Anesthesia: Essays and Researches

: 2020  |  Volume : 14  |  Issue : 2  |  Page : 326--330

Evaluating analgesic efficacy of single femoral nerve block versus combined femoral-sciatic nerve block post total knee arthroplasty

Achirabha Sinha1, Divya Arora2, Shailendra Singh3, Tanmoy Das1, Mohua Biswas1,  
1 Department of Anesthesiology, Apollo Gleneagles Hospital, Kolkata, West Bengal, India
2 Department of Anesthesiology, BRD Medical College, Gorakhpur, Uttar Pradesh, India
3 Department of Orthopedics, KGMU, Lucknow, Uttar Pradesh, India

Correspondence Address:
Dr. Divya Arora
Department of Anesthesiology, BRD Medical College, Gorakhpur, Uttar Pradesh


Background: With increasing knee replacement surgeries, there has been a constant search for effective pain control modality. Aims: We compared the analgesic effect of femoral nerve block (FNB) alone with combined femoral and sciatic nerve block (SNB) for postoperative pain management after total knee arthroplasty (TKA). Setting and Design: This was a prospective observational study. Methods: A total of 150 adult patients of American Society of Anesthesiologists physical status class I and II scheduled for elective TKA under spinal anesthesia with 3.4-mL bupivacaine 0.5% and 20-μg fentanyl were randomly allocated to two groups. Group F patients received a single shot FNB with 20 ml 0.375% ropivacaine and Group FS patients received combined FNB with 20 mL of 0.375% ropivacaine and SNB with 40 ml of 0.375% ropivacaine at the end of surgery. The primary outcome was the change in Numeric Rating Scale (NRS) scores between Groups F and FS at 6, 12, 18, 24, and 48 h later. The secondary outcome was total doses of opioid required in both groups. Results: The demographic data were comparable in both groups. The NRS scores were higher and statistically significant in Group F than that in Group FS at all five measured time points (P < 0.00001), and the total pain score with a mean of 15.43 in Group F and a mean of 9.61 in Group FS was statistically significant. Significantly more opioid consumption was seen postoperatively in Group F as compared to Group FS at 12, 18, 24, and 48 h as depicted by P < 0.00001. Conclusions: We conclude that the FNB, when combined with SNB, shows superior results than femoral block alone. SNB reduced pain scores and opiate consumption postoperatively up to 48 h.

How to cite this article:
Sinha A, Arora D, Singh S, Das T, Biswas M. Evaluating analgesic efficacy of single femoral nerve block versus combined femoral-sciatic nerve block post total knee arthroplasty.Anesth Essays Res 2020;14:326-330

How to cite this URL:
Sinha A, Arora D, Singh S, Das T, Biswas M. Evaluating analgesic efficacy of single femoral nerve block versus combined femoral-sciatic nerve block post total knee arthroplasty. Anesth Essays Res [serial online] 2020 [cited 2020 Nov 24 ];14:326-330
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With accelerating knee replacements being performed and the pain that follows it in the postoperative period, the need for adequate analgesia cannot be overemphasized. Early pain relief and early mobility defines the patient satisfaction and hence the overall success of the surgical intervention.[1],[2],[3],[4],[5] Regional nerve blocks, epidural catheter, and peri- or intra-articular infiltration of local anesthetics and opioids or postoperative opiates or nonsteroidal anti-inflammatory drugs (NSAIDs) are some commonly available means to achieve this, but it still stands as a challenge to appropriately control it.[5],[6],[7],[8],[9] Nowadays, regional nerve block is being preferred for postoperative analgesia and early mobility. It offers several advantages such as less risks of complications of retaining epidural catheter, decreased need for postoperative injectable analgesics, and hence decreased untoward effects of opiates or NSAIDs.[10],[11] Multiple studies established the efficacy of femoral nerve block (FNB) for pain control after total knee arthroplasty (TKA), but pain and discomfort is still seen to persist in the popliteal and medial aspects of the knee in many patients. A concomitant sciatic nerve block (SNB) was reported to alleviate this posterior knee pain. It is observed that SNB when given concomitantly with FNB significantly reduced posterior compartment of knee pain which helped in early mobilization.[2] In this study, we compared the analgesic effect of FNB alone versus combined FNB and SNB in unilateral TKA patients and assessed whether there is better pain relief in the combined nerve block group and reduced need for opioid in the postoperative period.


