Inter-fascial Plane Between the SArtorius Muscle and FEmoral Artery (ISAFE): a Novel Technique for Adductor Canal Catheter Insertion.

Introduction Total knee arthroplasty (TKA) is an effective treatment for end stage osteoarthritis, with over 75,000 TKA performed in Canada annually (https://www.cihi.ca/en/hip-and-knee-replacements-in-canada-cjrr-annual-report) and an incidence rate of 135 per 100000 of population, among OECD countries, in 2017 (https://www.oecd-ilibrary.org/sites/2fc83b9a-en/index.html?itemId=/content/component/2fc83b9a-en). Historically, TKA has been associated with a significant level of postoperative pain, which can be a barrier to an early discharge. In order to optimize analgesia and minimize opioid consumption and its associated side effects, regional anesthesia techniques traditionally used for TKA include peripheral nerve blocks such as femoral and adductor canal blocks (ACB). These blocks typically provide superior analgesia by anesthetizing peripheral nerves that supply sensory innervation to the surgical site. Specifically, the ACB is of great value as it does not cause the quadriceps weakness motor block that the femoral nerve block provides, thereby facilitating early patient mobilization and discharge. An even newer technique has also emerged called the IPACK (infiltration between the popliteal artery and capsule of the knee), which has been used in some centers to replace sciatic blocks to cover posterior knee pain experienced by many TKA patients, without affecting motor function of the lower leg and foot. Recently, continuous adductor canal blocks (CACB) via an inserted adductor canal catheter (ACC) have started to replace single injection blocks, as they extend the block duration and offer prolonged analgesia. Studies evaluating CACB have it to be superior when compared to single-injection adductor canal block (SACB) for inpatients post-TKA analgesia. Currently at Sinai Health, CACB has become the standard of care for inpatient TKA with all patients routinely being offered this analgesic modality.

Placing a successful ACC is not without risk or technical difficulty. The classic insertion approach involves placing the tip of the ACC near the saphenous nerve in the mid-thigh area. The proximity of the femoral artery (FA) and femoral vein (FV) to the saphenous nerve adds the risk of vascular puncture and intravascular placement of the ACC. Specifically, the FV is deeper and more difficult to visualize as it is compressible, and can be easily punctured if the needle is manipulated in its proximity. Intravenous placement of an ACC will result local anesthetic systemic toxicity (LAST), a potentially lethal albeit very rare complication, and therefore effort should be made to avoid this at all costs. Lastly, a more common obstacle when placing ACC is ensuring that the catheter stays inside the adductor canal. Since the adductor canal itself is very narrow, the catheter tip can easily migrate out of the canal with patient movement and mobilization, resulting in no sensory block and inadequate analgesia. It is not uncommon for patients to initially have well working CACB, but to experience significant rebound pain on postoperative days (POD) 1 or 2 due to catheter dislodgement out of the canal.

In order to address these issues we have developed a novel insertion approach for ACC is inserted into the inter-fascial plane between the Sartorius muscle and femoral artery (ISAFE). In this technique, the needle is inserted into the plane between the sartorius muscle and FA. A catheter is then threaded between the artery and muscle, well away from the FV. This facilitates keeping the needle away from the vein and maintaining more catheter length inside the adductor canal, thereby preventing catheter dislodgement. The insertion angle of the needle is shallower when compared to the classic ACC technique, allowing for better needle visualization, and steering clear of the FV. While the needle is still in close proximity to the FA, this vessel is easier to visualize, more difficult to puncture, and is much less likely to result in LAST.

While the ISAFE technique is an exciting novel approach for ACC insertion, it still requires evaluation in terms of analgesia efficacy and superiority in terms of reducing catheter dislodgement.

Significance There are no published prospective randomized controlled trials that compare insertion techniques for ACC and their respective outcomes in terms of catheter positioning, dislodgement, and safety. As TKA is a frequent type of surgery and has the prediction to increase its incidence for the next years, there is significant importance in investigations about interventions which may improve its recovery in an outpatient regime. A postoperative analgesic technique that offers better pain control, has less adverse effects, reduces the opioid analgesia requirement and is safe may have additional impact on decreasing health care cost and may lead to an enhanced recovery and better quality of life.