Comparative analysis of dual versus single subsartorial block for postoperative analgesia after total knee arthroplasty – A randomized, double-blind study

Abstract

Background and Aims:

This study compared the dual sub-sartorial block (DSB), which allegedly includes all pain generators of the anterior and posterior compartments of the knee joint, to the routinely used single sub-sartorial bock (SSB), in terms of analgesic efficacy and preservation of motor strength after unilateral total knee arthroplasty (TKA).

Material and Methods:

Sixty patients aged 18-80 years and ASA grade I-III undergoing unilateral TKA were randomised to two groups postoperatively to receive DSB or SSB. Patients in group DSB received distal femoral triangle block (15 ml) + proximal adductor canal block (20 ml), while group SSB received only proximal adductor canal block (20 ml). Primarily, the changes in pain intensity and pain control in terms of static and dynamic visual analogue score (VAS) with the duration of analgesia and cumulative dose requirement of rescue analgesic in the first 24 hours postoperatively were studied. Secondary outcomes were the postoperative degree of motor blockade, the ability of early ambulation, patient satisfaction and complications. Statistical analysis was done using the student t-test and Chi-square test using MedCalc version 12.4.3.0.

Result:

At all time intervals, the static and dynamic VAS scores were lower in the patients with the DSB group (P < 0.001) with longer duration of postoperative analgesia (14.96 ± 5.05 vs 6.03 ± 1.73 hours, P < 0.0001) and less requirement of total parenteral analgesic (1.06 ± 0.37 vs 2 ± 0.52, P < 0.0001) in first 24 hours postoperatively. A shorter time was required to finish the Timed Up and Go test for patients belonging to the DSB group (53.48 ± 4.06 vs 66.16 ± 6.23 seconds, P < 0.0001) in comparison to group SSB.

Conclusion:

DSB provided better pain control with a longer duration of analgesia and required fewer doses of parenteral analgesics in the first 24 hours postoperatively after TKA, as opposed to SSB. Neither block had incidences of motor weakness and other complications.

Introduction

Total knee arthroplasty (TKA) offers increased joint mobility and painless ambulation to patients. However, it is associated with considerable postoperative pain requiring effective management to facilitate early ambulation and rehabilitation, which ultimately reduces the length of hospital stay.[1,2] This mandates the provision of good analgesia with minimal opioid consumption and keeping the motor strength intact.[3] Presently, none of the techniques satisfies all the parameters as being procedure specific leading to complete analgesic coverage with preservation of motor strength and enhanced recovery after surgery.[4,5]

In the recent past, the adductor canal block (ACB) has become immensely popular due to the provision of satisfactory analgesia with the preservation of motor strength, enhancing functional recovery after TKA.[4] A newly introduced dual subsartorial block (DSB) involves the first injection at the distal femoral triangle block (FTB) followed by the proximal ACB. The distal femoral triangle (FT) targets the saphenous nerve (SN) and the nerve to the vastus medialis (NVM) with blockage of the subsartorial plexus with distal spread, covering the innervations of the anteromedial knee. The second injection employed at the proximal adductor canal involves the posterior branch of the obturator nerve with the inclusion of the popliteal plexus, aiming at the innervations of the intra-articular and posterior knee.[1]

The recently conducted pilot study using DSB for postoperative analgesia after total knee replacement surgery showed promising results.[6] So, we decided to compare this novel regional analgesia technique with the existing ACB with the primary aim of observing the changes in postoperative pain intensity and pain control in terms of static and dynamic visual analog scores with duration of postoperative analgesia and total dose of rescue analgesic needed within the first 24 h after TKA. We hypothesized that the DSB technique would be superior in providing postoperative analgesia compared to a single subsartorial block, the ACB. The postoperative degree of motor blockade, the ability of early ambulation, and the rate of patient satisfaction and complications were studied secondarily.

Material and Methods

This prospective, randomized, double-blind clinical study was conducted at a tertiary care center from December 2021 to November 2022 after getting permission from the Institutional Ethics Committee for Biomedical and Health Research and after it was registered with Clinical Trial Registry, India (registration number- CTRI/2021/12/038736, dated 12/20/2021). Written informed consent was obtained from all the participants regarding the utilization of their data for research and educational grounds. The study was conducted in compliance with the Declaration of Helsinki, 2013 and the Consolidated Standard of Reporting Trials guidelines.

