A Comparison Between Continuous Selective Femoral Blocks and Continuous Adductor Canal Blocks at Mid-Thigh in Total Knee Arthroplasty: What is the Best Method to Optimize Functional Achievement and Analgesia in Early Rehabilitation?

Recently, several articles have suggested or reported that Adductor Canal Blocks (ACBs) offer adequate or equal analgesia and may promote better performance in early rehabilitation following Total Knee Arthroplasty (TKA) when compared to the more commonly used Femoral Nerve Block (FNB). A common feature of these studies has been the use of moderate to high concentration local anesthetics (e.g. 0.2% or 0.5% Ropivacaine respectively) which when injected by a large motor nerve will inevitably cause weakness. However, the practice at our institution has long been a continuous femoral nerve block (CFNB) with a lower concentration local anesthetic (0.0625% Bupivacaine). Over the past several years the investigators have performed several thousand CFNBs using this technique which has offered the advantage of minimal motor weakness and adequate analgesia.

The primary goal of this study is to determine if our established practice of using a low concentration continuous FNB inserted about 5cm caudal to the groin crease (the apex of the femoral triangle) using a low infusion rate of 2ml/hr is comparable to the emerging practice of inserting a Continuous Peripheral Nerve Block (CPNB) in the anatomic adductor canal (AC) - infusing at 4ml/hr. A secondary goal is to study the effect of cumulative volume of local anesthetic infused through a FNB when at a rate of 2ml/hr compared to a rate of 4ml/hr in the 48-hour postoperative period.

Definitions of the location of the adductor canal are debated heavily in literature, but they seem to agree that the middle 1/3 of the thigh contains the proximal AC while the distal 1/3 of the thigh contains the adductor hiatus - the terminal end of the AC. Our study will require placement of the continuous ACB no more distal than 20cm cephalad to the superior pole of the patella due to placement prior to surgery and the need to keep the dressing out of the operative field. The CACB catheter will also not be placed any more proximal than 20cm distal to the ASIS. In addition to other exclusion criteria, these measurements will create an exclusion for patients with an iliac-to-patella distance less than 40cm. Iliac to Patella distance (IPD) will be measured at the pre-operative interview on the day of surgery with a measuring tape. External palpable landmarks of the Anterior superior iliac spine and the superior pole of the patella will be used.

The primary outcome is based upon the ability to perform rehabilitation exercises postoperatively to the extent that criteria for discharge can be met. The primary outcome measured is the time at which a patient gains the ability to successfully perform a 75-feet unassisted walk. On the Day of Surgery (DOS), prior to any walking attempt, a secondary outcome measure will be to perform a 5-second sustained straight leg raise. Other secondary outcomes will be the number of days admitted prior to discharge, and average pain scores on DOS, Postoperative Day (POD) #1, and POD#2. The Day of discharge will also be used as a secondary outcome. Earlier discharge is becoming a goal of almost all healthcare systems to minimize costs.