Question: If a patient suffers an intervertebral annulus fibrosis defect in the lumbar region, which ICD-10 code should I choose to represent the condition? AAPC Forum Subscriber Answer: It depends on the size of the defect. Payer policies might vary slightly, but any defect less than 6mm (or a Carragee type 1, 3, or 4 herniation) is generally considered small; code any defects 6mm or greater as large. If the physician decides that the defect is small, report M51.A1 (Intervertebral annulus fibrosus defect, small, lumbar region). If the physician decides that the defect is large, report M51.A2 (Intervertebral annulus fibrosus defect, large, lumbar region). If the physician doesn’t specify the defect’s size, report M51. A0 (Intervertebral annulus fibrosus defect, lumbar region, unspecified size).