Background/Aims: Total knee arthroplasty (TKA) can be associated with moderate to severe post-surgical pain. During the initial perioperative period this can generally be managed with a multimodal analgesic strategy, including the use of opiate based agents. With time most patients are able transition to simple oral analgesia however a percentage of patients develop a state of persistent or chronic post-surgical pain where the use of oral opiates may be considered. Although pain needs to be treated, long term use of opiate agents is not without complication or risk. With a move towards new pathways of TKA care in our institution we have performed a review to determine the incidence and risk factors for long term opiate use.
Methods: Hospital Research Board approval was obtained prior to study conduct. Patients admitted for primary unilateral TKA between 1st January 2014 – 31st December 2014 were retrospectively enrolled. Demographic, anaesthetic, surgical and pharmacy data were collated from pre-existing departmental databases. The primary endpoint was the need for an opiate prescription (either morphine or oxycodone) between 7 and 90 days’ post-surgery. Factors associated with the primary end point were determined through univariate then multivariate modelling. Analysis was completed with Deducer for R, Version 2.15.0 with a threshold for significance of 0.05 on two tailed testing.
Results: Three hundred and thirty-six patients underwent primary unilateral TKA during the study period. There were 135 males and 201 females. The median age (± interquartile range) was 67 (± 13) years. Pharmacy data was unavailable for 100 patients who were excluded from subsequent analysis. Between day 7 and 90 post surgery 65 patients (65 / 236 = 27.5%) required an opiate prescription. The predictors for a patient requiring an opiate prescription and the results of multi-variate modelling are shown in Figure One. Factors associated with the primary outcome in the final version of the model were length of hospital stay (p=0.003), pre-operative use of morphine or oxycodone preparations (p=0.003), post-operative paracetamol (p<0.0001) and gabapentin use (p=0.008) and readmission to hospital before 30 days’ post-surgery (p=0.0178).
Conclusion: These results confirm that a significant percentage of patients require prescriptions for opiate medications in the first 3 months after surgery. The factors associated in this series point to a group who experience greater levels of both pre and post-operative pain and may have longer or more complex hospital stays. Future work in this area should focus on strategies which optimise peri-operative care such that patient satisfaction and outcomes can be maximised. This may include the use of multi-disciplinary pathways which may allow earlier recognition of complications or abnormal pain states.
Counties Manukau Health