ICD-10-CM > M00-M99 > M65-M67 > M66 > M66.3 > M66.32 M66.32 Spontaneous rupture of flexor tendons, upper arm Non-Billable/Non-Specific Codes M66.321Spontaneous rupture of flexor tendons, right upper armM66.322Spontaneous rupture of flexor tendons, left upper armM66.329Spontaneous rupture of flexor tendons, unspecified upper arm