S83.409A Sprain of unspecified collateral ligament of unspecified knee, initial encounter

ICD-10-CM S83.409A: Sprain of unspecified collateral ligament of unspecified knee, initial encounter

ICD-10-CM code S83.409A identifies an initial encounter for a sprain of an unspecified collateral ligament in an unspecified knee, and it is classified under the semantic type of injury or poisoning. The terminology record is active for the 2026 version and has a parent concept for unspecified collateral ligament sprains. 1 3

Plain-language overview

Code S83.409A describes a sprain of an unspecified collateral ligament of an unspecified knee during an initial encounter, providing a diagnostic label for this specific injury presentation without identifying laterality. 1

What this code represents

The concept S83.409A is assigned the semantic type of injury or poisoning and holds an active record status within the 2026 ICD-10-CM terminology, establishing it as a valid diagnostic entity. 1 3

S83.409A is a narrower concept derived from the parent code S83.409, which denotes a sprain of an unspecified collateral ligament of an unspecified knee without the encounter specification. 1

Documentation considerations

Clinical findings useful for classifying knee instability into collateral ligament sprain categories include passive knee instability, joint pain, joint effusion, and movement coordination impairments. 2

An abbreviation for S83.409A is listed as sprain of unsp collateral ligament of unsp knee, init encntr, reflecting the unspecified nature of the affected knee and collateral ligament in documentation. 1

What the sources add

While the terminology record defines S83.409A as an active injury or poisoning concept, the clinical practice guideline connects collateral ligament sprains to functional impairments in joint stability and movement coordination. 1 2

The terminology record provides the official hierarchical structure and preferred name for S83.409A, whereas the clinical guideline outlines broader ICD categories and associated functional classifications for knee ligament injuries. 1 2

Questions to verify

The supplied sources do not establish whether S83.409A is a billable code, nor do they define specific payer coverage criteria or reimbursement guidelines for this initial encounter diagnosis. 1 2

Sources

1. ICD-10-CM S83.409A terminology record — National Cancer Institute Enterprise Vocabulary Services; accessed 2026-07-27.
2. Knee Stability and Movement Coordination Impairments: Knee Ligament Sprain — pmc.ncbi.nlm.nih.gov; accessed 2026-07-27.
3. EVS Explore — evsexplore.semantics.cancer.gov; accessed 2026-07-27.