Narrowing of the intervertebral foramina of the rib cage caused by connective tissue changes or disc material, classified under biomechanical lesions of the musculoskeletal system.

Documentation tips

What should appear in the chart to support M99.78.

Source · Editorial brief grounded in 5 cited references ↓

• Provider must explicitly document connective tissue involvement or disc material as the cause of foraminal narrowing at the rib cage — 'foraminal stenosis, thoracic rib cage, connective tissue etiology' satisfies this; a vague 'thoracic tightness' does not.
• Distinguish from bony/osseous foraminal stenosis at the rib cage (M99.68) — the clinical note should specify connective tissue hypertrophy, fibrosis, adhesion, or disc intrusion rather than osteophytic or bony narrowing.
• If imaging (MRI or CT) is referenced, document the relevant finding (e.g., foraminal narrowing at T5-T6 rib-cage level with soft-tissue component) to anchor the diagnosis to the record.
• When coding alongside segmental dysfunction codes (e.g., M99.02 for thoracic), document each as a distinct finding with its own clinical basis — do not use them interchangeably.
• Because M99.78 carries no laterality, ensure the note does not imply a unilateral finding that a more specific code elsewhere could capture; if laterality is clinically relevant, note it narratively.

Related CPT procedures

Procedure codes commonly billed with M99.78. Linking the right diagnosis to the right procedure is what establishes medical necessity.

Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis

Common coding pitfalls

The recurring mistakes coders make with M99.78 and adjacent codes.

Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓

• Using M99.78 when the foraminal stenosis is osseous/bony in origin — the correct code in that scenario is M99.68 (osseous stenosis of intervertebral foramina of rib cage).
• Defaulting to a thoracic disc or spondylosis code (M51.x or M47.x) when the documented etiology is a biomechanical connective tissue lesion — M99.78 is appropriate only when the provider frames the diagnosis within the biomechanical lesion framework.
• Applying M99.78 without adequate documentation of the connective tissue or disc mechanism, risking payer denial or audit recoupment for unspecified foraminal stenosis.
• Confusing M99.78 with M99.08 (segmental and somatic dysfunction of rib cage) — these are sibling subcategories under M99, not interchangeable; dysfunction and foraminal stenosis are distinct diagnoses requiring distinct clinical documentation.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Sibling codes

Other billable codes under M99.7 (laterality / anatomic variants).