2026 ICD-10-CM Diagnosis Code M99.9Biomechanical lesion, unspecified

ICD-10-CM Codes›M00–M99›M99›M99

ICD-10-CM M99.9
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M99.9 is a billable ICD-10-CM diagnosis code for biomechanical lesion, unspecified. 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. Coders also document this condition as lesion of lumbar spine. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Biomechanical lesions.

Code Identity

ICD-10-CM Code
M99.9
Billable Status
Yes — Valid for Submission
Code Describes
Biomechanical lesion, unspecified
Short Description
Biomechanical lesion, unspecified
Same as the full description in the CMS dataset.
Parent Code
M99
Biomechanical lesions, not elsewhere classified

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM99Biomechanical lesions, not elsewhere classified
CategoryM99Biomechanical lesions, not elsewhere classified
This CodeM99.9Biomechanical lesion, unspecified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Lesion of lumbar spine
  • Lesion of thoracic spine
  • Stenosis of intervertebral foramina

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.

    • Lesion(s) (nontraumatic)
      • biomechanical

Clinical ClassificationClinical

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

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

Clinical InformationClinical

  • Biomechanical Lesion

    a localized defect of soft tissue or bone that results in the altered function of an associated anatomic structure.

Convert M99.9 to ICD-9-CMHistory

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

ICD-9-CM
738.9 Acq deformity NOS
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 M99.9Overview

Is M99.9 (Biomechanical lesions, not elsewhere classified) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report biomechanical lesion, unspecified on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M99.9 group to?

When biomechanical lesion, unspecified 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.

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

Under the General Equivalence Mappings, biomechanical lesion, unspecified converts to ICD-9-CM 738.9 (acq deformity NOS). 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.