This study was conducted after clearance from the ethical committee, over a period of 1 year. The sample size was 150 with power 86.3% (from the different studies done, expected proportion of the patients, among the cases, had been assumed to be 60%). The formula used for sample size calculation was n = 4 pq.L−2, where n = required sample size, P = Approximate prevalence rate for which the study is to be conducted (to be obtained from previous study), q = 1 – p, and L = permissible error in the estimate. All patients were equally divided in two groups – Group F and Group FS. Anesthesiologists who did not perform the anesthesia enrolled the participants and assigned them to the group. Patients scheduled for unilateral TKA for degenerative arthritis, those belonging to American Society of Anesthesiologists (ASA) physical status Class I and II, those with weight 40–99 kg, and those who were fully able to understand the study contents from oral and written descriptions were included in the study. Patients for bilateral TKA, those belonging to ASA physical status class ≥3, those on regular narcotic use, those having allergies to any study drug, those with neuromuscular disease, and those with sensory disturbances of the legs were excluded from the study. Formal informed consent was obtained from the participants who fulfilled the above-mentioned inclusion and exclusion criteria. All patients received instruction in the use of the NRS pain scale [Figure 1], where the number 0 on the ruler represented no pain and the number 10 represented the most severe pain ever experienced by them, and they were asked to indicate the number that best reflected their pain on that scale.[12]{Figure 1}

The same team of surgeon performed all surgeries, and the same anesthesiologist performed the anesthesia for all cases. All patients were given subarachnoid block in L2–L4 space with 25G Whitacre spinal needle, and an equal amount of drug –0.5% injection bupivacaine 3.4 mL + injection fentanyl –0.4 mL (20 μg) was given to all the 150 participants. No additional narcotics or analgesics including fentanyl were administered during the operation. The operation was performed using the sub-vastus approach. All the participants underwent patellar resurfacing. On an average, the surgery took 2–2.5 h. After the surgery, the participants of Group F were moved to the supine position, and ultrasound-guided FNB was performed in combination with 0.5–1.0 mA nerve stimulation for 0.1 ms. After cleaning the site with antiseptic solution, we placed an echo-probe parallel to the inguinal ligament region to identify the femoral nerve and then inserted a 10-cm nerve stimulator needle (B Braun-stimuplex needle) using an in-plane approach from the lateral aspect of the ultrasound probe. After confirming the position by contraction of the quadriceps muscle and negative aspiration for blood, 20 mL of 0.375% ropivacaine was injected.

In Group FS, the patients were positioned in the lateral decubitus position tilted slightly forward. The foot on the side to be blocked positioned over the dependent leg so that the elicited motor response of the foot or toes could be easily observed. The landmarks (greater trochanter and posterior superior iliac spine) were outlined with a marking pen. A line between these two points was drawn and divided in half. Another line passing through the midpoint of this line and perpendicular to it was extended 4 cm caudal and marked as the needle insertion point. After disinfecting the skin, the needle was introduced perpendicular to the skin plane. Initially, the nerve stimulator was set to deliver a current intensity of 1.5 mA to allow for the detection of both twitches of the gluteal muscles as the needle passed through tissue layers and stimulation of the sciatic nerve. After an initial stimulation of the sciatic nerve was obtained, the stimulating current was gradually decreased until twitches are still seen or felt at 0.2–0.5 mA current. Typically, this occurred at a depth of 5–8 cm. After negative aspiration for blood, 40 mL of 0.375% ropivacaine was injected slowly on seeing motor response from the ankle joint.

FNB was given by the same technique as mentioned above.

The participants were administered injection paracetamol 1 g every 6 h intravenous (i.v.) round the clock postoperatively, irrespective of their pain score till 48 h. Injection pethidine 75 mg intramuscular (im) was given if Numeric Rating Scale (NRS) pain score was >3 in the postoperative period at 6, 12, 24, and 48 h. After that time or at any other time if they requested an analgesic and had an NRS score >3, injection tramadol 50 mg i.v. (maximum up to two doses) was administered.

The primary outcome was the change in NRS scores between Groups F and FS at the following five time points: after exiting the operating room at 6, 12, 18, 24, and 48 h later. Nurses in the ward who were blinded to the group allocations administered injection paracetamol as per dosage and injection pethidine 75 mg when patients complained of pain with NRS rating >3 and recorded the NRS scores. Other outcome measured was analgesic administered: times were recorded, and the total doses of opioid (injection pethidine) were noted and calculated.

