Mainstay Medical is a Dublin-based medical device company developing the ReActiv8 Restorative Neurostimulation system for the treatment of mechanical chronic low back pain (CLBP) caused by multifidus muscle dysfunction. The company is publicly listed and has accumulated the largest evidence base of any implantable neurostimulation system specifically indicated for mechanical CLBP.

ReActiv8 consists of an implantable pulse generator connected to two leads placed bilaterally along the nerves innervating the lumbar multifidus muscle. Patients self-administer twice-daily 30-minute stimulation sessions, which elicit controlled muscle contractions designed to restore neuromuscular control and functional stability of the lumbar spine. Unlike conventional spinal cord stimulation, which masks pain signals, ReActiv8 targets the underlying biomechanical dysfunction. The pivotal ReActiv8-B randomised controlled trial demonstrated 71% pain responder rates and 65% CLBP resolution at two years, with 60% of opioid users voluntarily reducing or eliminating opioid intake.

The system received FDA approval and is commercially available in the United States, Europe, and Australia. Mainstay's clinical programme distinguishes CLBP secondary to multifidus dysfunction from neuropathic pain, establishing a distinct therapeutic category and patient selection pathway separate from conventional SCS.