M20.12

Acquired lateral deviation of the left great toe at the first metatarsophalangeal joint, commonly presenting as a visible medial bony prominence (bunion) of the left foot.

Verified May 8, 2026 · 6 sources ↓

Status: Billable
Chapter: 13
Related CPT: 11
Region: Foot & ankle

Drawn from CDCICD10DataIcdcodesAssociationdatabaseAAPC

Documentation tips

What should appear in the chart to support M20.12.

Source · Editorial brief grounded in 6 cited references ↓

Explicitly state 'left foot' in the assessment — laterality must be documented by side name, not just 'affected foot.'
Record weight-bearing radiographic angles: HAV angle (>15°) and intermetatarsal angle (>9°) support clinical validation and medical necessity.
Document the acquired nature of the deformity; if onset was at birth or in early childhood, evaluate for congenital coding (Q66.212) instead.
Include subjective complaints (pain level, aggravating footwear, functional limitation) and objective findings (tenderness at medial MTP, erythema, reduced dorsiflexion ROM) in the progress note.
For surgical encounters, document conservative treatment history (orthotics, NSAIDs, wider footwear, physical therapy) to establish medical necessity for operative intervention.
When billing bilateral correction, confirm both M20.11 and M20.12 are on the claim with the appropriate laterality modifiers (RT/LT or TA/T5 series).

Related CPT procedures

Procedure codes commonly billed with M20.12. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

28292 $703.09

Hallux valgus correction (bunionectomy) with resection of the proximal phalanx base and sesamoidectomy when performed, by any method.

28295 $1,065.15

Surgical correction of hallux valgus (bunion) via proximal metatarsal osteotomy, involving realignment of the first metatarsal at its base with or without sesamoid removal.

28296 $883.45

Surgical correction of hallux valgus (bunion) via distal metatarsal osteotomy, with removal of the bony prominence and optional sesamoidectomy, using any fixation method.

28297 $1,030.75

Hallux valgus correction with bunionectomy (including sesamoidectomy when performed) and first metatarsocuneiform joint arthrodesis, any method.

28298 $860.41

Hallux valgus correction (bunionectomy) with sesamoidectomy when performed, using a proximal phalanx osteotomy by any method — the Akin-type procedure.

28299 $1,036.43

Surgical correction of hallux valgus (bunion) using a double osteotomy technique, with bunionectomy and sesamoidectomy when performed.

28300 $611.24

Osteotomy of the calcaneus (heel bone) to correct foot alignment, with or without internal fixation — encompasses Dwyer, Chambers, and sliding-type procedures.

28740 $848.38

Surgical fusion of a single midtarsal or tarsometatarsal (Lisfranc) joint using internal fixation to permanently immobilize that joint.

73630 $34.07

Radiologic examination of the foot requiring a minimum of three views, used to evaluate fractures, arthritis, tumors, or structural abnormalities.

73620 $28.72

Radiologic examination of the foot, two views — used to evaluate bone and joint abnormalities including fractures, arthritis, and structural deformities.

28290 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M20.12 and adjacent codes.

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

Confusing M20.12 with M21.612 (Bunion of left foot) — these codes are mutually exclusive; M20.12 captures the valgus structural deformity, while M21.612 is for an isolated bursal prominence without the associated toe deformity.
Defaulting to M20.10 (unspecified foot) when laterality is clearly documented in the record — always assign the specific laterality code.
Reporting a single bilateral code for bilateral hallux valgus — no such code exists; bill M20.11 and M20.12 together.
Using M20.12 for congenital presentations — if the deformity was present at birth or noted in early pediatric records, Q66.212 is the correct code.
Omitting pre-operative imaging angle measurements, which can trigger medical necessity audits for bunionectomy claims.

