New Regional Technique Controls Post-TKA Pain
by Michael Vlessides
San Diego—A new nerve block called the “iPACK” may provide an effective option for controlling posterior knee pain following knee replacement surgery.
The brainchild of a research team at St. Francis Hospital and Medical Center in Hartford, Conn., the iPACK is an ultrasound-guided infiltration of the interspace between the popliteal artery and the capsule of the knee with a local anesthetic solution that provides an alternative analgesic when combined with a femoral nerve block.
“Patients who are having total knee arthroplasty [TKA] need something for controlling pain in the back of the knee,” said Sanjay Sinha, MD, director of regional anesthesia at St. Francis and assistant clinical professor of anesthesiology at the University of Connecticut. “The problem with doing a sciatic nerve block is that it causes foot drop, and may mask surgically induced peroneal nerve injury.
“We had a solution where we performed a selective tibial nerve block, which spares the peroneal nerve and seems to work just as well as the sciatic nerve block for controlling pain,” he continued. “The problem with the tibial nerve block is that the sole of the foot is numbed, and approximately 20% of the patients experience weakness in the peroneal nerve distribution from the proximal spread of the local anesthetic, which is undesirable because it can be a marker for nerve injury.”
Dr. Sinha and his colleagues hypothesized that the iPACK would spare the main trunk of the tibial and peroneal nerves and block only the terminal branches innervating the posterior knee joint. Using the method, they scanned the popliteal fossa just proximal to the popliteal crease to visualize the femoral condyles.
The ultrasound probe was then moved proximally until the condyles disappeared and the shaft of the femur became visible. At this level, the needle was inserted in a medial to lateral direction between the popliteal artery and the femur, until the needle tip was 2 to 3 cm beyond the lateral edge of the popliteal artery, the researchers said. They then injected 30 mL of 0.2% ropivacaine with epinephrine as they gradually withdrew the needle.
To determine the safety and efficacy of the iPACK method, the investigators so far have enrolled 14 patients in a pilot study comparing the approach with tibial nerve block. All patients were premedicated with a multimodal analgesic regimen and had a femoral nerve catheter inserted. Patients were then positioned prone, and either an iPACK or tibial nerve block was performed (n=7 in each group). Ultrasound-guided tibial nerve blocks used a maximum of 15 mL of 0.2% ropivacaine.
“We are comparing the presence or absence of foot drop, as well as postoperative pain scores, and opioid consumption,” said Dr. Sinha, who reported the findings at the 2012 annual spring meeting of the American Society of Regional Anesthesia and Pain Medicine (abstract P52).
The researchers observed no statistically significant difference between treatment groups in pain scores in the first 48 hours after surgery, although they trended higher in patients who received tibial nerve blocks. Opioid consumption also was comparable between groups (Table). No patient in either group developed a foot drop.
Table. Median Opioid Consumption
iPACK Group (n=7) Tibial Group (n=7) P-Value
Intraoperative narcotics Hydromorphone, mg 0.60 0.40 0.87
Fentanyl, mcg 100 100 0.56
PACU narcotics Hydromorphone, mg 0.0 0.2 0.46
Floor narcotics POD 1 oxycodone, mg 11.0 17.0 0.49
POD 2 oxycodone, mg 0.0 10.0 0.63
PACU, postanesthesia care unit; POD, postoperative day
As a second part of the study, the investigators also simulated the iPACK technique in two fresh cadavers to determine the spread of injectate. Dissection of the popliteal fossa showed that the dye spread adequately in the tissue plane between the popliteal artery and the posterior knee capsule, sparing the tibial and peroneal nerve.
Although Dr. Sinha noted that the study is in its early stages, he was encouraged by these preliminary results. “It’s a safe procedure,” he added. “It’s quick and easy and works really well.”
Not for Patients With Odd Physiologies
Nevertheless, the iPACK is not for all patients. Dr. Sinha said it would be contraindicated in patients with an anatomic deformity of the knee, such as a cyst or aneurysm of the popliteal artery, and in those in whom the space cannot be well defined under ultrasound. “Otherwise, we’ve been doing it in most of our patients,” he said.
The iPACK also may help relieve surgeons of the responsibility of blindly injecting local anesthetic into the knee joint. “This is a more predictable approach,” said co-investigator Jonathan Abrams. “The reality is we’re asking surgeons to do a blinded procedure, when we don’t even do blinded blocks anymore. And some of the surgeons are uncomfortable; they don’t want to do it. So why should we force them to do something we wouldn’t do ourselves?”
Jeff Gadsden, MD, director of regional anesthesia at St. Luke’s-Roosevelt Hospital in New York City, said the iPACK technique represents a thoughtful solution to a problem that frustrates many orthopedic anesthesiologists: managing the tradeoff between providing targeted analgesia to the posterior knee or minimizing foot drop and missing a diagnosis of nerve injury.
“The sciatic nerve block has always been a somewhat imperfect strategy in this regard,” Dr. Gadsden said. “These results are not only promising, but they intuitively appear safer in that the pericapsular injection is visualized, which is not usually the case when performed by surgeons. I’m very interested to see what effect this has on patient mobility postoperatively compared with a traditional tibial or sciatic nerve block.”
