Acquired defect or stress fracture of the posterior vertebral arch (pars interarticularis) localized to the thoracic spine, classified under deforming dorsopathies.
Verified May 8, 2026 · 5 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 18
- Region
- Spine
Documentation tips
What should appear in the chart to support M43.04.
Source · Editorial brief grounded in 5 cited references ↓
- Specify 'thoracic region' or identify the exact thoracic level (e.g., T6, T8) in the assessment — site-unspecified defaults to M43.00, which is a weaker code for audit purposes.
- Reference the imaging modality and finding that confirms the diagnosis: CT demonstrating pars defect, SPECT-CT showing increased uptake, or MRI signal change at the pars interarticularis.
- Distinguish acquired from congenital origin in the note; congenital defects must be coded Q76.2 and cannot be coded M43.04.
- Document whether slippage is present — if vertebral displacement is noted, spondylolisthesis (M43.1x) replaces M43.04 for that level.
- Record symptom severity, duration, and any conservative care history (physical therapy, bracing) to support medical necessity for advanced imaging or surgical intervention.
Related CPT procedures
Procedure codes commonly billed with M43.04. 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 M43.04 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Coding M43.04 alongside Q76.2 (congenital spondylolysis) for the same condition — these are Excludes1 and cannot be billed together.
- Using M43.04 when vertebral slippage is documented — once listhesis is present, the correct code shifts to M43.1x for the thoracic region (M43.14), not M43.04.
- Defaulting to M43.00 (site unspecified) when the provider clearly documents or images confirm thoracic involvement — always assign the most specific site code supported by documentation.
- Applying 7th-character extensions to M43.04 — this is an M-code, not an S-code; no 7th-character extension is used.
- Confusing thoracic region (M43.04) with thoracolumbar region (M43.05) — if the defect spans or is documented at the T12–L1 junction, M43.05 is the correct code.
Clinical context
Source · Editorial summary grounded in 5 cited references ↓
M43.04 captures spondylolysis — a bony defect, typically of the pars interarticularis — specifically when located in the thoracic vertebral region (T1–T12). This distinguishes it from cervical (M43.02), lumbar (M43.06), and other spinal segment variants. Thoracic spondylolysis is less common than lumbar but does occur, particularly in athletes with repetitive extension loading. Use this code for acquired defects; congenital spondylolysis belongs under Q76.2 and is an Excludes1 condition — you cannot bill M43.04 alongside Q76.2 for the same condition.
Critically, spondylolysis (M43.04) and spondylolisthesis (M43.1x) are mutually exclusive at the code level — another Excludes1 pairing. If the pars defect has progressed to vertebral slippage, code the spondylolisthesis at the appropriate site under M43.1 instead. If both a defect and slip coexist at different levels, code each level separately with the appropriate code.
MS-DRG grouping lands in 551 (Medical back problems with MCC) or 552 (Medical back problems without MCC), so documentation of complicating comorbidities directly affects reimbursement tier. Confirm thoracic-level imaging — CT or MRI — is referenced in the note to substantiate the site-specific code over the unspecified M43.00.
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 ↓
01Can I use M43.04 if the provider documents a 'stress fracture' of the thoracic pars?
02What is the difference between M43.04 and M43.14?
03Do I need a 7th character for M43.04?
04Can M43.04 and Q76.2 be coded together for the same patient?
05Which MS-DRGs does M43.04 group to?
06If the defect is at the T12–L1 junction, should I use M43.04 or M43.05?
07What imaging documentation best supports M43.04?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026 (effective Oct 1, 2025)
- 02icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M40-M43/M43-/M43.04
- 03aapc.comhttps://www.aapc.com/codes/icd-10-codes/M43.04
- 04unboundmedicine.comhttps://www.unboundmedicine.com/icd/view/ICD-10-CM/866474/all/M43_04___Spondylolysis_thoracic_region
- 05CMS MS-DRG Grouper v43.0
Mira AI Scribe
The Mira AI Scribe captures the spinal region (thoracic, with specific level if documented), imaging confirmation of the pars defect, acquired vs. congenital origin, and whether any vertebral displacement is present. This prevents defaulting to unspecified M43.00, misfiring into the congenital Q76.2 category, or missing a co-existing spondylolisthesis that requires its own site-specific code.
See how Mira captures M43.04 documentation