Spontaneous rupture of tendons at more than one anatomical site, where the tendons involved do not fall under the extensor (M66.2x) or flexor (M66.3x) classifications and the rupture occurs through normal force applied to structurally compromised tissue.

Documentation tips

What should appear in the chart to support M66.89.

Source · Editorial brief grounded in 5 cited references ↓

• Name each ruptured tendon explicitly (e.g., 'patellar tendon and peroneal tendon') — 'multiple tendons' alone is insufficient for audit defense.
• Specify laterality for each involved site; the code itself is non-lateral, but procedure codes and operative reports will require right/left designation.
• Document the clinical basis for spontaneous (non-traumatic) classification: absence of acute injury mechanism, imaging findings (MRI/ultrasound showing degeneration or full-thickness tear without acute trauma), and any predisposing conditions such as fluoroquinolone use, rheumatoid arthritis, gout, or chronic corticosteroid therapy.
• Record whether ruptures are acute, subacute, or chronic at each site — this affects surgical planning and may affect payer medical necessity review.
• If a predisposing systemic condition (e.g., rheumatoid arthritis M05.x, renal failure N18.x) is present and treated concurrently, code it as an additional diagnosis to support medical necessity.

Related CPT procedures

Procedure codes commonly billed with M66.89. Linking the right diagnosis to the right procedure is what establishes medical necessity.

Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis

Common coding pitfalls

The recurring mistakes coders make with M66.89 and adjacent codes.

Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓

• Using M66.89 for extensor or flexor tendon ruptures at multiple sites — those belong to M66.29 (extensor, multiple sites) or M66.39 (flexor, multiple sites), not M66.89.
• Applying M66.89 when only a single 'other' tendon site is ruptured — use the appropriate single-site code (M66.80–M66.88) instead.
• Coding M66.89 for a traumatic rupture where abnormal force was applied to normal tissue — traumatic tendon ruptures are coded from the injury chapter (S-codes by body region), not M66.
• Omitting the Excludes2 note: rotator cuff syndrome (M75.1x) is excluded from M66 by an Excludes2 notation, meaning both codes can be reported if both conditions are independently documented, but the rupture must not be the same pathology as the rotator cuff syndrome already captured under M75.1x.
• Failing to distinguish M66.89 from M66.9 (spontaneous rupture of unspecified tendon) — M66.89 requires documented identification of multiple 'other' tendon sites; M66.9 is appropriate only when tendon type and site are genuinely unspecified.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Sibling codes

Other billable codes under M66.8 (laterality / anatomic variants).