Comparison of Ultrasound-Guided Femoral Nerve Block and Adductor  Canal Block for Postoperative Pain Control and Early Mobilization  Following Knee Surgery

Priya, Shanmuga; Keerthana, Vijaya

doi:10.65188/nurexus.1053

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ORIGINAL ARTICLE

Journal of MedVerse Research & Practice

ISSN: 3107-4278

Comparison of Ultrasound-Guided Femoral Nerve Block and Adductor

Canal Block for Postoperative Pain Control and Early Mobilization

Following Knee Surgery

Dr. Shanmuga Priya

1

, Dr. Vijaya Keerthana

2

Associate Professor, Professor

Department of Anaesthesia, Shyam Shah Medical College, Rewa, Madhya Pradesh.

Email ID: shangumapriya12@gmail.com,

Submission Date: 21.10.2025

Accepted Date: 17.11.2025

Published Date: 30.11.2025

article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits

unrestricted use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

Abstract

Background: Effective control of postoperative pain is essential after knee surgeries to promote early movement,

minimize postoperative complications, and improve overall patient outcomes. Femoral nerve block (FNB) is

widely used and provides dependable pain relief, but it often weakens the quadriceps muscle, which can delay early

mobilization. The adductor canal block (ACB), which largely preserves motor power, has emerged as an alternative

technique that may allow earlier ambulation without compromising analgesia.

Methods: This prospective, randomized observational study enrolled 100 adults aged 18–60 years with ASA

physical status I–II scheduled for elective knee surgery under neuraxial anesthesia. Participants were randomly

assigned to Group F (FNB, n = 50) or Group A (ACB, n = 50). Both groups received 20 mL of 0.25% bupivacaine

combined with 8 mg dexamethasone under ultrasound guidance. Pain was assessed using the Visual Analog Scale

(VAS) at 0, 2, 4, 6, 8, 12, 18, and 24 hours postoperatively. Quadriceps strength was evaluated through the straight-

leg-raise test. Intravenous tramadol 100 mg was administered when the VAS exceeded 4. Patient satisfaction at 24

hours was also recorded.

Results: Both techniques yielded similar analgesic profiles throughout the postoperative period, with slightly lower

VAS values in the FNB group at select time points. Quadriceps power was significantly better maintained in the

ACB group, allowing patients to ambulate earlier. Rescue analgesia requirements were comparable (FNB: 30%;

ACB: 36%), and mean tramadol use differed only slightly (FNB: 90 ± 30 mg vs. ACB: 100 ± 25 mg). High

satisfaction levels were noted in both groups, with 50% in the FNB group and 56% in the ACB group reporting

high satisfaction.

Conclusion: Ultrasound-guided ACB offers pain relief comparable to FNB while preserving quadriceps muscle

strength and enabling earlier ambulation. With consistently high patient satisfaction and better motor function,

ACB serves as an effective and motor-sparing option for postoperative pain management following knee surgeries.

Keywords: Adductor canal block, femoral nerve block, postoperative analgesia, quadriceps preservation, knee

surgery, early mobilization.

Introduction

Postoperative pain is one of the most common challenges following surgery and is often aggravated by

soft-tissue handling, inflammation, and reflex muscle spasm [1]. Although intraoperative anesthesia

provides adequate analgesia, many patients report significant pain once its effects subside, particularly

after orthopedic procedures [2]. Knee surgeries—such as arthroscopic interventions and reconstructive

operations - are known to produce considerable postoperative discomfort, which can interfere with sleep,

appetite, and active participation in physiotherapy sessions [3].

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Effective control of postoperative pain is therefore essential, as inadequate analgesia may delay

mobilization, hinder rehabilitation, extend hospital stay, and adversely affect patient satisfaction [4].

Multimodal analgesic regimens—using combinations of opioids, acetaminophen, nonsteroidal anti-

inflammatory drugs, alpha-2 agonists, NMDA antagonists, gabapentinoids, and dexamethasone—have

been shown to enhance pain relief and promote smoother recovery [5]. However, opioids can lead to

complications such as respiratory depression, nausea, vomiting, and opioid-induced hyperalgesia, while

NSAIDs alone often fail to adequately relieve moderate-to-severe postoperative pain [5]. Epidural

analgesia, although effective, is limited by technical constraints, side effects, and potential risks,

prompting increased interest in safer alternatives [6].

Peripheral nerve blocks (PNBs) have emerged as an important component of postoperative analgesia in

orthopedic surgery due to their targeted effect and opioid-sparing benefits [6]. Ultrasound guidance

further improves the precision of PNBs by enhancing visualization, reducing procedural attempts,

shortening onset time, and lowering complication rates [6]. The adductor canal block (ACB) selectively

anesthetizes the saphenous nerve within the mid-thigh region, providing sensory blockade to the medial

and anterior knee while largely maintaining quadriceps motor strength—an advantage that supports early

mobilization [1,3]. Conversely, the femoral nerve block (FNB) offers strong analgesia but frequently

compromises quadriceps function, increasing the risk of weakness and falls during initial ambulation

[2,4].Although ACB is often promoted as a motor-sparing alternative, clinical findings remain mixed.

