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Abstract
Background Hip arthroscopy causes severe pain during the first few hours in the postoperative care unit. This is probably due to the intraoperative stretching of the hip joint capsule. Pain relief requires high doses of opioids which may prolong recovery and may cause opioid-related adverse events.
The majority of hip joint capsule nociceptors are located anteriorly. The obturator nerve innervates the anteromedial part of the hip joint capsule. We hypothesized that a subpectineal obturator nerve block using 15 ml bupivacaine 5 mg/mL with added epinephrine 5 μg/mL would reduce the opioid consumption after hip arthroscopy.
Methods 40 ambulatory hip arthroscopy patients were enrolled in this randomized, triple-blind controlled trial. All patients were allocated to a preoperative active or placebo subpectineal obturator nerve block. The primary outcome was opioid consumption for the first 3 hours in the postanesthesia care unit. Secondary outcomes were pain, nausea, and hip adductor strength.
Results 34 patients were analyzed for the primary outcome. The mean intravenous morphine equivalent consumption in the subpectineal obturator nerve block group was 11.9 mg vs 19.7 mg in the placebo group (p<0.001). The hip adductor strength was significantly reduced in the active group. No other intergroup differences were observed regarding the secondary outcomes.
Conclusion We found a significant reduction in the opioid consumption for patients receiving an active subpectineal obturator nerve block. The postoperative intravenous morphine equivalent reduction the first painful 3 hours was reduced by 40% for patients receiving a subpectineal obturator nerve block in this randomized, triple-blind trial.
Trial registration number EudraCT database 2021-006575-42.
- Nerve Block
- Lower Extremity
- Pain, Postoperative
- Pain Management
- Ultrasonography
Data availability statement
Data may be obtained from a third party and are not publicly available.
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WHAT IS ALREADY KNOWN ON THIS TOPIC
Hip arthroscopy causes severe pain the first hours after surgery, demanding high doses of opioids. An iliopsoas plane block selectively anesthetizing the femoral nerve innervation of the hip joint reduces opioid requirements by 50% without impeding ambulation.
WHAT THIS STUDY ADDS
The subpectineal obturator nerve block reduces opioid consumption with approximately 40% in hip arthroscopy patients in the first three postoperative hours.
HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY
The subpectineal obturator nerve block significantly reduces opioid consumption after hip arthroscopy. Future research is required to explore whether this nerve block combined with the iliopsoas plane block may be the optimal solution to the problem of high opioid consumption and delayed ambulation after outpatient hip arthroscopy.
Introduction
The indication for hip arthroscopy is mainly resection of osteoarthritic bony outgrowths causing femoroacetabular impingement1 postponing the need for a hip arthroplasty.2 3
Hip arthroscopy is a fast-track outpatient procedure, but postoperative pain causes patient dissatisfaction, increased postoperative pain medication requirements and inpatient admissions.4 In our clinical experience, moderate to severe pain and high opioid consumption during the first 3 hours after hip arthroscopy impairs ambulation and delays home discharge.
During hip arthroscopy, strong traction is applied to the leg to pull the femoral head away from the acetabulum, temporarily separating the joint surfaces, which facilitates surgical interventions but also generates moderate to severe pain the first hours after surgery.
A femoral nerve block would increase the risk of fall by quadriceps paralysis.5 However, the iliopsoas plane block reduces opioid consumption more than 50% after hip arthroscopy by selective sensory blockade of the femoral nerve innervation of the hip joint.6 The nociceptors are mainly located in the anterior part of the hip capsule,7 which is innervated by the femoral nerve, the obturator nerve, and the accessory obturator nerve when present.8 9 Thus, the remaining pain after the distraction of the joint capsule during hip arthroscopy is probably transmitted by the obturator and accessory obturator nerves.
A cadaver study testing the subpectineal obturator nerve block documented effective spread to the obturator nerve branches innervating the hip joint capsule.10
Our research idea in the present study was to reduce the opioid consumption during the painful first 3 hours after hip arthroscopy by application of a subpectineal obturator nerve block. This has never been tested in a blinded, randomized controlled trial.
We hypothesized that an active versus placebo subpectineal obturator nerve block would decrease intravenous opioid consumption by a minimum of 40% from 30 to 17 mg during the first 3 hours after hip arthroscopy.
