Chin Ptosis after Sliding Genioplasty - how is it avoided and how common is it ? (photos)

Hi! I am planning to have a sliding genioplasty to fix my weak chin as I do not like the idea of an implant. I am looking into the risks associated with it (if you have other risks please share). Chin Ptosis seems to be a major one. I am wondering the following: 1) How common is it ? 2) How can it be avoided ? 3) If it does occur- how complicated is it to fix? Thank You!!