While several studies demonstrate comparable analgesia with better preservation of quadriceps strength

and faster functional recovery using ACB, other reports show minimal differences between the two

techniques in terms of pain scores or mobility outcomes [3–5]. Such variability may be influenced by

differences in local anesthetic volume, injection technique, surgical characteristics, and individual patient

factors.

Early ambulation is critical after knee surgery to prevent immobility-related complications such as joint

stiffness, venous thromboembolism, and extended hospitalization. Therefore, a direct comparison of

ultrasound-guided FNB and ACB is clinically relevant. This study aims to assess their impact on

postoperative pain relief, quadriceps strength, opioid requirement, and early mobilization. The results will

provide evidence to guide optimal analgesic strategies for enhancing recovery and improving patient

safety and satisfaction following knee surgery [1–6].

Materials and Methods

Study Design

This prospective, randomized, comparative observational study was conducted to compare the efficacy of

ultrasound-guided femoral nerve block and adductor canal block in providing postoperative analgesia and

facilitating early mobilization among patients undergoing elective knee surgery.

Study Setting and Duration

The study was carried out in the Department of Anaesthesiology at Shyam Shah Medical College and its

affiliated hospitals, Rewa, Madhya Pradesh, over a period of one year from April 2024 to March 2025.

Study Population

The study population comprised adult patients scheduled to undergo elective knee surgery under spinal

(neuraxial) anesthesia. Eligible participants were enrolled after satisfying the predefined inclusion and

exclusion criteria and were randomly allocated into study groups using the sealed envelope technique.

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Sample Size

A total of 100 patients were included in the study. The sample size was determined based on feasibility

and previous studies evaluating postoperative analgesia following peripheral nerve blocks. Patients were

randomly assigned into two equal groups of 50 participants each.

Inclusion Criteria

Patients aged between 18 and 60 years belonging to the American Society of Anesthesiologists (ASA)

physical status I or II, scheduled for elective knee surgery under spinal anesthesia, and willing to provide

written informed consent were included in the study.

Exclusion Criteria

Patients who refused participation, had hypersensitivity to local anesthetics or dexamethasone, cognitive

impairment, chronic opioid use, pre-existing neurological deficits involving the lower limbs,

coagulopathy, infection at the injection site, significant hepatic, renal, cardiac, or respiratory disease, or

any contraindication to spinal anesthesia or peripheral nerve block were excluded.

Data Collection Tool

Following written informed consent, all participants underwent a detailed pre-anesthetic evaluation that

included demographic characteristics, medical and surgical history, airway assessment, physical

examination, and baseline investigations including complete blood count, liver and renal function tests,

coagulation profile, electrocardiography, heart rate, blood pressure, and peripheral oxygen saturation. The

Visual Analog Scale (VAS) for pain assessment and the patient satisfaction scoring system were

explained before surgery. Under standard aseptic precautions, spinal anesthesia was administered at the

L3–L4 intervertebral space using a 25-gauge Quincke spinal needle with 2.5 mL of 0.5% hyperbaric

bupivacaine. Following successful spinal anesthesia, patients allocated to Group F received an

ultrasound-guided femoral nerve block using 20 mL of 0.25% bupivacaine combined with 8 mg

dexamethasone. The block was performed using an in-plane lateral-to-medial approach with deposition of

the drug adjacent to the femoral nerve. Patients in Group A received an ultrasound-guided adductor canal

block using the same volume and concentration of local anesthetic with dexamethasone, administered

beneath the sartorius muscle adjacent to the femoral artery at the mid-thigh level. Postoperatively, all

patients received intravenous diclofenac 75 mg and paracetamol 1 g as standard multimodal analgesia.

Pain intensity was evaluated using the 10-cm Visual Analog Scale at 0, 2, 4, 6, 8, 12, 18, and 24 hours

after surgery. Rescue analgesia with intravenous tramadol 100 mg was administered whenever the VAS

score exceeded 4. Quadriceps muscle strength was assessed at 6, 12, 18, and 24 hours using the straight

leg raise test and graded as normal power (Grade 0), mild weakness (Grade 1), or complete inability to

raise the leg (Grade 2). Patient satisfaction regarding postoperative pain management was evaluated at 24

hours using a five-point Likert satisfaction scale ranging from highly satisfied to highly dissatisfied. All

perioperative observations, analgesic requirements, motor function assessments, and satisfaction scores

were systematically recorded in a structured case record proforma.

