Femoral Nerve Injury: Expected Pattern of Sensory Loss
If a patient has lost sensation in the anterior thigh after hip surgery, you should expect sensory loss in the medial thigh as well, as both areas are innervated by the femoral nerve and its terminal branches. 1
Anatomical Basis
The femoral nerve provides sensory innervation to both the anterior and medial aspects of the thigh through its terminal branches 1:
- Anterior thigh sensation: Supplied by anterior cutaneous branches of the femoral nerve 1
- Medial thigh sensation: Supplied by the saphenous nerve and medial cutaneous branches, which are terminal sensory branches of the femoral nerve 1
When the femoral nerve is injured during hip surgery, both distributions are typically affected simultaneously because they share a common nerve origin 1.
Mechanisms of Femoral Nerve Injury in Hip Surgery
Surgical Causes
- Retractor placement: Improper positioning of the anterior acetabular retractor can compress the femoral nerve 2
- Excessive leg lengthening: Significant limb lengthening creates tension on the nerve, with this being a recognized risk factor 2
- Direct trauma: Surgical manipulation during the procedure 3
Anesthesia-Related Causes
- Regional block spread: Local anesthetic from femoral, fascia iliaca, or lumbar plexus blocks can cause temporary femoral nerve dysfunction affecting both anterior and medial thigh sensation 1
- Fascia iliaca blocks: Ultrasound-guided technique increases sensory loss in the medial thigh from 60% to 95% of cases, demonstrating the consistent involvement of medial thigh innervation 4
Clinical Presentation
The sensory loss pattern typically includes 1, 4:
- Anterior thigh: Loss of sensation over the front of the thigh
- Medial thigh: Loss of sensation along the inner aspect of the thigh
- Motor involvement: Quadriceps weakness (difficulty with knee extension) often accompanies sensory deficits 2
Important Distinction: Lateral Femoral Cutaneous Nerve
Do not confuse this with lateral femoral cutaneous nerve (LFCN) injury, which causes numbness over the lateral thigh and is the most common nerve injury in direct anterior approach hip arthroplasty, occurring in 16-36% of cases 5, 6. LFCN injury presents with lateral thigh numbness, not anterior and medial thigh sensory loss 5.
Prognosis
Complete motor recovery typically occurs within one year in cases of femoral nerve palsy following hip surgery 2. The overall incidence of femoral nerve palsy after primary total hip arthroplasty is approximately 0.3-1.1% 3, 2.