The grading of long-tubular-bone pseudarthrosis depends on the biological reaction or lack of reaction in pseudarthrosis or non-unions. Hypertrophic and oligotrophic pseudarthrosis belongs to biologically reacting non-unions, whereas non-reacting non-unions are necrotic pseudarthrosis and defective non-unions with partial decline or complete destruction of cortical substance. Pseudarthrosis is a serious disturbance or disorder within the regulation cycle in fracture healing, which consists of osteoregeneration, osteovascularization and stabilization. The causes and underlying reasons for disturbance of this regulation cycle are primarily massive destruction of the biological and functional very important unity of periost, cortical substance and medullary space. This can occur from trauma, but it happens more often from surgical procedures that do not take the biological principles of bone-healing into account. Surgical strategies and interventions that respect the importance of periosteal tissue, cortical tissue and medullary space do fill the biological principles of fracture-healing and fracture union.