Extending the duration of adductor canal blocks after total knee arthroplasty may improve pain control without compromising functional outcomes or delaying discharge.
Results of a prospective, randomized, open-label study show that a higher proportion of patients randomly assigned to 48-hour infusion experienced milder pain after total knee arthroplasty when compared with a single-shot injection and 24-hour infusion. Moreover, improvements in pain scores came without adversely affecting physical therapy performance parameters, the authors noted.
“Extending the duration of our adductor canal block catheter infusions up to 48 hours might benefit patients and place more patients in a minimal pain group,” said Lu Fan Cai, MD, assistant professor of clinical anesthesiology and critical care at the Perelman School of Medicine at the University of Pennsylvania, in Philadelphia. “What’s more, block duration had no effect on physical therapy or readiness for discharge. Based on these results, we’ve actually extended adductor canal block for total joints at our institution from 24 hours to 48 hours.”
As Dr. Cai reported, studies examining adductor canal catheters versus placebo have shown a reduction in opioid consumption at 48 hours (Anesth Analg 2014;118:1370-1377). Adductor canal block for analgesia also has emerged as an alternative to femoral nerve block. In a randomized trial examining discharge readiness after tricompartment knee arthroplasty, continuous adductor canal block demonstrated reduced time until adequate mobilization compared with continuous femoral nerve block (Anesthesiology 2015;123:444-456).
“Adductor canal catheters offer the advantage of sparing the motor nerve supply to most of the quadriceps muscle, which may facilitate physical therapy after total knee arthroplasty and may lead to reduction in falls after surgery,” Dr. Cai said, “but the ideal duration for the block remains unclear.”
Three Treatment Groups
To determine the optimal duration of maintenance of the adductor canal catheter, Dr. Cai and his colleagues enrolled 160 patients scheduled for primary total knee arthroplasty. All mentally competent and consenting patients of ASA physical status class I to III were included in the study. Patients were excluded from the study if they had allergies to the study medication, revision surgery, impaired kidney functions, coagulopathy, chronic pain syndromes or a body mass index greater than 40 kg/m2.
The researchers randomly assigned patients to one of three groups: single-shot injection (up to 20 cc of 0.5% ropivacaine); 24-hour infusion; and 48-hour infusion.
Primary anesthetic was up to the discretion of the anesthesiologist involved, Dr. Cai said, and the majority of anesthesiologists used a spinal anesthetic with hyperbaric bupivacaine. All patients received medications as per multimodal perioperative pain protocol in the patient receiving area (400 mg of gabapentin, 200 mg of celecoxib and 1 g of acetaminophen). Patients also received prophylaxis for postoperative nausea and vomiting during surgery.
Pain scores were self-reported at intervals up to postoperative day 2. The study’s primary end point was the percentage of patients with severe pain (7%-10%) on postoperative day 2. Secondary end points include assessment of the analgesic and physical therapy outcomes between the three groups.
As Dr. Cai reported at the 2017 annual spring meeting of the American Society of Regional Anesthesia and Pain Medicine (abstract 3425), analysis between the three study groups showed no significant difference in the proportion of patients with severe pain on postoperative day 2. However, on postoperative day 2, the 48-hour group had a lower percentage of patients with moderate pain scores (4%-6%) and a significantly higher proportion of patients with mild pain scores (0%-3%), the researchers reported.
In addition, said Dr. Cai, opioid requirements on postoperative days 1 and 2 showed no difference between groups. Functional recovery as measured by ambulation distance and Tinetti scale for gait and stability also were statistically similar in the three groups.
According to Daniel Sessler, MD, the Michael Cudahy Professor and Chair of the Department of Outcomes Research at the Cleveland Clinic, in Ohio, “it would be interesting to note the results of pain scores during physical therapy, because that’s important and not necessarily the same outcome.
“Also, some people might say that these are fairly subtle differences,” Dr. Sessler continued. “The distinction here is between statistical significance and something that will result as clinically important.”