Excerpt from Medicare's "incident to" guidelines...
"There must have been a direct, personal, professional service furnished by the physician to initiate the course of treatment of which the service being performed by the nonphysician practitioner is an incidental part, and there must be subsequent services by the physician of a frequency that reflects the physician's continuing active participation in and management of the course of treatment.
2 years is too long. I have known some practices to alternate the visits between the midlevel and the provider. I've seen others schedule the patient with the provider at every 3rd visit (assuming there haven't been any new issues). I recommend that your practice create a policy for the frequency that a provider needs to see patients under "incident to" guidelines.