Evaluation of the proximal adductor canal block injectate spread: a cadaveric study

Effects of popliteal plexus block after total knee arthroplasty: a randomized clinical trial

BACKGROUND AND OBJECTIVES

Motor-sparing peripheral nerve blocks enhance multimodal opioid-sparing strategies after total knee arthroplasty. We hypothesized that adding a popliteal plexus block to a femoral triangle block could reduce 24-hour opioid consumption after total knee arthroplasty, compared with standalone femoral triangle block or adductor canal block.

METHODS

This patient- and assessor-blinded, randomized controlled trial allocated 165 patients into three equally sized parallel groups, receiving either 1) popliteal plexus block+femoral triangle block, 2) femoral triangle block, or 3) adductor canal block. Intravenous oxycodone was administered via patient-controlled analgesia pumps. The primary outcome was 24-hour postoperative opioid consumption. Secondary outcomes were preoperative maximum voluntary isometric contraction and manual muscle tests of knee and ankle movement assessed before and after the nerve block procedure together with postoperative pain scores, mobilization, and 12-hour opioid consumption.

RESULTS

24-hour postoperative intravenous oxycodone consumption varied significantly between groups (p<0.01), with medians (IQR) of 6 mg (2-12) in the popliteal plexus block+femoral triangle block group, 10 mg (8-16) in the femoral triangle block group, and 12 mg (6-18) in the adductor canal block group. Median consumption in the popliteal plexus block+femoral triangle block group was reduced by -4 mg (95% CI -7.4 to -1.0, p<0.01) and -6 mg (95% CI -8.3 to -1.3, p=0.01) compared with groups of femoral triangle block and adductor canal block, respectively. No differences were found in pain scores, mobilization, or changes in preoperative muscle strength. Post hoc analysis revealed successful 24-hour opioid-free postoperative care among 12 patients with popliteal plexus block+femoral triangle block, as compared with two with femoral triangle block and six with adductor canal block.

CONCLUSION

Adding a popliteal plexus block to a femoral triangle block resulted in a statistically significant reduction of 24-hour postoperative opioid consumption after total knee arthroplasty. However, no differences were found in pain scores. Popliteal plexus block did not impair the lower leg muscles.

Proximal versus distal adductor canal catheters for total knee arthroplasty: a systematic review and meta-analysis of randomized controlled trials

PURPOSE

Total knee arthroplasty (TKA) is associated with severe postoperative pain. Continuous adductor canal blockade provides analgesia while preserving quadriceps muscle strength. Nevertheless, uncertainty still exists as to the optimal adductor canal catheter placement approach. We sought to conduct a systematic review and meta-analysis of randomized controlled trials (RCTs) comparing the analgesic effects of proximal vs distal adductor canal catheters in patients undergoing TKA.

SOURCE

We systematically searched PubMed, EMBASE, and Cochrane for RCTs comparing distal and proximal adductor canal catheters for TKA regarding critical clinical outcomes in adult patients. Statistical analysis was performed using R version 4.1.2 (R Foundation for Statistical Computing, Vienna, Austria). Heterogeneity was assessed using the Cochran Q test and I2 statistics. Trial sequential analysis (TSA) was performed to evaluate the risk of random errors and the uncertainty of our results. The risk of bias was appraised according to the RoB-2 tool.

PRINCIPAL FINDINGS

Six RCTs and 352 patients were included, of whom 151 (42.9%) were male, and 175 (49.7%) were randomized to undergo proximal adductor canal catheter placement. Due to the randomized nature of the studies, baseline characteristics were similar between groups. There were no statistical differences between proximal and distal adductor canal catheters regarding cumulative opioid consumption in the first 24 hr (mean difference [MD], -4.86; 95% confidence interval [CI], -15.19 to 5.47; P = 0.36; four RCTs; 240 patients); pain scores at rest (MD, 0.41; 95% CI, -1.23 to 0.40; P = 0.32; six RCTs; 350 patients); and pain scores with movement for the first 24 hr (MD, -0.25; 95% CI, -0.85 to 0.35; P = 0.42; four RCTs; 246 patients). In the TSA, the required information size was not reached, and the Z-curve did not cross the monitoring boundaries in any of the endpoints.

