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An Evaluation of Ultrasound-Guided Adductor Canal Blockade for Postoperative Analgesia After Medial Unicondylar Knee Arthroplasty

Henshaw, Daryl S. MD; Jaffe, Jonathan Douglas DO; Reynolds, Jon Wellington MD; Dobson, Sean MD; Russell, Gregory B. MS; Weller, Robert S. MD

doi: 10.1213/ANE.0000000000001162
Regional Anesthesia: Research Report

BACKGROUND: Unicondylar knee arthroplasty (UKA) is a commonly performed procedure with significant expected postoperative pain. Peripheral nerve blocks are 1 analgesic option, but some approaches may decrease quadriceps motor strength and interfere with early ambulation. In this study, we compared the analgesia provided by an adductor canal block (ACB) and a psoas compartment block (PCB) after UKA. We hypothesized that the ACB would provide equivalent analgesia, defined as a difference of <2 points on the pain scale (0–10 numeric rating scale [NRS]), at rest and with movement 6 hours after block placement.

METHODS: One hundred fifty patients undergoing medial UKA were randomly assigned to receive either an ACB or a PCB with 0.25% bupivacaine, 5 μg/mL epinephrine, and 1.67 μg/mL clonidine. All patients received multimodal analgesics, sham blockade at the alternate site, and a posterior capsule injection during surgery. Patients and observers were blinded to treatment groups. The primary end points were NRS pain scores with rest and movement at 6 hours. Secondary end points included quadriceps muscle strength at 6 hours (0–5 [5 being full strength]; Medical Research Council scale) as well as NRS pain scores, opioid consumption, and opioid-related side effects over 24 hours.

RESULTS: One hundred forty-seven patients were analyzed. Pain scores were equivalent at 6 hours with rest (ACB 1.0 ± 2 vs PCB 1.1 ± 2.2 [mean NRS ± SD]; 95% confidence interval of mean difference, −0.8 to 0.6; P < 0.0001) and with movement (ACB 1.6 ± 2.6 vs PCB 1.5 ± 2.8; 95% confidence interval of mean difference, −0.8 to 0.9; P < 0.0001). In addition, pain scores at rest and with movement at 12, 18, and 24 hours were equivalent. Quadriceps motor strength was significantly increased in the ACB group (Medical Research Council scale score, 4.0 ± 1.1 vs 2.5 ± 1.3 [mean ± SD]; P < 0.0001). No significant differences were found between groups for time to first analgesic or for cumulative opioid consumption at 6, 12, 18, or 24 hours. Other than an increase in the incidence of pruritus in the ACB group at 6 hours, there were no differences in opioid-related side effects.

CONCLUSIONS: An ACB provides equivalent analgesia after medial UKA when compared with a PCB. In addition, the ACB caused significantly less motor weakness. An ACB should be considered for postoperative analgesia after medial UKA.

Published ahead of print January 14, 2016

From the Departments of *Anesthesiology and Biostatistical Sciences, Wake Forest School of Medicine, Winston-Salem, North Carolina.

Accepted for publication December 8, 2015.

Published ahead of print January 14, 2016

Funding: All funding from the Department of Anesthesiology, Wake Forest School of Medicine.

Conflict of Interest: See Disclosures at the end of the article.

Reprints will not be available from the authors.

Address correspondence to Daryl S. Henshaw, MD, Department of Anesthesiology, Wake Forest School of Medicine, Medical Center Blvd., Winston-Salem, NC 27157. Address e-mail to dhenshaw@wakehealth.edu.

