Continuous Adductor Canal Block is superior to adductor canal block alone or adductor canal block combined with IPACK block (interspace between the popliteal artery and the posterior capsule of the knee) in postoperative analgesia and ambulation following total knee arthroplasty: randomized control trial

Abstract – Background ACB is given as a single injection or as a continuous block or combined with an IPACK block (interspace between the popliteal artery and the posterior capsule of the knee) to reduce postoperative knee pain after total knee arthroplasty. The aim of this study is to evaluate the technique of ACB that is superior in controlling postoperative pain, decrease opioid consumption
and facilitate ambulation in the immediate postoperative period.

Methods – A total of 171 patients were analyzed from a group of 180 patients who were randomized into three groups:

  1. ACB alone,
  2. Continuous ACB infusion via a catheter (CACB) and
  3. ACB combined with IPACK.

The primary outcome was pain at rest and after ambulation measured by the VAS scale every 8 h till 48 h after surgery. The secondary outcome measures were opioid consumption in morphine equivalents, ambulation distance measured in feet on postoperative day 2, timed up and go test, 30 s chair stand test, sitting active extension lag test, and maximal knee flexion at discharge.

Results – VAS scores at rest and after ambulation, opioid consumption was significantly lower (p<0.05%) in the CACB group compared to other study groups. Similarly, patients in CACB showed significantly (p<0.05%) better results in the secondary outcome measures. There were no significant differences in the outcomes between ACB and ACB combined with IPACK.

Conclusion – CACB allows better pain control and less opioid consumption in the immediate postoperative period after TKA compared to ACB alone or ACB with IPACK resulting in better ambulation and rehabilitation.


[1]. Moderate to severe postoperative pain after total knee arthroplasty (TKA) is a significant problem affecting about 58% of patients. Inadequate pain management results in prolonged hospital stay, delayed rehabilitation, decreased ambulation, and reduced patient satisfaction

[2]. Any delay in ambulation may increase the risk of postoperative complications such as venous thromboembolism and arthrofibrosis. Furthermore, studies have shown that severe postoperative pain after TKA is a risk factor for developing chronic pain leading to significant patient discomfort and suboptimal outcomes

[3]. This has necessitated the development of an appropriate analgesia regimen, which can provide adequate pain control but does not interfere with muscle function and rehabilitation. Peripheral nerve blocks such as femoral nerve block (FNB), adductor canal block (ACB), and local infiltration analgesias (LIA) techniques such as local infiltration of anesthesia in the interspace between the popliteal artery and the capsule of the posterior knee (IPACK) have shown efficacy in reducing postoperative pain significantly and have become popular recently

[4–7]. ACB is shown to provide pain relief by blocking the saphenous nerve, sensory nerve to vastus medialis, and articular branches of the Obturator nerve while sparing the different branches to the quadriceps muscle. The quadriceps sparing function of ACB results in better rehabilitation decreased risk of fall and better ambulation compared to FNB in numerous studies

[8, 9]. ACB can be administered as a single dose or as a continuous dose administered in the form of repeated boluses at specific predetermined intervals. Both single shot and continuous dose ACB have shown efficacy in pain control, but the advantages of one technique over another are debatable

[10]. However, ACB has no action on the posterior aspect of the knee and thereby does not relieve posterior knee pain. IPACK is a recent technique that has been shown to block the terminal sensory branches of the medial and lateral superior genicular nerves selectively without involving the motor branches of the tibial and peroneal nerves

[11]. A recent study has shown that the combination of ACB with IPACK results in reduced postoperative pain compared to ACB alone

[12]. However, no studies have been published directly comparing the efficacy of single-shot ACB, continuous ACB with the catheter, single-shot ACB, and IPACK in reducing postoperative pain and functional recovery in the immediate postoperative period.

The present randomized control study (RCT) was therefore designed to evaluate the comparative efficacy of three different techniques namely single shot ACB, continuous ACB with the catheter, single-shot ACB, and IPACK in controlling postoperative pain, ambulation in the immediate postoperative period, and opioid consumption.

Materials and methods

This double-blinded randomized clinical trial was conducted between March 2019 and June 2019 after approval from the institute ethics committee (SIEC/2019/321) and the trial registered with the national clinical trial registry (CTRI/2019/03/018239). The study was conducted according to the principles established in the declaration of Helsinki. All participants provided written informed consent for participation in the study, the publication of clinical, radiological details, and photographs.