A total of 60 patients of either sex, having American Society of Anesthesiologists (ASA) physical status I–III, admitted to the hospital, and posted for primary unilateral TKA under spinal anesthesia were included in the study. Patients having coagulation disorders, preexisting lower extremity neuromuscular disorders, procedure site infection, history of allergy or contraindications to the drugs utilized in the study (local anesthetics [LAs], paracetamol, opioids), those on chronic opioid use, and those unable to follow the study protocol were excluded. After a thorough preanesthetic evaluation and mandatory investigations, all the patients fulfilling the inclusion criteria were selected. Patients were explained about the study protocol, nature of the procedure, visual analog scale (VAS) score, and Timed Up and Go (TUG) test.

Before surgery, nil oral status was confirmed and an intravenous line was secured with an 18-G cannula in a recovery room. Inside the operation theater, the multipara monitor having heart rate, SpO₂, noninvasive blood pressure, and electrocardiography was attached and baseline parameters were recorded. Patients were preloaded with 8–10 ml/kg of Ringer’s lactate solution before receiving spinal anesthesia. Intravenous ondansetron (0.08 mg/kg) and pre-emptive analgesia with paracetamol (1 g) were given as premedication. Under all aseptic and antiseptic precautions, all patients were administered spinal anesthesia with 2.5 ml of 0.5% hyperbaric bupivacaine in a sitting position. At the end of the surgery, patients were randomly divided into two groups using computer-generated random numbers (www.randomizer.org) to receive either ultrasound-guided DSB (group DSB) or proximal ACB (group SSB). The numbers were then kept in a sealed opaque envelope, which was opened just before giving the block. DSB and SSB were performed by a single anesthesiologist throughout the study. The patients participating in the study and an observer recording the study parameters were blinded to the group allocation.

The blocks were performed keeping the patient in a supine position with external rotation of the thigh and abduction of the hip to assist the needle placement under ultrasound guidance. A broadband linear array ultrasound probe (8–14 MHz frequency) was used, with an imaging depth of 4–6 cm. Forty milliliters of total drug volume was prepared with 0.125% bupivacaine and 8 mg dexamethasone (0.5% bupivacaine 8 ml + sterile water 28 ml + 8 mg [4 ml] dexamethasone). The probe was positioned horizontally at the midthigh level over the anteromedial aspect. After identifying the sartorius muscle (STM), the femoral vessels lying underneath were confirmed using the color Doppler. The apex of FT was identified with overlapping of medial borders of the adductor longus muscle lying posteromedial to the femoral vessels and STM, creating a figure of “3” [Figure 1]. Upon advancing the ultrasound probe proximally further 1–2 cm from the apex of FT, the SN was located lateral to the femoral artery, appearing as a hyperechoic structure and NVM lying adjacent to it. For distal FTB, a 22-G, 100-mm echoplex needle was inserted in-plane from the lateral side of the thigh and advanced further in the intermuscular plane, connecting the vastus medialis muscle (VMM) and STM to target SN and NVM. Once the needle tip position was confirmed with adequate spread of 1–2 ml of sterile water delineating NVM within its muscular tunnel, a total of 15 ml of the prepared drug was deposited here [Figure 2]. For ACB, an ultrasound probe was moved distally 1–2 cm from the apex of FT. Following confirmation of the bilayered STM attributed to the presence of vasoadductor membrane (VAM) below the STM fascia, the needle was directed in-plane with lateral to medial inclination between STM and VMM. A total of 20 ml of the prepared drug was injected next to the femoral artery under VAM after negative aspiration. Each time while injecting LA, downward movement of the femoral artery with injection and coming back to normal position after the completion of injection, forming the “double bubble sign,” was confirmed [Figure 3]. The patients in group SSB received only a proximal ACB.

Figure 1.

Identification of the apex of the femoral triangle under ultrasound guidance with the meeting point of the medial border of STM and ALM forming the sign of 3. ALM = adductor longus muscle, FA = femoral artery, FV = femoral vein, STM = sartorius muscle, VMM = vastus medialis muscle

Figure 2.

First injection of LA solution at the distal femoral triangle, lateral to FA. FA = femoral artery, LA = local anesthetic, STM = sartorius muscle, VMM = vastus medialis muscle

Figure 3.

