ICD-10-CM > M00-M99 > M65-M67 > M66 > M66.3 > M66.36 M66.36 Spontaneous rupture of flexor tendons, lower leg Non-Billable/Non-Specific Codes M66.361Spontaneous rupture of flexor tendons, right lower legM66.362Spontaneous rupture of flexor tendons, left lower legM66.369Spontaneous rupture of flexor tendons, unspecified lower leg