2027 ICD-10-CM Diagnosis Code S83.121APosterior subluxation of proximal end of tibia, right knee, initial encounter

ICD-10-CM Codes›S00–T88›S80-S89›S83

ICD-10-CM S83.121A
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

S83.121A is a billable ICD-10-CM diagnosis code for posterior subluxation of proximal end of tibia, right knee, 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 562 through 563, 963 through 965. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Dislocations, initial encounter.

Code Identity

ICD-10-CM Code
S83.121A
Billable Status
Yes — Valid for Submission
Code Describes
Posterior subluxation of proximal end of tibia, right knee, initial encounter
Short Description
Posterior sublux of proximal end of tibia, right knee, init
Parent Code
S83.121
Posterior subluxation of proximal end of tibia, right knee

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionS80-S89Injuries to the knee and lower leg
CategoryS83Dislocation and sprain of joints and ligaments of knee
This CodeS83.121APosterior subluxation of proximal end of tibia, right knee, initial encounter

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Dislocation and sprain of joints and ligaments of knee (S83). 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 S83.121A: its own notes plus those printed at S83.1, S83, block S80-S89, 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 S83 Dislocation and sprain of joints and ligaments of knee applies to 351 codes
  • avulsion of joint or ligament of knee
  • laceration of cartilage, joint or ligament of knee
  • sprain of cartilage, joint or ligament of knee
  • traumatic hemarthrosis of joint or ligament of knee
  • traumatic rupture of joint or ligament of knee
  • traumatic subluxation of joint or ligament of knee
  • traumatic tear of joint or ligament of knee

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 S83.1 Subluxation and dislocation of knee applies to 108 codes
From S83 Dislocation and sprain of joints and ligaments of knee applies to 351 codes
  • derangement of patella (M22.0-M22.3)
  • injury of patellar ligament (tendon) (S76.1-)
  • internal derangement of knee (M23.-)
  • old dislocation of knee (M24.36)
  • pathological dislocation of knee (M24.36)
  • recurrent dislocation of knee (M22.0)
  • strain of muscle, fascia and tendon of lower leg (S86.-)
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 S83 Dislocation and sprain of joints and ligaments of knee applies to 351 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 S83 Dislocation and sprain of joints and ligaments of knee applies to 351 codes
  • The appropriate 7th character is to be added to each code from category S83
Values for category S83 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 S83.121A, its category, or a range that includes it.

Excludes2 1

These codes carry an Excludes2 note naming S83.121A: its condition is not part of those codes, and both may be reported when the patient has both.

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

Clinical ClassificationClinical

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

CCSR INJ007
Dislocations, initial encounter
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Dislocations

Dislocations are joint injuries that force the ends of your bones out of position. The cause is often a fall or a blow, sometimes from playing a contact sport. You can dislocate your ankles, knees, shoulders, hips, elbows and jaw. You can also dislocate your finger and toe joints.

Read the full article at MedlinePlus

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

Convert S83.121A to ICD-9-CMHistory

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

ICD-9-CM
836.52 Post disl prox tibia-cl
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 S83.121AOverview

Is S83.121A (Posterior subluxation of proximal end of tibia, right knee) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report posterior subluxation of proximal end of tibia, right knee, initial encounter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What does the 7th character A in S83.121A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for posterior subluxation of proximal end of tibia, right knee, such as an emergency visit or first evaluation.

What MS-DRG does S83.121A group to?

When posterior subluxation of proximal end of tibia, right knee, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 563, 964, 965, 562, 963, with relative weights from 0.8982 to 2.6361 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of S83.121A?

Under the General Equivalence Mappings, posterior subluxation of proximal end of tibia, right knee, initial encounter converts to ICD-9-CM 836.52 (post disl prox tibia-cl). The mapping is approximate, so confirm the match fits the documentation.