Risk Factors for Persistent Pain and Analgesic Use Following Hip and Knee Replacement

Hip and knee replacements are one of the most performed and highly successful musculoskeletal surgical interventions and the number of annual operations has increased continuously. The majority of these procedures are performed to reduce pain and to regain function in patients with late-stage osteoarthritis. While many patients have a very good clinical outcome, about 10% of hip replacement patients and 20% of knee replacement patients are dissatisfied after surgery, which is most often related to ongoing pain in the operated joint. Possibly related to persistent postoperative pain, about 12% of patients still use opioids long-term after joint replacement.

Recently, attempts have been made to identify those patients who do and do not benefit from the surgery in terms of pain relief, and who are at risk for the prolonged or increased use of analgesic drugs after surgery. However, previous studies on analgesic use in patients undergoing joint replacement have mostly focused on opioids. Thus, there is a gap in the literature concerning the use of non-opioid analgesic drugs in patients undergoing joint replacement. Additionally, it is not known whether glucose metabolism disorders are risk factors for persistent postoperative pain.

The present study examined the user rates of different analgesic drug types before and after joint replacement, and those preoperative factors that might be associated with a higher probability of persistent postoperative pain or prolonged analgesic use after hip and knee replacement. Analgesic use was studied using register data from the Social Insurance Institution (Kela), which was then combined with the prospective database of Coxa Hospital for Joint Replacement. Risk factors for persistent postoperative pain were examined using prospective clinical data from Coxa Hospital and a pain questionnaire that was sent to all included patients 1-2 years after joint replacement.

The proportion of patients who used analgesic drugs increased prior to hip or knee replacement, peaked in the immediate postoperative period, and decreased thereafter. A higher proportion of hip replacement patients redeemed analgesic drugs preoperatively than knee replacement patients, whereas prolonged use of analgesic drugs after surgery was more common in knee replacement patients than in hip replacement patients. In line with some earlier findings, a surprisingly large proportion of patients did not redeem any prescription analgesic drugs preoperatively. During the 3-month period preoperatively, less than half of patients redeemed prescription analgesic drugs. At 1 year after surgery, 24% of hip replacement patients and 24% of knee replacement patients still used at least one type of analgesic drug, and 5% of hip replacement patients and 7% of knee replacement patients still used opioids. The most common analgesic drug types throughout the study period were NSAIDs, followed by acetaminophen, and mild opioids, whereas the use of strong opioids and medication used for neuropathic pain was less common.

Persistent postoperative pain was reported by 20% of knee replacement patients and by 4% of hip replacement patients. Patients with previously diagnosed diabetes had an eight-fold increased risk for persistent postoperative pain, whereas other glucose metabolism disorders or metabolic syndrome had no association. The strongest preoperative predictors for any analgesic use (i.e. opioids, NSAIDs, or acetaminophen) 1 year after joint replacement were the preoperative use of any analgesics, antidepressants, and benzodiazepines. Those patients who had used both antidepressants and benzodiazepines (compared to those patients without preoperative use of these medications) were most likely to redeem opioids and other analgesics after surgery. The other significant preoperative predictors for any analgesic use 1 year after joint replacement were the greater number of comorbidities, and severe obesity, whereas bilateral knee replacement was a protective factor (compared to unilateral knee replacement).

Based on these results, patients with diabetes may have an increased risk for persistent postoperative pain after joint replacement. Moreover, especially those patients with preoperative use of analgesic drugs, antidepressants, or benzodiazepines, and those patients who are obese or have a higher number of comorbidities are at a higher risk for prolonged use of opioids and other analgesic drugs after surgery. There is a lack of good quality studies of interventions trying to reduce long-term postoperative pain or analgesic use in patients undergoing joint replacement. Thus, further studies are needed to find ways of reducing the risk for these unfavorable outcomes. Surgeons today should be aware of these risks and have a candid discussion with patients about the possibility of persistent postoperative pain or prolonged analgesic use before proceeding to elective joint arthroplasty. Additionally, pre-, and postoperative pain management should be sufficient and individually tailored to the needs of the patients, and adjustment of the preoperative risk factors and tailored follow-up assessments should be made if needeed.