Results of a small pilot study suggest that infiltration of local anesthetic between the popliteal artery and capsule of the knee (iPACK) may improve pain control after anterior cruciate ligament (ACL) repair. When compared with preoperative femoral nerve or adductor canal block/catheter techniques alone, supplemental iPACK reduced opioid consumption and discharge times in patients undergoing ACL repair at an ambulatory surgery center.
“This study advances the need for a prospective, randomized, double-blinded trial to better assess iPACK efficacy in patients undergoing ACL repair,” said Jillian S. Vitter, MD, an anesthesiology fellow at Ochsner Medical Center, in New Orleans.
As Dr. Vitter reported, approximately 100,000 ACL injuries occur in the United States each year, with the vast majority repaired in outpatient surgery centers. However, uncontrolled postoperative pain can lead to major delays in discharge as well as unanticipated admissions, which increase health care costs.
To target this posterior knee pain while avoiding some of the complications related to sciatic nerve block that impair discharge readiness (e.g., foot drop), Ochsner has been doing the iPACK block in patients undergoing total knee arthroplasty for several years, and recently began performing the block for ACL patients.
What Is an iPACK Block?
For the iPACK block, a patient’s knee is bent and externally rotated at the hip. Similar to a popliteal sciatic block, a curvilinear probe is then placed behind the knee.
“With this block, we think that we’re targeting some of the sensory nerve endings that are coming off of the sciatic nerve,” she added.
Following institutional review board approval, Dr. Vitter and her colleagues retrospectively reviewed the charts for all ACL repairs that took place at the main campus at Ochsner from November 2014 to December 2016. During that time, 19 patients underwent ACL repair and received either a preoperative femoral nerve or adductor canal block/catheter. Of these 19 patients, 11 also received an iPACK block preoperatively with 20 mL of 0.25% ropivacaine with epinephrine, which is Ochsner’s standard for total knee patients, Dr. Vitter noted. All adductor canal and femoral blocks were performed using 0.25% ropivacaine with epinephrine; patients who received bupivacaine or intra-articular injections of local anesthetic and adjuvants, such as ketorolac, were excluded from the study.
As Dr. Vitter reported at the 2017 annual spring meeting of the American Society of Regional Anesthesia and Pain Medicine (abstract 3819), there were no significant differences between the iPACK group and the non-iPACK group with regard to age, sex, body mass index, prior opioid use, intraoperative anesthetic type, femoral versus adductor canal nerve block catheter, local anesthetic volume or ACL graft source. According to Dr. Vitter, most patients in the study had hamstring grafts with or without allograft supplementation.
“Moreover,” Dr. Vitter said, “interquartile ranges showed very little overlap between the two groups, suggesting that there is a true difference, even though it is a small sample size.”
Finally, patients in the iPACK group met the criteria for home discharge sooner and had statistically significant shorter ambulatory surgery center discharge times compared with the non-iPACK group.
“Patients who received an iPACK met criteria for readiness at a median of 131 minutes compared to 199 minutes in the non-iPACK group,” Dr. Vitter said. “A difference of one hour and eight minutes is pretty significant if you’re in an ambulatory surgery center and trying to get patients out the door quickly.”
Dr. Vitter and her colleagues are currently enrolling patients in a randomized controlled trial with iPACK for total knee arthroscopy, and intend to do the same for ACL repair.
Samer Narouze, MD, PhD, clinical professor of anesthesiology and neurological surgery at Ohio University, in Athens, and the Ohio State University, in Columbus, and chairman of the Center for Pain Medicine at Western Reserve Hospital, in Cuyahoga Falls, Ohio, asked whether selection bias might have influenced these results.
“This is just a retrospective chart review, so there could definitely be selection bias,” Dr. Vitter said. “Whether or not a patient got iPACK was somewhat attending-specific. Some attendings performed it for everyone, while others didn’t. It was just luck of the draw for whoever was staffing that day.”