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

Priya S et al | DOI: 10.65188/nurexus.1053

Page 16

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

, Dr. Vijaya Keerthana

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

DOI: 10.65188/nurexus.1053

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,

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

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

This prospective, randomized, observational study will be conducted to compare postoperative analgesia

and early mobilization in patients undergoing knee surgery. The research will take place in the

Department of Anaesthesiology at Shyam Shah Medical College and its affiliated hospitals in Rewa,

Madhya Pradesh, over a period of one year from April 2024 to March 2025. Approval for the study has

been granted by the Institutional Ethics Committee before the recruitment of participants.

A total of 100 adult patients between 18 and 60 years of age, belonging to ASA physical status classes I

or II, and scheduled for elective knee surgery under neuraxial anesthesia will be included. Patients will be

randomly distributed into two groups using the sealed envelope method. Group F (n = 30) will receive an

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

dexamethasone. Group A (n = 30) will receive an adductor canal block with the same volume and

concentration of local anesthetic and adjuvant. Eligible participants will include adults aged 18 to 60

years who are clinically stable, fall under ASA I or II, and are planned for elective knee procedures under

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spinal anesthesia. Individuals will be excluded if they decline participation, have a known allergy to any

study drug, have cognitive impairment, a history of chronic opioid intake, pre-existing neurological

deficits, coagulopathy, or any significant systemic disease that would interfere with the protocol.

All patients will undergo a preoperative evaluation that includes a detailed history, physical examination,

airway assessment, and documentation of baseline vital parameters, including heart rate, blood pressure,

oxygen saturation, and ECG. Routine investigations such as complete blood count, liver and renal

function tests, and coagulation profile will be completed. The study objectives, pain assessment method

using the Visual Analog Scale, and the satisfaction scoring system will be explained to each patient, and

written informed consent will be obtained.

Spinal anesthesia will be administered at the L3 to L4 interspace using a 25-gauge Quincke needle, with

2.5 mL of 0.5 percent hyperbaric bupivacaine. For patients in Group F, the femoral nerve block will be

performed under ultrasound guidance at the junction of the mid and distal thigh. A lateral-to-medial in-

plane technique will be used to deposit the drug around the femoral nerve adjacent to the femoral artery.

For Group A, the adductor canal block will be carried out at the mid-thigh level by locating the femoral

artery and saphenous nerve on ultrasound and injecting the local anesthetic beneath the appropriate fascial

plane. Postoperatively, all patients will receive intravenous diclofenac 75 mg and paracetamol 1 g as part

of standard analgesic care. Pain intensity will be assessed using a 0 to 10 cm Visual Analog Scale at

intervals of 0, 2, 4, 6, 8, 12, 18, and 24 hours. If the VAS score exceeds 4, rescue analgesia in the form of

intravenous tramadol 100 mg will be provided. Quadriceps strength will be evaluated in the supine

position using the straight leg raise test at 6, 12, 18, and 24 hours and graded as follows: 0 for normal

power, 1 for mild weakness, and 2 for complete inability to raise the leg. Patient satisfaction will be

assessed at 24 hours using a 5 point rating scale that ranges from highly satisfied to highly dissatisfied.

All demographic variables, clinical findings, laboratory values, pain scores, quadriceps strength and

satisfaction scores will be recorded in a structured proforma. Statistical analysis will be performed using

SPSS software. Continuous variables will be presented as mean with standard deviation, while categorical

data will be expressed as percentages. Statistical tests such as t test, Chi square test, Mann Whitney U

test, or ANOVA will be applied as appropriate. A p value less than 0.05 will be considered statistically

significant.

Ethical approval for the present study was obtained from the Institutional Ethics Committee of Shyam

Shah Medical College, Rewa, Madhya Pradesh (Ref No: SSMC/IEC/2023/59027). A detailed Participant

Information Sheet was provided to all participants, and written informed consent was obtained prior to

their participation in the study.

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

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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

3.0 ± 1.0

3.2 ± 1.1

3.5 ± 1.2

3.6 ± 1.0

3.8 ± 1.0

3.7 ± 1.2

3.2 ± 0.9

3.5 ± 1.1

2.8 ± 0.8

3.1 ± 0.9

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)

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

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

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

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

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

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

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%)

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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.

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.

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.

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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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