CONCLUSION

These findings suggest that proximal vs distal adductor canal catheter placement in patients undergoing TKA may be equally effective for the outcomes of opioid consumption in the first 24 hr, pain scores at rest, and pain scores with movement in the first 24 hr. Nevertheless, TSA findings suggest insufficient power to definitively conclude no differences between the two techniques.

STUDY REGISTRATION

PROSPERO (CRD42022353576); registered 25 August 2022.

Ultrasound Evaluation of Subsartorial Spread Following Adductor Canal Block: A Case Series

Adductor canal block is a widely used regional anesthesia technique for total knee arthroplasty that helps in reducing post-surgical pain and opioid use. Anatomically, the adductor canal extends from the apex of the femoral triangle proximally to the adductor hiatus distally and is roofed by the sartorius and vasto-adductor fascia. All these serve as a potential path for the spread of the local anesthetic when it is injected inside the adductor canal during the block. Subsartorial space is of unique interest as it lies between the sartorius and vasto-adductor fascia, carrying the subsartorial plexus that can provide additional analgesia to the knee when the adductor canal block injectate spreads into it. While the spread can be variable, ultrasound can be a useful tool to evaluate this spread. This is a case series of patients who underwent total knee arthroplasty under spinal anesthesia and adductor canal blocks. We present the findings of ultrasound evaluation of the injectate spread following adductor canal blocks and evaluation of their analgesia effects.

Adductor canal block techniques do not lead to involvement of sciatic nerve branches: a radiological cadaveric study

INTRODUCTION

Low and high volume mid-thigh (ie, distal femoral triangle) and distal adductor canal block approaches are frequently applied for knee surgical procedures. Although these techniques aim to contain the injectate within the adductor canal, spillage into the popliteal fossa has been reported. While in theory this could improve analgesia, it might also result in motor blockade due to coverage of motor branches of the sciatic nerve. This radiological cadaveric study, therefore, investigated the incidence of coverage of sciatic nerve divisions after various adductor canal block techniques.

METHODS

Eighteen fresh, unfrozen and unembalmed human cadavers were randomized to receive ultrasound-guided distal femoral triangle or distal adductor canal injections, with 2 mL or 30 mL injectate volume, on both sides (36 blocks in total). The injectate was a 1:10 dilution of contrast medium in local anesthetic. Injectate spread was assessed using whole-body CT with reconstructions in axial, sagittal and coronal planes.

RESULTS

No coverage of the sciatic nerve or its main divisions was found. The contrast mixture spread to the popliteal fossa in three of 36 nerve blocks. Contrast reached the saphenous nerve after all injections, whereas the femoral nerve was always spared.

CONCLUSIONS

Adductor canal block techniques are unlikely, even when using larger volumes, to block the sciatic nerve, or its main branches. Furthermore, injectate reached the popliteal fossa in a small minority of cases, yet if a clinical analgesic effect is achieved by this mechanism is still unknown.

Chronic post-surgical pain after knee arthroplasty: a role of peripheral nerve blocks

Introduction

Peripheral nerve blocks are an efficient method of pain control after total knee arthroplasty (TKA), but there is no report of their impact on chronic post-surgical pain (CPSP).

Methods

This prospective observational study aimed to assess adductor canal block (ACB) and IPACK block (blocks vs. no blocks) on opioid consumption, postoperative pain score, chronic post-surgical pain 2 years after TKA.

Results

166 patients (82 vs. 84) were analyzed. Opioid consumption was less in the group with blocks (9.74 ± 3.87 mg vs. 30.63 ± 11.52 mg) (p < 0.001). CPSP was present in 20.24% of patients in the group without blocks and 6.1% of patients with blocks (p = 0.011). Predictor variables of CPSP included pain before surgery (cut-off of 5.5), pain at rest (cut-off of 2.35), pain during active movement (cut-off: 2.5), and opioid consumption (cut-off: 8 mg).

Conclusion

Peripheral nerve blocks provide adequate analgesia, significantly decrease opioid consumption, improve functional outcomes, and reduce CPSP 2 years after surgery.

