I have an indention on my buttocks from a cortisone shot as a child - what procedure is best for removal? (photos)

I would suggest Needle Subcision to release the scar tissue. Once the scar is lifted, you have several options for improving the texture of the skin, including Sculptra, Microneedling, or PDO smooth threads. If you have any hyperpigmentation issues or develop keloid scarring, that is important to tell the Doctor that treats you.
Dr. Scaljon

It will be challenging to remove such lesion completely, nevertheless a revised surgery fowled by Sculptra treatment could alter the scar significantly, but will never be gone fully.You need to have a consultation with a plastic surgeon to discuss all options

I would be careful using the term "removed" as this type of lesion cannot truly be removed. It could be revised, treated, altered, etc. but will never be gone, just maybe improved. Go see a plastic surgeon to discuss your options.

Best of luck!

Dallas Buchanan, MD
VIVIFY plastic surgery
Tampa, FL