Four stages are generally recognized in the progression of Osteoarthritis, although sometimes five stages (listing stage one as normal) or three stages where intermediate stages 2 and 3 are combined (as just a matter of degree).

There are four (generally accepted) stages in the progression of OA – ranging from “Mild” to “Severe.”

Stage 1 or Mild OA, occurs when some cartilage becomes worn, resulting in a thinner cartilage layer. Usually, there is no pain associated with this stage.

Stage 2 Continued damage to the cartilage results in a minor narrowing of the joint space and Osteocytes begin to appear. There are three types of cells in bone tissue; osteoblasts, osteoclasts and osteocytes. Osteocytes are considered to be mature osteoblasts, and they do not secrete bone matrix. Their function is to maintain the metabolism by the exchange of nutrients and to eliminate wastes. The purpose of the appearance of Osteocytes is not well understood. There is reducedbone remodeling processes with increased osteoblast activity in OA(1).

Stage 3  During this stage, cartilage deterioration begins to reduce the joint space which increases friction between the thinner cartilage pads. As a result, more cartilage is worn away and gaps begin to appear.

Stage 4 OA progresses through to its final stage when it is diagnosed as “severe”. At this point, a significant portion of the bones in the affected joint are touching each other – as is illustrated below:

There are four stages of increasing severity for osteoarthritis, ranging from minor to severe. (1) Corrado, A, Neve, A, Macchiarola, A, Gaudio,A, Marucci,A, Cantatore,FP, RANKL/OPG ratio and DKK-1 expression in primary osteoblastic cultures from osteoarthritic and osteoporotic subjects. J Rheumatol. 2013 May;40(5):684-94