2026 ICD-10-CM Diagnosis Code S20.221AContusion of right back wall of thorax, initial encounter
S20.221A is a billable ICD-10-CM diagnosis code for contusion of right back wall of thorax, 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 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 604 through 605, 963 through 965. Coders also document this condition as contusion of posterior chest wall. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Superficial injury; contusion, initial encounter.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Contusion of posterior chest wall
- Contusion of right chest wall
- Contusion of right half of posterior chest wall
Coding GuidelinesGuidance
The appropriate 7th character is to be added to each code from block Superficial injury of thorax (S20). 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
Bruises
A bruise is a mark on your skin caused by blood trapped under the surface. It happens when an injury crushes small blood vessels but does not break the skin. Those vessels break open and leak blood under the skin.
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Convert S20.221A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About S20.221AOverview
Is S20.221A (Contusion of right back wall of thorax) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report contusion of right back wall of thorax, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in S20.221A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for contusion of right back wall of thorax, such as an emergency visit or first evaluation.
What MS-DRG does S20.221A group to?
When contusion of right back wall of thorax, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 604, 605, 963, 964, 965, with relative weights from 0.9160 to 2.7338 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of S20.221A?
Under the General Equivalence Mappings, contusion of right back wall of thorax, initial encounter converts to ICD-9-CM 922.33 (interscplr reg contusion). 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.
