Background: Benefit of combined regional anesthesia during lower-extremity joint operation under general anesthesia have been reported. However, a peripheral nerve block presents a risk of nerve injury. Here we examined new type of block; iliac fossa block, in which a medicinal solution is injected into the iliac fossa distant from the nerve. Like a conventional fascia iliaca compartment block, the iliac fossa block can block the lateral femoral cutaneous nerve, the femoral nerve and the obturator nerve. In addition, because of the local anesthetic spread to the central side, the block can be expected to act on the lumbar plexus.
Methods: This study was approved by the Ethics Committee, and we informed consent from adult patients who were confirmed to undergo a total hip arthroplasty (THA) under general anesthesia. Patients who were contraindicated for regional anesthesia or had neurological disorders, diabetes mellitus, etc. were excluded. Although the securing of airway and the medication for general anesthesia were at the discretion of each anesthesiologist, fentanyl and remifentanil were used as opioids. In the iliac fossa block group after the induction of anesthesia, 40 ml of 0.25% ropivacaine was injected, in the control group, the block was not used. We determined the amount of fentanyl used during each surgery and the requirements of fentanyl as intravenous patient-controlled analgesia (IV-PCA) up to 48 hr post-surgery. The primary outcome was cumulative fentanyl requirements up to 48 hr post-surgery. We also checked the block area by cold test. The values were mean ± standard deviation, p value less than 0.05 was considered as significant in the unpaired t-test and Chi-squared test . 
Results: Age and BMI average were 60 years old and 24 kg / m 2, respectively, with no significant difference between the two groups. In regarding to intraoperative fentanyl dose, there was no significant difference between 208 ± 80 µg in the block group (n = 10) and 242 ± 61 µg in the control group (n = 13). The cumulative fentanyl requirements at 24 h postoperatively were significantly less in Group B than Group C; 274 ± 46 μg vs. 468 ± 305 μg (p = 0.03), at 48 h were no significant difference; 557 ± 138 μg vs. 788 ± 405 μg (p = 0.05)  The surgical time was significantly longer in the block group (p=0.01).
Conclusion: The postoperative fentanyl requirements were significantly less in the iliac fossa block group, and this block was useful for the postoperative analgesia of THA.

Iliac fossa block is useful for postoperative analgesia of total hip arthroplasty