Single-injection nerve blocks for total knee arthroplasty: femoral nerve block versus femoral triangle block versus adductor canal block-a randomized controlled double-blinded trial

INTRODUCTION

Femoral nerve block (FNB) is a well-established analgesic technique for TKA. However, it associates quadriceps weakness. Therefore, femoral triangle block (FTB) and adductor canal block (ACB) were proposed as effective alternative motor-spearing techniques. The primary objective was to compare quadriceps muscle strength preservation between FNB, FTB and ACB in TKA. The secondary objective was to analyze pain control and functional outcomes.

METHODS

This is a prospective, double-blinded RCT. From April 2018 to April 2019, patients who undergo a primary TKA were randomized into three experimental groups: FNB-G1/FTB-G2/ACB-G3. Quadriceps strength preservation was measured as the difference in maximum voluntary isometric contraction (MVIC) preoperatively and postoperatively.

RESULTS

Seventy-eight patients (G1, n = 22; G2, n = 26; G3, n = 30) met our inclusion/exclusion criteria. Patients with FNB retained significantly lower baseline MVIC at 6 h postoperatively (p = 0.001), but there were no differences at 24 and 48 h. There were no differences between the groups in functional outcomes at any time point. Patients in the FNB-G1 presented significant lower pain scores at 6 h (p = 0.01), 24 h (p = 0.005) and 48 h (p = 0.01). The highest cumulative opioid requirement was reported in ACB-G3.

CONCLUSION

For patients undergoing TKA, FTB and ACB preserve quadriceps strength better than FNB at 6 h postoperatively, but there are no differences at 24 and 48 h. Moreover, this early inferiority does not translate to worse functional outcomes at any time point. FNB is associated with better pain control at 6, 24 and 48 h after surgery, while ACB presents the highest cumulative opioid requirement.

CLINICAL TRIAL REGISTRATION

This study was registered in clinicaltrials.gov (NCT03518450; https://clinicaltrials.gov/ct2/show/NCT03518450 ; submitted March 17, 2018).

Anatomical study of the adductor canal: three-dimensional micro-computed tomography, histological, and immunofluorescence findings relevant to neural blockade

BACKGROUND

A precise anatomical understanding of the adductor canal (AC) and its neural components is essential for discerning the action mechanism of the AC block. We therefore aimed to clarify the detailed anatomy of the AC using micro-computed tomography (micro-CT), histological evaluation, and immunofluorescence (IF) assays.

METHODS

Gross dissections of 39 thighs provided morphometric data relevant to injection landmarks. Serial sectional images of the AC were defined using micro-CT and ultrasonography. The fascial and neural structures of the AC proper were histologically evaluated using Masson's trichrome and Verhoeff-Van Gieson staining, and double IF staining using choline acetyltransferase (ChAT) and neurofilament 200 antibodies.

RESULTS

The posteromedial branch insertion of the nerve to vastus medialis (NVM) into the lateral border of the AC proper was lower (14.5 ± 2.4 cm [mean ± SD] above the base of the patella) than the origin of the proximal AC. The AC consists of a thin subsartorial fascia in the proximal region and a thick aponeurosis-like vastoadductor membrane in the distal region. In the proximal AC, the posteromedial branch of the NVM (pmNVM) consistently contained both sensory and motor fibers, and more ChAT-positive fibers were observed than in the saphenous nerve (27.5 ± 11.2 / 104 vs. 4.2 ± 2.6 / 104 [counts/µm2], P < 0.001).

CONCLUSIONS

Anatomical differences in fascial structures between the proximal and distal AC and a mixed neural component of the neighboring pmNVM have been visualized using micro-CT images, histological evaluation, and IF assays.

Addition of infiltration between the popliteal artery and the capsule of the posterior knee (IPACK) to local infiltration analgesia for total knee arthroplasty: a prospective randomized controlled trial

BACKGROUND

Local infiltration analgesia (LIA) is a popular analgesic technique commonly administered during total knee arthroplasty (TKA). Recent studies have demonstrated that the infiltration between the popliteal artery and the capsule of the posterior knee (IPACK) can be complementary to analgesic modalities. However, the combined and relative efficacy of LIA and IPACK is unclear. We aimed to evaluate the analgesic and functional outcomes among LIA, IPACK, and LIA+IPACK.

