Acquired medial deviation of the great toe at the first metatarsophalangeal joint, laterality not documented or not specified by the treating provider.
Verified May 8, 2026 · 6 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 6
- Region
- Foot & ankle
Documentation tips
What should appear in the chart to support M20.30.
Source · Editorial brief grounded in 6 cited references ↓
- Document laterality by name — 'right foot' or 'left foot' — in every relevant note section (chief complaint, exam, assessment/plan) so coders can escalate to M20.31 or M20.32 instead of defaulting to M20.30.
- Specify 'acquired' versus congenital origin; note the precipitating cause (e.g., post-bunionectomy overcorrection, rheumatoid arthritis, traumatic injury) to support the M20.3x family over Q-code alternatives.
- Record imaging findings that confirm medial MTP deviation — weight-bearing X-ray views, intermetatarsal angle measurements, or MTP joint alignment — to substantiate the diagnosis on audit.
- If the patient has a history of hallux valgus surgery on the same foot, document that prior procedure explicitly; it clarifies the acquired etiology and supports medical necessity for any corrective intervention.
- For bilateral presentations, document each foot separately with its own laterality-specific code (M20.31 + M20.32) rather than defaulting to the unspecified M20.30.
Related CPT procedures
Procedure codes commonly billed with M20.30. 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 M20.30 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Using M20.30 when laterality is clearly stated in the record — if the note says 'right foot,' M20.31 is required; M20.30 on a laterality-documented chart is a specificity downgrade that can trigger a payer audit flag.
- Confusing hallux varus (medial deviation, M20.3x) with hallux valgus (lateral deviation, M20.1x) or hallux rigidus (MTP stiffness, M20.2x) — each is a distinct parent code with separate reimbursement implications.
- Applying M20.30 to congenital great-toe deformities — the M20 category carries an Excludes1 for congenital deformities and malformations of fingers and toes (Q66.-, Q68-Q70, Q74.-); those cases require Q-series codes, not M20.3x.
- Omitting secondary diagnosis codes for comorbidities such as inflammatory arthropathy (e.g., rheumatoid arthritis) that may have caused the varus deformity, missing an opportunity to capture CC/MCC weight in the MS-DRG grouping.
Clinical context
Source · Editorial summary grounded in 6 cited references ↓
M20.30 captures acquired hallux varus — a condition in which the great toe deviates medially (away from the second toe) at the MTP joint — when the operative or clinical note does not specify right or left foot. The 'acquired' designation distinguishes it from congenital great-toe deformities coded under Q66.-, Q68-Q70, or Q74.-; do not use M20.30 for congenital presentations.
This code sits under parent M20.3 (Hallux varus, acquired) alongside laterality-specific siblings M20.31 (right foot) and M20.32 (left foot). Because ICD-10-CM guidance consistently discourages unspecified codes when laterality is clinically documented, M20.30 should function as a last resort — appropriate only when the record genuinely does not identify the affected side (e.g., a legacy chart note, a referral without source documentation, or a bilateral presentation where no laterality distinction is needed for the encounter). If the foot is named in the note, escalate to M20.31 or M20.32.
Hallux varus in the acquired category typically results from overcorrection of hallux valgus surgery, inflammatory arthropathy, or trauma. Podiatric and orthopedic foot-and-ankle specialists are the primary users of this code. MS-DRG grouping falls under 564–566 (Other musculoskeletal system and connective tissue diagnoses, with or without CC/MCC), making accurate CC/MCC documentation on the claim meaningful for facility reimbursement.
Sibling codes
Other billable codes under M20.3 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 6 cited references ↓
01When is it acceptable to use M20.30 instead of M20.31 or M20.32?
02Can M20.30 be used for bilateral hallux varus?
03What distinguishes acquired hallux varus (M20.3x) from a congenital presentation?
04Which CPT procedures are commonly linked to M20.30 as a supporting diagnosis?
05Does M20.30 require a 7th-character extension?
06How does M20.30 affect facility MS-DRG assignment?
07Is M20.30 appropriate for post-surgical hallux varus overcorrection at the first post-op visit?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026 (effective Oct 1, 2025)
- 02icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M20-M25/M20-/M20.30
- 03aapc.comhttps://www.aapc.com/codes/icd-10-codes/M20.30
- 04aapc.comhttps://www.aapc.com/codes/icd-10-codes/M20.3
- 05pmc.ncbi.nlm.nih.govhttps://pmc.ncbi.nlm.nih.gov/articles/PMC8783617/
- 06aaos.orghttps://www.aaos.org/globalassets/quality-and-practice-resources/coding-and-reimbursement/resident-guide/resident-guide_icd10.pdf
Mira AI Scribe
The Mira AI Scribe captures the affected foot (right, left, or bilateral), the likely etiology (prior bunion surgery, inflammatory disease, trauma), MTP joint alignment on physical exam, and any imaging confirming medial great-toe deviation. That detail lets the coder assign M20.31 or M20.32 instead of the unspecified M20.30 — preventing specificity downgrades, reducing audit exposure, and preserving accurate laterality data for any subsequent corrective procedure authorization.
See how Mira captures M20.30 documentation