May 07, 2020
3 min read

Preoperative analgesic use, obesity predict prolonged use after joint replacement

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Obesity and the use of analgesics prior to hip or knee replacement are the strongest predictors of postoperative analgesic use among patients with osteoarthritis, according to data published in Arthritis Research & Therapy.

“Although hip and knee replacement are performed to reduce pain and regain function in patients with late-stage arthritis, 10% to 20% of patients continue to suffer from persistent pain after surgery,” Tuomas Jaakko Rajamäki, MD, of Tampere University, in Finland, and colleagues wrote. “... The analysis of persistent pain should also include non-opioid analgesics, which at present only applies to a few studies. Indeed, high levels of preoperative pain, knee surgery (compared to hip surgery), and younger age have all been associated with an increased overall consumption of analgesic drugs.”

“Furthermore, obesity, female gender, younger age, and depression are associated with an increased consumption of NSAIDs,” they added. “However, general comorbidities, such as diabetes, a risk factor for persistent pain, have only been analyzed in one previous study, in which no differences in overall analgesic consumption after knee replacement were reported. To the best of our knowledge, those factors related to the consumption of acetaminophen have not previously been analyzed in the literature.”

To determine whether postoperative analgesic use is linked to patient characteristics, and if these factors vary based on the type of analgesic used, Rajamäki and colleagues analyzed data from a previous study conducted at a single, publicly-funded orthopedic hospital in Finland. That study cohort included 13,261 hip replacements and 13,205 knee replacements between Sept.2, 2002, and Dec. 31, 2013. In addition, a prospective database of the hospital includes preoperative and postoperative clinical information on these patients.

Obesity and the use of analgesics prior to hip or knee replacement are the strongest predictors of postoperative analgesic use among patients with osteoarthritis
Obesity and the use of analgesics prior to hip or knee replacement are the strongest predictors of postoperative analgesic use among patients with OA, according to data.

For their own study, Rajamäki included all patients who had undergone a primary operation and had primary osteoarthritis as the indication for surgery — a total of 13,739 joint replacements. Among these cases were 6,238 hip replacements performed on 5,657 patients, and 7,501 knee replacements on 6,791 patients. The researchers analyzed redeemed prescriptions for acetaminophen, NSAIDs and opioids using the nationwide Drug Prescription Register. They then calculated user rates for analgesics, as well as the adjusted risk ratios for analgesic use 1 years following surgery.

According to the researchers, 26.1% of the included patients were still using analgesics 1 year following surgery. Significant predictors of overall analgesic use — acetaminophen, NSAID or opioid — were being 65 to 74.9years of age (RR = 1.1; 95% CI, 1.03-1.2), being older than75years (RR = 1.2; 95% CI, 1.1-1.3), female sex (RR = 1.2; 95% CI, 1.1-1.3), having a BMI of 30 to 34.9kg/m2 (RR = 1.1; 95% CI, 1.04-1.2), having a BMI of more than35kg/m2 (RR = 1.4; 95% CI, 1.3-1.6), and a higher number of comorbidities (RR = 1.2; 95% CI, 1.1-1.4).

Preoperative use of analgesics (RR = 2.6; 95% CI, 2.5-2.8) and knee surgery (RR = 1.2; 95% CI, 1.1-1.3) also predicted the use of analgesics. Further, simultaneous bilateral knee replacement, compared with unilateral procedure, was a protective factor (RR = 0.86; 95% CI, 0.77-0.96). Opioid use was associated with obesity, higher Charlson Comorbidity Index score, epilepsy, knee surgery, unilateral knee operation, total knee replacement and the preoperative use of analgesics or opioids.

“These results were essentially similar for all types of analgesics including acetaminophen, which seemed to replace NSAIDs in older patients and in patients with multimorbidity,” Rajamäki and colleagues wrote. “It is remarkable that older age and higher number of comorbidities predicted analgesic use despite these patients also being the most vulnerable to adverse drug events. Clinicians should therefore inform patients with obesity (especially BMI >35kg/m2) about the elevated risk for prolonged use of analgesics (including opioids) after surgery.” – by Jason Laday

Disclosures: Rajamäki reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.