2026 ICD-10-CM Diagnosis Code S42.309PUnspecified fracture of shaft of humerus, unspecified arm, subsequent encounter for fracture with malunion

ICD-10-CM Codes›S00–T88›S40-S49›S42

ICD-10-CM S42.309P
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

S42.309P is a billable ICD-10-CM diagnosis code for unspecified fracture of shaft of humerus, unspecified arm, subsequent encounter for fracture with malunion. The 7th character P reports a subsequent encounter for a fracture that has healed in a faulty position, called a malunion. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 564 through 566. The code is flagged as an unspecified code, since codes identifying laterality exist in the same family and exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Fracture of the upper limb, subsequent encounter.

Code Identity

ICD-10-CM Code
S42.309P
Billable Status
Yes — Valid for Submission
Code Describes
Unspecified fracture of shaft of humerus, unspecified arm, subsequent encounter for fracture with malunion
Short Description
Unsp fx shaft of humerus, unsp arm, subs for fx w malunion
Parent Code
S42.309
Unspecified fracture of shaft of humerus, unspecified arm

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionS40-S49Injuries to the shoulder and upper arm
CategoryS42Fracture of shoulder and upper arm
This CodeS42.309PUnspecified fracture of shaft of humerus, unspecified arm, subsequent encounter for fracture with malunion

Code EditsBilling

Medicare Code Editor checks that affect claim validity for S42.309P.

Unspecified codes
Unspecified codes exist in the ICD-10-CM classification for circumstances when documentation in the medical record does not provide the level of detail needed to support reporting a more specific code. However, in the inpatient setting, there should generally be very limited and rare circumstances for which the laterality (right, left, bilateral) of a condition is unable to be documented and reported. The following pages contain the list of unspecified ICD-10-CM diagnosis codes for which there is a more specific code to identify laterality (right, left, bilateral) within that code family.

Present on Admission (POA)Billing

S42.309P is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Closed fracture of humerus
  • Closed fracture of shaft of humerus
  • Closed multiple fractures of clavicle and/or scapula and/or humerus
  • Fracture malunion - upper arm
  • Fracture of humerus
  • Fracture of shaft of humerus
  • Multiple fractures of clavicle
  • Multiple fractures of clavicle, scapula and humerus
  • Multiple fractures of humerus
  • Multiple fractures of scapula
  • Open fracture of humerus
  • Open fracture of shaft of humerus
  • Open multiple fractures of clavicle and/or scapula and/or humerus

Coding GuidelinesGuidance

The principles of multiple coding of injuries should be followed in coding fractures. Fractures of specified sites are coded individually by site, to the level of detail furnished by medical record content.

A fracture not indicated as open or closed should be coded to closed. A fracture not indicated whether displaced or not displaced should be coded to displaced.

Initial vs. Subsequent Encounter for Fractures

Traumatic fractures are coded using the appropriate 7th character for initial encounter (A, B, C) while the patient is receiving active treatment for the fracture. The appropriate 7th character for initial encounter should also be assigned for a patient who delayed seeking treatment for the fracture or nonunion.

Fractures are coded using the appropriate 7th character for subsequent care for encounters after the patient has completed active treatment of the fracture and is receiving routine care for the fracture during the healing or recovery phase.

Care for complications of surgical treatment for fracture repairs during the healing or recovery phase should be coded with the appropriate complication codes.

Care of complications of fractures, such as malunion and nonunion, should be reported with the appropriate 7th character for subsequent care with nonunion (K, M, N) or subsequent care with malunion (P, Q, R).

The open fracture designations in the assignment of the 7th character for fractures of the forearm, femur and lower leg, including ankle are based on the Gustilo open fracture classification. When the Gustilo classification type is not specified for an open fracture, the 7th character for open fracture type I or II should be assigned (B, E, H, M, Q).

Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INJ041
Fracture of the upper limb, subsequent encounter
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Arm Injuries and Disorders

Of the 206 bones in your body, three of them are in your arm: the humerus, radius, and ulna. Your arms are also made up of muscles, joints, tendons, and other connective tissue. Injuries to any of these parts of the arm can occur during sports, a fall, or an accident.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert S42.309P to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
733.81 Malunion of fracture
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About S42.309POverview

Is S42.309P (Unspecified fracture of shaft of humerus, unspecified arm) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report unspecified fracture of shaft of humerus, unspecified arm, subsequent encounter for fracture with malunion on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character P in S42.309P mean?

The final character P reports a subsequent encounter where the unspecified fracture of shaft of humerus, unspecified arm has healed in a faulty position, called a malunion.

What MS-DRG does S42.309P group to?

When unspecified fracture of shaft of humerus, unspecified arm, subsequent encounter for fracture with malunion is the principal diagnosis on an inpatient stay, it groups to MS-DRG 564, 565, 566, with relative weights from 0.7493 to 1.5436 depending on complications. Higher weights mean higher Medicare reimbursement.

Is S42.309P exempt from POA reporting?

Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for unspecified fracture of shaft of humerus, unspecified arm, subsequent encounter for fracture with malunion on inpatient claims.

What is the ICD-9 equivalent of S42.309P?

Under the General Equivalence Mappings, unspecified fracture of shaft of humerus, unspecified arm, subsequent encounter for fracture with malunion converts to ICD-9-CM 733.81 (malunion of fracture). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.