2026 ICD-10-CM Diagnosis Code M99.00Segmental and somatic dysfunction of head region

ICD-10-CM Codes›M00–M99›M99›M99

ICD-10-CM M99.00
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M99.00 is a billable ICD-10-CM diagnosis code for segmental and somatic dysfunction of head region. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 555 through 556. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Biomechanical lesions.

Code Identity

ICD-10-CM Code
M99.00
Billable Status
Yes — Valid for Submission
Code Describes
Segmental and somatic dysfunction of head region
Short Description
Segmental and somatic dysfunction of head region
Same as the full description in the CMS dataset.
Parent Code
M99.0
Segmental and somatic dysfunction

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM99Biomechanical lesions, not elsewhere classified
CategoryM99Biomechanical lesions, not elsewhere classified
This CodeM99.00Segmental and somatic dysfunction of head region

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Compression of sphenobasilar synchondrosis
  • Flexion of sphenobasilar synchondrosis
  • Membranous articular strain
  • Sidebending-rotation of sphenooccipital synchondrosis
  • Somatic dysfunction of cranium
  • Somatic dysfunction of head region
  • Somatic dysfunction of occipitocervical region
  • Somatic dysfunction of sphenobasilar synchondrosis
  • Sphenobasilar extension
  • Sphenobasilar synchondrosis lateral strain
  • Sphenobasilar synchondrosis torsion
  • Sphenobasilar synchondrosis vertical strain

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Dysfunction
      • somatic
        • head region
    • Dysfunction
      • somatic
        • occipitocervical

Clinical ClassificationClinical

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

CCSR MUS012
Biomechanical lesions
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Spine Injuries and Disorders

Your backbone, or spine, is made up of 26 bone discs called vertebrae. The vertebrae protect your spinal cord and allow you to stand and bend. A number of problems can change the structure of the spine or damage the vertebrae and surrounding tissue. They include:

Read the full article at MedlinePlus

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

Convert M99.00 to ICD-9-CMHistory

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

ICD-9-CM
739.0 Somat dys head region
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 M99.00Overview

Is M99.00 (Segmental and somatic dysfunction) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report segmental and somatic dysfunction of head region on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M99.00 group to?

When segmental and somatic dysfunction of head region is the principal diagnosis on an inpatient stay, it groups to MS-DRG 555, 556, with relative weights from 0.8306 to 1.3218 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M99.00?

Under the General Equivalence Mappings, segmental and somatic dysfunction of head region converts to ICD-9-CM 739.0 (somat dys head region). 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.