Total knee arthroplasty (TKA) is commonly performed for patients with degenerative joint disease of both the lateral and the medial knee compartments. However, when only the lateral or medial compartment of the knee is affected, unicondylar knee arthroplasty (UKA) may be recommended. Compared with TKA, a UKA may allow for better range of motion, reduced intraoperative blood loss, and biomechanics more closely resembling that of a normal knee.1 In 2005, an estimated 44,990 UKAs were performed, which accounted for approximately 8% of all knee arthroplasties performed in the United States.2 From 1998 to 2005, the average yearly percentage increase in UKAs was 32.5%.2 Considerable increases in UKAs can be expected over the coming years because the estimated number of TKAs are expected to increase from 600,000 procedures in 2008 to >3.4 million procedures in 2030.3

Because significant pain is anticipated after knee arthroplasty, considerable research has focused on identifying the optimal analgesic regimen to provide satisfactory analgesia and also on minimizing opioid-related side effects and motor weakness, both of which can interfere with physical therapy, early ambulation, and discharge. Historically, a femoral nerve block (FNB), administered either by single injection or continuous infusion, has been used for patients undergoing knee arthroplasty and has been shown to improve patient outcomes when compared with IV patient–controlled analgesia.4,5 Importantly, continuous FNB techniques have been associated with an increased risk of falls after lower extremity arthroplasties.6 This has led investigators to search for alternative analgesic options to a FNB that may limit or reduce unwanted consequences of nerve blockade while continuing to provide satisfactory analgesia.

One alternative to a FNB is the psoas compartment block (PCB), which provides analgesia by anesthetizing all branches of the lumbar plexus, including the femoral and obturator nerves, with a single injection. The PCB has also been shown to cause lower extremity weakness similar to a FNB, which might be expected because of the proximal site of the block.7 Recently, adductor canal block (ACB) has been investigated as another alternative to the FNB and has been shown to provide equivalent analgesia8,9 while preserving quadriceps motor strength when these blocks are performed either as a single injection8,10–12 or as a continuous infusion.13

Many of the nerves that travel within the adductor canal, including the anterior cutaneous branches of the femoral nerve, the saphenous nerve, and branches of the obturator nerve, innervate the surgical area involved in a medial UKA, and, therefore, an ACB may be uniquely suited to provide postoperative analgesia.14–16 Local anesthetic injected directly into the canal may block these nerves while minimizing the quadriceps weakness that results from more proximal blockade, as occurs with a PCB. Additional advantages of an ACB, compared with a PCB, include a smaller volume/dose of local anesthetic, the ability to use ultrasound guidance, and a lower risk of bleeding in patients being treated with anticoagulants.

This study compared an ACB with a PCB for analgesia after medial UKA. The hypothesis was that the ACB and PCB would provide equivalent analgesia at rest and with movement 6 hours after block placement. In addition, quadriceps motor strength after the 2 analgesic blocks was compared.

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METHODS

This study was approved by the IRB of Wake Forest Baptist Medical Center and registered at Clinicaltrial.gov on March 21, 2013, by principal investigator Daryl Henshaw, MD, under registration number NCT0181853 before any patient enrollment. Written informed consent was obtained from all subjects before enrollment.

This study was a prospective, patient- and observer-blinded, randomized trial designed as an equivalency trial comparing a single-injection ultrasound-guided ACB with a single-injection nerve stimulator–guided PCB for analgesia after medial UKA. Block randomization of patients occurred preoperatively using sequentially numbered, opaque, sealed envelopes. Patients were sedated during block placement and received a sham PCB or ACB. Given the depth of sedation and the sham blockade, patients were blinded to their treatment arm. Providers performing the block were not blinded but were excluded from data collection. All data collection was performed by investigators on the pain service who were blinded to the treatment group.

All peripheral nerve blocks were performed preoperatively in a dedicated area for regional anesthesia by a core group of regional anesthesiologists familiar with the study protocol. All patients were followed up in-house for at least 24-hours after surgery. Unless contraindicated, all patients received oral preoperative multimodal analgesic medications including 1000 mg acetaminophen, 400 mg celecoxib, and 150 mg pregabalin. Patients being treated with gabapentin were given their home dose in lieu of pregabalin. If given preoperatively, acetaminophen was continued at 1000 mg every 6 hours, and celecoxib was continued at 200 mg twice daily. Patients were sedated for the block procedure at the discretion of the anesthesiologist performing the procedure using fentanyl, midazolam, and ketamine as indicated.

