Adductor Canal Block (ACB) provides Adequate Postoperative Analgesia in Patients Undergoing Total Knee Arthroplasty (TKA): Case Report

1. BACKGROUND

Osteoarthritis (OA) of the knee is one of the leading causes of disability among adults older than 65 years. End-stage arthritis of the knee is best managed with total knee arthroplasty (TKA) [1]. Pain is typically more severe after total knee replacement. Effective postoperative multimodal analgesia facilitates early physical rehabilitation to maximize the postoperative range of motion and prevent joint adhesions following knee replacement. It is important to balance pain control with the need for an alert and cooperative patient during physical therapy [2]. The approach to anesthetize the saphenous nerve within the adductor canal has been long entertained to provide analgesia to the medial aspect of the ankle and foot. However, the concept of using this block for TKA is a fairly recent innovation [3]. A saphenous nerve block has been reported as a supplement to multimodal analgesia protocols in knee replacement surgery patients. A more proximal (mid-thigh) approach and a larger volume of local anesthetic are used for this adductor canal block. The use of ultrasound (US) guidance has improved the success rates of saphenous blocks compared with field blocks below the knee and blind trans-sartorial approaches [4].

2. CASE

3. DISCUSSION

Following the introduction of Enhanced Recovery After Surgery (ERAS) by Henrik Kehlet in 1997, postoperative analgesia aims at facilitating early mobilization and rehabilitation, thereby enhancing recovery and minimizing postoperative morbidity [5]. The adductor canal block (ACB), also known as a saphenous nerve block, is predominantly a sensory block with only the motor nerve to the vastus medialis of the quadriceps muscle traverses the adductor canal [6]. The theoretical advantage of preserving quadriceps muscle strength provides better ambulation ability than traditional neuraxial or femoral nerve blocks (FNB), making it an alternative modality for postoperative analgesia in TKA [7-9]. A recent systematic review also suggested that ACB decreases opioid requirements when compared to placebo [7]. As the number of patients aged over 80 years undergoing TKA has been on the rise, decreasing opioid and other NSAIDs requirements by using ACB will be beneficial in reducing complications caused by these medications in the elderly [10].

ACB aims to have local anesthetic spread lateral to the femoral artery and deep to the sartorius muscle or more distal below the knee, adjacent to the saphenous vein [4]. The target is the two largest sensory contributors of the femoral nerve to the knee, the saphenous nerve and the branch of the vastus medialis, but also the terminal end of the posterior branch of the obturator nerve as it enters the distal part of the adductor canal [6]. The saphenous nerve is a terminal sensory branch of the femoral nerve. It supplies innervation to the medial aspect of the leg down to the ankle and foot. It also sends infrapatellar branches to the knee joint. The ACB results in anesthesia of the skin on the medial leg and foot [4].

Several studies have compared the effectiveness between ACB and FNB in the setting of TKA, and found that ACB is superior to FNB regarding sparing of quadriceps strength and faster knee function recovery, albeit not inferior to FNB regarding pain control or opioid consumption [11, 12]. However, Lim et al. found no statistically significant differences in analgesic effects, quadriceps strength, or functional recovery postoperatively between ACB and FNB [13]. This may be because of the fact that although the saphenous nerve block is a sensory block, an injection of a large volume of local anesthetic into the subsartorial space can result in a partial motor block of the vastus medialis due to the block of the femoral nerve branch to this muscle, often contained in the canal [4].

Nevertheless, no single regional anesthesia technique can provide ideal analgesia, especially without any motor weakness after TKA [14]. Some patients will not achieve adequate posterior knee analgesia as ACB pain relief is primarily limited to the anterior capsule of the knee [6, 14]. Infiltration between the Popliteal Artery and Capsule of the posterior Knee (IPACK) and genicular nerve block (GNB) combined with ACB has been studied to cover this problem with promising results [14, 15]. Combined ACB and local infiltration analgesia (LIA) also showed enhanced early ambulation with reduced and delayed rescue analgesia after TKA [16]. Both patients did not report any postoperative posterior knee pain for up to 48 hours in this report.

In ACB, the saphenous nerve can be blocked by up to 30-mL volume of a local anesthetic to provide moderate postoperative pain relief after knee surgery [17]. In general, the duration of action is affected by the concentration of the local anesthetic and the volume injected. Duration of action can also be prolonged with additives. However, there is still no unified agreement on choosing the best agents for ACB [18]. Nader et al. reported effective pain management in the postoperative period after TKA using 10 mL of bupivacaine 0.25% with epinephrine 1:300,000 [19]. Grevstad et al. reported that using 30 mL of ropivacaine 0.2% for ACB resulted in a mean VAS reduction of 32 mm during active flexion of the knee [6]. These findings were in line with this case report, where 20 ml of bupivacaine 0,25% provided adequate pain relief in both patients.

Regarding the optimal timing for ACB in TKA, Poonet al. compared the outcome between performing ACB at the post-anesthesia recovery unit (PACU) and before inducing general anesthesia. Despite no differences in opioid consumption, the latter resulted in a better intraoperative hemodynamic state [20]. In this report, ACB in TKA provided adequate postoperative analgesia.

CONCLUSION

Adductor canal block can be used to optimize multimodal analgesia by reducing opioid requirements and enhanced recovery after TKA. Further study about the use of ACB in TKA is needed to establish the effectiveness of this technique.

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