**1. Introduction**

Osteoarthritis (OA) is the most common chronic joint condition in the world and affects nearly 9 million people in the United Kingdom alone [1]. It manifests clinically as localised joint pain, stiffness and occasionally swelling.

OA can occur as a primary idiopathic phenomenon with no prior causative trauma, although more frequent are cases of secondary OA appearing as a result of preexisting joint damage [2]. This is often in the context of inflammatory arthropathy or previous injury. Risk factors for primary OA include advancing age, female sex, family history and obesity [1–3]. The disease can be restricted to a single joint or become more widespread, affecting multiple joints. In severe cases, it can progressively lead to significant deformity, loss of function and a reduced quality of life [1, 4].

Treatment has mainly focused on symptomatic relief from pain, physical approaches such as rehabilitation and physiotherapy, disease-modifying treatment (such as hydroxychloroquine) and surgery. Pain relief with systemic drugs has drawbacks. In particular, the use of non-steroidal anti-inflammatory drugs (NSAIDs) has been associated with significant adverse events including gastritis and increased risk of cardiovascular disease. In view of this, there has been increased interest in localised treatments for OA; specifically, therapies that are localised to the affected joint itself. These can be divided into topical treatment, such as anti-inflammatory gels, creams and thermotherapy, and more invasive local treatment including joint aspiration and intra-articular (IA) joint injection with corticosteroid and hyaluronans.