Patients received either a subarachnoid block (SAB; 12.5 mg bupivacaine with 20 μg fentanyl) or general anesthesia (GA). As is a standard practice at our institution, all patients were encouraged to have a SAB. GA was only performed when patients refused a neuraxial procedure or when the SAB was unsuccessful. Intraoperative medications were administered at the discretion of the anesthesia providers involved in the surgery. All patients received a posterior capsular injection consisting of 60 mL 0.25% bupivacaine with 5 μg/mL epinephrine, 10 mg morphine, and 30 mg ketorolac. This is routinely performed by the surgeon for all UKAs before wound closure to provide analgesia to the posterior aspect of the knee, which is innervated by the sciatic nerve. All patients were followed up by the acute pain service and had oral and IV opioids ordered as needed with doses increased if required for poorly controlled pain. All oral and IV opioids consumed were later converted to oxycodone equivalents for comparison purposes.17

Patients were interviewed at 6, 12, 18, and 24 hours after nerve blockade to assess pain scores (0–10 numeric rating scale [NRS]) and opioid-related side effects. At 6 hours, after confirmation of SAB resolution, all patients performed a straight leg raise (SLR) with the operative limb, and quadriceps motor strength was graded using the Medical Research Council (MRC) scale18 (0 = no voluntary contraction possible, 1 = muscle flicker, but no movement of limb, 2 = active movement only with gravity eliminated, 3 = movement against gravity but without resistance, 4 = movement possible against some resistance, and 5 = normal motor strength against resistance).

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Inclusion/Exclusion Criteria

Patients of age 18 to 85 years undergoing unilateral robotic-assisted (MAKOplasty) medial UKA were eligible for inclusion after giving written informed consent for peripheral nerve block and for either GA or spinal anesthesia.

Patients were excluded if they had a contraindication to an ACB or a PCB (including coagulopathy, recent anticoagulant medication usage, or infection at the procedure site), history of opioid addiction, preoperative opioid use (extended-release opioids or >40 mg oxycodone equivalents per day), allergies to study medications, or if placement of either the ACB or the PCB was unsuccessful.

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Nerve Block Procedures

After preprocedural time-out, routine monitoring was performed, and supplemental oxygen was administered while patients received sedation. Standard aseptic technique was used for all block procedures. Local anesthetics were injected incrementally with intermittent aspiration, and both blocks were performed using 21-gauge, 9-cm Stimuplex needle (Arrow™, Teleflex Inc., Morrisville, NC).

The PCB was performed using the landmarks first described by Capdevila et al.19 using 25 mL 0.25% bupivacaine with 5 μg/mL epinephrine and 1.67 μg/mL clonidine. Nerve stimulation was used, and a motor response of quadriceps contraction (current, 0.3–0.8 mA and pulse duration, 0.1 milliseconds) was deemed acceptable. ACB was performed in supine position at the mid-thigh level using ultrasound guidance (Sonosite Turbo™, Bothell, WA, with linear 13–6 MHz transducer) to identify the superficial femoral artery and vein within the adductor canal. The procedural needle was inserted in-plane from the anteromedial side of the thigh, through the sartorius muscle and fascia. Once located in the adductor canal, 15 mL 0.25% bupivacaine with 5 μg/mL epinephrine and 1.67 μg/mL clonidine was injected anterior to the artery and deep to the sartorius.

Sham blockade was performed for either the ACB or the PCB depending on randomization. Surface landmarks and intended needle insertion sites were marked with a skin marker at both block sites, and all patients had ultrasound imaging performed with ultrasound gel at the ACB site. For both blocks, 1% lidocaine was injected subcutaneously to create a skin wheal, and the procedural needle was then inserted through the skin but without subsequent advancement or injection.

All patients were evaluated for block success by checking pinprick sensation in the saphenous distribution on the lower medial leg using a 25-gauge Whitacre spinal needle and a 3-point scale (0 = normal sensation, 1 = touch without pinprick, and 2 = absence of sensation). Successful blockade was defined as a change from normal sensation at baseline (0) to a score of 1 or 2. Sensation was tested at 15 and 30 minutes after nerve block or after resolution of the spinal.

