2026 ICD-10-CM Diagnosis Code S86.399AOther injury of muscle(s) and tendon(s) of peroneal muscle group at lower leg level, unspecified leg, initial encounter

ICD-10-CM Codes›S00–T88›S80-S89›S86

ICD-10-CM S86.399A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

S86.399A is a billable ICD-10-CM diagnosis code for other injury of muscle(s) and tendon(s) of peroneal muscle group at lower leg level, unspecified leg, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 913 through 914, 963 through 965. Coders also document this condition as subluxation of peroneal tendon. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Injury to nerves, muscles and tendons, initial encounter.

Code Identity

ICD-10-CM Code
S86.399A
Billable Status
Yes — Valid for Submission
Code Describes
Other injury of muscle(s) and tendon(s) of peroneal muscle group at lower leg level, unspecified leg, initial encounter
Short Description
Inj musc/tend peroneal grp at low leg level, unsp leg, init
Parent Code
S86.399
Other injury of muscle(s) and tendon(s) of peroneal muscle group at lower leg level, unspecified leg

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionS80-S89Injuries to the knee and lower leg
CategoryS86Injury of muscle, fascia and tendon at lower leg level
This CodeS86.399AOther injury of muscle(s) and tendon(s) of peroneal muscle group at lower leg level, unspecified leg, initial encounter

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Subluxation of peroneal tendon

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Injury of muscle, fascia and tendon at lower leg level (S86). Use the following options for the applicable episode of care:

  • A - initial encounter
  • D - subsequent encounter
  • S - sequela

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 INJ025
Injury to nerves, muscles and tendons, initial encounter
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Leg Injuries and Disorders

Your legs are made up of bones, blood vessels, muscles, and other connective tissue. They are important for motion and standing. Playing sports, running, falling, or having an accident can damage your legs. Common leg injuries include sprains and strains, joint dislocations, and fractures (broken bones).

Read the full article at MedlinePlus

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

Convert S86.399A to ICD-9-CMHistory

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

ICD-9-CM
959.7 Lower leg injury 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 S86.399AOverview

Is S86.399A a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other injury of muscle(s) and tendon(s) of peroneal muscle group at lower leg level, unspecified leg, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in S86.399A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for other injury of muscle(s) and tendon(s) of peroneal muscle group at lower leg level, unspecified leg, such as an emergency visit or first evaluation.

What MS-DRG does S86.399A group to?

When other injury of muscle(s) and tendon(s) of peroneal muscle group at lower leg level, unspecified leg, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 913, 914, 963, 964, 965, with relative weights from 0.8855 to 2.7338 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of S86.399A?

Under the General Equivalence Mappings, other injury of muscle(s) and tendon(s) of peroneal muscle group at lower leg level, unspecified leg, initial encounter converts to ICD-9-CM 959.7 (lower leg injury 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.