A Selective Anterior Obturator Nerve Block for Total Hip Arthroplasty

Abstract

An 83 year-old male with history of hypertension, complete heart block with a pacemaker, ankylosing spondylitis, prostate cancer, obesity and obstructive sleep apnea was scheduled for a right total hip arthroplasty (THA) for degenerative hip disease. His daily analgesic medications included oxycodone 5 milligrams (mg) every 3 hours, gabapentin 600 mg nightly, acetaminophen 650 mg every 6 hours and meloxicam 15 mg daily. A focused airway examination revealed a Mallampati III oropharyngeal exam, thyromental distance less than 6 centimeters, limited mouth opening and limited jaw protrusion. After a lengthy discussion regarding his anesthetic options, the patient elected for general endotracheal anesthesia and agreed to an obturator nerve block in the recovery room if postoperative analgesia proved difficult. The patient had taken his nightly dose of gabapentin and morning dose of acetaminophen prior to hospital arrival. In the preoperative area, he was given celecoxib 200 mg in addition as part of a comprehensive preoperative multimodal therapy.The patient was taken to the operating room where general anesthesia was induced with fentanyl 25 micrograms (mcg), propofol and succinyl choline intravenously (IV) and an endotracheal tube was placed without complication. General anesthesia was maintained with sevoflurane and a total of hydromorphone 0.8 mg IV. After successful completion of the surgery, the patient reported a pain numerical rating score (NRS) of 7/10 for generalized right hip pain upon arriving in the post anesthesia care unit (PACU). He was noted to have increased spasticity and pain with manipulation of the hip. The patient agreed to proceed with the previously consented postoperative obturator nerve block. He remained in the supine position with approximately 15 degrees of hip abduction. Skin cleansing of the medial proximal thigh and inguinal area was performed with 2% chlorhexidine and 70% isopropyl alcohol (Chloraprep). A selected obturator nerve block was performed with in-plane ultrasound-guided technique (Sonosite, M-Turbo, 6 to 15 MHz, Bothell, WA) with a 21G needle (Sonoplex). A 20-milliliter (mL) bolus of 0.5% ropivacaine was injected between the adductor longus and adductor brevis muscles to anesthetize the anterior division of the obturator nerve (Figure 1). Twenty minutes after block completion, the patient was re-evaluated. His NRS scores had decreased to 4/10 and he had significant improvement of mobility of his right hip. No opioid was given in the PACU. He was able to tolerate hip flexion and rotation without increased pain. Furthermore, hip adductions appear grossly equal bilaterally.The patient was transferred to an inpatient orthopedics floor for continued postoperative care and rehabilitation. Scheduled acetaminophen 650 every 6 hours and gabapentin 600 mg nightly was ordered. His NRS scores remained at 4/10 and required no additional opioid medication. At 11 hours post obturator nerve block, the patient received his first oral opioid dose of oxycodone 15 mg for an NRS of 6/10. On po...