Adductor Canal Block for Total Knee Arthroplasty

Postoperative analgesia for total knee arthroplasty (TKA) is incredibly important as it allows for effective physical therapy and ultimately ensures proper function of the implanted joint hardware. Unfortunately, TKA is oftentimes associated with pain severe enough to limit participation in physical therapy which can ultimately result in prolonged hospitalizations and perhaps decreased joint function. A number of strategies have been reported to decrease the pain associated with TKA. Opioids are commonly utilized but they can be associated with a number of potential side effects including nausea, itching, respiratory depression, tolerance and the potential for abuse. Epidural analgesia has been utilized for postoperative analgesia but this strategy requires urinary catheterization (potential source of increased incidence of urinary tract infections), causes significant vasodilation with resulting hypotension and can cause bilateral lower extremity weakness that can undermine efforts at early physical therapy and rehabilitation. Femoral nerve blockade and femoral nerve catheters have the potential to decrease pain in the anterior knee but use of this technique is limited by incomplete analgesia and quadriceps motor weakness. Some groups have advocated for the substitution or addition of sciatic or obturator nerve blocks to femoral nerve blockade but this is at the expense of increased lower extremity weakness and little potential clinical benefit.1-5

In an effort to balance the need for effective postoperative analgesia with the need to maintain lower extremity muscle strength for active participation in physical therapy, a number of groups have begun to evaluate the adductor canal block. The adductor canal is located in the middle 1/3 of the thigh and includes the saphenous nerve and nerve to the vastus medialis. The primary advantage to adductor canal blockade versus femoral nerve blockade is a potential sparing of the nerves to the quadriceps muscle and therefore preservation of lower extremity motor strength.6-8 Kwofie et al reported in a study of 16 volunteers that there was no change in quadriceps strength or hip adduction following the injection of 15 ml of local anesthetic. This is interesting as the obturator nerve is reported to travel within the adductor canal and is responsible for hip adduction. Kwofie et al also reported that SSACNB resulted in significantly decreased impairments with balance compared to a SSFNB.9

To this point, the majority of studies evaluating adductor canal blockade have focused on continuous techniques and little has been done to evaluate single shot techniques. Continuous techniques have the potential to extend analgesia but this is at the expense of increased cost, effort, resource utilization and potentially increased risk of infection.

The safety of CACNB technique was highlighted by a study by Henningsen et al where no cases of nerve injury related to analgesic technique were reported in a series of 97 patients.10 Andersen et al compared a CACNB vs control in 40 patients and found that the intervention group reported decreased pain and sleep disturbances while retaining the ability to ambulate soon after surgery.11 Mudumbai et al evaluated 180 patients undergoing TKA and discovered that continuous adductor canal nerve blockade (CACNB) relative to continuous femoral nerve blockade (CFNB) resulted in greater ability to ambulate (37 m vs 6 m) on POD 1 and similar pain scores.8 Jaeger et al examined a similar group of 54 patients presenting for TKA and found that CACNB relative to CFNB resulted in decreased quadriceps weakness and no difference in pain, opioid consumption or weakness.12 Jenstrup et al reported that, compared to placebo, CACNB resulted in decreased pain with flexion and opioid consumption.13 Only recently has a study comparing SSACNB and SSFNB been published. This study demonstrated that SSACNB resulted in decreased postoperative quadriceps weakness and similar pain control to SSFNB.14 Of interest, previous research has demonstrated that 15 ml 0.5% ropivacaine is required to produce ultrasound guided femoral nerve blockade (including sensory and quadriceps motor weakness) but no such study has yet been done for the adductor canal block.15 It is possible that larger volumes of local anesthetic injected into the adductor canal could result in proximal spread of local anesthetic and increase quadriceps weakness and difficulty ambulating. It is also possible that decreased volumes of injection may result in inferior pain control and difficulties participating in physical therapy.