when the gap between the bone ends is less than 0.01 mm, and interfragmentary strain is less than 2%, contact healing can occur. in this case, cutting cones, which consists of osteoclasts, form across the fracture lines, generating cavities at a rate of 50–100 μm/day. osteoblasts fill up the cavities with the haversian system. this causes the formation of lamellar bone that orients longitudinally along the long axis of the bone. blood vessels form that penetrate the haversian system. remodelling of lamellar bone results in healing without callus formation.