Study Authors: Tuomas Jaakko Rajamäki, Pia A. Puolakka, et al.
Target Audience and Goal Statement: Orthopedists, orthopedic surgeons, rheumatologists, pain specialists
The goal of this study was to determine the risk factors for the increased use of opioids and other analgesics 1 year after hip or knee replacement surgery for patients with osteoarthritis.
- Was postoperative analgesic use associated with patient characteristics, such as obesity or other comorbidities, or did other clinical factors play a role?
Study Synopsis and Perspective:
One of the most commonly performed elective surgical procedures in the U.S. is total joint replacement. By 2030, “new hips or new knees to-go” will rise by an estimated 171% and 189% (635,000 and 1.28 million procedures), respectively. Knee and hip replacements are considered to be cost-effective procedures for end-stage arthritis, which causes ongoing pain, limited function, and diminished quality of life.
- Multiple factors predicted the ongoing use of analgesics 1 year after joint replacement surgery, with the strongest predictors being obesity and preoperative analgesic use, according to a single-center study from Finland.
- Note that older age and presence of comorbidities also led to increased postoperative analgesic use in this population.
Osteoarthritis — a degenerative joint disease — affects more than 32.5 million American adults, with women more likely to develop the disease than men, especially after the age of 50 years. Age, obesity, race, genetics, and joint injury or overuse are other known risk factors.
Knee and hip replacements to alleviate pain/regain function are considered clinically successful based on prosthesis-related outcomes, such as radiographic appearance of the prosthesis, implant survival, or surgeon-assessed outcome. However, up to 20% of patients continue to suffer from persistent pain after surgery. This may lead to long-term use of analgesics, despite the risks of adverse events with opioids and nonsteroidal anti-inflammatory drugs (NSAIDs), particularly among older individuals and those with comorbidities.
According to a study conducted in Finland, the strongest predictors of postoperative use of analgesics were obesity (especially body mass index [BMI] >35 kg/m2) and the preoperative use of analgesics. This study, published in Arthritis Research & Therapy, adds to earlier evidence that female gender, obesity, number of comorbidities, preoperative use of analgesics, and unilateral knee replacement (vs simultaneous bilateral procedure) were associated with the probability of using analgesic drugs 1 year after joint replacement, wrote Tuomas Jaakko Rajamäki, MD, of Tampere University, and colleagues.
Among patients whose BMI was above 35, the adjusted risk ratio for use of any analgesic medication a year after the procedure was 1.4 (95% CI 1.3-1.6).
Additionally, the adjusted risk ratio for postoperative analgesic use was 2.6 (95% CI 2.5-2.8) among those who reported preoperative use of these medications.
Recent attention has focused primarily on the excessive use of opioids in the general population, but little is known about the patient characteristics and risk factors associated with high postoperative use of analgesics, including not only opioids but also acetaminophen and NSAIDs.
Therefore, Rajamäki and team reviewed data on patients who underwent a primary hip or knee replacement for osteoarthritis from 2002 to 2013 in a single, publicly funded orthopedic hospital in Finland. They included 13,739 joint replacements (6,238 hip replacements performed on 5,657 patients and 7,501 knee replacements performed on 6,791 patients) in their analysis. Information on medications was obtained from a national drug prescription register. User rates of analgesics and the adjusted risks ratios for analgesic use 1 year after joint replacement were calculated.
Patients’ mean age was 68.7 years, 61.1% were women, and mean BMI was 29.1. Mean Charlson Comorbidity Index (CCI) was 1 in approximately 20% of the patients and above 2 in 7%. For the modified CCI used in this study, a score of 1 was assigned for heart failure, coronary artery disease, type 1 or 2 diabetes, chronic asthma or another severe obstructive pulmonary disease, dementia, disseminated connective tissue diseases, and rheumatoid arthritis and other comparable conditions. A score of 2 was assigned for uremia requiring dialysis, severe anemia in connection with chronic renal failure, leukemia and other malignant diseases of blood and bone marrow, and cancer.
