Continuous adductor canal block (CACB) is becoming increasingly popular for providing postoperative analgesia following knee arthroplasties. These continuous blocks are provided through inserted nerve catheters and effectively extend the duration of analgesia, thereby reducing opioid consumption. This, in turn, helps minimize opioid-related side effects, promotes early ambulation, and supports earlier discharge. However, catheter migration remains a significant concern, as the catheter tip can become displaced from the adductor canal due to movements associated with ambulation or physiotherapy. In this study, the investigators compare the migration rates of two different techniques for CACB catheters insertion: the Interfascial plane between SArtorious muscle and FEmoral artery (ISAFE) and the Out Of Plane parallel to Saphenous nerve (OOPS) techniques. Pain scores and opioid consumption on postoperative day 1 (POD1) will also be assessed as secondary outcomes. The hypothesis is that both techniques will result in similar migration rates of CACB catheter.

Joint replacement surgeries are often followed by significant early postoperative pain, necessitating effective pain management with minimal side effect. Over the years, various analgesic modalities have been employed, but each comes with its own limitations. Opioids are a commonly used class of oral and intravenous/intramuscular pain medications that provide excellent analgesic control, yet are associated with side effects, such as nausea, vomiting, sedation, constipation and respiratory depression. Non-steroidal anti-inflammatory drugs (NSAIDs) are frequently used as adjuvants alongside acetaminophen, but use is contraindicated in patients with bleeding disorders, gastric ulcers, or renal or liver impairment.

Peripheral nerve blocks have emerged as a highly effective pain management option with minimal side effects. Historically, femoral nerve blocks were used to control pain after knee replacement surgeries; however, the associated motor block delayed patient mobilization and hospital discharge. In contrast, adductor canal blocks (ACB) have demonstrated effective pain relief without causing important quadriceps weakness. While ACB is generally safer, it can be associated with complications such as vascular puncture, nerve injury, and, in rare cases, local anesthetic systemic toxicity (LAST). The use of ultrasound guidance, along with proper technique, significantly reduces the likelihood of these complications.

One limitation of any single-shot nerve block is the variability in the duration of its effect, depending on the local anesthetic used. CACBs address this issue by providing prolonged length for ACB and longer pain control. However, the insertion of CACB catheters carries similar risks to those of single-shot nerve blocks, in addition to the potential for catheter migration outside the adductor canal, which leads to loss of effectiveness. With proper techniques to increase safety and effectiveness, CACB holds great potential as a mainstay of postoperative analgesia for knee arthroplasty patients.

At Mount Sinai Hospital - Sinai Health System, CACB has become standard practice for knee arthroplasty patients. The catheter tip is placed near the saphenous nerve in the mid-thigh region under ultrasound guidance. The ISAFE (Interfascial plane between the SArtorius muscle and FEmoral artery) approach is used for catheter insertion, which has been shown to reduce catheter dislodgement by 26.3% compared to the conventional technique. Another technique for CACB catheter insertion, named OOPS (Out Of Plane parallel to Saphenous nerve), has demonstrated a lower incidence of catheter migration outside the adductor canal when compared to the conventional insertion technique. In the OOPS technique, the catheter is inserted through an ultrasound guided out-of-plane manner, parallel to the saphenous nerve, ensuring that it remains securely within the adductor canal, reducing the likelihood of dislodgement with patient movement.

SIGNIFICANCE Currently, no published studies directly compare the migration rates of the ISAFE and OOPS techniques for CACB catheter insertion. Effective postoperative analgesia promotes early ambulation, accelerating recovery and potentially reducing hospital stays. Techniques that minimize catheter migration can lead to better outcomes, while inadequate pain control remains a significant factor contributing to prolonged hospital stays. Optimized inserted CACB catheters facilitate same-day discharge and may help reduce healthcare costs.

OBJECTIVES The primary objective of this study is to compare the migration rates of CACB catheters when inserted using the ISAFE or OOPS techniques in patients undergoing primary total knee arthroplasty surgery.

The secondary objective is to evaluate postoperative pain, analgesic requirements and catheter-related complications.

HYPOTHESIS Both the ISAFE and OOPS techniques for CACB catheters insertion will result in similar catheters migration rate.

METHODS This will be a prospective, randomized, controlled trial, blinded for both patient and evaluator, which will recruit patients undergoing unilateral primary total knee arthroplasty at Mount Sinai Hospital - Sinai Health System. The recruitment of patients will start after approval from Hospital's Research and Ethics Board. Patients who meet the inclusion criteria will then be approached and informed about the details of the study in simple language. A written consent will be taken if the patients decide to participate in the study.

