Let me explain. Post traumatic arthritis happened after traumatic injury to the joint and supporting structures. If the joint for example had ligament injury(acl)arthritis could start in the joint in about 6-9 month.If the bone in the joint have break it well have arthritis set in itdepending on the severity of the fracture. If both the ligament and the bone were injured, this shorten the period of the arthritis.
See below. It typically takes years for the changes associated with post traumatic arthritis to develop.It is usually caused by an initial injury that makes the joint somewhat unstable and causes irregular weight bearing characteristics which then affects the cartilage weight bearing surface of the joint.