Purpose: Evaluate difference in postoperative opioid consumption when subjects receive a quadratus lumborum (QL) or lumbar plexus (LP) block preoperatively for total hip arthroplasty (THA).

Hypothesis: Preoperative QL and LP blocks will result in similar postoperative opioid consumption following hip arthroplasty.

With the goal of improving physical function and quality of life, the demand for total hip arthroplasty (THA) continues to grow. However, postoperative pain associated with THA remains a serious concern for patients. In the middle of a growing opioid epidemic, multimodal approaches utilizing both non-opioid analgesics and regional anesthetic techniques are being increasingly sought.

Regional anesthetic techniques are associated with both decreased opioid consumption and pain scores compared with systemic analgesia alone. However, regional techniques for THA are seldom compared. Lumbar plexus blocks are commonly performed for postoperative analgesia for THA. However, more recent case reports have described utilizing quadratus lumborum blocks for analgesia following hip fracture and THA.

This prospective study would randomize subjects to receive a lumbar plexus block or quadratus lumborum block prior to THA. The primary end point would be opioid consumption at 12 hours postoperative. Our hypothesis is that opioid consumption will not differ between groups.

The quadratus lumborum block is a fascial plane block. Originally described for abdominal surgery, numerous case reports and editorial publications have highlighted the effectiveness of quadratus lumborum (QL) blocks as an analgesic technique for hip fracture and hip arthroplasty. However, prospective randomized studies comparing QL blocks to other regional techniques for THA analgesia are lacking.

The lateral approach to the QL block is performed by injecting local anesthetic deep to the transversus abdominus abdominus apnoneurosis and superficial to the fascia transversalis with direct ultrasound guidance. After completing consent, placing monitors and providing mild sedation, the subject is positioned laterally and the muscular anatomy (external oblique, internal oblique, transverse abdominis, quadratus lumborum and latissimus dorsi muscles) identified. After placing a subcutaneous skin wheal with lidiocaine, a blunt regional anesthesia needle is inserted using in-plane ultrasound guidance. Local anesthetic is deposited incrementally with frequent aspiration in the anterolateral border of the quadratus lumborum muscle at the junction of the transversalis fascia, outside the anterior layer of the thoracolumbar fascia and superficial to the fascia transversalis.

Risks of anterior approach to the quadratus lumborum block are similar to most truncal blocks and include infection, bleeding, bowel perforation or local anesthetic toxicity (LAST). Infection risk is minimized by utilizing appropriate antiseptic and sterile technique as is standard for any regional procedure. Risk of a retroperitoneal hematoma is increased with the posterior approach to the quadratus lumborum block because of its transmuscular approach and likelihood of abdominal branches of lumbar arteries in the path of the needle. For this reason, the posterior approach to the quadratus lumborum block will not be used for this study. The risk of LAST is a risk with any regional procedure and is minimized by frequent aspiration, incremental local anesthetic injection and vital signs monitoring throughout.

The quadratus lumborum block is already a block utilized for a variety of surgical procedures to decrease postoperative pain. Potential benefits to the QL block over the common lumbar plexus block include more superficial block placement and ultrasound visualization. The investigator hypothesize that preoperative QL blocks will reduce opioid consumption similar to lumbar plexus blocks following elective hip arthroplasty.

Information regarding the study will be presented to subjects in the surgical clinic or preoperative anesthesia clinic in the preoperative period. Subjects will be educated on the role of regional anesthesia in postoperative analgesia. Subjects will be able to consider the study until the day of surgery. On the day of surgery, subjects may then choose to provide written consent or decline to participate.

Subjects will be enrolled on the day of surgery in the preoperative holding area.

After discussion in the preoperative holding area regarding risks and benefits of both the lumbar plexus and QL block, subjects will be consented if they choose to participate. Consent will be obtained from subject by an IRB approved CITI certified study team member that has been trained on the protocol. Written consent with a witness will be completed once all questions are answered and exclusion and inclusion verified. Copies of all documents will be provided to the subjects. Once subjects are consented, they will be assigned an enrollment number. Prior to subject enrollment, randomization will done by a statistician and randomized group (lumbar plexus block (current practice) or QL block) assigned based on the subject enrollment number.

