Our analysis of English routine NHS healthcare data indicated that primary care consultations and prescribed pain medicines were consistently higher for patients with chronic pain after TKR compared to patients without chronic pain. These differences were evident during the entire observational period of our analyses, persisting from 10 years pre-operative until eight years post-operative. There was a considerable difference in the prescription of opioids in the period after surgery, with a steep increase in costs for patients with chronic pain after TKR which peaked at seven years post-operative.
People living with chronic musculoskeletal pain make high use of healthcare and receive a large number of prescriptions for pain medicines [17, 18]. Our study is the first to quantify the impact of chronic pain after TKR on English primary care services. Chronic pain after TKR poses a considerable cost to primary care, given the high prevalence and long-term nature of this kind of pain. The consistently higher rate of primary care consultations and pain medicine prescriptions in the 10-year pre-operative period by patients who developed chronic pain after TKR highlights an increased healthcare utilisation even before their surgery. It was not possible to determine causes for these differences within our study, however risk factors for chronic post-surgical pain include multimorbidity, multi-site pain and mental health conditions , which could potentially contribute to increased use of healthcare services.
The cost of opioid prescriptions increased substantially after surgery for patients with chronic pain after TKR and remained high over the eight-year post-operative observational period. This suggests that opioids are prescribed for long-term management of chronic pain after TKR. However, opioids are no longer indicated for chronic pain , with clear evidence that they provide minimal relief of chronic pain symptoms, including pain due to osteoarthritis, and are associated with considerable harm . Our data from 2009-2016 shows a recent historical trend of high opioid prescription costs within primary care for patients with chronic pain after TKR. Further research is needed to evaluate current prescription patterns in light of recent national guidance advising against opioid prescription for patients living with chronic pain.
Our analyses used CPRD data, which contains detailed patient-level and prescription-level data on a large sample of patients from across England. However, limitations of our analyses should be acknowledged when interpreting the results. The data in CPRD are based on a subset of GP practices, and our analysis was restricted to those patients with linked HES records that completed a 6-month post-operative OKS, which may have limited the generalisability of the findings. The data only contain GP prescriptions and not pharmacy dispensations, and therefore it was not possible to confirm the quantity of medications that were bought. We also did not capture the costs to patients of purchasing their own pain medication, and this is an area which may warrant further research. We defined chronic pain status at six months post-operative, a time point at which pain outcomes generally plateau after TKR , however there can be within-person variability in longer-term outcomes  and we were unable to account for fluctuations in post-operative pain status.
In conclusion, our study demonstrated that increased primary care consultations and pain medicine prescriptions associated with chronic pain after TKR represent a considerable financial cost to primary care services in England and that patients with chronic pain after TKR are prescribed more opioid medications than those without chronic pain. Evaluation of interventions to reduce the risk of developing this pain condition and improve the early management of pain after TKR are needed to improve outcomes for patients and reduce costs to healthcare services.