In the event of difficulties during registration, a prudent registration plan should include a primary and secondary registration technique.
For example, a surgeon using skin surface registration should place virtual anatomic bony landmarks which can be used should the skin surface registration fail.
Similarly a surgeon using an oral appliance should consider placing bony anatomic landmarks in the event that the appliance is unavailable or not adequate for registration.
A final backup strategy is intraoperative registration, which can be used if the DRF is dislodged from the skull. Intraoperative registration is performed by defining four or more anatomic landmarks (drill holes, ink marks, or screws) on the skull after the initial registration has been completed.
Should the skull reference become dislodged during the procedure, these intraoperative landmarks can then be used to re-register the patient after the skull reference array is reapplied.