Study design

This was a population-based retrospective study of all adults (> 18 years of age) who underwent elective foot and ankle surgery at a Canadian tertiary hospital. Four of the five (80%) fellowship-trained foot and ankle surgeons from this metropolitan health region operated out of this hospital, so although this was a single center evaluation, this hospital represented the majority of elective foot and ankle surgeries performed in the health zone during the evaluation time-period.

Potential participants were identified using ICD-10 procedural codes for ankle fusion (OSGF/OSGG), ankle replacement surgery (OSRF/OSRG) or hindfoot reconstruction (OSGH/OSGJ/OSSH/OSSJ) that were performed no later than 31May 2017. The selected end date allowed us to ensure all administrative data would be available to evaluate community-based opioid dispensing up to six-months postoperatively (i.e., Dec 2017). As there was a further delay in accessing administrative data of up to six-months to allow the data custodian to check data integrity, we performed our chart review in the summer/fall of 2018 to ensure a complete administrative dataset for opioid dispensing.

As we intended to review 100 patients’ charts using a retrospective hospital population-based approach, we identified that 100 patients received the surgical procedures of interest between May 1, 2015 and May 31, 2017 at our hospital. Although the sample size was not based on an apriori sample size calculation, there was no selection bias as we included all eligible surgeries within the evaluation period.

This study received ethics approval from the University of Alberta Health Research Ethics Board who provided waiver of written informed consent to allow access to routinely collected administrative health data (PRO00075984). All relevant guidelines regarding privacy and protection of health data were followed throughout the study.

Phases of data collection

This study used 3 phases of data collection from 2 different data sources; the data sources are described below in detail. Phase 1 was preoperative, which extended from 180 days preoperatively to the date of surgery. Data for this first phase came from our provincial community-based dispensing data system, the Pharmaceutical Information Network (PIN). As this was dispensing data, the preoperative opioid use data reflects estimates of consumption based on prescribing practices. As the PIN does not record hospital-administered medications, Phase 2 of our data collection was the chart review where we were able to collect opioid consumption during the hospital stay as well as details around patients’ hospitalization. Finally, Phase 3 repeated the data evaluation performed in Phase 1, but looked at PIN data for 180 days postoperatively, again allowing estimation of opioid use based on dispensing practices. Phase 3 started on Day 1 postoperative, but only included community-based dispensing of opioids (i.e., through the PIN) to understand postoperative prescribing practices after hospital discharge. No in-hospital consumption of opioids was included in the Phase 3 post-discharge evaluation, which continued for 180 days postoperatively.

Data sources

Chart review

The chart review was conducted using a standardized data collection form completed by an experienced research associate. From the chart review, we were able to record the opioids consumed by patients during their hospital stay, which was transformed into a morphine equivalent dose (MED). Data on the participants’ age at surgery, sex, body mass index (BMI), smoking history, number and type of comorbidities, length of stay in hospital, destination of discharge (home versus rehabilitation hospital), postoperative complications, and readmission to hospital were also collected. For comorbidities, we specifically looked at recorded medical history to determine if any other chronic pain condition was identified and if the physician had identified that a patient was taking opioids for another condition.

Pharmaceutical Information Network (PIN)

Community-based opioid dispensing data were obtained from the PIN, a provincial pharmaceutical repository that maintains individual level pharmacotherapy records and includes dispensing information from all community pharmacies in Alberta, regardless of health insurance coverage.

A record was created in PIN each time a medication was dispensed from a pharmacy in Alberta and contained the drug information number (DIN), anatomic therapeutic code (ATC), date dispensed, dose and duration (days’ supplied) as well as prescriber classification. Each PIN entry was linked to patient’s Unique Lifetime Identifier (ULI), a unique number assigned to all persons who received health services in Alberta. Using opioid specific ATC codes, each patient’s PIN profile was queried for 180 days prior to and following the index surgery to determine their opioid dispensing history. The end-date for each dispensing was then calculated by adding the duration of the prescription to the dispensing date for each PIN entry as previously described [12].

Individual opioid prescriptions were then converted to a daily MED by multiplying the daily dose for each opioid by the corresponding MED to allow for standardized comparison across different opioid compounds [12]. Morphine conversion factors were based on the published conversion factors that align with Canadian opioid prescribing guidelines [7]. All datasets were deterministically linked using patient’s ULI that were previously scrambled with an algorithm that de-identified each ULI, but still preserved the ability to link across datasets.

Classification of opioid use

Preoperative long-term opioid users (OU) were defined as patients who had 90-days or more of continuous opioid dispensing’s within 180 days prior to surgery. These parameters were consistent with the definition of long-term opioid therapy (LTOT) [12, 13]. Preoperative intermittent OU had recorded opioid dispensing’s within the 180 days prior to surgery, but did not meet the threshold parameters for a preoperative long-term OU. Preoperative opioid naïve patients did not have a recorded opioid dispensing within 180 days prior to surgery. The 180-day opioid free period had been previously used in studies investigating LTOT and is the established threshold for opioid discontinuation [14]. The maximum allowable refill gap between prescriptions in an opioid utilization episode was 14 days, or 0.5 times the preceding prescription length, whichever was greatest [12].

Postoperative long-term OU, postoperative intermittent OU and postoperative non-OU were defined using the same parameters as those used to define preoperative opioid use within 180 days after the index surgery, but did not include hospitalization opioid consumption.

Statistical analysis

Descriptive statistics were used to characterize preoperative opioid dispensing patterns including dose (MED) and duration. Means with standard deviation (SD) or ranges were reported and were compared using Student’s t-test or one-way analysis of variance (ANOVA) for normally distributed variables. Ranges were selected to report PIN dispensing data while SD was used to report in-hospital opioid consumption. Categorical variables were represented as frequencies and proportions with Chi Square tests or Fishers Exact Test. Significance was set at p < 0.05 and statistics were performed using SAS (SAS institute), version 9.4.

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