Transient Femoral Nerve Palsy Complicating “Blind” Transversus Abdominis Plane Block

We present two cases of patients who reported quadriceps femoris weakness and hypoesthesia over the anterior thigh after an inguinal hernia repair under transversus abdominis plane (TAP) block. Transient femoral nerve palsy is the result of local anesthetic incorrectly injected between transversus abdominis muscle and transversalis fascia and pooling around the femoral nerve. Although it is a minor and self-limiting complication, it requires overnight hospital stay and observation of the patients. Performing the block under ultrasound guidance and injecting the least volume of local anesthetic required are ways of minimizing its incidence. 1. Introduction Transient femoral nerve palsy (TFNP) occurs in 5–8% of ilioinguinal/iliohypogastric nerve (IIN/IHN) blocks [1, 2]. To the best of our knowledge it has been reported only once following a transversus abdominis plane (TAP) block [3]. We present our experience with 2 cases of TFNP complicating “blind” TAP blocks for inguinal herniorrhaphy, investigate its mechanism, and discuss possible ways of prevention. 2. Case 1 An otherwise healthy, 26-year-old, nonobese, male patient was scheduled to undergo right inguinal hernia plug-and-patch repair as a day case, under TAP block anesthesia and conscious sedation. Twenty mL of 0,5% ropivacaine were administered by an experienced anesthesiologist, using the landmark-based “two-pop” technique as described by McDonnell et al. [4]. Surgery was uneventful, with a duration of 45 minutes. At the postoperative ward round, the patient was disturbed and reported inability to extend the ipsilateral knee joint. Clinical examination revealed quadriceps femoris paresis, hypoesthesia over the anterior aspect of the thigh, and absent patellar reflex. The patient and his family were reassured, and the self-limiting nature of the complication was explained. He was admitted overnight for observation. On the following morning, symptoms had completely remitted, and he was discharged. 3. Case 2 A 62-year-old, nonobese, male patient, with an unremarkable past medical history, was scheduled to undergo left inguinal hernia plug-and-patch repair as a day case, under TAP block anesthesia and conscious sedation. Twenty mL of 0,5% ropivacaine were injected into the TAP by the same anesthesiologist. Surgery was uneventful, with a duration of 50 minutes. Two hours postoperatively he suffered from a minor orthopedic injury (ankle sprain) on his attempt to stand up from bed. On clinical examination he was found to have quadriceps femoris muscle weakness (grade 1/5 according to Louisiana State