Botulinum neurotoxin type A (BoNT/A) more commonly referred to as Botox was originally used as treatment for neurological conditions with increased muscle tone and abnormal posture of the head and extremities. Today it is used for relief from many neuromuscular conditions such as myofascial pain, plantar fasciitis pain, muscle spasticity etc. Due to its early analgesic effects on these disorders it was hypothesized that BoNT/A may have similar effects when injected into a joint rather than a neuromuscular junction. This suggests that Botox may be another conservative treatment option patients suffering from knee Osteoarthritis.(Chen-Liang Chou et al, 2010).
Although we understand that BoNT/A can have analgesic effects; it is unclear if there is a single leading factor to attribute this to. BoNT/A is a paralytic neurotoxin which decreases muscle spasticity and inhibits the release of neurotransmitters such as acetylcholine (Ach). BoNT/A can also denervate both autonomic and sensory nerves (Binder WJ et al,2000).
In a study by Chen-Liang Chou et al researchers took a group of twenty four patients with stage III and IV advanced knee osteoarthritis and injected their knees with 4.0 mL of BoNT/A. Subjects received two injections over a six month period and were monitored on a monthly basis. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) was used to evaluate the outcomes. The therapeutic effects of the injections were not statistically significant until three months post the first injection. After that effects lasted approximately one month following each injection. These outcomes suggest that botox does provide pain relief in the short term providing only temporary relief.
Also noteworthy were the statistically significant decreases in joint stiffness following BoNT/A injection. Physical function scores however, remained relatively the same pre and post injection of BoNT/A.
More research is needed before this therapeutic modality can be broadly recommended.
Other injectable information can be seen at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1742771/pdf/v079p00449.pdf