2026 ICD-10-CM Diagnosis Code M84.421SPathological fracture, right humerus, sequela

ICD-10-CM Codes›M00–M99›M80-M85›M84

ICD-10-CM M84.421S
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M84.421S is a billable ICD-10-CM diagnosis code for pathological fracture, right humerus, sequela. The 7th character S marks it as a sequela code, which reports a problem that remains after the original condition has resolved. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 559 through 561. Coders also document this condition as pathological fracture - upper arm. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Pathological, stress and atypical fractures, sequela.

Code Identity

ICD-10-CM Code
M84.421S
Billable Status
Yes — Valid for Submission
Code Describes
Pathological fracture, right humerus, sequela
Short Description
Pathological fracture, right humerus, sequela
Same as the full description in the CMS dataset.
Parent Code
M84.421
Pathological fracture, right humerus

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM80-M85Disorders of bone density and structure
CategoryM84Disorder of continuity of bone
This CodeM84.421SPathological fracture, right humerus, sequela

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Pathological fracture - upper arm
  • Pathological fracture of right humerus

Clinical ClassificationClinical

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

CCSR MUS020
Pathological, stress and atypical fractures, sequela
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 M84.421S to ICD-9-CMHistory

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

ICD-9-CM
905.2 Late effect arm fx
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 M84.421SOverview

Is M84.421S (Pathological fracture, right humerus) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report pathological fracture, right humerus, sequela on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character S in M84.421S mean?

The final character S makes this a sequela code: it reports a lingering problem that remains after the pathological fracture, right humerus itself has resolved, not the original event.

What MS-DRG does M84.421S group to?

When pathological fracture, right humerus, sequela is the principal diagnosis on an inpatient stay, it groups to MS-DRG 559, 560, 561, with relative weights from 0.8039 to 1.8649 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M84.421S?

Under the General Equivalence Mappings, pathological fracture, right humerus, sequela converts to ICD-9-CM 905.2 (late effect arm fx). 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.