As more and more total knee replacements and anterior cruciate ligament reconstructions shift to the outpatient setting, a novel regional anesthesia technique called an adductor canal block has emerged to help manage pain for days. The block can reduce the need for opioids, and facilitate early post-operative ambulation and rehabilitation. And when augmented with a continuous catheter and infusion pump, you can extend its effective duration for several days, providing high-quality pain control during the peak period of post-surgical inflammation. In our practice, we leave adductor canal catheters in for up to 4 full days.
'Best analgesic protocol
for knee arthroplasty'
Similar to traditional femoral nerve blocks, adductor canal blocks provide rapid-onset analgesia. But unlike femoral blocks, they spare the quadriceps so the leg can maintain motor strength. They carry the same very rare risks as other nerve blocks, such as nerve injury and local anesthesia toxicity, but a nerve injury that occurs with an adductor canal block is likely to be a sensory neuropathy, as opposed to the quadriceps weakness and atrophy that can result from a femoral nerve injury.
A recent study (osmag.net/nJU5nT) by Stanford's Christopher Webb, MD, and Edward R. Mariano, MD, concludes that "when not contraindicated, intraoperative neuraxial anesthesia combined with a continuous adductor canal block and a multimodal medication regimen for post-operative pain control is the best analgesic protocol for knee arthroplasty."
The block is performed with an injection of local anesthetic at the mid-thigh. The anatomical boundaries of the adductor canal are the sartorius muscle medially, the vastus medialis anterolaterally and the adductor magnus (and femoral artery and vein) posteriorly. The technique would be very challenging to perform solely with landmarks, but with high-frequency ultrasound and a little practice, you can easily visualize the muscles, vessel landmarks, needle and injected local anesthetic.
The canal contains several nerve branches that provide sensory innervation to the knee, including the saphenous nerve, the nerve to vastus medialis and the posterior branch of the obturator nerve. The saphenous nerve is probably the most important, but the total analgesia is likely due to the cumulative effect of blocking all 3 branches. That's why it's not simply called a "saphenous nerve block" when it's used for knee analgesia.
NEW POST-OP OPTION
Thanks to a recent FDA approval, multimodal pain strategists have another player to consider — an injectable NSAID that reduces opioid consumption when given post-operatively.
Dyloject (diclofenac sodium), manufactured by Hospira, also adds a level of convenience. It can be administered in a small-volume intravenous bolus over 15 seconds, versus the 15 to 30 minutes that can be needed to administer full doses of other injectable non-opioid analgesics.
In 2 controlled studies, patients who'd had abdominal/pelvic surgery or orthopedic surgery had lower pain scores and were less likely to require rescue medication (IV morphine) after being given Dyloject. In the abdominal/pelvic group, 63% of patients took rescue medication in the first 48 hours after surgery, compared with 92% of those given a placebo. The corresponding numbers were 74% and 92% for the orthopedic patients.
Dyloject won't replace opioids, as the manufacturer is quick to point out, but it's one more way to help minimize their use.
How it's done
Here are the steps I use to place non-stimulating adductor canal catheters pre-operatively, using a catheter-through-needle approach and ultrasound guidance. The entire procedure typically takes less than 10 minutes to perform.
- I sterilely prep the mid-thigh region widely with chlorhexidine and then apply a clear plastic drape with the adhesive fenestration placed where the needle will be inserted.
- The block nurse hands me my ultrasound probe, which I grasp through the plastic drape, thus maintaining a separate non-sterile field (probe) and a sterile field (needle insertion site).
- With ultrasound, I identify the most important landmarks: the deep border of the sartorius muscle, the femoral artery, and, if possible, the saphenous nerve (not always clearly visible in all patients). The goal is to place the needle tip and local anesthetic adjacent to the saphenous nerve in the space deep to sartorius muscle and antero-lateral to the femoral artery.
