M66.80

Spontaneous (non-traumatic) rupture of a tendon that does not fall under the specifically classified extensor (M66.2), flexor (M66.3), or other named tendon categories, with no body site documented or determinable from the record.

Verified May 8, 2026 · 5 sources ↓

Status: Billable
Chapter: 13
Related CPT: 13
Region: General

Drawn from CDCICD10DataAAPCHealthCMS

Documentation tips

What should appear in the chart to support M66.80.

Source · Editorial brief grounded in 5 cited references ↓

Provider must name the specific body region (e.g., forearm, ankle, hand) — without it, M66.80 is the only defensible code and specificity is lost.
Document the tendon by name (e.g., peroneal, posterior tibial, patellar) to confirm this is an 'other tendon' rupture and not a rotator cuff (M75.1-) or named extensor/flexor tendon rupture.
Record whether the rupture was atraumatic or occurred under normal load — this is the definitional basis for the entire M66 category and distinguishes it from traumatic rupture coded with S-codes.
Note any predisposing conditions (fluoroquinolone use, corticosteroid history, inflammatory arthropathy, dialysis) that explain why normal force caused rupture; these may warrant additional codes.
Imaging findings (MRI or ultrasound showing full-thickness tear vs. partial) should be recorded to support the spontaneous rupture diagnosis and guide procedure coding.

Related CPT procedures

Procedure codes commonly billed with M66.80. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

27680 $408.49

Surgical release of a single flexor or extensor tendon in the leg or ankle to free it from scarring or adhesions restricting motion.

27681 $489.66

Tenolysis of multiple flexor or extensor tendons in the leg and/or ankle, performed through separate incisions to free adhesions and restore function.

26440 $642.63

Surgical release of a flexor tendon adhered within the palm or finger, restoring gliding function through the tendon sheath.

24357 $384.44

Percutaneous repair of the elbow tendon, performed through a minimally invasive approach without a large open incision.

24358 $500.01

Open tenotomy of the lateral or medial elbow with debridement of soft tissue and/or bone, performed for conditions such as lateral epicondylitis (tennis elbow) or medial epicondylitis (golfer's elbow).

24359 $616.91

Open elbow tenotomy with soft tissue and/or bone debridement plus tendon repair or reattachment, performed at the lateral or medial epicondyle for conditions such as epicondylitis.

28200 $504.35

Surgical repair of a flexor tendon in the foot — primary or secondary — without the use of a free graft, reported per tendon.

28202 $608.56

Delayed repair of a foot flexor tendon using a free graft harvested from a separate donor site; reported per tendon repaired and includes graft procurement.

73221 $205.08

MRI of any upper extremity joint — shoulder, elbow, or wrist — performed without contrast material.

73721 $204.41

MRI of a lower extremity joint (hip, knee, or ankle) performed without contrast material.

26441 View procedure details

73223 View procedure details

73723 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M66.80 and adjacent codes.

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

Using M66.80 when the body site is clearly documented — the moment site is known, a more specific M66.8x child code (e.g., M66.841 for right hand) is required.
Confusing M66.80 with M66.20 (extensor tendons, unspecified site) or M66.30 (flexor tendons, unspecified site) — those families have their own unspecified-site codes; M66.80 is reserved for tendons that are neither extensor nor flexor as classified here.
Applying M66.80 to rotator cuff rupture — the Tabular List Excludes2 note under M66 directs rotator cuff syndrome to M75.1-; these are not interchangeable.
Coding a traumatic tendon rupture (caused by abnormal force on normal tissue) with M66.80 — traumatic ruptures belong in the injury chapter (S-codes) with the appropriate 7th-character encounter extension.
Failing to query for laterality before assigning M66.80 — payers increasingly deny unspecified codes when site documentation is present elsewhere in the record.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

M66.80 is the unspecified-site fallback within the M66.8 family (spontaneous rupture of other tendons). Use it only when the operative or clinical note fails to identify the body region involved. The M66.8x family covers tendons that are not rotator cuff (excluded under M75.1-), not extensor tendons (M66.2-), and not flexor tendons (M66.3-). 'Spontaneous' under M66 means the rupture occurred under normal mechanical load applied to tissue that was already compromised — not that the mechanism was unknown.

Site-specific codes exist for shoulder (M66.81x), upper arm (M66.82x), forearm (M66.83x), hand (M66.84x), thigh, lower leg, ankle/foot, and other/multiple sites. If the provider documents any of these regions, you must use the site-specific code rather than M66.80. Staying at M66.80 when laterality and site are documented is a specificity failure that will flag on payer audits.

When the tendon type is known but the site is not, M66.80 still applies within the 'other tendons' parent. If the tendon type is also unspecified, verify whether M66.9 (spontaneous rupture of unspecified tendon, unspecified site) is more accurate. Document query to the provider before defaulting to M66.80.

Sibling codes

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

M66.89

Spontaneous rupture of other tendons, multiple sites

M66.88

Spontaneous rupture of other tendons, other sites

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 5 cited references ↓

01When is M66.80 the correct code rather than a more specific M66.8x code?

M66.80 is correct only when the clinical documentation genuinely does not identify the body site of the ruptured tendon. If any site is documented — shoulder, hand, ankle, etc. — you must use the corresponding site-specific child code under M66.8.

02Does M66.80 cover rotator cuff rupture?

No. The Tabular List places an Excludes2 note on M66 directing rotator cuff syndrome to M75.1-. Rotator cuff ruptures are coded separately and M66.80 should not be used for them.

03How does M66.80 differ from M66.9?

M66.80 specifies that the ruptured tendon is in the 'other tendons' category — meaning not an extensor (M66.2) or flexor (M66.3) tendon — but the site is unspecified. M66.9 is used when both the tendon type and the site are unspecified.

04Can M66.80 be used for a partial tendon tear?

M66 category language references rupture; a partial tear may qualify if the provider documents it as a spontaneous rupture under normal load. If the provider documents only a partial tear without using rupture language, verify the diagnosis before assigning M66.80.

05Should a predisposing drug cause (e.g., fluoroquinolone-induced tendon rupture) change the code from M66.80?

The principal diagnosis remains M66.80 (or the site-specific equivalent), but you should add an adverse effect code from the T36-T50 range to identify the drug responsible, per ICD-10-CM Official Guidelines for adverse effects.

06Is M66.80 valid for an initial outpatient encounter, or only inpatient?

M66.80 is a billable code valid in both outpatient and inpatient settings. There are no encounter-type restrictions; it carries no 7th-character extension requirement since it is an M-code, not an injury S-code.

07What ICD-9-CM code did M66.80 replace?

M66.80 maps from ICD-9-CM 727.69 (nontraumatic rupture of other tendon), which was also used for other tendon ruptures not elsewhere classified per the DoD AFHSB surveillance case definition crosswalk.

Sources & references

Editorial content was developed using the following public sources. Last verified May 8, 2026.

Mira AI Scribe

Mira's AI scribe captures the affected body region, tendon name, mechanism (atraumatic vs. traumatic), any predisposing systemic factors (steroids, fluoroquinolones, inflammatory disease), and imaging results (MRI/ultrasound grade). Capturing these details at the encounter prevents a fallback to M66.80 and ensures the most specific M66.8x site-and-laterality code is assigned — avoiding payer denials for unspecified coding.

See how Mira captures M66.80 documentation