Perioperative management and interventions:

The subjects will have surgeries booked in advance and the details of the surgical date will be provided at the Pre Admission Unit (PAU) for pre-anesthesia consult a few days before surgery. The details of the study will be explained to the patient and a consent form will be provided for the patient to take home to review. The patients will have at least 24 hours between pre anesthesia consult and the surgery to decide and consent for participation in the study.

The research participants will be randomized to one of the two groups using a computer-generated random numbers table. Randomization will be done at the start of the study and all numbers will be allocated to one of the two study groups:

Interventional group: ISAFE group; Control group: OOPS group. Once the numbers are generated, the method to allocate participants to the respective study intervention will be sequentially numbered opaque sealed envelopes. Every patient will receive a study number following the order of entrance in the study. The researcher who collects the data will be blinded to which group each patient will be randomized to. All patients will receive the same perioperative management with the exception of the CACB catheter insertion technique, which will depend on the assigned group. The sealed envelopes containing details of the insertion technique associated with each number will be prepared at the start of the study. Once the patient is recruited, the professional performing the CACB catheter insertion will open the envelope associated with the number to perform the allocated technique. The list of study numbers and the allocated groups will be kept by the research assistant under password protection and will be shared with other researchers at the end of the study. The research coordinator and the assessor, who performs ultrasound on postoperative day 1 (POD1) for catheter position, will be blinded to the randomization. The person performing the CACB catheter insertion will not be blinded as the professional will need to know which approach to use.

Perioperative management for all the patients will be the same. All the patients will be brought to the block room where a safety check will be performed by the block room team. Standard Canadian Anesthesia Society monitoring will be done. Midazolam 0.5 -2 mg and fentanyl 25- 150 mcg can be administered for anxiolysis and analgesia. The ipsilateral thigh is cleaned with chlorhexidine and alcohol sticks and ACB (15-20 ml of 0.5% ropivacaine with epinephrine 1: 200000) and IPACK block (10-15 ml of 0.25% ropivacaine with epinephrine 1: 200000) will be performed under ultrasound guidance (Sonosite X-port ultrasound machine). Cumulative dosage of ropivacaine will be pre-emptively calculated to be less than 3 mg/kg, and volumes of injected solutions will be adjusted accordingly. All patients will receive spinal anesthesia, after the peripheral nerve blocks. Intraoperatively, the patients will also receive Cefazolin IV (2 g if weight < 120 kg and 3 g if weight > 120 kg), tranexamic acid IV (20 mg/kg), dexamethasone IV (0.1 mg/kg), Ondansetron IV (4 mg). The surgeons will infiltrate the surgical site with 200 mg of 0.2% Ropivacaine at the end of the procedure.

After surgery the patients will be transferred to the Post Anesthesia Care Unit (PACU). In the PACU an Pajunk® (Sonolong® Continuous Peripheral Nerve Block Catheter) CACB catheter will be inserted under sonographic guidance (Sonosite X-port). The CACB catheter will be inserted postoperatively to avoid any displacement due to intraoperative movement or tourniquet inflation and deflation. To rule out intravascular placement of the catheter, 5-10 ml of normal saline with epinephrine 1:200000 will be injected through the CACB catheter after negative aspiration and patient monitored for any heart rate changes. The catheter will be secured using glue and adhesive device to mitigate possible migration. After applying sterile dressing, the catheter will be connected to an elastomeric pump that can deliver Ropivacaine 0.2% at a rate of 5 ml/h, for up to 60 h, as per Mount Sinai Hospital - Sinai Health System practice for CACB. The patients will be discharged home by the orthopedic team, after meeting the discharge criteria, and can go home with the infusion if the patients leave the hospital before completing 48 hours of the infusion. The patients will be educated about monitoring for local anesthetic toxicity, transient muscle weakness and details of removing the catheter after infusion bottle finishes. A printed educational pamphlet containing all the above details will also be provided to the patient at discharge. The pamphlet also contains the contact number of Acute Pain Service (APS), where the patient can contact the anesthesia department in case of any adverse effects or questions about the nerve block catheter. The patients are contacted by a member of the Acute Pain Service team by phone, once daily, for the duration of the infusion. This is already done as a standard of care for all knee arthroplasty patients.

The CACB catheter insertion technique will be according with the group the patient is randomized to.

