Mary,
Here's some information I have...
"If the surgeon harvests and places the bone via the same incision, by taking, for example, bone tissue from the ribs, spinous process or laminar fragments, it would be appropriate to select the autograft code 20936. If the surgeon harvests and removes the bone through a skin or fascial incision, then makes a second, separate incision to place the bone in the spine, it would need to be determined if the graft is structural or morselized."
Structural autograft=20938
Structural allograft=20931
Morselized autograft=20937
Morselized allograft=20930
The op note should indicate structural v/s morselized
Does this help?