The study was conducted in patients who underwent unilateral tri-compartmental TKA for primary osteoarthritis between the age groups of 45–80 years with an American Society of Anesthesiologists (ASA) functional status of I–III. Exclusion criteria included patients who underwent bilateral or revision total knee replacement, knee flexion deformity of≥30°, varus-valgus deformity of≥30°, arthritis due to rheumatoid disease or trauma or septic arthritis, creatinine>1.2, renal or hepatic dysfunction, known allergy to any study medication, chronic opioid use, BMI> 40, chronic pain unrelated to knee joint, pre-existing neuropathy, arrhythmia, epilepsy, had a history of bleeding diathesis or prior vascular surgery on femoral vessels on operated site and difficulty in comprehending visual analog scale (VAS) pain scores.

The sample size calculation and the randomization Sample size were calculated based on the difference in the primary outcome which was different in pain scores assessed using the VAS score. We chose the smallest value for the equivalence effect that would be clinically significant and determined that a 10 mm difference on the pain scale would be the inferiority limit. Power analysis was applied prior to enrolment using a two-sided test at an alpha level of 0.05 and power of 80%, to determine the required sample size for statistical significance. Based on our previous study


12], we determined a total of 50 patients in each group is sufficient to be 80% sure that the lower limit of a one-sided 95% confidence interval (CI) will be above the non-inferiority limit.

The patients were assigned treatment in one of three cohorts:

Group I: Single infiltration adductor canal block (ACB alone).

Group II: Continuous adductor canal block using the catheter with bolus infusions.

Group III: Single infiltration adductor Canal Block with IPACK block (interspace between the popliteal artery and the posterior capsule of the knee.

A total of 233 consecutive patients were screened among which 53 patients were found ineligible based on the selection criteria. A total of 180 patients were included in the study and were randomly allocated to the three study groups equally using a block randomization method with randomly mixed block sizes of two, four, and six, with sizes of block concealed from the executor.

The random allocation cards were made in sealed envelopes using computer-generated random numbers and patients as well as one of the authors (R.T.) were blind to the treatment used. Sealed opaque envelopes with sequential numbering having the patient assignment were made accessible to the anesthetist (K.J.) who administered the anesthetic blocks by himself.

Anesthesia and surgical technique

All the surgeries were performed by two fellowship-trained joint replacement surgeons under spinal anesthesia using the medial parapatellar approach and tourniquet. Posterior stabilized knee prosthesis without patellar resurfacing was done in all the patients.

An adductor canal catheter was placed in all the patients studied using the technique described by Lee et al.

[13] A18G Tuohy needle was introduced into the adductor canal under ultrasound guidance (USG) (SonoSite™, Inc., Bothell, WA 98021, USA). Following dilation of the adductor canal with normal saline, a 21G catheter was threaded up to 3–5 cm beyond the needle tip in a caudal direction. The guidewire was removed upon the catheter exiting the needle tip while threading to avoid inadvertent advancement of the catheter out of the space. The catheter was then manipulated and normal saline injected to confirm the catheter tip location within the adductor canal on ultrasound visualization. Twenty milliliters of 0.2% ropivacaine was injected as a loading dose in all the patients. Only patients in Group II received a continuous infusion of 0.2% ropivacaine via a catheter at 5 ml/h for 48 h after which the catheter was removed.

In the postoperative ward, the infusion was temporarily stopped to facilitate physiotherapy and was resumed promptly after cessation of activity in group II patients. For patients in Group III, after ACB block was given, an IPACK block was given additionally using the technique described by Kim et al.

[14]. The patient was placed in a supine position and knee placed in a position of 90° flexion, the anesthesiologist identified the popliteal artery, in a short-axis view, at the popliteal creasen and moved cephalad just beyond the femoral condyles, at the level where the condyles merge with the shaft of the femur. The tibial and peroneal nerves were visualized superficial to the popliteal artery. After identifying the space between the femur and popliteal artery, a 22 G 10 cm long Stimuplex needle was advanced in-plane from medial to lateral. The tip was positioned at the middle of
the femur and near the lateral border near the periosteum. Subsequently, 20 ml of 0.2% ropivacaine was injected.

For deep vein thrombosis prophylaxis, 3 doses of 40 mg enoxaparin sodium subcutaneously started on the day of surgery followed by oral apixaban 2.5 mg for the next 14 days was given. All the patients received oral celecoxib 200 mg and gabapentin 300 mg preoperatively 10 h before surgery. Postoperatively, intravenous paracetamol 1 g was given every 8 h for 3 days followed by oral
paracetamol 1 g every 8 h along with Gabapentin 300 mg given orally once daily for a period of 4 weeks. Oxycodone immediate-release tablets or intravenous morphine was considered in the form of rescue analgesia in patients experiencing breakthrough pain.

All patients underwent a standard supervised rehabilitation program and were discharged from the hospital 3 days after surgery. Adductor canal catheter was removed after 48 h of surgery on postoperative day 2.

