ICD-10-CM > M00-M99 > M65-M67 > M66 > M66.3 > M66.33 M66.33 Spontaneous rupture of flexor tendons, forearm Non-Billable/Non-Specific Codes M66.331Spontaneous rupture of flexor tendons, right forearmM66.332Spontaneous rupture of flexor tendons, left forearmM66.339Spontaneous rupture of flexor tendons, unspecified forearm