Ultrasound-Guided Posterior Femoral Cutaneous Nerve Block: A Cadaver Study
Christopher Johnson, M.D., Rebecca Johnson, M.D., Adam Niesen, M.D., David Stoike, M.D., Wojciech Pawlina, M.D.
Department of Anesthesiology and Perioperative Medicine
Department of Anatomy
Mayo Clinic, Rochester, MN
Complete anesthesia of the posterior thigh requires blockade of both the sciatic and posterior femoral cutaneous nerves (PFCN). Local anesthetic spread from a sciatic nerve block is sometimes insufficient to anesthetize PFCN, especially with subgluteal and anterior approaches (1-3). A separate PFCN block may be required to ensure complete blockade for surgeries involving the posterior thigh. The goals of this study were to identify any anatomic barriers to local anesthetic spread between the sciatic nerve and PFCN, and to define an ultrasound-guided subgluteal approach that reliably blocks PFCN in a cadaveric model.
After receiving Institutional Review Board Biospecimen Subcommittee approval, a single operator (CJ) performed bilateral, dynamic ultrasound-guided injections in 4 unembalmed human cadavers in the prone position. Using a 13-6 mHz linear probe placed in a transverse orientation at the infragluteal crease, the sciatic nerve and PFCN were located lateral to the long head of biceps femoris. Using a 20 gauge, 4-inch echogenic needle and colored aqueous latex solutions, 15 ml of blue solution was injected perineural to the sciatic nerve; 10 ml of yellow solution was injected within the potential space between fascia lata and the deep investing fascia of biceps femoris. After latex polymerization (≥ 48 hours after injection), the 8 gluteal regions and posterior thighs were dissected to expose the sciatic nerve and PFCN.
All 4 cadavers were male, with a median age of 81, median weight of 65.7 kg, and median BMI of 21.1 kg/m2. On ultrasound examination, PFCN was readily visualized immediately deep to gluteus maximus, and lateral and superficial to the sciatic nerve. The sciatic nerve and PFCN were found on dissection to be coated with their respective colored latex in all specimens. There was negligible mixing between the colored injectates except in 2 thighs (both in the same cadaver). Notably, PFCN was found within a separate fascial plane from the sciatic nerve in all specimens. Within the gluteal region, PFCN was consistently adhered to the deep surface of gluteus maximus, buried within the muscle's deep fascia. In the thigh, PFCN emerged from the lower border of gluteus maximus, deep to fascia lata but superficial to the investing fascia of biceps femoris in 7 of 8 specimens. In one specimen, PFCN was found deep to the biceps femoris fascia, just superficial to the muscle belly. PFCN gave off several small branches in the proximal thigh. All branches were covered in yellow latex, except for the inferior cluneal nerves which were inconsistently covered.
Ultrasound-guided subgluteal PFCN blockade is a feasible technique that can be used to complement a sciatic block when complete anesthesia of the posterior thigh is required. The consistent fascial separation between the sciatic nerve and PFCN, as well as the lack of mixing between latex injectates in most cases, suggests that individual blocks of each nerve could result in more reliable PFCN blockade. Investigation of this technique in vivo would further determine both its practicality and clinical utility.
1.Ota et al. "Ultrasound-guided anterior approach to sciatic nerve block: a comparison with the posterior approach."Anesth Analg. 2009 Feb;108(2):660-5.
2.Cuvillon et al. "Comparison of the parasacral approach and the posterior approach, with single- and double-injection techniques, to block the sciatic nerve." Anesthesiology. 2003 Jun;98(6):1436-41.
3.Barbero, et al. "Anterior sciatic nerve block and patient height." Reg Anesth Pain Med. 2004 Jun;98(6):1785-8.