2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

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 2027 (October 1, 2026 through September 30, 2027) 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 2027, published by CMS and the National Center for Health Statistics.

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to S86.399A: its own notes plus those printed at S86, block S80-S89, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From S86 Injury of muscle, fascia and tendon at lower leg level applies to 216 codes
  • injury of muscle, fascia and tendon at ankle (S96.-)
  • injury of patellar ligament (tendon) (S76.1-)
  • sprain of joints and ligaments of knee (S83.-)
From Block S80-S89 Injuries to the knee and lower leg applies to 4,680 codes
  • burns and corrosions (T20-T32)
  • frostbite (T33-T34)
  • injuries of ankle and foot, except fracture of ankle and malleolus (S90-S99)
  • insect bite or sting, venomous (T63.4)
From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes
  • code to identify any retained foreign body, if applicable (Z18.-)

Code Also

A second code may be needed to fully describe the condition; the note gives no sequencing direction.

From S86 Injury of muscle, fascia and tendon at lower leg level applies to 216 codes
  • any associated open wound (S81.-)

Notes

General instructions on how these codes are used.

From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes
  • Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
  • The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.

7th Character

Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.

From S86 Injury of muscle, fascia and tendon at lower leg level applies to 216 codes
  • The appropriate 7th character is to be added to each code from category S86
Values for category S86 Encounter: Initial, Subsequent, Sequela
  • Ainitial encounter this code
  • Dsubsequent encounter
  • Ssequela

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name S86.399A, its category, or a range that includes it.

Excludes2 2

These codes carry an Excludes2 note naming S86.399A: its condition is not part of those codes, and both may be reported when the patient has both.

  • S76 Injury of muscle, fascia and tendon at hip and thigh level
    injury of muscle, fascia and tendon at lower leg level (S86) names S86, which includes this code
  • S83 Dislocation and sprain of joints and ligaments of knee
    strain of muscle, fascia and tendon of lower leg (S86.-) names S86.-, which includes this code

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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

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 964, 965, 914, 913, 963, with relative weights from 0.9281 to 2.6361 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.