Inclusion Criteria:  Primary OA according to the American College of Rheumatology criteria1. Self-reported pain, aching, or stiffness of the index knee on most days of the past month, and a knee pain score of greater than 40 out of 100 on a visual analogue scale (VAS). Radiological OA greater than Kellgren-Lawrence (K-L) grading scale 2 Patients aged over 18 years Patient willing to undergo synovial sampling at 3 months post injection.  Exclusion Criteria:  Previous trauma with significant alteration in bone architecture Symptoms of spinal disease Prior injection in the last 12 months Joint re-placement operation on the other knee Cognitive disorders Inflammatory arthritis (i.e., rheumatoid arthritis, spondylarthritis and gout) Fibromyalgia Auto-immune disease (i.e., connective tissue disorders) Previous history of septic arthritis. Unwilling or unable to give informed consent