Materials and methods
The trial was conducted from October 27, 2022 with the inclusion of the first patient to November 17, 2023, at Horsens Regional Hospital, Denmark. It included 40 patients scheduled for hip arthroscopy. The study was registered on December 15, 2021, in the EudraCT database (2021-006575-42, https://www.clinicaltrialsregister.eu/ctr-search/trial/2021-006575-42/DK). The trial was monitored by the Good Clinical Practice Unit at Aalborg and Aarhus University Hospital. Written, informed consent was obtained from all subjects prior to inclusion. The present trial was initiated before unblinding and analysis of the data from our study of the effect of the iliopsoas plane block on opioid consumption after hip arthroscopy.6
Population
Inclusion criteria were femoroacetabular impingement disease, primary hip arthroscopic surgery, general anesthesia with propofol and remifentanil, age ≥18, and informed consent. Exclusion criteria were inability to cooperate, inability to understand and/or speak Danish, allergy to bupivacaine or epinephrine, intolerance to morphine and oxycodone, chronic pain treated with more than one daily dose of opioids, treatment with opioid antagonists, antipsychotics or antiepileptics, abuse of alcohol/drugs, previous hip surgery, and pregnancy.
Randomization and blinding
The study was designed as a randomized, triple-blind superiority trial. Patients were allocated in two groups 1:1 to receive an active or a placebo subpectineal obturator nerve block. The active block was 15 mL bupivacaine 5 mg/mL with added epinephrine 5 μg/mL (Aspen Nordic, Ballerup, Denmark) while placebo was 15 mL saline 9 mg/mL (Fresenius Kabi, Copenhagen, Denmark). REDCap (Research Electronic Data Capture, Vanderbilt University, Nashville Tennessee, USA)11 was used as a data capture system and for online randomization of patients in blocks of 4, 6 or 8. Two intensive care nurses trained per protocol (PP) performed the randomization and double control of the study medicine. The nurses worked in another hospital section and did not have any other role in the study. The data were analyzed before unblinding of allocation.
Anesthesia
Peroral paracetamol 1000 mg (GlaxoSmithKline Consumer Healthcare, Brøndby, Denmark) and ibuprofen 400 mg (Orifarm Generics, Odense, Denmark) were administered before general anesthesia by propofol (Fresenius Kabi, Copenhagen, Denmark) and remifentanil (Fresenius Kabi, Copenhagen, Denmark). Remifentanil was the sole intraoperative opioid. Airways were managed with laryngeal masks (Ambu, Ballerup, Denmark) except for one patient who was endotracheally intubated (Smiths Medical, Minneapolis, USA). All patients had intravenous droperidol 0.625 mg (Carinopharm, Eime, Germany), ondansetron 4 mg (Fresenius Kabi, Copenhagen, Denmark) and dexamethasone 8 mg (Hameln Pharma, Copenhagen, Denmark) for antiemetic prophylaxis.
Subpectineal obturator nerve block
The subpectineal obturator nerve block targets the fascial plane between the pectineus and external obturator muscles12 (figure 1). It was carried out in general anesthesia before surgery by the principal investigator (CJ) guided by ultrasound (Sonosite X-Porte, Fujifilm, Sonosite, Bothell, Washington, USA) with a 15–6 MHz linear transducer and using a 22-gage, 80 mm, SonoTAP needle (Pajunk. Medizintechnologie, Geisingen, Germany).
Left: Ultrasound image of the right infrainguinal region. The white line indicates the out of plane block needle approach targeting the fascial plane between the pectineus and external obturator muscles. It is mandatory that the needle tip pierces the epimysial fascia on the deep side of the pectineus muscle thereby obtaining interfascial spread of the injectate inside the subpectineal compartment between the juxtaposed epimysial fascia of the pectineus and external obturator muscles. Right: The set-up of the subpectineal nerve block procedure. A, artery; AB, adductor brevis muscle; AL, adductor longus muscle; AM, adductor magnus muscle; OE, obturator external muscle; PECT, pectineus muscle; V, vein.
Median pain scores (NRS 0–10) the first 3 hours in the postanesthesia care unit (PACU) at rest and activity with 45° flexion of the hip. Time points are shifted per group along the x-axis to separate data points graphically. NRS, Numeric Rating Scale; SOB, subpectineal obturator nerve block.
All nerve block procedures were video recorded and captured in the hospital electronic medical image storage system (Systematic Healthcare, Aarhus, Denmark).13 All videos were reviewed by an expert regional anesthetist (TFB) before unblinding. Patients were excluded from the data analysis, if the video did not document correct spread of injectate in the subpectineal space.
