AAOS Now

Published 12/1/2015
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Jennie McKee

Patient Opioid Use May Be Modifiable Risk Factor for TJA

Study finds weaning off opioids leads to better WOMAC, UCLA Activity Scores

"More than one-quarter of U.S. adults have experienced chronic pain from arthritis," said Kevin J. Bozic, MD, MBA. "Opioids are increasingly being prescribed for musculoskeletal pain, particularly arthritis."

According to Dr. Bozic, opioid use has been shown by many investigators to have a negative impact on total joint arthroplasty (TJA) outcomes, "leading to an increased risk of complications and a decrease in functional outcomes and patient satisfaction."

Dr. Bozic and his fellow researchers—including primary investigator Long-Co Nguyen, BS—sought to determine whether chronic opioid use is a modifiable risk factor for patients with severe arthritis of the hip or knee who undergo TJA. Their findings suggest that TJA patients who decrease their opioid use prior to surgery may have improved clinical outcomes that are comparable to patients who used no opioids. The research was presented during the 2015 annual meeting of the American Association of Hip and Knee Surgeons.

Conducting the study
The retrospective cohort study involved 41 patients who were regular opioid users and had successfully weaned (defined as achieving a 50 percent reduction in morphine equivalent dose) prior to undergoing total hip or total knee arthroplasty. Those patients were matched with a cohort of 41 opioid users who did not wean prior to TJA. A third matched cohort comprised 41 "opioid-naïve" TJA patients—that is, patients who had not used opioids preoperatively.

"Our power analysis suggested that we needed 41 subjects per group to achieve 80 percent power to detect a significant difference between the control and intervention groups," said Dr. Bozic.

"Patients were matched based on primary diagnosis, the affected joint, ASA class, sex, body mass index (BMI), age, and daily morphine equivalent dose," he said.

The researchers analyzed patient-reported outcomes at 6 to 12 months postoperatively using the UCLA activity score, the physical and mental components of the Short Form-12 version 2 (SF-12v2), and WOMAC. They also performed paired t-tests and ANOVA to assess differences in TJA outcomes.

Assessing results
"When we looked at patient characteristics, we found no differences in mean age, sex, or primary diagnosis across the three groups, due to the matching. We did find a difference in baseline functional scores, with patients who weaned prior to surgery having lower baseline functional scores going into surgery than patients in the control group," said Dr. Bozic.

"As other authors have shown, patients in the opioid naïve group had significantly better improvement in their functional outcomes after surgery than either group of opioid users," he continued. "Their final patient-reported outcome scores for both functional and mental health were higher at 6 to 12 months than patients who were opioid-dependent."

Compared to opioid users who had not weaned prior to surgery, the cohort of chronic opioid users who had successfully weaned had significantly better scores in the following areas:

  • WOMAC (43.7 vs. 17.8, P = 0.001)
  • SF-12v2 physical (10.5 vs. 1.85, P = 0.003)
  • UCLA activity (1.49 vs. 0, P = 0.001)

The researchers found no statistical difference between the two groups in SF-12v2 mental scores (2.48 vs. 4.21, P = 0.409).

Of greatest interest, said Dr. Bozic, was that opioid users who successfully cut their usage in half prior to surgery had essentially the same degree of improvement in functional outcomes as the patients who never used opioids.

"But that enthusiasm is somewhat tempered by the fact that patients who weaned did not achieve the same final outcome as opioid-naive patients because they started at a lower baseline," he said.

Study limitations included its retrospective nature, its reliance on self-reporting, and its focus on opioid use.

"We relied on self-reporting for preoperative opioid use, which means that true opioid use may be underreported," he said. "And we did not assess other risk factors, such as smoking or chronic back pain, which are known to affect pain and functional outcomes following hip or knee replacement."

According to Dr. Bozic, other researchers have already shown that chronic opioid use negatively affects TJA outcomes.

"But I think our contribution is that opioid use appears to be a modifiable risk factor," he said. "If we encourage patients to reduce their use of opioids prior to surgery, it may improve outcomes. Patients who weaned in our study had similar improvements in functional outcomes to patients who never took opioids, but their final patient-reported outcomes were lower. Because of that, we think that patients who use opioids should be counseled on expectations and preferably referred to programs that are designed to help them reduce their dose prior to surgery."

Further research is needed to define the duration and reduction of morphine-equivalent dose that would be needed to mitigate its hyperanalgesic effect, added Dr. Bozic.

Dr. Bozic's coauthors for "Preoperative Reduction of Opioid Use Prior to Total Joint Arthroplasty" included Ms. Nguyen and David Sing, BS. The authors' disclosure information can be accessed at www.aaos.org/disclosure

Jennie McKee is a senior science writer for AAOS Now. She can be reached at mckee@aaos.org

Bottom Line

  • This study sought to determine whether chronic opioid use is a modifiable risk factor in patients with severe osteoarthritis of the hip or knee who undergo total joint arthroplasty.
  • The study involved three groups of 41 patients each—an opioid-dependent group that reduced opioid usage prior to surgery, an opioid-dependent group that did not wean prior to surgery, and a control group that had not used opioids at all. 
  • When the researchers compared the patients who weaned to the opioid-dependent group, the patients who weaned had a significantly better improvement in their physical function scores. They also had significantly better final functional status scores compared to opioid-dependent patients.
  • Patients who weaned had essentially the same amount of improvement in functional outcomes as the patients in the control group, but they did not achieve the same final outcome because they started at a lower baseline.
  • The authors concluded that opioid use is a modifiable risk factor for arthroplasty patients.