Understanding Pain Mechanisms in Knee Osteoarthritis

Inclusion Criteria: * Radiographically defined OA knee changes (K/L \> 2); * Must have self-reported knee pain (measuring at least 30 mm to 80 mm on a 100 mm VAS for rest, use or night pain); * Able to give informed consent; * Aged 45 years and older; * All genders; * Able to perform the six-minute walk test. Exclusion Criteria: * Aged less than 45 years; * Breastfeeding or pregnancy; * Not having the capacity to consent; * Non-English speakers; * Major medical, neurological and psychiatric co-morbidities; * Hip OA (ipsilateral or contralateral); * Fibromyalgia; * Sensory dysfunctional illness; * Chronic pain conditions other than OA; * Presence of local or systemic infection or suspicion of infection in the knee joint, overlying soft tissue or elsewhere; * History of septic arthritis in the knee to be injected; * Acute haemarthrosis in the joint to be injected; * Recent trauma within 72 hours; * Prosthetic joint; * Presence of broken skin or rash over the area to be injected; * Severe coagulopathy (can take aspirin or anti-platelets inhibitors such as clopidogrel); * Any anti-coagulant therapy (e.g. warfarin); * Severe liver disease or severe kidney disease; * Known hypersensitivity, allergy or intolerance to local anaesthetic / bupivacaine; * Recently taken other medicines containing local anaesthetic / bupivacaine within 1 month; * Surgery planned within 3 months of entry to study; * Neuropathic pain medications such as opioid analgesics, antiepileptic drugs such as pregabalin / gabapentin, and tricyclic antidepressants such as amitriptyline when taken for neuropathic pain treatment; * Current or recent intake centrally-active medication (e.g. have recently taken monoamine oxidase inhibitor (MAOI)); * Complete heart block; * The presence of any contraindication for MRI.