S42.399A Other fracture of shaft of unspecified humerus, initial encounter for closed fracture

ICD-10-CM S42.399A: Other fracture of shaft of unspecified humerus, initial encounter for closed fracture

ICD-10-CM code S42.399A identifies an initial encounter for a closed fracture of the shaft of an unspecified humerus. The terminology is active and classified as an injury or poisoning concept. Clinical references note that humeral shaft fractures involve assessing tolerances and treatment options, while surveillance algorithms use such codes to define osteoporotic fractures. 1 2 4

Plain-language overview

Code S42.399A translates to an initial encounter for a closed fracture of the shaft of an unspecified humerus, serving as an active injury or poisoning concept within the ICD-10-CM version 2026 terminology. 1

What this code represents

The code S42.399A represents a specific diagnosis for an initial encounter for a closed fracture of the shaft of an unspecified humerus, and it has a parent concept designated as S42.399. 1

Within the same unspecified humerus shaft fracture category, S42.399A is distinct from S42.399B, which represents an initial encounter for an open fracture rather than a closed one. 5

Coding details

The S42.399 category distinguishes laterality for closed fractures, offering specific alternatives like S42.391A for the right humerus and S42.392A for the left humerus, whereas S42.399A lacks laterality. 5

The broader category for unspecified humerus shaft fractures includes subsequent encounter variants for routine healing, delayed healing, nonunion, and malunion, which are distinct from the initial encounter code S42.399A. 5

Clinical context

Clinical literature establishes that a complete assessment of patients with suspected humeral shaft fractures includes an initial neurovascular examination to identify associated injuries. 2

Documentation considerations

The code S42.399A explicitly designates the humerus as unspecified, while the same coding list provides distinct alternatives for right and left humerus closed fractures. 5

Coverage and utilization context

A surveillance algorithm defines osteoporotic humerus fractures using diagnosis codes in any care setting, but excludes cases with evidence of major trauma on the day of diagnosis. 4

What the sources add

While the terminology record defines the code structure and clinical literature discusses treatment tolerances, the surveillance source adds operational context by applying such codes within an osteoporotic fracture algorithm. 1 2 4

Sources

1. ICD-10-CM S42.399A terminology record — National Cancer Institute Enterprise Vocabulary Services; accessed 2026-07-27.
2. Bookshelf — ncbi.nlm.nih.gov; accessed 2026-07-27.
3. EVS Explore — evsexplore.semantics.cancer.gov; accessed 2026-07-27.
4. Disclaimer — sentinelinitiative.org; accessed 2026-07-27.
5. ICD-10-CM 2024 | S42.39 - Other fracture of shaft of humerus — unboundmedicine.com; accessed 2026-07-27.