Surgery
Surgery was performed by one surgeon (BL). The patient was supine with the hip internally rotated. A perineal post facilitated traction of the affected leg. The arthroscopy port holes (maximum two) were infiltrated using 5 mL of bupivacaine 2.5 mg/mL with added epinephrine 5 μg/mL (Aspen Nordic, Ballerup, Denmark).
Outcomes
A pilot study indicated that the median length of stay in the postanesthesia care unit (PACU) until eligibility for home discharge was 3 hours. Consequently, the follow-up time was 3 hours in the present trial.
The primary outcome was intravenous morphine equivalent consumption for the first 3 hours in the PACU.
The secondary outcomes were (1) Numeric Rating Scale (NRS) pain score (0–10, 0 is ‘no pain’ and 10 is ‘maximum pain’) at rest and during 45° flexion of the hip measured at PACU arrival and every 30 min for 3 hours; (2) relative adductor strength difference comparing preblock to postoperative (time of home discharge) adductor strength: the numerator was postoperative minus preoperative strength and the denominator was preoperative strength; (3) length of stay in the PACU defined as time from arrival until discharge readiness according to the standard of the Danish Society of Anesthesia and Intensive Care Medicine14 (see below); (4) postoperative postoperative nausea and vomiting (PONV) scores; (5) frequency of vomiting; (6) consumption of antiemetics, and (7) patient satisfaction.
Intraoperative hip traction time (from application until termination of hip traction), duration of anesthesia (time from anesthesia induction until airway device removal), and intraoperative consumption of propofol and remifentanil were reported as patient characteristics.
Assessment of outcomes
All patients were educated presurgically in the NRS, the patient-controlled analgesia (PCA) pump and dosing of 5 mg intravenous morphine (Abcur AB, Helsingborg, Sweden) when the NRS score exceeded 3. The PCA pump settings were as follows: no basal rate, 5 mg bolus with 20 min lockout and a 15 mg maximum hourly dose. In case of insufficient pain control the primary investigator could bypass the PCA-settings and administer an extra 5 mg intravenous bolus after assessing the patient. Data were stored electronically and transferred to REDCap after home discharge. In case of known intolerance to morphine, it was substituted by 5 mg intravenous oxycodone (2care4 Generics Aps, Esbjerg, Denmark). A 5 mg intravenous oxycodone equals 6.67 mg intravenous morphine. The patients were requested to assess the NRS score (0–10) of pain at rest and with a 45° active hip flexion, from the time of arrival in PACU and every 30 min. The PACU nurses were trained per protocol (PP). The reported NRS scores were recorded in the PACU patient file.
The baseline maximum voluntary isometric contraction force (Newtons) of the hip adductor muscle strength was tested prior to block application by the primary investigator. It was reassessed by the PACU nurses just prior to home discharge. Muscle strength data were recorded directly in the secure, online database system REDCap by separate accesses for the primary investigator and the PACU nurses.
The hip adductor strength was tested supine with a wedge placed from the groin beyond the feet. A dynamometer (Powertrack II Commander, JTECH Medical, Utah, USA) was placed between the wedge and the limb, 5 cm proximal to the medial malleolus.15
The patient was instructed by a prerecorded audio file to perform three consecutive maximum hip adductor muscle contractions for 5 s with 30 s intermissions. The maximum value of the three tests was captured for statistical analysis.
Every 30 min PONV was assessed on a verbal scale (none, mild, moderate, and severe). Moderate and severe PONV was primarily treated with ondansetron 2 mg intravenous (repeated after 30 min to a maximum of 4 mg intravenous) and second with droperidol 0.625 mg intravenous. Prior to home discharge, patient satisfaction was NRS scored from 0 to 10. PACU nurses recorded the PONV scores, episodes of vomiting, PONV treatment, length of stay, and patient satisfaction in the PACU patient file.
Patients were home discharged after the 3 hours follow-up complying with the Danish standard14: awake, SpO2>97%, respiratory frequency 10–20, heart rate 50–100, systolic blood pressure >100 mm Hg, NRS pain score ≤3, and none or mild nausea. In case of quicker readiness for home discharge, the time was recorded but the patient completed the 3 hours follow-up PP.
The primary investigator registered all intraoperative data (hip traction time, anesthesia time, and consumption of propofol and remifentanil) in the anesthesia file, and transferred the data to REDCap.
Power calculation and statistical analysis
A non-blinded pilot study in patients (n=15) scheduled for hip arthroscopy due to femoroacetabular impingement syndrome indicated that the mean (SD) of intravenous morphine the first three postoperative hours was 17 (12) mg vs 30 mg (12) for subpectineal obturator nerve block versus no block, respectively. The minimum number of patients required to detect a significant statistical difference would be 34 patients for a 5% significance level and 90% power (www.sealedenvelope.com/power/continuous-superiority). 40 patients were enrolled to account for dropouts and exclusions.
