2026 ICD-10-CM Diagnosis Code S13.121SDislocation of C1/C2 cervical vertebrae, sequela
S13.121S is a billable ICD-10-CM diagnosis code for dislocation of C1/C2 cervical vertebrae, sequela. The 7th character S marks it as a sequela code, which reports a problem that remains after the original condition has resolved. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 562 through 563. The code is exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Injury, sequela.
Code Identity
Code Classification
Present on Admission (POA)Billing
S13.121S is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Closed dislocation atlantoaxial joint
- Closed traumatic dislocation of cervical vertebra
- Closed traumatic dislocation of first cervical vertebra
- Dislocation of atlantoaxial joint
- Open dislocation atlantoaxial joint
- Open dislocation of first cervical vertebra
- Open dislocation of second cervical vertebra
- Subluxation of atlantoaxial joint
- Trauma causing partial dislocation of atlantoaxial joint
- Traumatic complete dislocation of atlantoaxial joint
- Traumatic dislocation of atlantoaxial joint
Coding GuidelinesGuidance
The appropriate 7th character is to be added to each code from block Dislocation and sprain of joints and ligaments at neck level (S13). 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.
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.
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Convert S13.121S to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About S13.121SOverview
Is S13.121S (Dislocation of C1/C2 cervical vertebrae) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report dislocation of C1/C2 cervical vertebrae, sequela on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character S in S13.121S mean?
The final character S makes this a sequela code: it reports a lingering problem that remains after the dislocation of C1/C2 cervical vertebrae itself has resolved, not the original event.
What MS-DRG does S13.121S group to?
When dislocation of C1/C2 cervical vertebrae, sequela is the principal diagnosis on an inpatient stay, it groups to MS-DRG 562, 563, with relative weights from 0.8955 to 1.4248 depending on complications. Higher weights mean higher Medicare reimbursement.
Is S13.121S 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 dislocation of C1/C2 cervical vertebrae, sequela on inpatient claims.
What is the ICD-9 equivalent of S13.121S?
Under the General Equivalence Mappings, dislocation of C1/C2 cervical vertebrae, sequela converts to ICD-9-CM 905.6 (late effect dislocation). 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.
