SEATTLE – The most important predictor of chronic postoperative pain after elective knee arthroscopy is preoperative opioid use, according to a single-center retrospective study.

Background information in the study, published recently in the journal Anesthesia & Analgesia, notes that chronic postoperative pain is common after elective surgery, with known risk factors including perioperative pain and post-traumatic stress disorder (PTSD).1

“Military veterans are a population at particular risk for PTSD and hence may be at increased risk for chronic pain after surgery,” write the authors from VA Puget Sound Healthcare System, the University of Washington and the Cleveland Clinic Lerner Research Institute. “Our goal was to identify risk factors for chronic postoperative pain in young veterans after minor elective surgery, including the contribution of PTSD.”

For the study, the researchers reviewed the medical and pharmacy records of 145 veterans — 87% male with a median age of 39 — undergoing elective knee arthroscopy from 2007 to 2010 at the VA’s Puget Sound health system. With the review focused during the period beginning 3.5 months before surgery and 3.5 months after, the team looked at demographics, American Society of Anesthesiologists physical status class, comorbidities, anesthesia medications and opioid prescriptions. PTSD was documented by inclusion either on the patient’s problem list or the clinical notes. Use of postoperative opioid prescription longer than three months after surgery was used as a surrogate for chronic postoperative pain.

The prevalence of PTSD was 32% and associated with increased incidence of smoking and preoperative opioid use. Preoperative opioids were prescribed in 44% (63 of 145) of the patients: in 64% (30 of 47) of patients with PTSD, compared with 34% (33 of 98) in patients without PTSD.

Chronic postoperative pain was identified in 30% (43 of 145) of patients. The strongest independent predictor of chronic postoperative pain was an opioid prescription before surgery, with an odds ratio of 65.3. In patients older than 27.5 years who did not receive opioids before surgery, PTSD may also have been a risk factor for chronic postoperative pain, the authors noted.

“For patients not taking opioids preoperatively, PTSD may increase the risk of prolonged postoperative opioid prescriptions and chronic postoperative pain, potentially related to patient age,” they conclude.

1 Rozet I, Nishio I, Robbertze R, Rotter D, Chansky H, Hernandez AV. Prolonged opioid use after knee arthroscopy in military veterans. Anesth Analg. 2014 Aug;119(2):454-9. doi: 10.1213/ANE.0000000000000292. PubMed PMID: 24977636.