ICD-10-CM > M00-M99 > M40-M43 > M40 > M40.3 M40.3 Flatback syndrome Non-Billable/Non-Specific Codes M40.30Flatback syndrome, site unspecifiedM40.35Flatback syndrome, thoracolumbar regionM40.36Flatback syndrome, lumbar regionM40.37Flatback syndrome, lumbosacral region