2027 ICD-10-CM Diagnosis Code S56.591AOther injury of other extensor muscle, fascia and tendon at forearm level, right arm, initial encounter

ICD-10-CM Codes›S00–T88›S50-S59›S56

ICD-10-CM S56.591A
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

S56.591A is a billable ICD-10-CM diagnosis code for other injury of other extensor muscle, fascia and tendon at forearm level, right arm, 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. 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
S56.591A
Billable Status
Yes — Valid for Submission
Code Describes
Other injury of other extensor muscle, fascia and tendon at forearm level, right arm, initial encounter
Short Description
Inj extn musc/fasc/tend at forearm level, right arm, init
Parent Code
S56.591
Other injury of other extensor muscle, fascia and tendon at forearm level, right arm

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionS50-S59Injuries to the elbow and forearm
CategoryS56Injury of muscle, fascia and tendon at forearm level
This CodeS56.591AOther injury of other extensor muscle, fascia and tendon at forearm level, right arm, initial encounter

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Injury of muscle, fascia and tendon at forearm level (S56). 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 S56.591A: its own notes plus those printed at S56, block S50-S59, 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 S56 Injury of muscle, fascia and tendon at forearm level applies to 432 codes
  • injury of muscle, fascia and tendon at or below wrist (S66.-)
  • sprain of joints and ligaments of elbow (S53.4-)
From Block S50-S59 Injuries to the elbow and forearm applies to 4,362 codes
  • burns and corrosions (T20-T32)
  • frostbite (T33-T34)
  • injuries of wrist and hand (S60-S69)
  • 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 S56 Injury of muscle, fascia and tendon at forearm level applies to 432 codes
  • any associated open wound (S51.-)

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 S56 Injury of muscle, fascia and tendon at forearm level applies to 432 codes
  • The appropriate 7th character is to be added to each code from category S56
Values for category S56 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 S56.591A, its category, or a range that includes it.

Excludes2 2

These codes carry an Excludes2 note naming S56.591A: its condition is not part of those codes, and both may be reported when the patient has both.

  • S46 Injury of muscle, fascia and tendon at shoulder and upper arm level
    injury of muscle, fascia and tendon at elbow (S56.-) names S56.-, which includes this code
  • S53 Dislocation and sprain of joints and ligaments of elbow
    strain of muscle, fascia and tendon at forearm level (S56.-) names S56.-, 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

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 S56.591A to ICD-9-CMHistory

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

ICD-9-CM
959.3 Elb/forearm/wrst inj 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 S56.591AOverview

Is S56.591A a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other injury of other extensor muscle, fascia and tendon at forearm level, right arm, initial encounter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What does the 7th character A in S56.591A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for other injury of other extensor muscle, fascia and tendon at forearm level, right arm, such as an emergency visit or first evaluation.

What MS-DRG does S56.591A group to?

When other injury of other extensor muscle, fascia and tendon at forearm level, right arm, 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 S56.591A?

Under the General Equivalence Mappings, other injury of other extensor muscle, fascia and tendon at forearm level, right arm, initial encounter converts to ICD-9-CM 959.3 (elb/forearm/wrst inj NOS). The mapping is approximate, so confirm the match fits the documentation.