Anterior Quadratus Lumborum Block Does Not Provide Superior Pain Control After Hip Arthroscopy

A Double-Blinded Randomized Controlled Trial

Stephen C. Haskins, M.D.; Audrey Tseng, B.A.; Haoyan Zhong, M.P.A.; Marko Mamic, M.D.; Stephanie I. Cheng, M.D.; Jemiel A. Nejim, M.D.; Douglas S. Wetmore, M.D.; Struan H. Coleman, M.D.; Anil S. Ranawat, M.D.; Danyal H. Nawabi, M.D.; Bryan T. Kelly, M.D.; Stavros G. Memtsoudis, M.D., Ph.D., M.B.A.


Anesthesiology. 2021;135(3):433-441. 

In This Article

Materials and Methods


This randomized double-blinded trial received institutional review board approval, was registered at (NCT03432650; principal investigator: Stephen C. Haskins, M.D.; February 12, 2018), and adheres to Consolidated Standards of Reporting Trials guidelines. The trial was conducted in accordance with the original protocol. Although no changes to methods and definitions were made during this trial, the clinical trial registration was updated after the completion of a previous trial to correct an original oversight. The full trial protocol can be obtained upon request. Written informed consent was obtained from all participants before surgery.

Patient Recruitment

Patients 18 to 80 yr of age being treated with an ambulatory hip arthroscopy by a participating surgeon coinvestigator between June 2018 and December 2019 were eligible for this study. All patients were enrolled at a single site and were approached by the research study staff on the day of surgery. Exclusion criteria encompassed hepatic or renal insufficiency, age younger than 18 and older than 80 yr, allergy or intolerance to one of the study medications, chronic gabapentin/pregabalin use (regular use for longer than 3 months), chronic opioid use (daily opioids use for longer than 3 months), contraindication for spinal anesthesia, non-English speakers, and any arthroscopy procedures including lipogems, revisions, or repair of the gluteus medius. Study enrollment ceased when the target sample size was obtained.

Randomization and Blinding

Patients were randomized in a 1:1 ratio, via a computer-generated randomization schedule, to receive a single shot anterior quadratus lumborum block (30 ml 0.5% bupivacaine with 2 mg preservative-free dexamethasone) or no block. A statistician who was not involved in the analysis of the data prepared the randomization schedule. A research assistant provided an opaque card with the randomization written on it to the coinvestigator anesthesiologist on the day of surgery if a patient enrolled. The cards were prepared by research staff who had access to the randomization schedule but were not otherwise involved in the study. Upon patient arrival to the operating room, the investigator anesthesiologist assigned to the case opened a sequentially numbered sealed opaque envelope containing assignment. Coinvestigator anesthesiologists were unblinded and administered the block, but research assistants enrolling and collecting data were blinded. Patients were also blinded as the anterior quadratus lumborum block was performed under deep sedation.

Study Interventions

All patients received either a spinal (4 ml mepivacaine) or combined spinal–epidural anesthetic (5 ml of 2% lidocaine) with deep IV sedation (up to 5 mg of midazolam, IV fentanyl, and IV propofol infusion titrated to effect). Intraoperative antiemetics consisted of IV ondansetron (4 mg) and IV dexamethasone (4 mg). Intraoperative analgesics were IV fentanyl (maximum 100 mcg), IV acetaminophen (maximum 1,000 mg), and IV ketorolac (maximum 30 mg). Up to 2 mg of IV hydromorphone hydrochloride was given at the anesthesiologist's discretion at the end of the case.

Block Procedure

Anterior quadratus lumborum block was performed on the ipsilateral surgical side under deep IV sedation to ensure adequate patient blinding, but before performing neuraxial technique using an X-Porte ultrasound system (FujiFilm SonoSite, USA) with a curvilinear transducer (5–2 MHz, C60xp) and a 22-gauge, 4-in needle (Chiba) in the lateral decubitus position using a sterile technique. The patient was placed in the lateral decubitus position with the operative side facing up. The transducer was placed in the transverse position immediately cephalad to the iliac crest at the level of the posterior axillary line. The needle was inserted in-plane in a posterolateral to anteromedial fashion until the needle tip transversed the quadratus lumborum muscle and pierced the fascia between the quadratus lumborum and the psoas major muscle. Thirty milliliters of 0.5% bupivacaine with 2 mg preservative-free dexamethasone was injected with an endpoint of separation of the quadratus lumborum and psoas major muscles (Figure 1). Experienced regional anesthesiologists performed all block procedures.

Figure 1.

Ultrasound image of anterior quadratus lumborum block. The hashed arrow indicates needle placement. The local anesthesia is injected anterior to the quadratus lumborum muscle with an endpoint demonstrating a fusiform separation of the local anesthesia in the fascial plane between the quadratus lumborum muscle and the psoas major muscle.

Point-of-care Ultrasound to Assess for Intra-abdominal Fluid Extravasation

To assess intra-abdominal fluid extravasation, the operating room anesthesiologist, trained in the focused assessment with sonography for trauma examination, evaluated the patient preoperatively to assess for fluid within the abdomen or pelvis. Postoperatively, the same anesthesiologist repeated the examination, and patients with new fluid in either compartment were diagnosed to have intra-abdominal fluid extravasation. The amount of fluid present was graded as "small," "moderate," or "large." To increase the ultrasound examination's sensitivity, the patients were placed in the Trendelenburg position while evaluating the perihepatic and perisplenic space and reverse Trendelenburg to evaluate the pelvic compartment. An anesthesiologist blinded to the case reviewed images independently. In points of disagreement, the images were reviewed by a third independent expert to reach a consensus.