MATERIALS AND METHODS

A total of 120 patients undergoing primary TKA were randomly allocated to 1 of 3 groups: LIA (50 mL of 0.25% ropivacaine and 2.0 μg/mL epinephrine); IPACK (20 mL of 0.25% ropivacaine and 2.0 μg/mL epinephrine); and LIA+IPACK. The primary outcome was the visual analog scale (VAS) pain score. Secondary outcomes were opioid use, knee range of motion (ROM), quadriceps muscle strength, mobilization distance, timed up and go (TUG) test, and postoperative complications.

RESULTS

The mean VAS pain scores were significantly higher after using IPACK alone than after using LIA+IPACK and LIA within 24 hours (all p＜0.05). LIA+IPACK had lower mean VAS pain scores than LIA when the knees were at rest (within 12 hours, p < 0.05) and flexion (within 8 hours, p＜0.05). Patients receiving LIA+IPACK and LIA had significantly lower morphine equivalents (ME) than those receiving IPACK alone within 24 hours (26.3, 28.9 versus 47.8, both p＜0.05) and during hospitalization (98, 101.6, versus 128.4 both p＜0.05). Both LIA+IPACK and LIA had higher ROM (within two days), higher level of muscle strength (within 12 hours), longer mobilization distances (within one day), and shorter TUG time (till discharge) compared with IPACK alone (all p＜0.05), while LIA+IPACK only had a higher knee ROM than LIA on the first postoperative day (p＜0.05). There was no significant difference in any other outcomes.

CONCLUSIONS

This randomized controlled trial demonstrated that there were significantly lower pain scores, less opioid consumption, and better functional results with LIA+IPACK and LIA when compared with IPACK alone, suggesting that IPACK alone was inferior for pain control.

Motor-Sparing Effect of Adductor Canal Block for Knee Analgesia: An Updated Review and a Subgroup Analysis of Randomized Controlled Trials Based on a Corrected Classification System

OBJECTIVE

Discrepancies in the definition of adductor canal block (ACB) lead to inconsistent results. To investigate the actual analgesic and motor-sparing effects of ACB by anatomically defining femoral triangle block (FTB), proximal ACB (p-ACB), and distal ACB (d-ACB), we re-classified the previously claimed ACB approaches according to the ultrasound findings or descriptions in the corresponding published articles. A meta-analysis with subsequent subgroup analyses based on these corrected results was performed to examine the true impact of ACB on its analgesic effect and motor function (quadriceps muscle strength or mobilization ability). An optimal ACB technique was also suggested based on an updated review of evidence and ultrasound anatomy.

MATERIALS AND METHODS

We systematically searched studies describing the use of ACB for knee surgery. Cochrane Library, PubMed, Web of Science, and Embase were searched with the exclusion of non-English articles from inception to 28 February 2022. The motor-sparing and analgesic aspects in true ACB were evaluated using meta-analyses with subsequent subgroup analyses according to the corrected classification system.

RESULTS

The meta-analysis includes 19 randomized controlled trials. Compared with the femoral nerve block group, the quadriceps muscle strength (standardized mean difference (SMD) = 0.33, 95%-CI [0.01; 0.65]) and mobilization ability (SMD = -22.44, 95%-CI [-35.37; -9.51]) are more preserved in the mixed ACB group at 24 h after knee surgery. Compared with the true ACB group, the FTB group (SMD = 5.59, 95%-CI [3.44; 8.46]) has a significantly decreased mobilization ability at 24 h after knee surgery.

CONCLUSION

By using the corrected classification system, we proved the motor-sparing effect of true ACB compared to FTB. According to the updated ultrasound anatomy, we suggested proximal ACB to be the analgesic technique of choice for knee surgery. Although a single-shot ACB is limited in duration, it remains the candidate of the analgesic standard for knee surgery on postoperative day 1 or 2 because it induces analgesia with less motor involvement in the era of multimodal analgesia. Furthermore, data from the corrected classification system may provide the basis for future research.

A Practical Guide to Lower Extremity Nerve Blocks for the Sports Medicine Surgeon

BACKGROUND

Peripheral nerve blocks (PNBs) are vital in the administration of surgical analgesia and have grown in popularity for use in lower extremity arthroscopic procedures because of their capacity to safely and effectively control pain. The number and specificity of PNBs, however, have made choosing the best option for a procedure nebulous for orthopaedic surgeons.