Second injection of LA solution at the proximal adductor canal and visualization of downward movement of FA with injection and coming back to normal position after the completion of injection forming the “double bubble sign”. FA = femoral artery, LA = local anesthetic, STM = sartorius muscle

Immediately after giving the block, the patient was monitored for 1 h in the post-anesthesia care unit to look for any hemodynamic changes that may arise due to LA systemic toxicity (LAST). Postoperatively, an observer who was blinded to group allocation followed up with the patients at 4, 8, 12, and 24 h and assessed the variations in postoperative pain intensity in both groups using a VAS score ranging from 0 (no pain) to 10 (worst pain). It was assessed at rest and during 45° knee flexion. Whenever the VAS score became ≥ 4, rescue analgesia in the form of intravenous paracetamol (1 g) was given and the time was noted down. The duration of analgesia was considered as the time from the injection of LA to receiving the first dose of rescue analgesic. A cumulative dose of rescue analgesic received in the first 24 h after surgery was recorded in both groups. The extent of motor blockade was evaluated with the Bromage scale [Annexure 1]. The assessment of the postoperative ability of early ambulation was done by the TUG test, where the time taken by the patient to get out of bed, walk 3 m, return to the bed, and sit down was noted at the end of 24 h from surgery. Patients were asked to rate their satisfaction regarding the method of providing the postoperative analgesia, where 1- highly satisfied, 2- slightly satisfied, 3-neither satisfied nor dissatisfied, 5- slightly dissatisfied, and 5- highly dissatisfied. Any complications like LAST, vascular injury, hematoma, motor blockade, nerve injury, or infection were noted in both groups.

The sample size was calculated from the previously conducted pilot study with 10 patients in the same institute. Taking the parameter “duration of analgesia,” it was 15.7 + 8.83 h in group DSB and 10.24 + 9.85 h in group SSB. Adding the standard effect size of 0.6, at an alpha error 0.05 and a beta error of 0.2, a total of 45 patients needed to be studied. We included 60 patients (30 patients/group) in this study. The master chart was prepared in a Microsoft Excel sheet. Continuous data like age, VAS score, duration of analgesia, the cumulative dose of rescue analgesics, the extent of motor blockade, TUG test, and patient satisfaction score were analyzed by Student’s “t”- test and were displayed as mean ± standard deviation. The presentation of nonparametric data like sex, ASA grading, and complications was done as numbers or percentages, and the Fisher’s exact test or the Chi-square test was utilized to examine them. The final statistical analysis was done using the MedCalc, version 12.4.3.0(MedCalc Software Ltd; Ostend, Belgium). The significance was determined by P value, where P < 0.05 was considered significant.

Results

All patients were studied and analyzed. There were no dropouts [Figure 4]. The two groups were comparable to each other concerning age, gender, and ASA physical status [Table 1]. Postoperatively, at all the time intervals till 24 h, the mean VAS scores at rest and with knee flexion were significantly lower in group DSB compared to group SSB [Figures 5 and 6]. The duration of analgesia was prolonged in patients in the DSB group in comparison to those in the SSB group (14.96 ± 5.05 vs. 6.03 ± 1.73 h, P < 0.0001, 95% confidence interval [CI] -10.88 to -6.98, degree of freedom 58) [Table 2]. The cumulative dose requirement of intravenous rescue analgesics was higher in the patients belonging to the SSB group (2 ± 0.52 vs. 1.06 ± 0.37, P < 0.0001, 95% CI 0.71 to 1.17, degree of freedom 58) than in those of group DSB [Table 2].

Figure 4.

CONSORT flow diagram. CONSORT = Consolidated Standards of Reporting Trials

Table 1.

Demographic data

Parameter	Group DSB (n=30)	Group SSB (n=30)	P
Age (years)	61.2±6.86	64.23±9.04	>0.05
Gender (M: F)	10:20	12:18	>0.05
ASA II/III	19/11	21/9	>0.05

Values are presented as mean±SD or numbers. Statistical analysis: Fisher’s exact test or Pearson’s Chi-square test, except for age for which Student’s t-test was applied. ASA=American Society of Anesthesiologists, SD=standard deviation

Figure 5.

Postoperative VAS scores at rest at different time intervals. SD = standard deviation, VAS = visual analog scale

Figure 6.

Postoperative VAS scores with 45° knee flexion at different time intervals. SD = standard deviation, VAS = visual analog scale

Table 2.