Normality of distribution was assessed by quantile-quantile plots. Continuous, normally distributed data were presented as mean (SD), and intergroup differences were analyzed with Student’s t-test, in case of equal intergroup variance. Ordinal data were presented as median and IQR. Intergroup differences of continuous non-normal and ordinal data were analyzed with Mann-Whitney test (STATA V.18.0 (StataCorp).
Results
40 patients were enrolled (figure 2).16 Five patients were excluded—blinded to allocation—by video assessment of adequacy of spread of injectate in the subpectineal compartment. One patient was excluded due to extracapsular calcification impeding surgical access to the hip joint. Oxycodone was administered to four patients due to previous adverse effects of morphine.
Consolidated Standards of Reporting Trials diagram of patient flow throughout the study. Placebo (gray); subpectineal obturator nerve block (black).
No intergroup demographic differences were observed (table 1).
Patient characteristics
Secondary perioperative outcomes are reported in table 2.
Secondary perioperative outcomes
Primary outcome
The intravenous morphine equivalent consumption for the first three postoperative hours was 11.9 mg (5.8) vs 19.7 mg (6.7) (p<0.001), for active versus placebo subpectineal obturator nerve block, respectively (figure 3). The mean group difference was 7.8 mg (3.5–12.2) (40%), which equals an oral morphine equivalent reduction of 23.4 mg.
Scatter plot of the difference between an active and placebo subpectineal obturator nerve block on consumption of intravenous morphine equivalents during the first three postoperative hours. A random scatter of 0–4 mg was applied on both the x-axis and y-axis to separate data points graphically. Gray/Black diamond, mean opioid consumption. IV, intravenous; SOB, subpectineal obturator nerve block.
Secondary outcomes
The intergroup hip adductor strength difference was statistically significant. No intergroup pain NRS score differences were observed during the 3 hour follow-up (figure 4). No intergroup differences were observed for any other secondary outcome (table 2). No adverse events including no falls occurred during the 3 hours follow-up.
Discussion
This is the first randomized clinical trial assessing the effect of the subpectineal obturator nerve block on opioid consumption after hip arthroscopy. The reduction of 7.8 mg (3.5–12.2) intravenous morphine corresponds to 23.4 mg oral morphine the first three postsurgical hours.
Recently, we demonstrated a 50% reduction in opioid consumption of an iliopsoas plane block the first 3 hours after hip arthroscopy.8
Both the iliopsoas plane block and the PENG block involves injection of local anesthetic in the fascial compartment deep to the iliopsoas muscle, but neither result in spread of injectate to the obturator nerve.17 Thus, it may be relevant to combine a subiliopsoas and a subpectineal injection for analgesia after hip arthroscopy.
Two randomized controlled trials have shown no pain relief of the subpectineal obturator nerve block after hip arthroplasty.18 19 Hip arthroscopy differs from hip arthroplasty by the strong intraoperative traction of the hip joint capsule—assumingly causing postsurgical pain. Thus, the effective pain relief with subpectineal obturator nerve block after hip arthroscopy does not translate to any effect on pain after hip arthroplasty.
No intergroup difference was observed in pain scores. However, satisfactory pain control required 40% larger morphine consumption in the placebo group versus the active group.
It may be conjectured that an intra-articular injection could offer a more straightforward procedural approach to anesthetize the joint capsule nociceptors compared with nerve blocks. However, a previous study compared the effect of intra-articular injection versus femoral nerve block on pain after hip arthroscopy.20 Femoral nerve block resulted in significantly lower postsurgical pain scores. The problems with femoral nerve block were a higher frequency of patient fall for the duration of the nerve block and delayed ambulation. Selective anesthesia of the sensory innervation of the femoral nerve innervation of the hip does not increase the risk of fall.6 In the present study, we demonstrate that selective obturator nerve block equally contributes to reduce opioid consumption after hip arthroscopy.