Statistical analysis

Data were entered into a Microsoft excel spreadsheet and then analyzed by SPSS 24 IBM, NY, USA and Graph Pad Prism version 5 Graptstats, Bangalore, India. Data had been summarized as mean and standard deviation for numerical variables and count and percentages for categorical variables. Two-sample t-tests for a difference in mean involved independent samples or unpaired samples. Paired t-tests were a form of blocking and had greater power than unpaired tests. A Chi-squared test was any statistical hypothesis test wherein the sampling distribution of the test statistic is a Chi-squared distribution when the null hypothesis is true. Unpaired proportions were compared by Chi-square test or Fisher's exact test, as appropriate. In each case, the formula for a test statistic that either exactly follows or closely approximates a t-distribution under the null hypothesis is given. In addition, the appropriate degrees of freedom were given in each case. Each of these statistics can be used to carry out either a one-tailed test or a two-tailed test. Once a t-value is determined, a P value can be found using a table of values from Student's t-distribution. If the calculated P value is below the threshold chosen for statistical significance (usually the 0.10, the 0.05, or 0.01 level), then the null hypothesis is rejected in favor of the alternative hypothesis. P ≤ 0.05 was considered statistically significant.


All the 150 eligible patients who got enrolled were randomized and allocated to the intervention. They completed the study and none was lost to follow-up [Figure 2]. No statistically significant differences were found between the groups regarding patient demographic profiles or clinical characteristics [Table 1]. A significant difference was found in NRS score for pain between Groups FS and F [Figure 3]. The NRS scores were higher and statistically significant (P < 0.00001) in Group F than in Group FS at all time points, i.e., at 6 h (mean pain score in Group F – 1.61 vs. Group FS – 1.21), at 12 h (mean pain score in Group F –3.79 vs. Group FS – 1.59), 18 h (mean pain score in Group F – 3.30 vs. Group FS – 2.00), 24 h (mean pain score in Group F – 3.71 vs. Group FS – 2.87), and 48 h (mean pain score in Group F – 3.01 vs. Group FS – 1.95), and the total pain score with a mean of 15.43 in Group F versus 9.61 in Group FS was statistically significant, after the patients exited the operating room [Figure 4]. Although opioid consumption between the two groups at 6 h postoperatively was no different, at 12, 18, 24, and 48 h after the surgery, significant differences were seen in opioid consumption in the two groups, as depicted by P < 0.00001 [Figure 5]. In addition, the total mean opioid consumption (injection pethidine 75 mg im) was higher in Group F versus Group FS [Figure 6].{Figure 2}{Table 1}{Figure 3}{Figure 4}{Figure 5}{Figure 6}


With increasing numbers of TKA, there are efforts to study various available options that aim to reduce the postoperative pain in an attempt to hasten the functional recovery and minimize the opioid-related systemic side effects. Regional nerve blockade is the favored alternative these days. Femoral nerve being the central nerve supply to the maximum portion of the knee joint, is considered the gold standard,[13] but the role of SNB in TKA pain is doubtful. The present study was undertaken to assess and compare the effect of adding a single-shot SNB to single-shot FNB on analgesia post-TKA. It was seen that NRS scores at five time points, after exiting the operating room – at 6, 12, 18, 24, and 48 h later, were higher and statistically significant for Group F than Group FS. This could be well explained because the SNB acts by blocking the posterior knee pain at a proximal position in the perigluteal region. Furthermore, the total pain score was higher and statistically significant for Group F compared to Group FS. The results drawn in our analysis were in concurrence with those of studies by Wegener et al.,[2] Nagafuchi et al.,[4] and Pham Dang et al.[14]

The second postoperative outcome was opioid consumption, and it was no different between the two groups at 6 h postoperatively, however at 12, 18, 24, and 48 h after the surgery, statistically significant differences were seen in opioid consumption in the two groups (P [et al.,[2] Morin et al.,[3] Pham Dang et al.,[14] and Cook et al.[15] However, Nagafuchi et al.b4] observed no difference between the groups in the total analgesics required, which may have resulted from FNB alone providing sufficient analgesia, such that the effect of the adjunctive technique is masked.


We considered and compared only two postoperative factors, that is, postoperative pain and opioid requirement, and no other factors such as postoperative duration of motor and sensory block, which can delay the mobilization of patients. In our study, we have compared only the total dose of injection pethidine and not considered injection paracetamol or other opioids such as injection Tramadol given on demand. In addition, a fixed dose of ropivacaine was given in our study, but depending on the choice of local anesthetics and their doses, the results may vary. The study design was an observational one rather than a randomized trial, which is expected for better extrapolation and validation of the outcomes.


Group FS had reduced pain scores and pethidine consumption postoperatively up to 48 h that was statistically significant, hence proving the superiority of combined SNB and FNB. The SNB, by reducing postoperative pain in the posterior compartment of knee in TKA patients, acts as a useful adjunct to FNB.

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Conflicts of interest

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