Neurosurgery and Orthopaedics do a co-surgery of a spinal fusion. Our Neurosurgeon does the decompression and then as co-surgery they do the fusion, and instrumentation with Ortho. For billing, we currently bill the Neurosurgeon the decompression (63001), then the fusion as a co-surgery (22590 mod 62), and not the instrumentation. Ortho bills the fusion as a co-surgery (22590 mod 62) and they also bill the instrumentation (22840). My question is even though the instrumentation can't be billed as a co-surgery, can actually bill the Neurosurgeon as an assistant?