Although the studies conducted so far are small and look at short-term results, the results of these recent studies are “impressive,” says Dr. Felson. “A lot of [current treatments for OA pain] don’t work, and this one may actually work.”

He points to a Minneapolis-based study published in the Journal of Rheumatology in 2010 that looked at 54 patients experiencing chronic pain after total knee arthroplasty. Some were given an intraarticular injection of 100 units of botulinum toxin type-A and some were given an identical placebo. The results were significant: 71 percent of those injected with botulinum toxin achieved clinically meaningful reduction in pain and improved, measurable physical function in the joint compared to 35 percent of those receiving the placebo shot.

Even surgical replacement of a hip or knee joint eroded by OA may not eliminate pain and mobility issues, says Dr. Felson.

“No one is quite sure of the reason for pain after knee arthroplasty, but a significant percentage of patients have pain after surgery,” he says.

Traditional medications to treat OA pain include NSAIDs or corticosteroids, which target inflammation, and analgesics, which act on the central nervous system to block pain signals. Botulinum toxin could be a welcome alternative, says Dr. Hsu, because it appears that the localized injections do not cause the type of systemic side effects of NSAIDs or corticosteroids, or the dependence issues of narcotic analgesics.

“If it does get widespread use at some point, then I anticipate people would get maintenance injections every three to four months or so,” he notes. Some studies are exploring the use of the toxin in conditions like hip and knee OA and frozen shoulder, or adhesive capsulitis, the inflammation of connective tissue in the shoulder joint capsule. Dr. Hsu sees botulinum toxin as a potential auxiliary treatment for OA patients with uncontrolled pain. “I cannot predict that this will be the only treatment people with osteoarthritis will get, but for people with advanced disease, people who feel hopeless, this may provide hope that something can be done” to treat their pain.

Pain Results Promising

Recently published studies explore the use of botulinum toxin in different joints and in patients who have either had total joint replacement or not. Another study has raised further interest by suggesting that botulinum toxin might someday be used to treat inflammation as well.