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.

Inclusion Criteria:

1. The subject is scheduled for elective unilateral TKA

2. The subject is ≥ 18 years and ≤ 80 years;

3. The subject's weight is between 70-120 kg; and

4. The subject's primary anesthesia care team has planned for a neuraxial anesthetic
(i.e. spinal, epidural or combined-spinal epidural).

5. The patient agrees to receive an adductor canal block.

6. American Society of Anesthesiologists class 1-3

Exclusion Criteria:

1. Subject is < 18 years of age or >80 years of age;

2. Subject is non-English speaking;

3. Subject is known or believed to be pregnant;

4. Subject is a prisoner;

5. Subject has impaired decision-making capacity; per discretion of the Investigator

6. Symptomatic untreated gastroesophageal reflux or otherwise at risk for perioperative
aspiration;

7. Any condition for which the primary anesthesia care team deems neuraxial anesthesia
inappropriate;

8. Significant pre-existing neuropathy on the operative limb;

9. Significant renal, cardiac or hepatic disease per discretion of the investigator.

10. American Society of Anesthesiologists class 4-5

11. Known hypersensitivity and/or allergies to local anesthetics

12. Chronic Opioid Use (daily or almost daily use of opioids for > 3 months)