Study parameters

Parameter	Group DSB	Group SSB	Mean difference	95% CI	P
Duration of analgesia (hours)	14.96±5.05	6.03±1.73	−8.93	-10.88 to−6.98	<0.0001
Number of doses of rescue analgesics required in 24 h	1.06±0.37	2±0.52	0.94	0.71 to 1.17	<0.0001
TUG (s)	53.48±4.06	66.16±6.23	12.68	9.96 to 15.40	<0.0001
Patient satisfaction	2.03±0.76	3.26±1.17	1.23	0.72 to 1.74	<0.0001
Complications
Infection	Nil	Nil			-
Hematoma	Nil	Nil
Vascular injury	Nil	Nil
Nerve injury	Nil	Nil
LAST	Nil	Nil
Motor blockade	Nil	Nil

Values are presented as mean±standard deviation. Statistical analysis: Student’s t-test. CI=confidence interval, DSB=dual subsartorial block, LAST=local anesthetic systemic toxicity, TUG=Timed Up and Go

In both groups, no motor blockade was observed and it remained comparable at all time intervals [Figure 7]. At 24 h, a shorter time was required to finish the TUG test by the patients belonging to the DSB group than those in the SSB group (53.48 ± 4.06 vs. 66.16 ± 6.23 s, P < 0.0001, 95% CI 9.96 το 15.40, degree of freedom -58) [Table 2].

Figure 7.

Bromage scale

A higher level of satisfaction was observed in patients, with those in the DSB group having lower mean patient satisfaction scores compared to those in the group SSB (P < 0.0001, 95% CI 0.72 to 1.74, degree of freedom 58) [Table 2]. No complications like hematoma, vascular injury, nerve injury, LAST, motor blockade, or infection were noted in either group till 24 h [Table 2].

Discussion

Our study resulted in the provision of more effective and longer duration of postoperative analgesia as shown by lower static and dynamic VAS scores at all time intervals with decreased requirement of rescue analgesics till 24 h after TKA employing DSB in comparison to SSB. No motor blockade was observed at any time interval in either group. Better analgesia with preservation of quadricep strength in the patients belonging to the DSB group led to early ambulation after surgery and a higher level of satisfaction.

Anterior knee pain at the incision site is due to medial aspect dissection conducted by SN, subsartorial plexus, and peripatellar plexus. Posterior knee pain is due to bone cutting and implant fitting, mainly carried by the popliteal plexus. The postoperative pain-generating elements after TKA essentially include the periosteal rim of the cut bones, medial retinaculum, residues of the anterior joint capsule, transacted nerves, microfractures, skin/subcutaneous tissues overlying the incision, and postsurgical inflammation.[1,6] Many different techniques are being practiced to ameliorate postoperative pain after TKA. The use of intrathecal morphine for TKA proved to be better than placebo but equivalent to single-shot and continuous nerve block catheters as suggested by the Procedure Specific Postoperative Pain Management (PROSPECT) working group.[5] Reduced postoperative opioid consumption in the immediate (6–12 h) period was observed, but was associated with an increased risk of pruritus and nausea–vomiting when used in >100 µg dosage.[5,7] A recent study utilizing intrathecal morphine in a dose of 150 µg failed to demonstrate the same.[8] Despite the provision of good analgesia, recent recommendations are not in favor of continuous epidural analgesia due to unintended motor blockade and bladder–bowel dysfunction requiring frequent dose adjustment.[4,5] The femoral nerve block was considered to be the gold standard, but failed to remain so due to its association with higher chances of quadriceps weakness, especially with continuous infusion leading to decreased mobility and a negative impact on functional recovery.[4,5,9,10] The sciatic nerve block provides superior analgesia, but performance after surgery remains challenging and the possibility of a fall due to motor weakness interferes with early recovery.[4,5]

ACB is a technique that covers sensory innervations mainly from the anterior knee, thus sparing the posterior aspect.[4] Preservation or increase in the quadriceps function after receiving ACB in patients having severe post-TKA pain represented the analgesic efficacy in conjunction with motor-sparing properties of ACB in comparison to FNB.[9,10] ACB combined with infiltration between the popliteal artery and knee capsule (IPACK) block offered better analgesia with less opioid consumption and better patient satisfaction due to analgesic coverage on dual aspects of the knee joint, but had the disadvantage of difficulty in accessing the area for performing the IPACK block due to bandaging over the knee joint.[11] Recently, the combination of single-shot ACB with periarticular LA infiltration (LIA) has been advocated over a single technique.[5] The inconsistent benefits and concerns with potential infection preclude the use of continuous infusion with ACB or LIA. To date, the ambiguity regarding the optimal volume and site of infiltration with LIA remainsremains.[5]

