PARIS – Adding local anesthetic to the wound during total hip replacement surgery for osteoarthritis reduced chronic pain, according to a double-blind, randomized controlled trial.
At 12 months postoperative, the number of patients with severe pain was 8.6% with standard care, compared with 1.4% among those who also received 60 mL of 0.25% bupivacaine with lidocaine (Xylocaine) 1% with adrenaline 100 mcg/20 mL injected directly into the wound prior to closure.
The difference was statistically significant (P = .004; odds ratio, 10.19), but the confidence intervals were wide (95% C.I., 2.10-49.55) because of the small number of patients with severe pain, Vikki Wylde, Ph.D., said at the World Congress on Osteoarthritis.
She noted that 7%-23% of patients report moderate to severe chronic pain in the long term after total hip replacement, according to a recent systematic review (BMJ Open 2012:2:e000435), and that the severity of postoperative pain is a known risk factor for chronic postsurgical pain.
Local anesthetic wound infiltration has been shown to be effective at reducing the severity of acute postoperative pain after total hip replacement (J. Am Coll. Surg. 2006:203:914-32), but this is the first double-blind trial to assess its long-term effects.
Investigators at high-volume orthopedic centers in the United Kingdom randomly assigned 322 patients undergoing total hip replacement for osteoarthritis to standard care (spinal anesthesia with or without general anesthesia) alone or with local anesthetic infiltration. The primary outcome was WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) pain scale scores at 12 months postoperatively.
Use of in-patient analgesia or length of hospitalization did not differ between the groups, said Dr. Wylde, a research associate with the University of Bristol, England. Acute postoperative pain severity was also similar, except that patients in the intervention group reported less severe pain on postoperative night 2 (P = .008). This was unexpected, but the study was not powered to detect differences in these secondary measures, and no conclusions can be drawn from these data, she said at the meeting, sponsored by the Osteoarthritis Research Society International.
There were no differences in other secondary measures including the WOMAC function or stiffness scales or in ICOAP (Intermittent and Constant Osteoarthritis Pain) scores.
Local anesthetic infiltration, however, significantly reduced neuropathic pain at 12 months, as assessed using the PainDETECT questionnaire, Dr. Wylde said.
"Our study suggests that local anesthetic infiltration is unlikely to change long-term pain outcomes for the majority of patients, but potentially can improve pain relief for a small number of patients who may otherwise go on to develop severe long-term pain after surgery," she concluded.
In a separate interview, Dr. Jeffrey Katz, codirector, Brigham Spine Center, Brigham & Women’s Hospital and professor at Harvard Medical School, both in Boston, said the study was very interesting mechanistically and potentially interesting from a public health standpoint because there are about 400,000 hips done a year in the United States and thus 4,000 or so of these patients are having chronic pain. Moreover, the problem of chronic pain after surgery is even more common in the knee than in the hip.
"The difference in severe pain of 8% vs. 1% or 2% is a striking difference, but it’s a small incidence, and so it does bear replication," he added. "I thought it was a very exciting study and think it’s important information for folks to begin to work with and might change practice."
Dr. Wylde reported funding from the National Institute for Health Research, London.