Answer: The most accurate way to differentiate segmental (22842-22844) from nonsegmental (22840) posterior instrumentation is to count the number of fixation points.
If the surgeon attaches the instrumentation to the spine at only two points, the device is nonsegmental (regardless of the number of vertebrae spanned).
If the surgeon attaches the device to at least three points (on three different segments), the instrumentation is segmental.
In some cases, the orthopedic surgeon will place a metal cage or other prosthetic device for stabilization in an area where he has removed a large portion of the vertebra. This represents a third type of instrumentation, which you should report using 22851 (Application of intervertebral biomechanical device[s] [e.g., synthetic cage(s), threaded bone dowel(s), methylmethacrylate] to vertebral defect or interspace).
Report only a single unit of 22851, regardless of how many devices the surgeon places at one level. If the surgeon places devices on multiple spinal levels, however, you may report multiple units of 22851 (one unit for each individual spinal level).
Example: The surgeon places two cages at level T6. Report 22851 x 1.
Alternatively, the surgeon places two cages at level T6 and a third cage at level T5. Report 22851 x 2.
Some payers may require that you append modifier 59 (Distinct procedural service) to the -additional- units of 22851 to distinguish them as occurring at separate anatomic locations.