The subacute course of IVDD starts one week after the initial event and goes for about 6 weeks until the disease enters the chronic stage. Within one week, the secondary damage to the spinal cord has occurred with the release of the inflammatory mediators and changes in blood flow and swelling. Healing begins in the subacute phase, swelling is dissipating and blood flow is returning. Stem cell administration is most effective during this stage and administration into the subarachnoid space or direct injection into the spinal cord are both effective routes. There is evidence that repeated administration every two weeks may be more effective. Homing of stem cells (the migration of the stem cells to the area of damage) is effective as long as the healing process is active. This time period is usually the first six weeks after a spinal cord injury. After this time direct injection into the spinal cord is more effective and injections above (toward the head) the lesion and into the lesion are most effective.