Design: This prospective, single blinded clinical trial will randomize subject to receive a lumbar plexus or QL block prior to THA. The randomization will be created by a statistician prior to subject enrollment.

Groups: Subjects will be randomized to receive a preoperative lumbar plexus (n = 100) or QL (n = 100 ) block prior to THA.

Potential participants that are on the operating room schedule for THA will be screened for eligibility via chart review.

Once subjects have signed an informed consent, they will be assigned an enrollment number. Numbers would be assigned sequentially with the first enrolled subject receiving "001," the second subject receiving "002," and the last subject receiving number "184." Randomization will be created prior to the study starting by a statistician with half of the research subject number being assigned to receive a QL block and the other half assigned to receive a lumbar plexus block, which is our current standard of care. The regional anesthesia team will open the envelope labeled with the subject's assigned number to reveal the randomization.

Following informed consent, all subjects will be positioned, prepped and sedated for the randomized regional anesthesia procedure in the preoperative holding area. The subject will be positioned in the lateral decubitus position with the operative side up and pulse oximetry and blood pressure cuff placed for monitoring. As part of routine care, the subject will receive sedation for their comfort. All subjects would receive 20 ml of 0.5% ropivacaine in their nerve block regardless of randomization. The relevant anatomy will then be identified using either surface landmarks (lumbar plexus block) or an ultrasound (quadratus lumborum block). All participants, regardless of group assignment, will be positioned, have an area on their back and side cleaned, have an ultrasound placed, and numbing medication placed just below the skin at both block sites (skin wheal). This will be done so that participant and the team collecting result will be blinded. Subject, surgeon, intraoperative anesthesia team and data collectors would all be blinded to the allocated group.

Subjects randomized to the lumbar plexus block group will receive a subcutaneous lidocaine skin wheal 3-4 cm lateral to midline on the operative side along the intercristal line. A nerve stimulator will be sent to 1-1.5mA and a stimulating needle inserted perpendicular to the skin. The needle will be advanced slowly until the quadriceps muscle is stimulated and maintained at less than 0.6mAs. Ropivacaine (20ml, 0.5%) will be injected slowly with frequent aspiration to rule out inadvertent intravascular needle placement.

Subjects randomized to the quadratus plexus block group will receive a subcutaneous lidocaine skin wheal that will be placed after ultrasound identification of external oblique, internal oblique, transverse abdominus and quadratus lumborum muscles. A needle will then be advanced under ultrasound guidance below the internal oblique aponeurosis and lateral to the quadratus lumborum muscle. Ropivacaine (20ml, 0.5%) will be injected slowly with frequent aspiration to rule out inadvertent intravascular needle placement. Local anesthetic injection will also be observed with real time ultrasound guidance.

The participant's chart will be reviewed for data collection.

Participants will also be asked to perform a Visual Analog Scale pain score preoperatively (baseline), postoperatively (once awake) and approximately 24 hours post operatively.

Care in the perioperative period will otherwise be standardized. In the post-anesthesia care unit (PACU), hydromorphone or morphine will be titrated by the PACU nurse for the subject's comfort.

Inclusion Criteria:

• Age greater than or equal to 18 years-old
• Undergoing elective hip arthroplasty.

Exclusion Criteria:

• Local anesthetic allergy
• Chlorhexidine allergy
• Subjects with a weight less than 40kg
• Subjects that are unable or choose not to give informed consent
• Emergency surgery
• Known preoperative substance abuse
• Allergy to all opioids

All subjects will be positioned, prepped and sedated for the randomized regional anesthesia procedure in the preoperative holding area. The subject will be positioned in the lateral decubitus position with the operative side up and pulse oximetry and blood pressure cuff placed for monitoring. As part of routine care, the subject will receive sedation for their comfort. All subjects would receive 20 ml of 0.5% ropivacaine in their nerve block regardless of randomization. The relevant anatomy will then be identified using either surface landmarks (lumbar plexus block) or an ultrasound (quadratus lumborum block). Surface anatomy will be marked with a marking pen for both groups to keep the intraoperative and surgical team blinded. The skin will be cleaned with chlorhexidine. Subject, surgeon, intraoperative anesthesia team and data collectors would all be blinded to the allocated group.