Ethical Considerations

The study protocol was approved by the Institutional Ethics Committee of Shyam Shah Medical College,

Rewa, prior to commencement of the study. Written informed consent was obtained from all participants

after explaining the objectives, procedures, benefits, and potential risks of the study in their local

language. Confidentiality of patient information was maintained by assigning unique identification

numbers, and all data were used exclusively for research purposes in accordance with the Declaration of

Helsinki and ICMR ethical guidelines.

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Statistical Analysis

Data were entered into Microsoft Excel and analyzed using the Statistical Package for the Social Sciences

(SPSS) software version 26.0. Continuous variables were expressed as mean ± standard deviation, while

categorical variables were presented as frequencies and percentages. The normality of continuous data

was assessed using the Shapiro–Wilk test. Comparisons of continuous variables between the two groups

were performed using the independent sample t-test for normally distributed data and the Mann–Whitney

U test for non-normally distributed data. Repeated pain scores over different postoperative time intervals

were compared using repeated-measures analysis of variance (ANOVA). Categorical variables, including

quadriceps muscle strength grading, rescue analgesic requirement, and patient satisfaction scores, were

compared using the Chi-square test or Fisher's exact test, as appropriate. A p-value of less than 0.05 was

considered statistically significant.

Results

Table 1: Demographic Characteristics of Study Participants

Parameter

Group F (n=50)

Group A (n=50)

Total (n=100)

Age (years, mean ± SD)

45 ± 10

44 ± 9

44.5 ± 9.5

Gender (M/F)

28 / 22

30 / 20

58 / 42

ASA I / II

30 / 20

32 / 18

62 / 38

BMI (kg/m², mean ± SD)

26 ± 3

25.5 ± 3

25.8 ± 3

The study population was comparable between the two groups in terms of age, gender distribution, ASA

physical status, and BMI. The mean age was 44.5 ± 9.5 years, with a balanced male-to-female ratio

(58:42). ASA I and II patients were similarly distributed across groups, and mean BMI values were also

comparable (25.8 ± 3 kg/m²), indicating that both groups were well-matched for baseline characteristics,

reducing potential confounding factors for postoperative outcomes.

Table 2: Postoperative VAS Scores (Mean ± SD)

Time post-op (hrs)

Group F

Group A

2

3.0 ± 1.0

3.2 ± 1.1

4

3.5 ± 1.2

3.6 ± 1.0

6

3.8 ± 1.0

3.7 ± 1.2

8

3.2 ± 0.9

3.5 ± 1.1

12

2.8 ± 0.8

3.1 ± 0.9

24

1.5 ± 0.6

1.8 ± 0.7

Postoperative pain, measured using the Visual Analog Scale (VAS), showed that both groups experienced

moderate pain in the early hours following knee surgery, with Group F (Femoral Nerve Block) having

slightly lower scores at most time points compared to Group A (Adductor Canal Block). At 2 and 4 hours,

VAS scores were comparable (3.0 ± 1.0 vs 3.2 ± 1.1 at 2 hrs; 3.5 ± 1.2 vs 3.6 ± 1.0 at 4 hrs). By 6–8

hours, pain remained similar in both groups, while at 12 and 24 hours, Group F continued to demonstrate

marginally lower pain levels (2.8 ± 0.8 vs 3.1 ± 0.9 at 12 hrs; 1.5 ± 0.6 vs 1.8 ± 0.7 at 24 hrs).

Table 3: Quadriceps Muscle Strength Assessment (Straight Leg Raise Test)

Time post-op (hrs)

Group F (n=50)

Group A (n=50)

6

Grade 0: 20 Grade 1: 15 Grade 2: 15

Grade 0: 40 Grade 1: 10 Grade 2: 0

12

Grade 0: 30 Grade 1: 10 Grade 2: 10

Grade 0: 45 Grade 1: 5 Grade 2: 0

24

Grade 0: 40 Grade 1: 5 Grade 2: 5

Grade 0: 50 Grade 1: 0 Grade 2: 0

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Quadriceps strength assessment showed that Group A (Adductor Canal Block) better preserved motor

function than Group F (Femoral Nerve Block). At 6 hours postoperatively, 40 patients in Group A had

normal strength versus only 20 in Group F. By 12 hours, most Group A patients maintained full strength,

while Group F still had some weakness or paralysis. After 24 hours, all Group A patients had recovered,

whereas Group F had 10 patients with residual impairment.

Table 4: Rescue Analgesic Requirement (Tramadol 100 mg IV)

Parameter

Group F (n=50)

Group A (n=50)

Patients requiring rescue

15 (30%)

18 (36%)

Total dose (mg, mean ± SD)

90 ± 30

100 ± 25

Rescue analgesia was required in 30% of patients in Group F and 36% in Group A. The mean total dose

of tramadol administered was slightly higher in Group A (100 ± 25 mg) compared to Group F (90 ± 30

mg), indicating comparable analgesic efficacy between the femoral nerve block and adductor canal block.

