Opiate prescription after hip and knee arthroplasty: a retrospective cohort study

Total hip arthroplasty (THA) and total knee arthroplasty (TKA) are two of the most successful operations in orthopaedic surgery.^1–3 They have been shown to reduce pain, improve function and improve quality of life.^1,2,4,5 Some reports suggest that opiate analgesia may be ineffective for chronic non-cancer pain.^6–10 The use of opiate analgesia prior to total joint arthroplasty (TJA) has been associated with suboptimal clinical outcomes, complications and an increased length of stay (LOS) in hospital.^{5,6,8,11–18}

To our knowledge, pre- and post-operative opiate use has not been analysed in rural Australasian population patients undergoing TJA.^{8,9,12,19–25} Patients in these settings often have difficulty accessing healthcare, present at a later stage of disease and suffer worse outcomes compared to urban patients.^26–30

Opiate analgesia is known to cause socio-economic harm internationally in association with prescription and non-prescription use.³¹ As a result, our centre has guidelines for the prescription of opiate analgesics (Appendix Figure 1).

The primary aim of the study was to describe the use of opiates before, immediately after and 1 year after elective THA and TKA. A secondary aim was to compare prescribing practices following these procedures to local guidelines.

Methods

Study sample

A retrospective cohort study of elective primary THA and TKA was performed between January 2018 and April 2019. Patients were assessed against exclusion criteria using physical and electronic medical records.

Setting

Southland Hospital is a 157-bed secondary-level facility located in Invercargill, Southland, New Zealand. Southland Hospital provides care for a large geographic catchment and more than 100,000 people.

Exclusion criteria

Patients were excluded if they received a non-elective arthroplasty, had unavailable or incomplete records, had a single-stage bilateral arthroplasty or had deceased prior to 1-year follow-up.

Data sources

Data were collected from physical and electronic records. Our facility’s electronic record is linked to community prescription dispensing.

Data analysis

Statistical analysis presented in Table 1 was performed using the Student’s unpaired t-Test. Data analysis was performed using Microsoft Excel software.

Data interpretation

Prescriptions written for use “as required” (PRN) were interpreted as being used at the full dose. Dosages were quantified in morphine milligram equivalents (MME).³²

Results

Study sample

The flow of patients to achieve the study sample is shown in Figure 1, and 157 patients were included in the analysis.

Characteristics of the study sample, split by whether patients received a THA or TKA and by use of opiates in the pre-operative period, are shown in Table 1. Pre-operative use of opiates was present in 59/90 (66%) of patients who received a THA and 33/67 (49%) who received a TKA.

View Figure 1–4, Table 1.

Changes in opiate use with time

Figures 2 and 3 show the change in opiate use by time period for patients who received a THA and TKA. In both groups there was a similar change with time. In all, 108/157 (69%) were prescribed a higher dose of opiates on discharge than they had used in the 24 hours before discharge. After 1 year, 130/157 (83%) of patients were no longer prescribed opiates.

Opiate prescriptions compared to local guidelines

Opiate prescriptions on discharge compared to local guidelines are shown in Figure 4. In summary, 84/157 (67%) of all discharge prescriptions and 84/126 (67%) of opiate discharge prescriptions did not follow the local guidelines for dosing. In addition, 90/157 of all prescriptions and 90/126 (71%) of opiate prescriptions did not follow the local guidelines for duration of prescription.

Discussion

Opiate analgesics are widely used to manage post-operative pain following orthopaedic procedures including TJA.^9,21,22 Opiates are reported to be an effective analgesic agent for acute post-operative pain; however, they are associated with risks of addiction and overdose.^6,8,10,33 The negative impact of these drugs on patients undergoing orthopaedic surgery has been well documented.^8,11–14 Most reports have been from high-volume urban centres, limiting the generalisability to rural settings.^26–30

In New Zealand, population-specific barriers to healthcare have been described.^26–30 Observations from urban centres may not be transferrable to rural centres, necessitating an understanding of opiate use in patients undergoing TJA in rural settings.³⁴ To our knowledge, there have been no published clinical reports examining these issues in patients undergoing elective TJA in rural Australasian centres.^{8,9,12,19–25}

Half of TKA patients (49%) and two thirds of THA patients (66%) used opiates pre-operatively, with only 13% and 19% respectively using opiate analgesia 1-year post-operatively.

We have found rates of pre-operative opiate use in a rural population that are two to three times those of the wider New Zealand population prior to TJA.²¹ We believe this is an important observation and it suggests rural patients may be at higher risk of suboptimal outcomes when compared to urban cohorts. Anecdotally, access to arthroplasty in our rural centre is limited by long waiting lists, secondary to insufficient access to operating theatres and inpatient beds.

Twenty percent of patients (25/126) who were prescribed opiates continued to use these 1-year post-operatively. This is higher than has been reported in some other cohorts.^8,9,21,24,35 While this study was not designed to assess the indication for ongoing use, the medical record of these patients was reviewed in attempts to identify possible reasons for ongoing opiate use. Seventeen (65%) suffered from arthritis in another joint, four (15%) had ongoing pain in the operated joint, one (4%) had spinal stenosis, one (4%) had advanced cancer and one (4%) underwent another surgical procedure around the time of follow-up. Only one (4%) patient did not have an identifiable reason for ongoing opiate use. Of note, this chart review was performed retrospectively and therefore the reasons for opiate use in these patients are uncertain.

Limitations

This study has several limitations. It was a retrospective design. Using a consecutive non-selected patient cohort aimed at assessing the patterns of opiate use, the sample size was relatively small but accurately reflects the demographics of the patient population that is managed in rural centres of New Zealand. Although some statistically significant associations were identified, multiple statistical tests were performed and these may be spurious due to Type I error inflation. For comparisons that were not statistically significant, the small sample size may have also increased Type II error where important associations may not have been identified. As such, this study was not designed to assess the contribution of other comorbidities to the use of opiates in this population, nor was it capable of assessing associated complications. The cohort is unlikely to be generalisable to urban centres given the disparity in healthcare provision between rural and urban populations.

Conclusion

Both pre-operative opiate use and post-operative opiate prescribing exceeded expectations. Rates of pre-operative opiate use in rural patients undergoing THA or TKA are 2–3 times those reported in urban New Zealand settings. Prescriptions practices in our centre commonly deviate from guidelines and increased oversight of junior staff is required to foster safe prescribing practices. Further research in this field should review disparities in access to TJA, the timing of presentation, stage of disease, comorbidities and the time between presentation surgery.

View Appendix.