LAUSR

Geoffrey Moore in his 1991 bestseller ‘‘Crossing the Chasm’’ described a gap in technology adoption between so called ‘‘early adopters’’ and ‘‘mainstream adopters’’ which was defined as the ‘‘chasm’’ (Figure 1). While this was applied to marketing and selling of disruptive technologies, its concept can equally be applied to new treatments in medicine. What does it take for a treatment to become mainstream? In April 2015, a publication by Yuji Okuno and colleagues ignited interest among the global Interventional Radiology community, with the description of a novel endovascular treatment for osteoarthritic knee pain. The premise of the technique is the embolization of abnormal synovial neo-vessels which arise from the genicular arteries of the knee as a consequence of chronic inflammation. The hypothesis is that these neo-vessels are associated with perivascular nerve fibers which result in pain; blocking these neo-vessels is, therefore, a potential target for symptom relief in this patient group. So far, it seems genicular artery embolization (GAE) holds potential to plug a therapeutic gap in patients with mild-tomoderate osteoarthritis (OA) who have knee pain refractory to currently available conservative treatments (physiotherapy, oral analgesia, and intra-articular steroid injection) but are not deemed eligible for knee replacement. Thurs far, less than 200 patients have been treated with GAE in the published literature. If GAE proves to be successful, it will become a much-needed option in the armamentarium of clinicians taking care of this sub-group of patients. Furthermore, as the opioid crisis grips the western world, GAE has been shown to offer a sustained therapeutic effect in comparison with current conservative treatment options, and may reduce dependence on oral analgesics to treat this condition. Intra-articular steroid injections have also been found to be inferior to physical therapy in terms of pain relief for patients with knee OA in a randomized controlled trial; it is, therefore, evident a novel and durable treatment option is required. With any therapeutic innovation, the natural history from conception to full acceptance as a treatment option can be illustrated by the Gartner hype cycle (Figure 2). We are currently in a period of rising expectations, but soon we may find ourselves at a peak of inflated expectations with a looming trough of disillusionment, where in order for this procedure to become mainstream it will have to overcome Moore’s ‘‘chasm.’’ These concepts can be combined into a ‘‘hypechasm’’ diagram (Figure 3). It is, therefore, worth considering what are the factors that could influence the trajectory of embolization for osteoarthritis as a treatment option. Heading toward a peak of inflated expectation, embolization for osteoarthritis may hold promise in joints beyond the knee. Even more excitingly, it may prove to be useful in other musculoskeletal pathology, such as rheumatoid arthritis and sports injuries. The vast majority of data supporting musculoskeletal embolization is from Japan, where Imipenem-Cilastatin (IPM-CN) has been used as the embolic agent, a drug traditionally used as an antibiotic. There is a paucity of data about how IPM-CN works as an embolic agent. It is thought to be a temporary agent with an embolic action anecdotally lasting only minutes. However, the exact size of the particles and mechanism of degradation is unknown. If the degradation rate is as fast as described in the literature, the question remains as to how this agent can have an embolic effect. Data from Europe and the USA on the other hand, has mainly involved the use of permanent embolic agents, with short-term outcomes appearing comparable to IPM-CN. Perhaps, the most interesting question therefore to emerge from the evidence so far, is how a temporary embolic agent can have a therapeutic effect for musculoskeletal embolization. A proposed theory is that the perineural synovial neo-vascularity is disorganized and remains occluded even after temporary embolic agents have degraded, due to the inability of these neo-vessels to recanalize; a phenomenon which would otherwise occur in normal vessels. While this may be a plausible explanation, there is no pathological proof of this. Let us not forget lessons from other recently proposed interventional radiology procedures, like ‘‘liberation therapy’’ for chronic