Table 5: Patient Satisfaction at 24 Hours

Satisfaction Level

Group F (n=50)

Group A (n=50)

Highly satisfied

25 (50%)

28 (56%)

Satisfied

18 (36%)

15 (30%)

Neither satisfied/dissatisfied

5 (10%)

6 (12%)

Dissatisfied

2 (4%)

1 (2%)

Highly dissatisfied

0 (0%)

Patient satisfaction was generally high in both groups. In Group F, 50% of patients were highly satisfied

and 36% satisfied, whereas in Group A, 56% were highly satisfied and 30% satisfied. A small proportion

reported neutral or dissatisfied responses, and no patients were highly dissatisfied, indicating overall

positive perception of analgesia in both the femoral nerve block and the adductor canal block groups.

Discussion

The present study compared ultrasound-guided femoral nerve block and adductor canal block for

postoperative pain relief and early mobility in patients undergoing knee surgery. Both techniques

offered effective analgesia, with mean VAS scores at 2, 4, 6, 8, 12, and 24 hours remaining within

acceptable ranges. Although the FNB group demonstrated slightly lower pain scores at 6 hours (3.8 ±

1.0) than the ACB group (3.7 ± 1.2), this minor difference did not translate into a meaningful clinical

advantage. These findings are consistent with earlier reports by Marhofer et al. and Jaeger et al., who

documented equivalent analgesic efficacy between femoral nerve block and adductor canal block,

indicating that either technique can be used reliably for postoperative pain control following knee

surgery. A notable benefit of ACB in the current study was its superior preservation of quadriceps

muscle power. At the 6-hour assessment, 40 participants in the ACB group retained full strength,

compared to only 20 individuals in the FNB group. Complete motor weakness was identified in 15

patients receiving FNB and was not observed in any patient who received ACB. Similar motor-sparing

effects of ACB have been reported by Lund et al. and Siddiqui et al., who emphasized that

preservation of quadriceps strength facilitates early ambulation, supports physiotherapy participation,

and reduces the risk of postoperative falls.

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In terms of supplemental analgesia, 30 percent of patients in the FNB group and 36 percent in the

ACB group required rescue tramadol, with average consumption of 90 ± 30 mg and 100 ± 25 mg,

respectively. These observations are in agreement with findings reported by Hussien et al., who noted

that while ACB may produce a slightly less intense sensory block than FNB, this difference is

clinically minimal and does not compromise overall analgesic effectiveness, particularly when

balanced against the advantage of motor function preservation. Patient satisfaction scores were high in

both groups, with 50 percent of individuals in the FNB group and 56 percent in the ACB group

reporting a high level of satisfaction. The marginally higher satisfaction observed in the ACB group

may be attributed to improved early mobilization and greater confidence related to preserved limb

control. Similar trends have been described by Apfelbaum et al. and Kehlet and Dahl, who highlighted

the importance of effective pain control combined with early functional recovery in improving overall

patient satisfaction following surgery.

Strengths

This prospective randomized study employed ultrasound-guided peripheral nerve blocks with

standardized anesthetic techniques and postoperative analgesic protocols, thereby improving

procedural accuracy and minimizing performance bias. Serial assessment of pain, quadriceps muscle

strength, rescue analgesic consumption, and patient satisfaction provided a comprehensive evaluation

of postoperative analgesia and functional recovery.

Limitations

The study was conducted at a single tertiary care center with a relatively limited sample size, which

may restrict the generalizability of the findings. In addition, follow-up was limited to the first 24

postoperative hours, and long-term functional recovery, rehabilitation outcomes, and chronic

postoperative pain were not evaluated.

Conclusion

In the present study, both ultrasound-guided femoral nerve block (FNB) and adductor canal block (ACB)

offered effective postoperative analgesia for patients undergoing knee surgery. Although overall pain

relief was comparable between the two techniques, ACB showed a clear benefit by better preserving

quadriceps muscle strength, enabling earlier mobilization and supporting quicker functional recovery. The

need for rescue analgesia and the level of patient satisfaction was similar in both groups, confirming that

ACB maintains analgesic efficacy. Based on these findings, ACB can be considered a safe, efficient, and

motor-sparing alternative to FNB, particularly advantageous in postoperative settings where early

ambulation is a priority.

Conflict of interest: Nil

Source Of Fund: Nil

Acknowledgement: I sincerely appreciate the unwavering support provided by my department during

the course of this study, and I am also grateful to the institution’s management for facilitating and

enabling its successful completion.

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