Quadriceps Strength Assessment

Before surgery and upon resolution of the neuraxial block in the PACU, a blinded research assistant independently assessed each patient for quadriceps weakness. The patient was placed supine with a cushion underneath the knee, resulting in a 45-degree angle at the knee. Quadriceps strength of both legs was assessed with a dynamometer placed on the anterior of the ankle, between the malleoli. Patients were instructed to extend their legs three times each, with a 30-s pause between each attempt. After each attempt, the strength was recorded, and patients rated their pain using a numerical rating scale. A blinded assessor determined analgesia in the L1 to L3 dermatomal distribution by touch and temperature discrimination using an alcohol swab.

Postoperative pain medications included oxycodone 5/10 mg with IV hydromorphone hydrochloride 0.5 mg every 5 min for breakthrough pain in the PACU. Patients were prescribed oxycodone/oxycodone with acetaminophen (unless contraindicated) and an oral nonsteroidal anti-inflammatory drug (naproxen or indomethacin).


The primary outcome, numerical rating scale pain scores at rest and movement, was assessed at 30 min and 1, 2, 3, and 24 h after PACU arrival. Secondary outcomes included the presence of intra-abdominal fluid extravasation after surgery, opioid use, the incidence of antiemetic use, the incidence of hospital admission, time to discharge from PACU, patient satisfaction with pain management, change in quadriceps strength, the incidence of urinary retention, and hypotension. Questionnaires were also administered assessing opioid-related symptoms and adverse effects using the opioid-related symptom distress scale during PACU stay, and on postoperative day 1.[16] The opioid-related symptom distress scale uses 4-point Likert scales to evaluate the frequency, severity, and bothersomeness of 12 symptoms. The composite score ranges from 0 to 4. The Quality of Recovery 40 was also administered in the PACU and on postoperative day 1. The Quality of Recovery 40 is a 40-item questionnaire that assesses five dimensions of recovery after surgery and anesthesia—comfort, emotions, physical independence, patient support, and pain—and has a mean time to completion of 5 min.[17] The self-administered Leeds assessment of neuropathic symptoms and signs of pain scale was performed 6 months after surgery if the patient had persistent hip pain. A post hoc subgroup analysis of the intra-abdominal fluid extravasation groups (anterior quadratus lumborum block vs. control) was performed to assess pain scores at rest and movement in the first 24 h. This analysis was performed post hoc because the incidence of intra-abdominal fluid extravasation is low, and patients could not be prospectively randomized to either have or not have intra-abdominal fluid extravasation. However, given that intra-abdominal fluid extravasation is an independent indicator of postoperative pain, the analysis was performed post hoc to evaluate for a difference.

Statistical Analysis

The balance on demographics and surgical variables was compared by calculating standardized differences, where the difference in means or proportions was divided by the pooled SD. An imbalance was defined as a standardized difference with an absolute value greater than 1.96 × (2/48)1/2 = 0.4.[18] Continuous variables are summarized as mean ± SD or median with interquartile range. Categorical variables are summarized as counts and percentages. All analyses were performed on an intention-to-treat basis.

The primary outcomes, numerical rating scale pain score at rest and numerical rating scale pain score with movement at 30 min and 1, 2, 3, and 24 h after PACU arrival, were compared between the quadratus lumborum block and no block groups using regression based on a generalized estimating equations approach, with treatment group, time (30 min and 1, 2, 3, and 24 h after PACU arrival), and baseline numerical rating scale pain score as fixed effects, and participant as a random effect. An unstructured correlation model was used. The adjusted marginal means of pain scores aggregated across all time points were reported separately by group, with contrast for the difference in groups and 95% CI. P value is adjusted using Bonferroni adjustment for two primary outcomes. A P value less than 0.025 was considered significant for the primary outcome. As secondary outcomes, we added a time times treatment interaction term to the generalized estimating equations model to examine numerical rating scale difference at each observed time. For other secondary outcomes, continuous secondary outcomes measured at a single time point were analyzed using independent t tests or Wilcoxon rank sum tests. Categorical secondary outcomes measured at a single time point were compared between groups using chi-square and Fisher exact tests. Secondary outcomes measured at multiple time points per patient were analyzed using the generalized estimating equations method with time and treatment interactions. Effect sizes for continuous and binary secondary outcomes are presented as differences in means, and odds ratios, respectively, with corresponding 95% CI and unadjusted P values. A P value less than 0.05 in secondary outcomes should be interpreted as suggestive.

All statistical hypothesis tests were two-sided. Statistical analyses were performed with SAS Version 9.4 (SAS Institute, USA).

Previous literature found the mean ± SD for numerical rating scale pain at rest and with movement 24 h after surgery to be 3.3 ± 3.0 and 5.5 ± 3.0, respectively.[2] We determined that a sample size of 40 patients per group would provide 80% power at a two-sided alpha level of 0.025 to detect a 1.3-point difference in numerical rating scale pain score at rest or numerical rating scale pain score with movement 24 h after surgery between the anterior quadratus lumborum block and no anterior quadratus lumborum block groups.[19] We planned to enroll a total of 96 patients to account for attrition and protocol violations (20%).