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Outcomes

The primary end points were a comparison of rest and movement NRS pain scores at 6 hours after nerve block placement. Secondary end points included quadriceps motor strength at 6 hours, rest, and movement NRS pain scores at 12, 18, and 24 hours, and opioid consumption and opioid-related side effects (nausea, vomiting, and pruritus) at 6, 12, 18, and 24 hours. The time to first analgesic dose was also compared.

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Power Analysis

The 2 nerve block approaches were compared under the hypothesis that the ACB would provide analgesia that was equivalent to PCB for patients undergoing medial UKA. By using an 11-point NRS (0–10), the study was powered to find that the 2 nerve block procedures did not differ by >2 points when measured 6 hours after the nerve blockade with the assumption that differences of <2 points are not clinically significant.20 Preliminary data from 27 UKAs (10 PCBs and 17 ACBs) indicated average pain scores of 2.30 ± 2.55 with movement 6 hours after blockade. Assuming an α level of 0.025, we estimated that 70 patients per group would provide a power of 97.2%. Allowing for potential dropout, 75 patients per group (150 total patients) were enrolled.

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Statistical Analysis

Data were analyzed per protocol using SAS™, version 9.4 (SAS Institute Inc., Cary, NC). To test for differences between study arms, patient characteristics were analyzed using independent t tests for continuous variables and Fisher exact tests for categorical variables with a conventional α level of 0.05. Equivalence (in terms of the impact of each block on pain) was tested using the 2 one-sided tests option available within PROC TTEST in SAS.21 If μAC denotes the average verbal pain score using the ACB, and μLP using the lumbar plexus block, the 2 one-sided tests procedure requires rejecting both of the null hypotheses μAC − μLP > 2 and μAC − μLP ≤ 2 to declare equivalence; the equivalence test is conducted by performing 2 separate tests. Given that 2 primary outcomes were specified (pain with rest and movement at 6 hours), an adjustment was made to account for multiple comparisons using the Bonferroni correction: α = 0.05/κ, where κ is the number of comparisons; for the primary outcomes, α = 0.025 was used for assessing statistical significance. All secondary outcomes were compared using a conventional α level of 0.05.

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Post Hoc Analysis

A subgroup analysis was performed including only patients who received SAB to evaluate the possible influence of anesthetic type on postoperative pain outcomes. The outcomes evaluated in this subgroup analysis were pain scores with rest and movement at 6, 12, 18, and 24 hours.

In addition, to investigate whether differences in baseline pain scores affected postoperative pain outcomes, analysis of covariance (ANCOVA) models, adjusting for baseline pain scores, were fit for the scores observed at the measured time interval of 6, 12, 18, and 24 hours, both with rest and movement.

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RESULTS

Two hundred four patients were screened for eligibility between April 2013 and May 2015. Of these, 33 did not meet inclusion criteria and 21 declined participation. Ultimately, 150 patients were enrolled. After enrollment, 3 patients were withdrawn and excluded from the final analysis. The remaining 147 patients were analyzed per protocol (Fig. 1).

Figure 1

Figure 1

As detailed in Table 1, the 2 groups did not differ by age, race, sex, surgical side, anesthetic type, body mass index, or preoperative opioid use. Baseline pain scores with movement were equivalent; however, the 2 groups did differ in regard to baseline pain scores at rest, because the PCB group had significantly higher baseline NRS pain scores at rest (1.8 ± 2.3 vs 2.7 ± 2.5; P = 0.034). There were no significant differences between groups related to preoperative or intraoperative medication administration, whether viewed as an average dose per patient with all patients included (Table 1) or as an average dose per patient with only those patients receiving each medication analyzed (Table 2). Both groups received similar multimodal analgesic medications preoperatively.