Three months preoperatively, 43.1% of patients filled at least one prescription for any type of analgesic drug, most commonly NSAIDs (29.7%), followed by acetaminophen (12.8%), and opioids (11.3%). One year after surgery, the proportion of patients who filled a prescription for at least one type of analgesic drug decreased to 26.1%; NSAIDs were still the most common (15.5%), followed by acetaminophen (10.1%), and opioids (6.7%).
Age was a clear predictor of analgesic use, reported by 29% of those older than 75, 26.2% of those 65 to 75, and 23.7% of those younger than 65 (P<0.001). In an adjusted model, those older than 75 had a risk ratio of 1.2 (95% CI 1.1-1.3) for the use of any analgesic compared with those younger than 65. The risk ratio among the oldest patients was also higher for acetaminophen, at 2.2 (95% CI 1.9-2.5), but was lower for NSAIDs, at 0.77 (95% CI 0.68-0.86).
Women more often filled prescriptions for analgesics then men (28.8% vs 22%, P<0.001), and had a higher risk ratio for any analgesic use, at 1.2 (95% CI 1.1-1.3), and for acetaminophen, at 1.4 (95% CI 1.2-1.6), and NSAIDs, at 1.2 (95% CI 1.1-1.3).
When the researchers considered the specific joint replaced, they found that more patients having knee rather than hip surgery used any analgesics postoperatively (28.8% vs 23%, P<0.001).
Severe obesity (BMI above 35) was not only associated with any postoperative analgesic use, but also with all types of analgesics:
- Acetaminophen, RR 1.6 (95% CI 1.4-2.0)
- NSAIDs, RR 1.5 (95% CI 1.3-1.7)
- Opioids, RR 1.4 (95% CI 1.1-1.8)
Furthermore, those with the highest BMIs also had greater preoperative analgesic use (RR 1.3, 95% CI 1.2-1.4). In addition, risk ratios for preoperative and postoperative use were elevated for those whose BMIs were in the lower range of obesity, at 30-35 (RR 1.1, 95% CI 1.05-1.2 and RR 1.1, 95% CI 1.04-1.2).
The researchers noted that diabetes and other comorbidities were not significant independent predictors of postoperative analgesic use.
Study limitations included the lack of information on over-the-counter drugs, the inability to analyze all postoperative complications, and the lack of examination of other key factors, such as preoperative pain, the intensity of pain, and the prevalence of persistent pain.
Source Reference: Arthritis Research & Therapy 2020; DOI: 10.1186/s13075-020-02184-1
Study Highlights and Explanation of Findings:
A single-center analysis of more than 13,000 hip and knee replacements in an unselected osteoarthritis population showed that older age, female gender, obesity, number of comorbidities, preoperative use of analgesics, and unilateral knee replacement were associated with a higher probability of using analgesic drugs 1 year after surgery. Individual comorbidities had little or no effect.
“The associations related to obesity, gender, operated joint, and preoperative use of analgesics were similar for different types of analgesic agents whereas the associations with different comorbid conditions were more mixed,” the researchers wrote.
Strikingly, obesity was correlated with a higher risk ratio for the consumption of all the studied analgesic drugs both pre- and postoperatively. Indeed, the findings showed obesity predicted the use of all analgesic drugs (acetaminophen, NSAIDs, and opioids) after hip or knee replacement. Drug use was more frequent, especially when patient BMI exceeded 35 kg/m2 — echoing evidence from the literature. Rajamäki and team noted that obesity was also associated with analgesic use in the general population.
Although patients with simultaneous bilateral knee surgery used more analgesics before the procedure and fewer analgesics after, the researchers stated that it was not clear if replacing both knees should be preferred in bilateral osteoarthritis.
Some of the other findings in the study included the associations of obesity, epilepsy, and overall comorbidities with more opioid use after both hip and knee replacement surgery. In contrast, increased use of acetaminophen in older patients, those with more comorbidities, and those with neurodegenerative diseases could possibly be explained by avoidance of NSAIDs and opioids in these patient groups, noted Rajamäki and colleagues.
“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,” they wrote. “Clinicians should therefore inform patients with obesity (especially BMI > 35 kg/m2) about the elevated risk for prolonged use of analgesics (including opioids) after surgery.”
Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco