Associations between early postoperative pain outcome measures and late functional outcomes in patients after knee arthroplasty

Introduction/Aim Early rehabilitation, return to daily life activities and function are the ultimate goals of perioperative care. It is unclear which pain-related patient-reported outcome measures (PROM) mirror treatment effects or are related with early and late functional outcomes. Methods We examined associations between two approaches of pain management (scheduled vs 'on demand') and PROMs on post-operative days one and five (POD1, 5) with function on POD5 and 3 months after surgery in patients undergoing Total Knee Arthroplasty (TKA) in a single centre. The scheduled pain management consisted of pain assessment and routine administration of non-opioid drugs, and a weak opioid based on severity of pain reported by patients. The 'on demand' group received non-opioids and/or a weak opioid only when asking 'on demand' for analgesics. Results On POD1, patients in the scheduled treatment group reported reduced severity of worst pain, less interference of pain with activities in-bed and sleep, and a higher proportion got out of bed. On POD5, these patients reported as well significantly less worst pain, spent significantly less time in severe pain, experienced less interference of pain with activities in bed, and felt less helpless. Furthermore, tests of function, extension and flexion ranges, Barthel index and 6 minutes walking test on POD5, and the Knee Injury and Osteoarthritis Outcome Score (KOOS) 3 months later were significantly better in the scheduled treatment group compared to the 'on demand' treatment group. Pain related PROMs assessed at POD1 and especially at POD5 are associated with better knee range of motion, better performance in activities of daily living, and faster gait speed, as well as less pain, better performance in activities of daily living, as well as higher knee-related quality of life 3 months postoperatively. Conclusions Our study demonstrates that severe postoperative pain after TKA might have long lasting consequences, and even small improvements in treatment, although being far from optimal, are accompanied by improved outcomes.