Table 1

Table 1

Table 2

Table 2

The primary outcomes of NRS pain scores at 6 hours after block placement were equivalent both at rest (ACB 1.0 ± 2 vs PCB 1.1 ± 2.2 [mean NRS ± SD]; 95% confidence interval of mean difference, −0.8 to 0.6; P < 0.0001) and with movement (ACB 1.6 ± 2.6 vs PCB 1.5 ± 2.8; 95% confidence interval of mean difference, −0.8 to 0.9; P < 0.0001) as depicted in Figures 2 and 3, respectively. In addition, NRS pain scores at 12, 18, and 24 hours both at rest and with movement were also equivalent between groups. (Note: Given the design of the study as an equivalency trial, P < 0.025 for the primary outcomes of rest and movement pain at 6 hours allowed rejection of the null hypothesis and indicated equivalency between groups. For secondary pain outcomes, P < 0.05 indicated equivalency.)

Figure 2

Figure 2

Figure 3

Figure 3

There was no difference between the groups in cumulative opioid consumption (milligrams of oxycodone equivalents) at 6, 12, 18, or 24 hours or the time to the first analgesic. The incidence of pruritus was significantly higher in the ACB group at 6 hours, but there were no other differences in the incidence of opioid-related sided effects. (Table 3)

Table 3

Table 3

Quadriceps motor strength comparisons are shown in Table 4. The mean motor strength score was significantly higher in the ACB group compared with the PCB group (4.0 ± 1.1 vs 2.5 ± 1.3, P < 0.0001). The ACB group had a significantly higher percentage of patients who had a score of either 5 or 4 (72% vs 21%, P < 0.0001).

Table 4

Table 4

Subgroup analyses of rest and movement pain for only patients who received a SAB are depicted in Figures 4 and 5, respectively. These analyses found that the ACB and PCB groups reported equivalent rest and movement pain scores at all time intervals.

Figure 4

Figure 4

Figure 5

Figure 5

ANCOVA testing demonstrated that there were no significant differences in rest or movement pain scores between the ACB and PCB groups at any measured time interval when these outcomes were adjusted for baseline pain scores. Significant differences were indicated by a P < 0.05; none of these tests approached statistical significance (6 hours: rest, P = 0.72 and movement, P = 0.75; 12 hours: rest, P = 0.86 and movement, P = 0.38; 18 hours: rest, P = 0.65 and movement, P = 0.19; and 24 hours: rest, P = 0.62 and movement, P = 0.27).

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DISCUSSION

The PCB is an attractive analgesic option for patients undergoing medial UKA because it blocks both the femoral and the obturator branches of the lumbar plexus with a single injection, which is not possible with FNB alone.22 Because these nerves innervate the medial aspect of the knee, a PCB has historically been the analgesic procedure of choice at our institution for this particular surgery. Recently, as providers have explored the utility of the ACB for postoperative pain management after knee arthroplasty, it has presented an alternative to the PCB because it also blocks sensory nerves from the medial knee, but with the possible advantage of reduced quadriceps dysfunction, earlier ambulation, and discharge readiness.

Multiple previous studies have demonstrated preserved motor strength with an ACB when compared with a FNB, both after single-injection techniques or continuous infusions.8,10–13 However, no prospective study has compared either analgesia or quadriceps motor strength after an ACB with that which follows a PCB. Although our recent investigation comparing an ACB with a PCB for patients having medial UKA demonstrated an increase in the number of steps walked during the first physical therapy session in the ACB group, this was done retrospectively, included a small number of patients, and did not objectively measure motor strength or analgesia.23 Although the preservation of motor strength might be expected to be superior with an ACB, given the proximal nature of the PCB, the possibility of inadequate or inferior analgesia prompted this prospective investigation.

