Prolonged pain after hip or knee surgery cause increased use of analgesics. As observed from this single- centre analysis- obesity, higher age, female gender, number of comorbidities, use of analgesics preoperatively, and patients with unilateral knee replacement had a higher probability of using analgesic drugs 1 year after surgery. 

The study authors recognized the risk factors associated with the increased use of opioids and other analgesics a year after surgery and concentrated on the comorbidities and surgery-related factors.

All patients who underwent a primary hip (6238 patients) or knee (7501 patients) replacement surgery for osteoarthritis from the year 2002 - 2013 were included. The nationwide Drug Prescription Register was used to redeem prescriptions for acetaminophen, non-steroidal anti-inflammatory drugs (NSAIDs), and opioids (mild and strong). One year post-joint replacement, the rate of analgesic consumption and the adjusted risks ratios for analgesic use were assessed.

It was found that 3591 (26.1%) patients were still using analgesics 1 year following the surgery. Generally, the notable predictors of overall analgesic use were (risk ratio (95% CI)) age 65–74.9 years (reference < 65); age > 75 years; female gender; body mass index (BMI) 30–34.9 kg/m2 (reference < 25 kg/m2); BMI > 35 kg/m²; and a higher number of comorbidities (as per the altered Charlson Comorbidity Index score). Considering the clinical factors, the preoperative analgesic usage was found to be 2.6 (2.5–2.8), and for knee surgery was 1.2 (1.1–1.3), anticipated the use of analgesics, however immediate bilateral knee replacement (compared to unilateral procedure) was a protective factor with a value of 0.86 (0.77–0.96). Opioid use was found to be associated with obesity, greater CCI score, epilepsy, knee versus hip surgery, unilateral versus bilateral knee operation, total versus unicompartmental knee replacement, and use of analgesics/opioids preoperatively.

The closest predictors of increased use of analgesics postoperatively were obesity (BMI higher tha 35 kg/m²) and preoperative use of analgesics. Moreover, despite more chances of adverse effect exposure to the older age and a high number of comorbidities these were found to be associated with higher analgesic use postoperatively.