M20.40

Acquired hammer toe deformity affecting one or more lesser toes, with laterality not documented or unspecified in the medical record.

Verified May 8, 2026 · 6 sources ↓

Status: Billable
Chapter: 13
Related CPT: 5
Region: Foot & ankle

Drawn from CDCicd10data.com —AAOSAAPCAllZone Medical

Documentation tips

What should appear in the chart to support M20.40.

Source · Editorial brief grounded in 6 cited references ↓

Document laterality explicitly — 'right foot' or 'left foot' — to support M20.41 or M20.42 instead of the unspecified M20.40.
Specify which toe(s) are affected (2nd, 3rd, 4th) and whether the deformity is flexible or rigid at the PIP joint — this drives treatment planning and surgical justification.
Record imaging findings (X-ray results, joint angulation, structural changes) to support clinical validation of the acquired deformity.
Note the acquired nature explicitly; distinguish from any congenital toe conditions in the patient's history to satisfy the Type 1 Excludes rules under M20.
If comorbid corns, callosities, or skin breakdown are present over the PIP joint, code those separately (e.g., L84) — they are not captured by M20.40 alone.

Related CPT procedures

Procedure codes commonly billed with M20.40. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

28285 $548.44

Surgical correction of hammertoe deformity, which may involve interphalangeal joint fusion, partial or total phalangectomy, arthroplasty, or other procedures that restore normal toe alignment.

28286 $430.20

Surgical correction of a hammertoe deformity at the proximal interphalangeal joint, which may involve soft-tissue release, partial or complete bone resection, and stabilization of the affected toe.

73630 $34.07

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

11055 View procedure details

11056 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M20.40 and adjacent codes.

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

Using M20.40 (unspecified foot) when the operative or clinic note clearly names the right or left foot — always assign M20.41 or M20.42 when laterality is documented.
Coding mallet toe or claw toe as M20.40 — mallet toe (DIP joint deformity) and claw toe belong under M20.5X_, not M20.4.
Assigning M20.40 for a congenital hammer toe deformity — M20.4 is explicitly for acquired conditions; congenital deformities map to Q66.-, Q68–Q70, or Q74.- per the Type 1 Excludes note.
Omitting secondary codes for associated soft-tissue complications (corns, ulcerations) that are separately billable and clinically significant.

Clinical context

Source · Editorial summary grounded in 6 cited references ↓

M20.40 codes an acquired hammer toe (or toes) when the treating provider has not specified whether the affected foot is right or left. The deformity involves abnormal flexion at the proximal interphalangeal (PIP) joint of the second, third, or fourth toe — producing the characteristic bent, hammer-like appearance. Because the condition is classified as 'acquired,' it excludes congenital toe deformities (Q66.-, Q68–Q70, Q74.-) and congenital absence of toes (Q72.3-).

Use M20.40 only when laterality is genuinely absent from the documentation. If the note specifies the right foot, use M20.41; left foot, use M20.42. Defaulting to M20.40 when a laterality-specific code is available is a documentation and specificity failure that can trigger payer edits. Clinically, the provider should assess whether the deformity is flexible or rigid at the PIP joint — that distinction drives conservative versus surgical treatment but does not change the ICD-10 code selection within the M20.4 subcategory.

Hammer toe is distinct from mallet toe and claw toe, even though all three involve lesser toe flexion deformities. Mallet toe involves the DIP joint and maps to M20.5X_ (other acquired toe deformities). Claw toe involves both the MTP and IP joints and also maps to M20.5X_ or other deformity codes depending on documentation. Do not default to M20.40 for mallet or claw toe presentations — code specificity matters for accurate episode data and downstream surgical authorization.

Sibling codes

Other billable codes under M20.4 (laterality / anatomic variants).

M20.41

Other hammer toe(s) (acquired), right foot

M20.42

Other hammer toe(s) (acquired), left foot

Frequently asked questions

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

01When is M20.40 the correct code versus M20.41 or M20.42?

Use M20.40 only when laterality is genuinely absent from the documentation. If the note specifies right foot, assign M20.41; left foot, assign M20.42. Laterality-specific codes are always preferred when the information is available.

02Does M20.40 cover mallet toe and claw toe?

No. M20.4 covers hammer toe only — abnormal PIP joint flexion deformity. Mallet toe (DIP joint) and claw toe (combined MTP and IP joint) are coded under M20.5X_ (other acquired deformities of toes). Assigning M20.40 to either of those diagnoses is a specificity error.

03Can M20.40 be used for a congenital hammer toe?

No. The M20.4 subcategory is restricted to acquired deformities. Congenital toe deformities are excluded by the Type 1 Excludes note and map to Q66.-, Q68–Q70, or Q74.- depending on the specific condition.

04What CPT code pairs with M20.40 for surgical correction?

CPT 28285 (correction of hammertoe, e.g., interphalangeal fusion or tendon transfer) is the standard surgical pairing for acquired hammer toe. Append a laterality modifier (-T digit modifiers or -RT/-LT as applicable) and ensure the diagnosis code laterality matches.

05Should I code a corn or callus over a hammer toe separately?

Yes. A corn or callosity overlying the PIP joint (L84) is a distinct condition and should be coded separately when documented and addressed clinically. M20.40 does not capture associated skin pathology.

06Is M20.40 valid for bilateral hammer toes?

There is no single bilateral hammer toe code in the M20.4 subcategory. If both feet are affected and documented, assign M20.41 and M20.42 together. M20.40 is for unspecified laterality, not confirmed bilateral disease.

07Does the flexible vs. rigid distinction affect the ICD-10 code?

No — both flexible and rigid hammer toe deformities map to M20.4 (with appropriate laterality). However, documenting flexibility or rigidity is important for medical necessity, particularly when requesting authorization for surgical intervention.

Sources & references

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

01CDC ICD-10-CM Tabular List 2026 — https://icd10cmtool.cdc.gov/
02icd10data.com — https://www.icd10data.com/ICD10CM/Codes/M00-M99/M20-M25/M20-/M20.40
03AAOS OrthoInfo: Hammer Toe — https://orthoinfo.aaos.org/en/diseases--conditions/hammer-toe/
04AAPC Codify: M20.40 — https://www.aapc.com/codes/icd-10-codes/M20.40
05AAPC Outpatient Facility Coding Alert — https://www.aapc.com/codes/scc_articles/article_pdf/53/icd-10-coding-learn-the-basics-of-hammer-toe-coding-using-this-guide-157917
06AllZone Medical Solutions Foot Surgery Coding Guide — https://www.allzonems.com/blogs/foot-surgery-medical-coding-icd10-cpt-hcpcs-guide/

Mira AI Scribe

Mira's AI scribe captures the affected foot (right, left, or bilateral), specific toe(s) involved, PIP joint flexibility status, imaging findings confirming structural deformity, and any documented conservative care history. Complete capture of laterality prevents defaulting to the unspecified M20.40 and supports the higher-specificity codes M20.41 or M20.42, reducing the risk of payer edits and medical necessity denials for surgical procedures like 28285.

See how Mira captures M20.40 documentation