ISAFE group:

Patient is positioned in supine position, with the hip abducted and the knee slightly flexed. A linear high-frequency transducer is applied in the transverse plane in the mid-thigh area, at the level where the superficial femoral artery (FA) lies underneath the midpoint of the sartorius muscle (SM). The needle is inserted in-plane, coming from lateral to medial, from a point of entry through the skin 2-3 cm lateral to the ultrasound probe. The needle is advanced piercing through the posterior fascia of the SM approximately 1-2 cm lateral to the FA, and entering the adductor canal. The needle angle is then decreased further, and is directed beneath to the posterior fascia of SM. The needle is advanced into inter-fascial space between the FA and SM. Hydro-dissection with saline or Dextrose 5% is necessary for opening up the inter-fascial space and separating the FA from the SM. Once the needle tip has passed the "12 o'clock" position of the FA, a continuous nerve block catheter is inserted through the needle into an antero-medial position to the artery, thereby facilitating over-threading the catheter a small distance.

OOPS group:

Patient is positioned in supine position, with the hip abducted and the knee slightly flexed. A linear high-frequency transducer is applied in the transverse plane in the mid-thigh area, at the level where the superficial FA lies underneath the midpoint of the SM. After local infiltration of skin and subcutaneous, the Tuohy needle is inserted in an out of plane manner, lateral to the FA. After entering the adductor canal, the probe is turned 90 degrees to see the needle in plane. After flattening the needle gently, the catheter is threaded into the canal.

Standard post operative oral analgesic regimen will be prescribed for all the patients, including: Acetaminophen 650 mg QID; Celebrex 100-200 mg BID; Hydromorphone 1-2 mg prn Q4h.

Sample size The sample size was calculated based on two previous studies looking into migration rate for CACB catheters. One study evaluated 97 patients and demonstrated that ISAFE technique results in 18.6% migration rate, while the conventional technique showed an incidence of migration of 44.9%. Another study involved 67 patients, and showed a migration rate of 14.7% for the OOPS technique, in comparison to 72.7% of migration for the conventional technique. If an average estimated migration rate for the tunneled techniques (ISAFE and OOPS) from these two studies (16.65%) is considered and the average migration rate for the conventional technique, from the same studies (58.8%), a sample of 20 subjects in each group would be needed for a comparison between tunneled and conventional, considering alpha of 5% and a power of 80%. Considering this sample of 40 subjects as enough for a study comparing migration rates between two techniques, and the hypothesis for this study is that ISAFE and OOPS techniques are equivalent in terms of catheter migration, a base sample of 40 patients is defined. Considering for possible drop-outs during the study execution, a range of 20% is added, reaching a total of 48 patients (24 in each group).

Study data analysis The normal distributed variables will be described as mean ± standard deviation. The non normal distributed variables will be presented as median (minimum-maximum). Qualitative variables will be described as frequency of occurrence. The statistical tests that will be used are Student t test, Kruskal Wallis and Chi square test. SPSS 13.0 for Windows (SPSS Inc, Chicago, IL, USA) and GraphPad Prism Version 4.00 for Windows (GraphPad Software, San Diego, CA, USA) will be used for statistical analysis.

Inclusion Criteria:

• Non-pregnant patients older than 18 years of age;
• Patients undergoing unilateral primary total knee arthroplasty in an inpatient regime;
• American Society of Anesthesiologist (ASA) physical status Class I - IV patients;
• With sufficient understanding and co-operation about usage of a perineural catheter for pain management;
• With body mass index (BMI) under 45;
• With no history of strong opioid use of more than 30 mg of oral morphine equivalent (OME)/day during the 2 weeks preceding the surgery;
• No alcohol or drug use disorder history;
• With no contra-indication for the performance of ACB and IPACK block;
• With no contra-indication for spinal anesthesia;
• With no contra-indication for CACB catheter insertion (local site infection, systemic infection, anatomical abnormality);
• With no contra-indication for the medications to be used accordingly with the study protocol (ropivacaine, lidocaine, mepivacaine, midazolam, fentanyl, propofol, cefazolin, tranexamic acid, dexamethasone, ondansetron, celecoxib, acetaminophen, hydromorphone);
• Speak and understand the English language;
• Agree to participate on this study through the signature of the consent form.

Exclusion Criteria:

• They have a failed spinal anesthesia and needs for a conversion to general anesthesia;
• The peripheral nerve blocks are not possible to be performed due to technical difficulties;
• A deviation of the protocol occurs (not follow the standardized postoperative analgesia orders; need an emergency re-operation of the same knee, in less than 24 hours, due to a surgical complication; have an important perioperative complication, leading to abnormal level of conscience);
• CACB catheter has issues on its function and needs to be removed before the migration assessment
• Patient decides to withdraw from the study.

Anonymized REDCap data base , after conclusion of the study.

At the conclusion of the study