PURPOSE

To present a narrative literature review of the PNBs available for arthroscopic hip and knee procedures that is adapted to an audience of orthopaedic surgeons.

STUDY DESIGN

Narrative literature review.

METHODS

A combination of the names of various lower extremity PNBs AND "hip arthroscopy" OR "knee arthroscopy" was used to search the English medical literature including PubMed, Cochrane Library, ScienceDirect, Embase, and Scopus. Placement technique, specificity of blockade, efficacy, and complications were assessed. Searches were performed through May 2, 2021.

RESULTS

A total of 157 studies were included in this review of lower extremity PNBs. Femoral nerve, lumbar plexus, sciatic nerve, and fascia iliaca compartment blocks were most commonly used in arthroscopic hip surgery, while femoral nerve, 3-in-1, and adductor canal blocks were preferred for arthroscopic knee surgery. Each block demonstrated a significant benefit (P > .05) in ≥1 of the following outcomes: intraoperative morphine, pain scores, nausea, and/or opioid consumption. Combination blocks including the lateral femoral cutaneous nerve block, obturator nerve block, quadratus lumborum block, and L1 and L2 paravertebral block have also been described. Complication rates ranged from 0% to 4.8% in those administered with ultrasound guidance. The most commonly reported complications included muscular weakness, postoperative falls, neuropathy, intravascular and intraneural injections, and hematomas.

CONCLUSION

When administered properly, PNBs were a safe and effective adjuvant method of pain control with a significant potential to limit postoperative narcotic use. While blockade choice varies by surgeon preference and procedure, all PNBs should be administered with ultrasound guidance, and vigilant protocols for the risk of postoperative falls should be exercised in patients who receive them.

Comparison of Femoral Nerve Catheter, Adductor Canal Catheter, and Periarticular Liposomal Bupivacaine Infiltration for Postoperative Analgesia After Primary Total Knee Arthroplasty

BACKGROUND

Peripheral nerve catheters are used to provide analgesia after total knee arthroplasty (TKA) and have been shown to decrease pain and opioid use, to facilitate participation with physical therapy (PT), and to hasten discharge. More recently, pericapsular infiltration using liposomal bupivacaine (LB) has been employed as an alternative analgesic approach.

METHODS

This retrospective study compared outcomes for three analgesic approaches: femoral nerve catheter (FNC), adductor canal catheter (ACC), and intraoperative LB infiltration. The primary outcome was numeric rating scale (NRS) pain scores at 24 hours. Secondary outcomes included pain scores at 12, 36, and 48 hours, time-to-first opioid, cumulative opioid use, distance walked, and time-to-discharge.

RESULTS

Pain scores at 24 hours were significantly lower in both the ACC and FNC cohorts when compared to the LB cohort (3.1 versus 4.6 [P = .017] and 2.4 versus 4.6 [P < .0001]). The ACC and FNC groups did not differ significantly at that timepoint (P = .27). Similar comparisons were found at 12 and 36 hours, while at 48 hours the FNC group was superior. Time to first opioid and opioid consumption favored the ACC and FNC groups. Walking distance favored the ACC group. Both the ACC and LB groups had a faster time-to-discharge than the FNC group.

CONCLUSION

Both ACCs and FNCs provided superior analgesia at 24 hours compared to LB, while being equivalent to each other. Pain scores at 12 hours and 36 hours as well as opioid consumption through 48 hours mirrored this finding. Although various differences were found between groups in terms of time-to-first analgesic, walking distance and time-to-discharge, the ACC approach appeared to optimally balance analgesia, ambulation, and time-to-discharge.

Butorphanol as an Adjuvant to Ropivacaine for Adductor Canal Blocks in Total Knee Arthroplasty Patients: A Randomized, Double, Blind Study

Background

The objective of this study was to observe the effects of butorphanol as an adjuvant to ropivacaine for the adductor canal block (ACB) on postoperative analgesia in patients undergoing total knee arthroplasty (TKA).

