Abstract
Introduction
The prescription of opioids has increased in the last two decades. Recently, several states have developed online Prescription Drug Monitoring Programs aimed at preventing overprescribing of controlled substances. Unicompartmental knee arthroplasty (UKA) has been shown to provide improved early functional outcomes, faster recovery, and less postoperative morbidity and pain than total knee arthroplasty (TKA). The aim of this study is to evaluate differences in opioid prescription requirements between patients undergoing TKA and UKA.
Methods
We retrospectively reviewed consecutive series of primary TKA from January 2017 to July 2017 and primary UKA from January 2016 to July 2017 using standardized perioperative pain protocols. All patients that underwent any other procedure 6 months prior to and after index surgery were excluded, resulting in 740 TKA and 241 UKA. Demographic and comorbidity information was collected for all patients. Opioid prescriptions, morphine milligram equivalents (MME), sedatives, benzodiazepines, and stimulants were collected from State Controlled Substance Monitoring website 6 months prior and after index procedures. Univariate and multivariate analysis were performed for patients that had a second prescription and continued use (defined as more than 6 months postoperatively).
Results
Patients undergoing UKA had a second opioid prescription filled 50.2% of the time compared to 60.5% for TKA (p=0.006). In addition, continued opioid use after 6 months was 8.3% in UKAs compared to 11.8% in TKAs (p=0.149). When controlling for potential confounders, patients undergoing UKA were less likely to require a second prescription than TKA patients (adjusted odds ratio: 0.603 (95% Confidence Interval (CI): 0.425–0.855). In addition, continued use of opioids after 6 months was also reduced compared to patients undergoing TKA (adjusted OR: 0.51, 95% CI: 0.27–0.97) in the multivariate analysis. Other independent predictors of continued opioid use include obesity (OR 1.79, 95% CI 1.07–3.00) and preoperative opioid use (OR 1.66 per script, 95% CI: 1.49–1.86). Our models for second script and continued use reported AUC scores of 0.65 and 0.85, respectively.
Conclusion
Patients with UKA are less likely to require a second opioid prescription and have continued opioid use even when controlling for a variety of potential confounders. Given the reduced opioid requirements associated with UKA, this study supports that orthopaedic surgeons should adjust their prescription patterns and educate patients regarding expected analgesic needs. Due to the retrospective nature of this study we were unable to precisely quantify the amount of opioids consumed in these patient groups. An ongoing prospective study will more accurately determine the duration and quantity of opioid use after UKA compared to TKA.