- Having identified this space in the short axis, I rotate my probe 45 degrees to achieve an oblique view of the adductor canal. This accomplishes 2 goals. First, it forces my needle insertion to be a little more proximal in the thigh and therefore not below the expected lower margin of the tourniquet (if the insertion is 3 hands' breadths above the patella, you can safely ensure you are above the lower margin of the tourniquet). Second, it lets the catheter eventually be threaded down (parallel to) the adductor canal, especially if the curved Touhy bevel is rotated to face down the thigh.
- After placing a small lidocaine skin wheal with a 25g needle, I insert an 18g Touhy needle several centimeters away from the transducer in-plane and obliquely towards the canal. The blunt Touhy needle passes through the sartorius muscle and when it penetrates the deep border of the sartorius, I can usually feel a distinct pop.
- I then have the block nurse inject several milliliters of local anesthetic to confirm that I am in the canal. If I've succeeded, I'll see the anesthetic spread and open up the canal by pushing the sartorius more superficially, the vastus medialis more deeply and the femoral artery postero-medially away from the injection. Often I'll also see the saphenous nerve move away from the injection, although this isn't necessary to achieve a successful block.
- Depending on the quality of the spread, I bolus up to 20 ml of 0.25% bupivacaine. But we've demonstrated that as little as 10 ml can result in adequate spread throughout the adductor canal (bit.ly/blockjockscadaver).
- I rotate the needle 90 degrees so the Touhy bevel faces down the leg. Then I thread the catheter 3 to 4 centimeters down the canal. Resistance should be minimal during threading. Keep in mind that significant resistance usually means the catheter is obstructed and coiling, instead of threading.
- As I remove the Touhy needle, I advance a few extra centimeters of catheter slack to further prevent dislodgement with future leg movement. Ultimately the catheter depth marking at the skin will be between 10 to 15 centimeters.
- I perform a test dose injection with 3 ml of 1.5% lidocaine with 1:200,000 epinephrine and use ultrasound visualization to confirm proper extravascular catheter tip location in the adductor canal.
- Lastly, I wipe the ultrasound gel off the leg, apply liquid adhesive widely, apply skin sealant to the insertion site to reduce leakage, coil the catheter around the insertion site, apply several steri-strips, and apply a large clear plastic dressing to ensure that the lower margin of the dressing remains proximal to the eventual lower margin of the tourniquet and avoids interfering with the surgeon's sterile field.
At what point do patients emerge from anesthesia? The somewhat ambiguous answer to that question recently helped save a large anesthesia group from what might have been a very costly legal decision.
The crux of a False Claims Act brought by a former employee and joined by the federal government was the assertion that Anesthesia Associates of Kansas City (Mo.) (AAKC) had defrauded Medicare by consistently billing at the "Medical Direction" rate, rather than at the lower "Medical Supervision" rate.
The allegation hinged on the fact that AAKC's anesthesiologists, who typically rotated among up to 4 operating rooms at the same time, were rarely in ORs when procedures were completed and patients were transferred to recovery. Instead, AAKC assigned a CRNA to each patient and the CRNAs typically transferred the patients to recovery, where anesthesiologists checked on them later. The key: To qualify for the Medical Direction rate, anesthesiologists directing CRNAs have to satisfy 7 conditions, including "personally (participating) in the most demanding aspects of the anesthesia plan, including, if applicable, induction and emergence."
If anesthesiologists aren't present when procedures are completed and patients are taken out of the OR, the former employee argued, then they aren't present for "emergence," at least as its meaning is widely understood and accepted in the medical community.
AAKC countered that emergence is a process. It begins in the OR, they said, but it extends into recovery, and different patients emerge from anesthesia at different rates. By checking on patients in recovery, it argued, its anesthesiologists satisfied that requirement.
Searching for a definitive definition of emergence, a U.S. District Court found none. That lack of clarity, it said, meant that AAKC's interpretation of the rule, while "opportunistic," was nonetheless plausible. So it dismissed the case.
Interestingly, however, the court may have nudged open the possibility of another complaint by acknowledging that the failure of anesthesiologists to be present during extubation might have made a more compelling argument that they weren't "personally (participating) in the most demanding aspects" of cases. But the former employee raised that issue too late in the legal process for it to be considered in this case.