ICD-10-CM > M00-M99 > M65-M67 > M66 > M66.2 > M66.21 M66.21 Spontaneous rupture of extensor tendons, shoulder Non-Billable/Non-Specific Codes M66.211Spontaneous rupture of extensor tendons, right shoulderM66.212Spontaneous rupture of extensor tendons, left shoulderM66.219Spontaneous rupture of extensor tendons, unspecified shoulder