2027 ICD-10-CM Diagnosis Code S23.421DSprain of chondrosternal joint, subsequent encounter

ICD-10-CM Codes›S00–T88›S20-S29›S23

ICD-10-CM S23.421D
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

S23.421D is a billable ICD-10-CM diagnosis code for sprain of chondrosternal joint, subsequent encounter. The 7th character D marks it as a subsequent encounter code, used during routine care in the healing or recovery phase. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 949 through 950. The code is exempt from POA reporting. Coders also document this condition as complete tear, chondrosternal ligament. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Sprains and strains, subsequent encounter.

Code Identity

ICD-10-CM Code
S23.421D
Billable Status
Yes — Valid for Submission
Code Describes
Sprain of chondrosternal joint, subsequent encounter
Short Description
Sprain of chondrosternal joint, subsequent encounter
Same as the full description in the CMS dataset.
Parent Code
S23.421
Sprain of chondrosternal joint

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionS20-S29Injuries to the thorax
CategoryS23Dislocation and sprain of joints and ligaments of thorax
This CodeS23.421DSprain of chondrosternal joint, subsequent encounter

Present on Admission (POA)Billing

S23.421D is exempt from POA reporting on inpatient claims to general acute care hospitals. Review the other POA exempt codes in Injuries to the thorax (S20-S29).

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Complete tear, chondrosternal ligament
  • Complete tear, rib ligament
  • Complete tear, sternum ligament

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Dislocation and sprain of joints and ligaments of thorax (S23). 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 S23.421D: its own notes plus those printed at S23, block S20-S29, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From S23 Dislocation and sprain of joints and ligaments of thorax applies to 108 codes
  • avulsion of joint or ligament of thorax
  • laceration of cartilage, joint or ligament of thorax
  • sprain of cartilage, joint or ligament of thorax
  • traumatic hemarthrosis of joint or ligament of thorax
  • traumatic rupture of joint or ligament of thorax
  • traumatic subluxation of joint or ligament of thorax
  • traumatic tear of joint or ligament of thorax
From Block S20-S29 Injuries to the thorax applies to 1,602 codes
  • injuries of breast
  • injuries of chest (wall)
  • injuries of interscapular area

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 S23 Dislocation and sprain of joints and ligaments of thorax applies to 108 codes
  • dislocation, sprain of sternoclavicular joint (S43.2, S43.6)
  • strain of muscle or tendon of thorax (S29.01-)
From Block S20-S29 Injuries to the thorax applies to 1,602 codes
  • burns and corrosions (T20-T32)
  • effects of foreign body in bronchus (T17.5)
  • effects of foreign body in esophagus (T18.1)
  • effects of foreign body in lung (T17.8)
  • effects of foreign body in trachea (T17.4)
  • frostbite (T33-T34)
  • injuries of axilla
  • injuries of clavicle
  • injuries of scapular region
  • injuries of shoulder
  • 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 S23 Dislocation and sprain of joints and ligaments of thorax applies to 108 codes
  • any associated open wound

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 S23 Dislocation and sprain of joints and ligaments of thorax applies to 108 codes
  • The appropriate 7th character is to be added to each code from category S23
Values for category S23 Encounter: Initial, Subsequent, Sequela
  • Ainitial encounter
  • Dsubsequent encounter this code
  • Ssequela

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

Clinical ClassificationClinical

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

CCSR INJ061
Sprains and strains, subsequent encounter
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Chest Injuries and Disorders

The chest is the part of your body between your neck and your abdomen (belly). The medical term for your chest is thorax.

The full article covers:

  • What is the chest?
  • What are chest injuries and disorders?
  • How are chest injuries and disorders diagnosed?

Read the full article at MedlinePlus

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

Convert S23.421D to ICD-9-CMHistory

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

ICD-9-CM
V58.89 Other specfied aftercare
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 S23.421DOverview

What is the ICD-10 code for sprain of chondrosternal joint, subsequent encounter?

The ICD-10-CM code for sprain of chondrosternal joint, subsequent encounter is S23.421D (sometimes written as S23421D). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is S23.421D (Sprain of chondrosternal joint) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report sprain of chondrosternal joint, subsequent encounter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What does the 7th character D in S23.421D mean?

The final character D marks a subsequent encounter: use it for routine care while the sprain of chondrosternal joint is healing, after active treatment has ended.

What MS-DRG does S23.421D group to?

When sprain of chondrosternal joint, subsequent encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 950, 949, with relative weights from 0.7661 to 1.1231 depending on complications. Higher weights mean higher Medicare reimbursement.

Is S23.421D exempt from POA reporting?

Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for sprain of chondrosternal joint, subsequent encounter on inpatient claims. The code appears in the Injuries to the thorax (S20-S29) range of the CMS exempt list.