Clinical context

Source · Editorial summary grounded in 6 cited references ↓

M20.12 is the billable code for acquired hallux valgus of the left foot — the classic bunion deformity in which the hallux drifts laterally while the first metatarsal deviates medially. Use it when the deformity is documented as acquired (not congenital) and the affected side is confirmed as the left foot. Clinical validation typically requires a hallux abductus valgus (HAV) angle greater than 15° and an intermetatarsal (IM) angle greater than 9° on weight-bearing radiographs, along with documented lateral deviation of the hallux and medial deviation of the first metatarsal.

For right-foot involvement, use M20.11. When laterality is not specified in the record, fall back to M20.10. Bilateral hallux valgus does not have a single bilateral code — report M20.11 and M20.12 together. Do not confuse M20.12 with M21.612 (Bunion of left foot); the tabular list mutually excludes them. M20.12 captures the structural toe deformity; M21.612 is reserved for an isolated bursal prominence without the underlying valgus deformity. If the deformity is congenital, Q66.212 (Congenital metatarsus primus varus, left foot) applies instead.

This code supports a wide range of encounters: conservative management (orthotics, footwear modification, physical therapy), pre-operative evaluation, and surgical procedures including osteotomies, Lapidus arthrodesis, and soft-tissue corrections. MS-DRG v43.0 groups M20.12 within DRGs 564–566 (Other musculoskeletal system and connective tissue diagnoses with MCC, CC, or without CC/MCC).

Sibling codes

Other billable codes under M20.1 (laterality / anatomic variants).

M20.11

Hallux valgus (acquired), right foot

M20.10

Hallux valgus (acquired), unspecified foot

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 6 cited references ↓

01What is the difference between M20.12 and M21.612?

M20.12 captures the acquired hallux valgus structural deformity (lateral toe drift with medial metatarsal deviation). M21.612 is for an isolated bunion — a bursal prominence at the first MTP without the underlying valgus deformity. The ICD-10-CM tabular list mutually excludes them, so you cannot bill both for the same foot at the same encounter.

02How do I code bilateral hallux valgus?

There is no single bilateral hallux valgus code. Report M20.11 (right foot) and M20.12 (left foot) together on the claim, each with the appropriate laterality modifier.

03Can M20.12 be used for a congenital bunion deformity?

No. M20.12 is explicitly for acquired deformities. If the hallux valgus or associated metatarsus primus varus was present at birth or confirmed as congenital, use Q66.212 (Congenital metatarsus primus varus, left foot) and document the congenital nature in the record.

04What radiographic findings support M20.12?

Weight-bearing radiographs showing a hallux abductus valgus (HAV) angle greater than 15° and an intermetatarsal (IM) angle greater than 9° are the standard clinical validation thresholds. Document both angles in the note to support medical necessity, particularly for surgical authorization.

05Which CPT codes are commonly paired with M20.12?

Bunionectomy procedures (28290–28299) are the most common surgical pairings. Lapidus arthrodesis (28740) is used when first tarsometatarsal joint fusion is performed. Weight-bearing foot X-rays (73620, 73630) support the diagnosis code at imaging encounters.

06What should the provider document to avoid a claim denial for bunion surgery under M20.12?

Document the specific left-foot laterality, radiographic angle measurements, duration and severity of symptoms, functional limitations, and a history of failed conservative care (orthotics, footwear modification, anti-inflammatories, physical therapy). Missing any of these elements is a common trigger for medical necessity denials.

07Is M20.12 valid for FY2026 claims?

Yes. M20.12 has been a stable, billable code since FY2016 with no changes through FY2026 (effective October 1, 2025), per the CDC ICD-10-CM Tabular List 2026.

Sources & references

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

Mira AI Scribe

Mira AI Scribe captures the documented side (left), clinical findings (lateral hallux deviation, medial MTP prominence, tenderness, erythema), ROM measurements, and radiographic angles (HAV and IM) from the encounter note to populate M20.12 accurately. This prevents laterality downcoding to M20.10, blocks erroneous crossover to M21.612, and ensures surgical claims carry the imaging evidence required for medical necessity review.

See how Mira captures M20.12 documentation