Outcome Measures Assessed

Postoperative pain at rest assessing using the visual analog scale (VAS) was the primary outcome measure of this study. Secondary outcome measures assessed were opioid consumption in orphine equivalents and ambulation ability at the time of discharge. VAS scores were recorded at 81,624, 324,048 h postoperatively, and after physiotherapy sessions which included ambulation on POD 1, POD 2. Ambulation ability was assessed as ambulation distance measured in feet on POD2, timed up and go (TUG) test

[15], 30 s chair stand test

[16], sitting active extension lag test

[17] and maximal knee flexion at discharge. The TUG test measures the time it takes a person to stand up from a chair, walk a distance of 3 m and return to the chair. The 30-s chair stand test assesses how many times a person is able to rise from a chair and sit down again in 30 s, with the arms kept crossed over the chest. Preoperative and postoperative data collection was done by an independent assessor (K.K.) who was blinded to the type of intervention in the study group.

Statistical analysis

Data were analyzed by Microsoft Excel and Graph Pad Prism software. Data were summarized by mean±SD for continuous variables and percentages for categorical variables. The comparison between three groups was done by one-way analysis of variance test (ANOVA)/Kruskal–Wallis test and followed by post hoc multiple comparisons (Bonferroni’s) test for continuous variables. The comparison between the three groups was done by the chi-square test for categorical variables. The nature of the hypothesis testing was 2 tailed and a p-value less than 0.05 was considered as statistically significant.


Among a total of 180 patients, 171 patients were available for final analysis (58 patients in group I, 57 patients in Group II, and 56 Patients in Group III). Two patients were excluded from the group I due to the requirement for ICU stay following the development of thromboembolism postoperatively. Three patients were excluded from group II due to catheter induced complications requiring early removal of catheters. Four patients were excluded from group III in which two patients required ICU stay due to cardiac events and two patients required general anesthesia due to unsuccessful spinal anesthesia

(Fig. 1). There were no significant differences in the demographic data, preoperative status, BMI (p 0.140),

ASA grade (p 0.906) and operative time (p 0.584) among the three groups

(Table 1). Postoperative pain scores assessed in the form of the VAS scale were found to be significantly lower in group II (CACB) compared to the other two groups throughout all the time points (Table 2). Similarly, the VAS score after ambulation was found to be significantly better in group II compared to the other groups
(Table 2). However, no significant difference was observed in the VAS scores at rest and after ambulation between group I (SACB) and group III (SACB+IPACK). There was significantly less opioid consumption in morphine milliequivalents (p<0.011) in group II compared to other groups (Table 3). Patients in group II showed significantly better responses on the TUG test, 30 s chair test, active quadriceps holding time, and extension lag (p<0.05) (Table 3). Patients in group II recorded better knee flexion at time of discharge (96.670±4.756 (Group II) versus. 92.320±8.526 (Group I) versus 92.410±6.300 (Group III)) as well as better ambulation distance

(Table 4). Intergroup comparison of all the studied parameters showed no significant difference between group I and group III. None of the patients in any group showed treatment-related side effects or complications.


This prospective double-blinded randomized control trial evaluating the efficacy of three different techniques of local anesthesia blocks concludes that CACB offers better pain control in the immediate postoperative period along with better ambulation capacity without having any adverse side effects compared to SACB or SACB+IPACK. Furthermore, CACB has shown reduced opioid consumption compared to the other groups in this study thereby reducing the chance of opioid dependence as well as the adverse side effects of excessive opioid intake.

This study also concludes that the addition technique of IPACK to ACB may not add any additional benefit in postoperative pain control, ambulation, opioid consumption, or rehabilitation compared to ACB alone. Ambulation ability assessed by the TUG test, 30-s chair test, ambulation distance, maximum flexion at discharge, extension lag showed significantly better results in the CACB group than the other two groups.

Numerous studies have been published showing the efficacy of ACB over other regional block techniques such as femoral nerve block (FNB) or a sciatic nerve block (SCB) in controlling lower limb pain

[6, 18]. However, the technique and duration of ACB is still a matter of debate as studies have shown that a single shot ACB can give similar analgesia as a continuous ACB while avoiding the risks associated with an indwelling catheter required in CACB. Elkabassany et al.

[10] conducted an open-label randomized control trial evaluating the efficacy of SACB versus CACB (administered as two different regimens) in providing analgesic benefits and physiotherapy outcomes. They concluded that all three groups showed no difference in opioid use, hospital stay, or functional outcomes although the proportion of patients in SACB reporting severe pain was more than the other two groups. Another RCT performed in 177 patients comparing opioid consumption in patients who underwent single shot ACB with/without intravenous dexamethasone versus CACB showed similar outcomes in all the three groups

[13]. The recent technique of IPACK has shown promising results in controlling posterior knee pain and is recommended as a combination with ACB to provide better results. A prospective study comparing SACB with SACB+IPACK by Sankineani et al.