As demonstrated in this study, the 2 nerve blocks provided equivalent pain control over a 24-hour period after nerve block placement. Equivalency was assumed if verbal pain scores were within 2 points on an 11-point pain scale (0–10). Although the clinical relevance of a 2-point difference could be debated, this end point was based on the previously published studies.20

The only baseline difference identified between the 2 study groups was a higher baseline NRS pain score with rest in the PCB group. Although the 2 groups were not different in regard to baseline pain scores with movement, it is possible that a difference in baseline resting pain scores could have affected the comparison of postoperative pain between the 2 groups because a higher baseline level of pain might conceivably lead to higher postoperative pain scores. To investigate this possibility, post hoc ANCOVA analysis was performed. This allowed for a comparison of postoperative pain scores while accounting for the unanticipated difference in baseline resting pain scores that occurred despite randomization. The results of the ANCOVA analysis demonstrate that there were no differences in postoperative pain scores at any time interval between the 2 groups and are consistent with our previous results. In addition, the equivalency of the 2 nerve blocks is further supported by the lack of difference in both the time to first analgesic and the cumulative opioid consumption over 24 hours.

We chose NRS pain scores at the 6-hour time point as the primary outcome to ensure that both nerve blocks would still be active and that the SAB, when used for surgery, would have resolved. During the 24-hour study period, the mean NRS pain scores for both groups, both at rest and with movement, increased over time. This may have occurred secondary to the resolution of the blocks or could have been a function of increased activity by the patients. The time to first analgesic did not differ between groups, which may suggest that the blocks had a similar duration. In addition, there did not appear to be a divergence in pain scores at any particular time point further suggesting that both blocks provided equivalent pain control during the study period. Further studies would be needed to determine the duration of analgesia provided by an ACB and to determine the optimal dose and volume.

The only difference between groups in relation to the incidence of opioid-related side effects was a higher incidence of pruritus in the ACB group at 6 hours. Because the 2 groups were statistically similar regarding opioids administered both preoperatively and intraoperatively for sedation, as well as being similar in opioids consumed at 6 hours, IV and oral opioids were unlikely to have contributed to this result. Although the 2 groups did not differ statistically in regard to anesthetic type, the ACB group did have more patients who received a SAB compared with the PCB group, and the effect of spinal opioids could have potentially contributed to the increased incidence of pruritus in the ACB group at this time point. However, the subgroup analysis of spinal anesthetic-only patients also found a higher incidence of pruritus in the ACB group at 6 hours. Given the small number of patients in either group that had pruritus, it is possible that this difference occurred by chance or was related to variables not directly measured in the study.

The effects of spinal fentanyl could have also influenced analgesia at 6 hours, although this effect would have been unlikely to affect pain scores at 12, 18, or 24 hours. However, some studies have suggested that patients who have spinal anesthesia, compared with GA, have better postoperative analgesia even when peripheral nerve blocks are not used.24 For this reason, despite the anesthetic type not being significantly different between groups, the subgroup analysis of only patients receiving a SAB was performed to investigate whether the intraoperative anesthetic possibly affected the comparison of postoperative pain scores. The results of this subgroup analysis confirmed the finding of block equivalency, in terms of analgesia, at all time points and support that the original results were not affected by a difference in the number of GA patients between groups. Given the small number of patients who received GA, a subgroup analysis was not performed on this group.

Although there are several ways to quantify muscle strength, including dynamometry, we chose to grade motor strength in this study during the SLR test because this is the test used by physical therapists at our institution to determine whether patients will require a knee immobilizer to participate in therapy. Patients with a grade of 5 or 4 on the MRC scale typically can ambulate and participate with therapy without the use of a knee immobilizer, whereas patients with a score of 3, 2, or 1 will typically require the knee immobilizer and assistance during therapy. In this study, the percentage of patients with an MRC score of 5 or 4 was significantly higher in the ACB group, which suggests that these patients would have been able to participate earlier in therapy without a knee immobilizer than if they had received a PCB. Still, 28% of patients in the ACB group had motor weakness as demonstrated by a motor strength score of 3, 2, or 1; therefore, an ACB may not totally eliminate the potential for quadriceps motor weakness and the need for assistance during physical therapy. In addition, ACB may not totally eliminate the risk of falling, and further studies would be needed to assess this risk. Assessing motor strength before allowing patients to ambulate would still be advisable. At our institution, patients undergoing UKA typically stay until the first postoperative day because this allows the surgical team to monitor for potential complications, such as hemarthrosis, and to initiate physical therapy while the patient is hospitalized. Therefore, despite the preservation of quadriceps motor strength after an ACB, length of stay may not be affected. However, because not directly measured in this investigation, future studies would be needed to evaluate any potential effect that ACB has on time to discharge readiness.

