Pericapsular Nerve Group Block (PENG): A Randomized, Triple-Masked, Placebo-Controlled Clinical Trial

Following painful surgical procedures of the hip, postoperative analgesia is often provided simply with intravenous and oral analgesics. Peripheral nerve blocks using local anesthetic have been investigated, and while they do provide analgesia, they all carry a high risk of inducing weakness of the quadriceps and/or hip adductors. This, in turn, results in an unacceptably high risk of subsequent falls, and peripheral nerve blocks are therefore not standard-of-care at most health centers. For example, at the University of California San Diego hospitals, no peripheral nerve block is provided even for the most painful hip surgery, hip arthroplasty. This results in a strong dependence on opioid analgesics which frequently provide inadequate analgesia and have undesirable side effects for both individuals and society. Peripheral nerve blocks with local anesthetic can provide analgesia for over 12 hours without any systemic side effects. Thus, it would be preferable to provide peripheral nerve blocks to patients having painful hip surgery to reduce pain as well as decrease opioid use and their associated adverse side effects. Recently, a new type of block has been reported to provide analgesia to the hip joint: the "pericapsular nerve group" (PENG) block. Twenty case reports and series have been published suggesting potent analgesia while not inducing any motor block. However, no randomized, controlled clinical trial is available to validate the technique and quantify both risks and benefits. The investigators therefore propose such a study.

This investigation will be a randomized, triple-masked, placebo-controlled, parallel-arm, human subjects clinical trial. Adults undergoing painful unilateral primary hip arthroscopy with general anesthesia will be offered enrollment. Of note, the investigators will be using standard-of-care analgesics including oral and intravenous opioids as well as surgeon-infiltrated local anesthetic directly into the wound under an FDA-approved purpose and do not plan to research a possible change of indication or use of these medications as part of this research project. These treatments will be administered in both groups constituting our institution standard-of-care.

Following written, informed consent, all participants will have a peripheral intravenous catheter inserted and standard noninvasive monitors applied. The investigators will evaluate muscle strength with an isometric force electromechanical dynamometer (MicroFET2, Lafayette Instrument Company, Lafayette, IN) to measure the force produced during a maximum voluntary isometric contraction (MVIC) in a seated position with the knees flexed at 90º. For quadriceps femoris evaluation, the dynamometer will be placed on the ipsilateral anterior tibia perpendicular to the tibial crest just proximal to the medial malleolus. For hip adductor evaluation, the femoral shaft will be held at 30º off midline and the dynamometer placed over the medial femoral epicondyle (adductor tubercle). For all measurements, participants will be asked to take 2 seconds to come to maximum effort contracting the target muscle(s), maintain this effort for 5 sec, and then relax. The measurements immediately prior to perineural ropivacaine administration will be designated baseline measurements, and all subsequent measurements will be expressed as a percentage of the pre-infusion baseline. Participants who cannot perform these maneuvers will have their data excluded from the muscle strength calculations (i.e., a "zero" will not be entered for these participants).

Participants will then be randomized using a computer-generated list to one of two treatment groups (blocks of 4): a PENG block with 20 mL of either (1) bupivacaine 0.375% or (2) normal saline [epinephrine added to both]. Investigational pharmacists will create the lists and fill syringes with one of the two possible study solutions and provide investigators with syringes that will not identify the treatment. Bupivacaine and normal saline are identical in appearance, and all investigations, patients, and clinical staff will remain masked to treatment group. Following enrollment completion, the Investigational Drug Service will provide the statistician with lists of the treatment groups labeled "A" and "B". Only following statistical analysis will the specific treatment groups be identified by the Investigational Drug Service so that the investigators may prepare the manuscript reporting the results (termed "triple masked").

All blocks will be placed by a regional anesthesia fellow or resident under the direct supervision and guidance of a regional anesthesia attending (or by the attending themselves). Participants will have supplemental oxygen administered via a nasal cannula or face mask and placed in the supine position. Intravenous midazolam and fentanyl will be titrated for patient comfort, while ensuring that patients remain responsive to verbal cues.