With DSB, distal FTB aims SN and NVM directly, and the farthest spread of the drug underneath STM but above VAM targets the subsartorial plexus, which comprises the medial femoral cutaneous nerve (MFCN), an infrapatellar branch of SN, and anterior division of the obturator nerve.[1,6,12] Sparing of FN affecting the quadriceps function on the proximal drug spread in distal FT has been proved in a dye study.[6] Proximal ACB when followed by dista l FTB involves SN and the posteromedial branch of NVM usually terminating as the superio r medial genicular nerve and spreading further to the popliteal plexus formed by the articular branches from the tibial, common fibular, sciatic, and posterior divisions of the obturator nerves, which suggests a greater analgesic effect by capturing all essential innervations to the knee joint capsule in comparison to distal ACB.[1,6,13] So, DSB combining the distal FTB and proximal ACB leads to complete analgesia over the medial, anterior, and posterior aspects of the knee joint. Hence, better analgesic coverage is represented as lower active and passive VAS scores with prolonged duration of postoperative analgesia. Adequate analgesia with preservation of motor strength facilitated patients in the DSB group to finish the TUG earlier than those in group SSB. The analgesic coverage provided by the drug spread after DSB is supported by cadaveric studies.[12,13,14] The VAS scores in the study conducted by Sonawane et al.[6] using DSB with 10/20 or 20/10 ml in FT/AC, respectively, were observed to be lower compared to the DSB group of our study, which may be due to the administration of a multidrug analgesic regimen.[6] A recent study combining distal FTB and distal ACB reported superior preservation of motor functions at 3 and 6 h with requirement of lower doses of opioids at 24 h postoperatively in comparison to FNB.[2] Preference to proximal ACB over distal one is advisable to avoid proximity to the surgical area.[6] Currently, in addition to peripheral nerve blocks, perioperative paracetamol, nonsteroidal anti-inflammatory drugs, and reserving opioids are being proposed as rescue analgesics to avoid opioid-related side effects in the postoperative period.[5]

Moreover, a recent study advocated blocking the intermediate femoral cutaneous nerve (IFCN) separately using triple injection peri-sartorial (TIPS) block involving DSB with supra-sartorial injection and demonstrated lower active VAS scores with less consumption of morphine in the first 24 postoperative hours with greater distances while ambulating the patients with a higher degree of knee extension.[15] The novel para-sartorial compartment (PASC) block invented by Pascarella et al.[16] and recently recommended by Gungor and Atalay[17] described combining FTB with the IFCN blockade. The technique involves injections in three different compartments: inside FT targeting SN, subsartorial aiming MFCN and NVM, and supra-sartorial focusing IFCN. It has successfully demonstrated a reduction in pain score with preservation of motor strength while targeting only the anterior region of the knee joint. The authors suggested that blockade of SN, MFCN, and IFCN by this technique may achieve complete anesthesia of the incisional area involved in TKA. The inconsistency seen in the results after receiving the most popular ACB as a pain-relieving mode after TKA may be due to employing different approaches and different LAs with different concentrations and adjuvants used for the same.[18,19,20,21]

We did not encounter any complication during the study in any of the groups. The provision of better analgesia with a shorter time to complete TUG using a higher concentration of LA in ACB (0.5% bupivacaine) at a cost of increased incidence (20%) of buckling was reported by Armanious et al.[9] Alabd et al.[15] reported nausea in 20% of patients receiving TIPS block.

The limitations of the study included the complete analgesic coverage of DSB only when the incision is medial parapatellar, sub-vastus, and mid-vastus. We did not follow-up the patients after 24 h to assess the late postoperative recovery in each group. Further research is required to assess the efficacy of this DSB block for analgesia after the above-mentioned incision site for functional analysis and enhanced recovery with a reduction of the hospital stay.

Conclusion

DSB is better at controlling the postoperative pain with the provision of prolonged duration of postoperative analgesia and reduced consumption of parenteral analgesics during the first 24 h and early ambulation leading to better patient satisfaction after TKA, as opposed to SSB. Neither block had incidences of motor weakness and other complications.

Conflicts of interest

There are no conflicts of interest.

Annexure 1: Bromage grade

Grade 1 – the patient was able to do free movement of legs and feet

Grade 2 – the patient was just able to flex knees with free movement of feet

Grade 3 – the patient was unable to flex the knee, but with free movement of feet

Grade 4 – the patient was unable to move legs or feet

Funding Statement

Nil.