Although not by design, a strength of this study is that 92% of the surgeries were performed by a single surgeon, and variability in surgical trauma between groups was likely reduced. The limitations of this study include a lack of standardization for intraoperative care for study patients. Although there was no difference found between groups in the number of patients who received either GA or SAB, the anesthetic type was not controlled. In addition, both preoperative sedation medications and intraoperative medications were not standardized. In this study, the same investigator did not perform all SLR motor strength assessments, and some variability in this subjective scoring outcome could have affected the grades given to study subjects. Another critique of the study with respect to generalizability of approach is the inclusion of a posterior capsule injection performed by the surgical team. This infiltrative technique has been shown to improve outcomes after TKA when combined with a FNB by blocking pain in the sciatic nerve distribution of the knee joint as an alternative to sciatic nerve blockade and was administered to all patients because it is a routine practice at our institution.25 In addition to the posterior capsular injection, all patients received a multimodal oral analgesic regimen unless contraindicated, and the majority of patients received spinal fentanyl. It is possible that the combination of these interventions contributed to the overall analgesic efficacy of both nerve block approaches and the appearance of their equivalency.

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CONCLUSIONS

This study demonstrated that for patients undergoing medial UKA using multimodal analgesia and posterior capsular infiltration, an ACB provides equivalent analgesia to a PCB as evidenced by equivalency in postoperative pain scores. The time to first analgesic and opioid consumption during 24 hours were similar after the 2-block approaches. In addition, the ACB caused significantly less quadriceps motor weakness. This block approach should be considered as an analgesic option for patients undergoing medial UKA.

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DISCLOSURES

Name: Daryl S. Henshaw, MD.

Contribution: This author helped design the study, conduct the study, collect and analyze the data, and prepare the manuscript.

Attestation: Daryl S. Henshaw approved the final manuscript. He attests to the integrity of the original data and the analysis reported in this manuscript. He also reviewed the original study data and the data analysis and is the archival author.

Conflicts of Interest: Daryl S. Henshaw has received material support from the iFlow Corporation for an unrelated study. He also serves as a consultant to Teleflex Medical (Arrow).

Name: Jonathan Douglas Jaffe, DO.

Contribution: This author helped design the study, conduct the study, collect and analyze the data, and prepare the manuscript.

Attestation: Jonathan Douglas Jaffe approved the final manuscript. He also attests to the integrity of the original data and the analysis reported in the manuscript. He also reviewed the original study data and the data analysis.

Conflicts of Interest: The author declares no conflicts of interest.

Name: Jon Wellington Reynolds, MD.

Contribution: This author helped design the study, conduct the study, collect and analyze the data, and prepare the manuscript.

Attestation: Jon Wellington Reynolds approved the final manuscript. He also attests to the integrity of the original data and the analysis reported in the manuscript.

Conflicts of Interest: The author declares no conflicts of interest.

Name: Sean Dobson, MD.

Contribution: This author helped conduct the study, collect and analyze the data, and prepare the manuscript.

Attestation: Sean Dobson approved the final manuscript.

Conflicts of Interest: The author declares no conflicts of interest.

Name: Gregory B. Russell, MS.

Contribution: This author helped design the study, interpret and analyze the data, and prepare the manuscript.

Attestation: Greg Russell approved the final manuscript. He also attests to the integrity of the analysis of the data.

Conflicts of Interest: The author declares no conflicts of interest.

Name: Robert S. Weller, MD.

Contribution: This author helped design the study, conduct the study, collect and analyze the data, and prepare the manuscript.

Attestation: Robert S. Weller approved the final manuscript.

Conflicts of Interest: Robert S. Weller has received material support from the iFlow Corporation for an unrelated study.

This manuscript was handled by: Terese T. Horlocker, MD.

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