Spinal fusion or ankylosis affecting the cervicothoracic junction — the transitional segment spanning the lower cervical and upper thoracic vertebrae (typically C7–T1).

Documentation tips

What should appear in the chart to support M43.23.

Source · Editorial brief grounded in 4 cited references ↓

• Specify the region by name — 'cervicothoracic' or the affected vertebral levels (e.g., C7–T1) — so the code assignment is unambiguous and not defaulted to an unspecified region.
• Document whether the fusion is pathological/disease-process in origin (supports M43.23) versus surgically created (requires Z98.1 arthrodesis status) — the distinction determines the correct code family.
• Record imaging findings that confirm bony ankylosis or bridging osteophytes at the cervicothoracic junction, such as CT or plain film findings describing fusion of facet joints, anterior longitudinal ligament ossification, or syndesmophytes.
• If ankylosing spondylitis is the underlying cause of the cervicothoracic ankylosis, code M45.0– first; M43.23 should not be used when AS is documented as the etiology.
• Note functional limitations (range-of-motion deficits, neurological symptoms, myelopathy) to support medical necessity when M43.23 is paired with procedure codes for surgical intervention or imaging.

Related CPT procedures

Procedure codes commonly billed with M43.23. 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 M43.23 and adjacent codes.

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

• Using M43.23 for a patient with a prior surgical cervicothoracic fusion: post-procedural arthrodesis status codes to Z98.1, not M43.23 — reserving M43.23 for disease-process ankylosis.
• Conflating cervicothoracic fusion (M43.23) with cervical-only fusion (M43.22) or thoracic-only fusion (M43.24) — the cervicothoracic code applies specifically to the C7–T1 transition zone; verify documented levels before assigning.
• Assigning M43.23 when ankylosing spondylitis is the documented underlying condition — AS has its own region-specific codes under M45.0– and the Type 1 Excludes note at M43.2 prohibits using M43.23 for AS-driven ankylosis.
• Omitting a congenital fusion code (Q76.4) when the patient has Klippel-Feil syndrome with cervicothoracic involvement — the M43.2 parent code explicitly excludes congenital spinal fusion, redirecting to Q76.4.

Clinical context

Source · Editorial summary grounded in 4 cited references ↓

Sibling codes

Other billable codes under M43.2 (laterality / anatomic variants).