5/5 strength)
• Inability to extend the knee against resistance or gravity indicates significant femoral nerve injury 2

Sensory Examination

• Examine the anterior thigh for numbness or altered sensation, as this is supplied by the anterior femoral cutaneous nerve branches 1, 3
• Test the medial thigh and medial leg for sensory loss, which indicates involvement of the saphenous nerve and medial cutaneous branches—both terminal sensory branches of the femoral nerve 1
• Assess for allodynic paresthesias (painful sensations to light touch) in the distribution described above 4

Reflex Testing

• Check the patellar (knee-jerk) reflex, which will be diminished or absent with femoral nerve injury since this reflex arc depends on intact femoral nerve function 1

Specific Considerations for Post-Surgical Context

• Distinguish between surgical injury and regional anesthesia effects: If the patient received a femoral nerve block, fascia iliaca block, or lumbar plexus block perioperatively, temporary femoral nerve dysfunction with quadriceps weakness is expected and should resolve as the local anesthetic wears off 1
• Timing matters: Immediate postoperative deficits may represent direct surgical trauma, nerve compression from positioning, or residual regional anesthesia effects 2
• Consider that anterior approaches to femoral surgery can directly injure the anterior femoral cutaneous nerve branches, causing anterior medial thigh pain and numbness while sparing quadriceps function 3

Documentation

• Document the specific distribution of sensory loss (anterior thigh, medial thigh, medial leg) to differentiate femoral nerve injury from other nerve injuries 1, 3
• Record quadriceps strength bilaterally for comparison 2
• Note whether symptoms are unilateral or bilateral 3

Common Pitfalls

• Do not assume all postoperative numbness is from regional anesthesia—if quadriceps weakness persists beyond expected block duration (typically 12-24 hours for single-shot blocks), suspect true nerve injury 2
• Isolated medial thigh numbness without quadriceps weakness may represent injury to cutaneous branches only, not the main femoral nerve trunk 3
• Hip positioning during surgery (excessive flexion beyond 90 degrees or extension beyond comfortable range) can contribute to femoral nerve compression, though evidence for causation is limited 5, 6

When to Escalate

• If motor deficits or sensory loss persist beyond 24-48 hours post-surgery, obtain electrodiagnostic studies (EMG/nerve conduction studies) to confirm femoral nerve injury and assess severity 7, 4
• Consider imaging (MRI or CT) if there is concern for compressive lesions such as hematoma, abscess, or surgical debris causing delayed nerve compression 7