Methods

Seventy-four patients undergoing TKA were included and randomly divided into two groups: Group BR received 20 ml of 0.33% ropivacaine plus 1 mg butorphanol and Group R received 20 ml of 0.33% ropivacaine plus 1 ml normal saline for ultrasound-guided adductor canal blocks. The primary outcomes were the duration of the sensory block and the pain visual analogue scale (VAS), and secondary outcomes included the number of PCIA attempts (patient-controlled intravenous analgesia) and the time to first pressing and rescue analgesia. Other outcomes included knee active range of motion (ROM), quadriceps strength, the time to first mobilization, the duration of postoperative hospital stay, Knee Society Score (KSS), and postoperative complications.

Results

Since two patients in each group rejected postoperative assessments, 35 patients were included in each group. Compared with Group R, Group BR had longer duration of sensory blocks (18.42 ± 3.46 vs. 15.36 ± 2.29 h, p < 0.01) and lower postoperative pain scores within 24 hours at rest and within 12 hours with activity (p < 0.01). The number of PCIA attempts decreased within 48 hours after surgery (4.5 ± 1.2 vs. 7.8 ± 1.5 times, p < 0.01), and the time to first pressing was later (20.31 ± 2.59 vs. 16.25 ± 2.31 h, p < 0.01). In addition, Group BR had bigger knee ROM at within 24 hours after the operation than Group R (68.37 ± 4.70°vs. 59.21 ± 6.41,85.67 ± 5.17 vs. 74.37 ± 4.68°, 97.62 ± 5.43 vs. 84.18 ± 4.49°, p < 0.01). There was no significant difference between the two groups (p > 0.05) in terms of rescue analgesia, quadriceps strength, the time to first mobilization, the duration of postoperative hospital stay, the KSS function scores, and postoperative complications.

Conclusions

Butorphanol plus ropivacaine ultrasound-guided adductor canal block can prolong the duration of sensory block, relieve early postoperative pain, and improve the range of motion of the knee joint, without affecting the occurrence of postoperative complications. Name of the Registry. Chinese Clinical Trial Registry. Trial Registration Number. ChiCTR2100041859. URL of Trial Registry Record. http://www.chictr.org.cn/edit.aspx?pid=119731&htm=4. Date of Registration. 08/01/2021 0:00:00.

Optimal location for continuous catheter analgesia among the femoral triangle, proximal, or distal adductor canal after total knee arthroplasty: a randomized double-blind controlled trial

Background

Pain management after total knee arthroplasty is essential to improve early mobilization, rehabilitation, and recovery. Continuous adductor canal (AC) block provides postoperative analgesia while preserving quadriceps strength. However, there have been inconsistencies regarding the optimal location for continuous catheter block. We compared continuous femoral triangle, proximal AC, and distal AC blocks for postoperative analgesia after total knee arthroplasty.

Methods

Patients undergoing unilateral total knee arthroplasty were randomly assigned to three groups: femoral triangle, proximal AC, or distal AC. The surgeon performed periarticular local anesthetic infiltration. After surgery, an ultrasound-guided perineural catheter insertion procedure was performed. The primary endpoint was pain scores at rest in the morning on the first postoperative day. Secondary endpoints included pain scores at rest and during activity at other time points, quadriceps strength, and opioid consumption.

Results

Ninety-five patients, 32 in the femoral triangle group, 31 in the proximal AC group, and 32 in the distal AC group, completed the study. Analysis of the primary outcome showed no significant difference in pain scores among groups. Secondary outcomes showed significantly lower pain scores at rest and during activity in the distal AC group than in the femoral triangle and proximal AC groups in the morning of the second postoperative day. Quadriceps strength and opioid consumption did not differ among groups.

Conclusions

Continuous femoral triangle, proximal AC, and distal AC blocks in the setting of periarticular local anesthetic infiltration provide comparable postoperative analgesia after total knee arthroplasty.

Trial registration number

NCT04206150.

Fascial plane blocks: a narrative review of the literature

Fascial plane blocks (FPBs) are increasingly numerous and are often touted as effective solutions to many perioperative challenges facing anesthesiologists. As 'new' FPBs are being described, questions regarding their effectiveness remain unanswered as appropriate studies are lacking and publications are often limited to case discussions or technical reports. It is often unclear if newly named FPBs truly represent a novel intervention with new indications, or if these new publications describe mere ultrasound facilitated modifications of existing techniques. Here, we present broad concepts and potential mechanisms of FPB. In addition, we discuss major FPBs of (1) the extremities (2) the posterior torso and (3) the anterior torso. The characteristics, indications and a brief summary of the literature on these blocks is included. Finally, we provide an estimate of the overall level of evidence currently supporting individual approaches as FPBs continue to rapidly evolve.

