We use -51 when we do more than 1 postop pain injection/catheter placement. For example, when surgeon does a total knee replacement, our docs will many times do a sciatic block with a femoral catheter nerve block. We put our -51 on the least expensive charge of the two, so it might look like 64448-59, 64445-59,51. We recently saw guidance on this in (I think) the Pain Pink Sheet from Decision Health. Other than this scenario, we don't use the -51.