M20.10

Acquired lateral deviation of the great toe (hallux valgus / bunion) where the treating clinician has not documented or cannot determine which foot is affected.

Verified May 8, 2026 · 5 sources ↓

Status: Billable
Chapter: 13
Related CPT: 9
Region: Foot & ankle

Drawn from CDCICD10DataAAPCUnboundmedicine

Documentation tips

What should appear in the chart to support M20.10.

Source · Editorial brief grounded in 5 cited references ↓

Specify laterality by name (right or left foot) in every note — this single step eliminates the need for M20.10 in most encounters.
Record weight-bearing radiograph findings including hallux valgus angle (HVA) and intermetatarsal angle (IMA) to support severity and surgical necessity.
Document whether the deformity is acquired versus congenital; acquired status is required for the entire M20.1x family.
Note conservative care history — orthotics, shoe modification, padding — if surgical intervention is being planned, as payers frequently require it.
For bilateral cases, document each foot separately in the assessment; assign both M20.11 and M20.12 rather than defaulting to M20.10.

Related CPT procedures

Procedure codes commonly billed with M20.10. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

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.

28292 $703.09

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

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.

28293 View procedure details

28294 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M20.10 and adjacent codes.

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

Using M20.10 when the operative or imaging report clearly identifies the affected foot — specificity is available, so the unspecified code is not justified and risks claim denial.
Assigning M20.10 for a congenital bunion deformity — congenital hallux valgus belongs in the Q66 category, not M20.1x.
Confusing hallux valgus (M20.1x) with hallux rigidus (M20.2x) or hallux varus (M20.3x) — verify the documented deformity type before selecting the code.
Failing to code bilateral deformity correctly by using M20.10 as a proxy — bilateral disease requires M20.11 and M20.12 reported together.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

M20.10 captures documented, acquired hallux valgus when laterality is not specified in the clinical record. It sits under parent code M20.1 alongside M20.11 (right foot) and M20.12 (left foot). Use M20.10 only when the operative report, clinic note, or imaging report genuinely omits or cannot confirm sidedness — not as a shortcut when the affected foot is known.

This code is appropriate for initial and follow-up encounters alike, provided documentation remains laterality-neutral. If a subsequent note specifies the foot, update the code to M20.11 or M20.12 accordingly. M20.10 is a billable, reimbursable code, but payers — particularly Medicare Advantage and commercial plans — frequently flag unspecified laterality codes for review or denial when the deformity is clearly unilateral and the foot should be identifiable from the record.

Do not use M20.10 for congenital deformity; congenital hallux valgus maps to the Q66 category. Also distinguish hallux valgus (M20.1x) from hallux rigidus (M20.2x) and hallux varus (M20.3x) — all three are distinct deformities with their own code families. When the bunion is truly bilateral, assign M20.11 and M20.12 together; there is no single bilateral code in this family.

Sibling codes

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

M20.11

Hallux valgus (acquired), right foot

M20.12

Hallux valgus (acquired), left foot

Frequently asked questions

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

01When is it acceptable to use M20.10 instead of M20.11 or M20.12?

Only when the clinical record genuinely does not identify which foot is affected. If the provider's note, imaging report, or operative report names the side, use the laterality-specific code — M20.11 for right, M20.12 for left.

02Can M20.10 be used for bilateral hallux valgus?

No. For bilateral disease, assign both M20.11 (right) and M20.12 (left). M20.10 does not represent bilateral involvement; it represents an unspecified single foot.

03What is the correct code for a congenital bunion deformity?

Congenital hallux valgus does not belong in M20.1x. Route congenital deformities to the appropriate Q66 subcategory. The M20.1x family is restricted to acquired conditions.

04Which CPT codes most commonly pair with M20.10 on a claim?

Bunionectomy procedures most commonly paired include 28296 (Lapidus-type or with metatarsal osteotomy), 28297, 28298, 28299 (other bunionectomy variants), and 28292 (Keller-type). Imaging codes 73630 and 73620 support pre-operative workup.

05Will payers deny a claim coded with M20.10?

Not automatically, but M20.10 is an unspecified laterality code and is subject to additional documentation scrutiny by Medicare Advantage and many commercial payers. Denials or requests for records are more likely when the deformity is clearly unilateral and sidedness should be apparent from the record.

06How does M20.10 differ from M20.11 and M20.12?

The sixth character distinguishes them: 0 = unspecified foot, 1 = right foot, 2 = left foot. All three describe the same acquired hallux valgus deformity — the only difference is documented laterality.

07Should M20.10 be updated mid-treatment if laterality becomes documented?

Yes. If a subsequent encounter note or imaging report specifies the affected foot, update the diagnosis code to M20.11 or M20.12 for that date of service and all future encounters.

Sources & references

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

01CDC ICD-10-CM Tabular List 2026 (effective October 1, 2025)
02
icd10data.com
https://www.icd10data.com/ICD10CM/Codes/M00-M99/M20-M25/M20-/M20.10
03
icd10data.com
https://www.icd10data.com/ICD10CM/Codes/M00-M99/M20-M25/M20-/M20.1
04
aapc.com
https://www.aapc.com/codes/icd-10-codes/M20.10
05
unboundmedicine.com
https://www.unboundmedicine.com/icd/view/ICD-10-CM/912181/all/M20_10___Hallux_valgus__acquired___unspecified_foot

Mira AI Scribe

Mira captures laterality, deformity type (acquired vs. congenital), weight-bearing radiograph angles (HVA, IMA), symptom duration, and conservative care history from the encounter note. That documentation drives the code to M20.11 or M20.12 and prevents M20.10 from appearing on the claim — avoiding the unspecified-laterality audit flag and supporting surgical authorization requests.

See how Mira captures M20.10 documentation