Cadaveric study investigating the phrenic-sparing volume for anterior suprascapular nerve block

BACKGROUND

This cadaveric study investigated the maximum effective volume of dye in 90% of cases (MEV90), required to stain the suprascapular nerve while sparing the phrenic nerve during the performance of an anterior suprascapular nerve block.

METHODS

In cadaveric neck specimens, using ultrasound guidance, the block needle was advanced until its tip was positioned underneath the omohyoid muscle next to the suprascapular nerve. The dye was injected in order to achieve circumferential spread around the latter. Successful phrenic-sparing suprascapular nerve block was defined as the non-staining of the phrenic nerve on dissection. Volume assignment was carried out using a Biased Coin Design, whereby the volume of dye administered to each cadaveric specimen depended on the response of the previous one. In case of failure (ie, stained phrenic nerve), the next one received a lower volume (defined as the previous volume with a decrement of 2 mL). If the previous cadaveric specimen had a successful block (ie, non-stained phrenic nerve), the next one was randomized to a higher volume (defined as the previous volume with an increment of 2 mL), with a probability of b=0.11, or the same volume, with a probability of 1 - b=0.89.

RESULTS

Thirty-one cadavers (56 cadaveric neck specimens) were included in the study. Using isotonic regression and bootstrap CI, the MEV90 for phrenic-sparing anterior suprascapular nerve block was estimated to be 4.2 mL (95% CI 3.0 to 5.0 mL). The probability of a successful response was estimated to be 0.90 (95% CI 0.84 to 0.96).

CONCLUSION

For ultrasound-guided anterior suprascapular nerve block, the MEV90 of dye required to spare the phrenic nerve is 4.2 mL. Further studies are required to correlate this finding with the MEV90 of local anesthetic in live subjects.

Continuous block at the proximal end of the adductor canal provides better analgesia compared to that at the middle of the canal after total knee arthroplasty: a randomized, double-blind, controlled trial

Background

The optimal position for continuous adductor canal block (ACB) for analgesia after total knee anthroplasty (TKA) remians controversial, mainly due to high variability in the localization of the the adductor canal (AC). Latest neuroanatomy studies show that the nerve to vastus medialis plays an important role in innervating the anteromedial aspect of the knee and dives outside of the exact AC at the proximal end of the AC. Therefore, we hypothesized that continuous ACB at the proximal end of the exact AC could provide a better analgesic effect after TKA compared with that at the middle of the AC (which appeared to only block the saphenous nerve).

Methods

Sixty-two adult patients who were scheduled for a unilateral TKA were randomized to receive continuous ACB at the proximal end or middle of the AC. All patients received patient-controlled intravenous analgesia with sufentanil postoperatively. The primary outcome measure was cumulative sufentanil consumption within 24 h after the surgery, which was analyzed using Mann-Whitney U tests. P-values < 0.05 (two-sided) were considered statistically significant. The secondary outcomes included postoperative sufentanil consumption at other time points, pain at rest and during passive knee flexion, quadriceps motor strength, and other recovery related paramaters.

Results

Sixty patients eventually completed the study (30/group). The 24-h sufentanil consumption was 0.22 μg/kg (interquartile range [IQR]: 0.15–0.40 μg/kg) and 0.39 μg/kg (IQR: 0.23–0.52 μg/kg) in the proximal end and middle groups (P = 0.026), respectively. There were no significant inter-group differences in sufentanil consumption at other time points, pain at rest and during passive knee flexion, quadriceps motor strength, and other recovery related paramaters.

Conclusions

Continuous ACB at the proximal end of the AC has a better opioid-sparing effect without a significant influence on quadriceps motor strength compared to that at the middle of the AC after TKA. These findings indicates that a true ACB may not produce the effective analgesia, instead, the proximal end AC might be a more suitable block to alleviate pain after TKA.

Trial registration

This study was registered at ClinicalTrials.gov (NCT03942133; registration date: May 06, 2019; enrollment date: May 11, 2019).