Spontaneous rupture of flexor tendons, unspecified upper arm

This code describes the non-traumatic tearing of a flexor tendon in an unspecified upper arm. This spontaneous rupture occurs without an external force or injury, often due to underlying degenerative changes, inflammatory conditions, or systemic diseases weakening the tendon structure.

Apply this code when documentation clearly indicates a spontaneous (non-traumatic) rupture of a flexor tendon in the upper arm, and the specific side (right or left) is not documented. This diagnosis is typically supported by imaging studies (e.g., MRI, ultrasound) confirming the tear and a patient history ruling out acute injury.

• Ensure the documentation explicitly states "spontaneous" or "non-traumatic" to differentiate from traumatic ruptures.
• Avoid using this code if the specific upper arm (right or left) is identified; instead, use the more specific M66.321 or M66.322.
• Look for associated conditions like rheumatoid arthritis, chronic steroid use, or fluoroquinolone antibiotic use, which can predispose to spontaneous tendon ruptures, and code them as secondary diagnoses.