[12] has shown better pain control, knee ROM and ambulation in patients receiving SACB+IPACK. However, the authors concluded that the lack of a CACB group was a limitation of the study. A recent RCT published by Patterson et al.

[19] comparing the outcomes between CACB versus CACB+IPACK reported less pain in the IPACK group in the post-anesthesia care unit (PACU) which was however not long-acting in nature. They concluded that there was no difference in opioid consumption, physical therapy, or hospital stay between both the study groups and recommended that IPACK may be used as rescue analgesia rather than as a routine analgesia technique.

This study is the first double-blinded RCT to study all the three techniques of SACB, CACB, SACB+IPACK and our results are similar to the study by Patterson et al.

[19] and differs from Sankineani et al. [12], in that IPACK did not offer any additional benefit in controlling pain and opioid consumption. Our study however shows results that are in contrast to those published by Elkabassany et al. [10] and Lee et al.

[13], by showing that CACB is more effective than SACB in pain control and provides better ambulation ability in patients. One of the postulated benefits of CACB in the technique described us is due to the spread of the local anesthesia caudally along the adductor canal to the popliteal region thereby blocking the popliteal plexus and the articular branch of the Obturator nerve

[20]. This can result in decreased posterior knee pain similar to IPACK but remains sustained due to the continuous infusion of local anesthesia through the catheter. While this trial was designed and executed carefully to have homogenous study groups as well as blinding the assessors to the type of intervention done to avoid bias, some limitations still exist in our study. Patient satisfaction and ambulation after surgery are also dependent on many other variables such as patient’s mental status, age, BMI, and gender, and hence a matched cohort of the study groups would have been better. However, patients in all the study groups recorded VAS scores after 24 h that is less than 3 which is clinically not significant but patients in the ACB group recorded VAS scores more than 5 within 24 h after surgery demonstrating clinical superiority of CACB and ACB+IPACK over ACB alone.

This assumes clinical significance when clinicians want to adopt fast track protocol after surgery wherein patients are encouraged to ambulate on the same day. The other limitation of the study is that all the ambulation tests were performed on POD 2 but should probably have been performed on the day of surgery to assess the usefulness of the described techniques in facilitating a fast track protocol for mobilization after TKA. The third limitation of the study is that the concentration of ropivacaine used in this study was 0.2%, which is considerably lower than the concentration of 0.375% and 0.5% described by other studies

[21,22]. However, the optimal dose and concentration of local anesthetic mixture are a matter of considerable controversy and depend on patient characteristics and country

[23]. We opine that different drug concentrations and the addition of adjuvants may lead to different results and can be investigated in future studies. However, the concentration used by us was similar in the three study groups and based on earlier published studies proving its efficacy

[24, 25]. We used the lowest possible safest drug concentration and drug to reduce the complication of local anesthesia systemic toxicity (LAST), which can occur if the dose of local anesthesia exceeds the tolerable limit for a patient

[26]. It can manifest with clinical symptoms such as perioral numbness, altered sensorium, tinnitus, the altered sensation of taste, convulsions, or cardiac arrhythmias

[27]. Although two patients from group III (ACB+IPACK) documented cardiac events, they were not attributed to LAST. The rate of ropivacaine infusion through the catheter was prefixed at 5 ml/h and it is possible that better pain control could be obtained with a larger dose and hence a study needs to be done to determine the appropriate infusion rate of ropivacaine in CACB without causing LAST. In this study, we have only studied one technique of CACB, which involves continuous infusion and not evaluated intermittent bolus injections technique and therefore cannot conclude which is a better technique to use. There are some disadvantages reported with the use of adductor canal catheter use such as hematoma

[28], Catheter displacement, neuropathy

[29] and rarely myositis

[30]. An additional disadvantage of using continuous infusion rather than a repeated bolus injection technique is that the patients may have to be connected to a syringe pump which might hinder their ambulation abilities. Our study also reported three such cases in the CACB group wherein we had to remove the catheter within 24 h due to catheter dislodgement and excluded those patients from the study.

However, our patients did not report any discomfort during physiotherapy and ambulation due to the presence of the syringe pump as it was temporarily disconnected when the patient was ambulating and was reconnected later after cessation of activity.


In conclusion, the present study showed that CACB using a continuous infusion technique provides better pain control, decreased opioid consumption, and superior ambulation capacity in the immediate postoperative period compared to ACB, ACB+IPACK in patients undergoing unilateral TKA without any significant adverse side effects.