Acquired spondylolysis (a defect or stress fracture of the vertebral arch) localized to the occipito-atlanto-axial region — the bony junction involving the occiput, atlas (C1), and axis (C2).
Verified May 8, 2026 · 5 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 10
- Region
- Spine
Documentation tips
What should appear in the chart to support M43.01.
Source · Editorial brief grounded in 5 cited references ↓
- Specify the anatomical region explicitly — 'occipito-atlanto-axial' or 'C1-C2' — in the clinical note to support the site-specific code over M43.00 (unspecified site).
- Document whether the spondylolysis is acquired vs. congenital; if congenital origin is suspected or confirmed, Q76.2 replaces M43.01.
- Record imaging modality and findings — CT best characterizes the bony defect, and the report should describe the specific arch or pars defect at this level.
- Note the presence or absence of associated instability or vertebral translation; if slip is documented, evaluate whether M43.11 (spondylolisthesis, occipito-atlanto-axial region) better captures the full picture.
- Document symptom burden: neck pain, occipital neuralgia, myelopathic signs, or neurological deficits, which may affect medical necessity determinations for surgical procedures.
Related CPT procedures
Procedure codes commonly billed with M43.01. 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 M43.01 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Using M43.01 and M43.11 together on the same claim — the tabular Excludes1 note under M43.0 prohibits coding spondylolysis and spondylolisthesis at the same site simultaneously; choose the code that reflects the documented primary pathology.
- Defaulting to M43.00 (unspecified site) when the provider has clearly documented involvement of the C1-C2 or craniocervical junction — always code to the highest documented specificity.
- Coding M43.01 when the record supports a congenital defect — congenital spondylolysis maps to Q76.2, not M43.01.
- Confusing this code with cervical region (M43.02) or cervicothoracic region (M43.03) — the occipito-atlanto-axial region is anatomically distinct and limited to the occiput-C1-C2 complex.
Clinical context
Source · Editorial summary grounded in 5 cited references ↓
M43.01 codes acquired spondylolysis of the uppermost cervical spine, specifically the articulations between the occiput, C1 (atlas), and C2 (axis). This is an anatomically uncommon site for spondylolysis compared to the lumbar region, and its presence at this level raises concern for structural instability at the craniocervical junction. Use this code when imaging confirms a pars interarticularis defect or arch defect in this region and there is no documented congenital origin.
Do not use M43.01 for congenital spondylolysis — that belongs under Q76.2. There is also a Type 1 Excludes relationship between M43.0 (spondylolysis) and M43.1 (spondylolisthesis): if vertebral slippage is also present, code the spondylolisthesis separately using M43.11 for the same region; you cannot use both M43.01 and M43.11 on the same claim per the tabular excludes logic. If the defect is at a different cervical level (e.g., C2-C3 junction), M43.02 (cervical region) or M43.03 (cervicothoracic region) may be more accurate.
Clinical workup typically includes CT or MRI of the cervical spine and craniocervical junction to characterize the defect. Flexion-extension radiographs may be ordered to assess instability. Document whether the finding is incidental or symptomatic, as that distinction can affect medical necessity for advanced imaging and surgical consultation.
Sibling codes
Other billable codes under M43.0 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 5 cited references ↓
01What distinguishes M43.01 from M43.00?
02Can M43.01 and M43.11 be coded together for the same encounter?
03Is Q76.2 ever the right code instead of M43.01?
04What imaging best supports M43.01 for documentation purposes?
05Which CPT codes commonly pair with M43.01 in an orthopedic or spine practice?
06Is M43.01 valid for FY2026 billing?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026 (FY2026, effective October 1, 2025)
- 02icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M40-M43/M43-/M43.01
- 03icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M40-M43/M43-/M43.1
- 04aapc.comhttps://www.aapc.com/codes/icd-10-codes/M43
- 05cms.govhttps://www.cms.gov/medicare/coding-billing/icd-10-codes
Mira AI Scribe
Mira AI Scribe captures the specific spinal level (occiput, C1, C2), imaging findings confirming the arch or pars defect, onset context (acquired vs. congenital), and presence or absence of vertebral translation. This prevents a drop to unspecified M43.00, avoids a congenital misclassification to Q76.2, and flags when concurrent spondylolisthesis documentation would require a coding review.
See how Mira captures M43.01 documentation