The study has some limitations. First, the 3-hour follow-up presents a limitation that may raise concern about cumulated opioid consumption for the duration of the nerve block. The 3-hour time period being investigated is logically chosen in regard to the outcomes of interest. In our clinical experience, the first 3 hours after hip arthroscopy is the typical duration of moderate to severe postsurgical pain. Accordingly, both groups were home discharged with NRS pain scores ≤3 (figure 4). We find it clinically relevant to know that selective blockade of the obturator nerve reduces opioid consumption by 40% equal to 23.4 mg oral morphine during the first 3 critical hours after hip arthroscopy. It is academically interesting to know that the obturator nerve nociceptors in the hip joint play an important role in pain after hip arthroscopy—as opposed to pain after hip arthroplasty.18 19
Second, 5 out of 39 patients were excluded, unless the blinded video recordings unambiguously displayed visible and accurate spread of the injectate in the targeted subpectineal space. This is a strict criterion for adequacy of spread and some excluded procedures may have performed clinically successful spread without translating into clearly visible accurate spread on the video screen. Thus, exclusion cannot be translated into failure. Five out of 39 would be a high failure rate in an intention-to-treat (ITT) analysis. The choice between ITT and PP analysis when designing a clinical trial depends on various factors. If the purpose of the trial is to assess the real-world effectiveness of a treatment regardless of adherence or protocol deviations, then ITT is preferred. However, the present study is a ‘proof-of-concept’ study, accordingly designed and carried out as a PP analysis. We intended to assess whether an accurately performed subpectineal obturator nerve block would reduce opioid consumption after hip arthroscopy compared with placebo nerve block.
For clarity, we have made a post hoc ITT analysis of the enrolled 39 patients. It showed a mean (SD) intravenous morphine consumption of 12.3 mg (5.9) vs 19.5 mg (8.3) for the active versus placebo group, respectively (p=0.004). The fact that the differences of the primary outcome between PP and ITT analyses are minor (7.8 mg vs 7.2 mg) supports the robustness of the findings. This small variation suggests that the overall effect of the treatment is consistent regardless of the analysis method, indicating that the exclusions did not introduce significant bias.
Third, the present study was specifically powered to assess whether subpectineal obturator nerve block would reduce opioid consumption in the first 3 hours after hip arthroscopy. However, it was not powered to evaluate the frequency and effects of opioid-related adverse effects. Satisfactory postsurgical pain control typically requires large doses of opioids as verified by the present trial: The mean (SD) intravenous morphine consumption in the placebo group was 19.7 mg (6.7) during the first 3 postsurgical hours. The mean 19.7 mg intravenous morphine is equivalent to 59.1 mg oral morphine. The clinical problem is that the relatively high consumption of opioids required to control pain the first three postsurgical hours produces frequent adverse effects of opioids. A high frequency of opioid-related adverse effects has a well-known negative impact on patient satisfaction, nursing hours, fast-track ambulation and home discharge.
Fourth, the power calculation indicated that 34 patients with 17 patients allocated to each group would be required to detect a statistically significant intergroup difference. Only 16 patients were allocated to the placebo block group. Nonetheless, due to the overestimation of the variance in the a priori power calculation, the 40% reduction of morphine consumption for active versus placebo subpectineal obturator nerve block turned out to be highly significant (p<0.001).
Fifth, a subpectineal obturator nerve block is not a selective sensory nerve block, as it reduces the ability to adduct the hip. Hip adductor strength decreased by 80% in the active vs 38% in the placebo group. However, this did not entail clinically significant impediment of ambulation or walking or increase the risk of fall in the present study. It is a limitation of the study that the postsurgical ability to ambulate with subpectineal obturator nerve block was not assessed PP. However, our previously published findings indicate that Timed-Up-and-Go time was not affected by the subpectineal obturator nerve block compared with postsurgical controls without this block.21
The perspective is that it may be possible to deliver hip arthroscopy as a fast-track outpatient procedure with efficient pain-free and opioid-free ambulation and home discharge by combining two nerve blocks. Further studies are warranted to corroborate this viewpoint.
In conclusion, an active versus placebo subpectineal obturator nerve block reduces the intravenous opioid consumption approximately 40% during the first three postsurgical hours.
Data availability statement
Data may be obtained from a third party and are not publicly available.
Ethics statements
Patient consent for publication
Ethics approval
This study involves human participants and was approved by the Central Denmark Region Committee on Health Research Ethics (reference number 1-10-72-374-21). Participants gave informed consent to participate in the study before taking part.
Acknowledgments
We would like to thank all the patients involved in the study as well as the nurses at the Department of Anesthesiology and Intensive Care, Horsens Regional Hospital.
References
Footnotes
Contributors All authors participated in the design of the study, implementation of the study and writing of the manuscript. TFB acted as the guarantor for the overall content.
Funding The study was funded by the Health Research Foundation of Central Denmark Region and the Salling Foundation.
Disclaimer The content is solely the responsibility of the authors.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.