Hard Lumps in Buttocks After Fat Transfer

Regardless where the fat is injected, hard lumps should not occur. Usually fat has a chance to live when small amounts are delivered into a well vascularized space (enough blood circulation to create a neighborhood of oxygen-rich cells to make the new cells survive). If however, there is a large amount in one area, the center of the fat mass may die as oxygen can't travel the distance through all these new cells from the outside of the mass.  Cysts can occasionally form but delayed infections can also develop. Hematomas are blood collections and they may solidify after a while. These can get infected and even calcify after many months.  You should be seen by your surgeon for an evaluation.

fat grafting to the buttock can have an area of fat necrosis, which result in hardening and lumpiness.

It also could be an oil cyst.

All will resolve, cyst can be aspirated.

Some areas of firmness are quite common after fat transfer.  The firm areas are collections of fat that are not viable and your body is reacting around them to get rid of them.  This process will take time, perhaps 3-6 months, depending upon the amount of each area.  Let your doctor give you specific advice.