How long does it take to develop arthritis in the spine? i have been told i have developed pseudarthrosis and/or arthritis due 2 mva 3 months ago in l5

Usually it takes --: Up to 15 years. I think you are too young to get it now and only after 3 months from injury to l5. One might develop some features of arthritis early on. Pseudoarthrosis is not arthritis. It means a false-joint and usually develops at a fracture site due to incomplete healing of the bone with too early motion at the fracture site, so that site acts like an extra joint.