Coordinated efforts with major medical organizations are being made to decrease opioid prescriptions and exposure [5, 6]. To our knowledge, no study has quantified a decrease in opioid requirement in a VA population after implementation of a protocol including intraoperative spinal anesthesia and a postoperative multimodal analgesic regimen including adductor canal block after TKA. The analgesic protocol described in this study aligns with recommendations from both the CDC and the AAOS to decrease opioid use and abuse by maximizing non-opioid medications and limiting the size and number of opioid prescriptions. However, it is important to note that public and medical opinion of opioids, as well as prescribing practices, have changed over time with a trend toward lower opioid utilization. The interventions, as part of the described protocol, are a result of these changes and attempt to minimize opioid use while maximizing postoperative analgesia.
Our data showed a significant decrease in total opioid requirement through POD 1, IV opioid requirement, and opioid prescriptions provided at the first postoperative visit. The Protocol group required only 6.7% of the intravenous opioids and 30.9% of the total opioids required by the Traditional group. This substantial difference in intravenous opioid requirement, 166.2 MED, is equivalent to 8 mg of intravenous hydromorphone or 55 mg of intravenous morphine. The difference in total opioid requirement was similar at 166.9 MED, equivalent to 111 mg of oral oxycodone.
Decreasing opioid use has the additional benefit of improving outcomes, as higher doses of opioids have been associated with increased length of stay, greater rates of DVT, and postoperative infection . These complications occurred in a stepwise manner, suggesting a dose-response gradient that makes the sizable decrease noted in our data of greater relevance . While the side effects of opioids are well known, there are limited data on opioid dosing and its effect on perioperative outcomes .
A significant decrease in the percentage of patients receiving an opioid prescription at the first postoperative visit suggests a decrease in the number of patients on prolonged opioids after TKA with implementation of modern analgesic modalities. The duration of postoperative opioid use has been found to be the strongest predictor of misuse, and each postoperative refill increases the probability of misuse by 44% . In addition, opioid use for greater than three months after TKA is associated with increased risk of periprosthetic infection, increased overall revision rate, and stiffness at one year postoperatively . While not entirely under the control of the surgeon, measures to decrease the number of postoperative opioid refills may lead to a decrease in opioid misuse.
In the Traditional group, older patients tended to receive less opioids. This is likely explained by physiologic changes in opioid metabolism associated with aging. These include decreased renal and hepatic opioid metabolism and alterations in overall body composition, which increase relative potency and duration of action of opioids in the elderly [21, 22]. No difference in opioid utilization by age was found for the Protocol group. This suggests that opioid utilization was at a level low enough that age differences in opioid metabolism did not result in a difference in opioid utilization.
Patients in the Protocol group demonstrated significantly greater maximal knee extension on POD 1 compared to the Traditional group. No difference in maximal flexion was found. This difference in extension may partially be explained by the use of an ACB. One benefit of ACB is greater quadriceps strength and less near fall events when compared to femoral nerve block [11, 15].
Our results corroborate the findings of similar studies. A randomized controlled trial comparing a multimodal analgesic regimen with a periarticular injection without a postoperative ACB to a hydromorphone PCA revealed a significant decrease in opioid use in the multimodal analgesic group . Along with lower opioid requirements, the multimodal analgesic group had lower visual analog scale (VAS) pain scores, fewer adverse effects, faster progression to physical therapy milestones, and higher satisfaction .
In our study population, patients receiving the multimodal analgesic regimen were significantly more likely to discharge to home rather than a post acute care (PAC) facility. This is pertinent as discharge to PAC facilities has been associated with increased rates of major complications, 30 day readmission, and 30 day reoperation [25, 26]. In addition, discharge to an inpatient rehabilitation or skilled nursing facility has not been found to result in higher functional outcomes, despite $3.2 billion dollars being spent yearly on rehabilitation services after primary TKA [27, 28].
A unique aspect of our study is the continuation of the ACB catheter through the time of hospital discharge. The catheter is removed on POD 5 by the patient. Discharging with the ACB catheter allows the benefit of the local anesthetic to be continued through the fifth postoperative day and may result in decreased opioid use after discharge. This may play a role in the lower refill rates at the first postoperative clinic visit, but data on opioid use after discharge was unavailable in this study.
A component of our described analgesic protocol included spinal anesthesia intraoperatively. The differences between groups in regards to anesthesia type can be attributed to this protocol change. A significantly greater percentage of patients in the Protocol group received spinal anesthesia, while more patients in the Traditional group received general anesthesia. While patients who received spinal anesthesia may have enhanced analgesia in the immediate postoperative period, no differences in opioid outcomes were seen based on anesthesia type. Known benefits of intraoperative spinal anesthesia include decreased perioperative blood loss and a smaller decrease in hemoglobin postoperatively, as well as lower rates of in hospital complications including PE, pneumonia, cerebrovascular events, and acute renal failure .
One limitation was a protocol change regarding length of stay. This occurred during the study period and resulted in a significantly shorter length of stay in the Protocol group. Because of this, opioid use data were analyzed only through midnight at the end of POD 1. Patients who discharged on POD 1 did not have opioid use data available for the full duration of the first postoperative day. This difference may exaggerate the decrease in opioid requirements, as opioids used after discharge but prior to midnight on POD 1 were unable to be recorded. However, opioids taken at home are oral opioids with a low MME compared to intravenous opioids received by the Traditional group who remained hospitalized. In addition, if taken as prescribed, patients at home would only have enough time to take a few doses of opioids prior to the midnight cutoff. We do not believe this difference in time of opioid use creates any meaningful effect on the data. Other limitations include a lack of pain scores to compare each group’s subjective rating of pain, the retrospective nature of the study, and a largely homogenous male VA population.