M43.28 identifies pathological or acquired ankylosis (bony fusion) of the spinal joints within the sacral and sacrococcygeal region, distinguishing it from surgical arthrodesis status and congenital spinal fusion.
Verified May 8, 2026 · 5 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 5
- Region
- Spine
Documentation tips
What should appear in the chart to support M43.28.
Source · Editorial brief grounded in 5 cited references ↓
- Document the specific anatomical region explicitly as 'sacral' or 'sacrococcygeal' — vague 'low back fusion' language will not support M43.28 specificity.
- Distinguish acquired ankylosis from surgical arthrodesis in the clinical note; if the fusion is post-operative status, Z98.1 is correct instead of M43.28.
- Record imaging findings that confirm bony fusion or ankylosis at the sacral/sacrococcygeal level (CT or MRI findings, loss of joint space, trabecular bridging).
- For sacroiliac joint injection claims, document pre- and post-injection pain relief percentages and fluoroscopic needle placement per CMS Article A59246 requirements.
- Confirm the etiology is acquired/pathological, not congenital — if congenital, the correct code is Q76.4, which is a Type 1 Excludes for M43.2.
Related CPT procedures
Procedure codes commonly billed with M43.28. 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 M43.28 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Using M43.28 for post-surgical arthrodesis status — that is Z98.1; M43.28 is for disease-state (pathological) ankylosis only.
- Coding ankylosing spondylitis with sacral involvement as M43.28 — ankylosing spondylitis maps to M45.0-, which is a Type 1 Excludes under M43.2.
- Submitting M43.28 without supporting imaging documentation when used as the justifying diagnosis for sacroiliac joint injections — CMS requires the medical record to support the selected ICD-10-CM code.
- Conflating sacrococcygeal fusion with coccydynia or sacroiliitis (M46.1) — these are distinct conditions with their own codes and must be differentiated by clinical and imaging findings.
Clinical context
Source · Editorial summary grounded in 5 cited references ↓
M43.28 applies when a patient has documented non-surgical, acquired fusion of the sacral or sacrococcygeal spinal joints — for example, ankylosis resulting from chronic inflammatory or degenerative disease at that level. The Applicable To note under M43.2 specifies 'Ankylosis of spinal joint.' This is a disease-state code, not a procedure status code.
Do not use M43.28 for surgical arthrodesis status — that belongs under Z98.1. Congenital spinal fusion is excluded and belongs under Q76.4. Ankylosing spondylitis with sacral involvement codes to M45.0-, not M43.28. Pseudoarthrosis after fusion or arthrodesis goes to M96.0. These Type 1 and Type 2 Excludes notes are hard stops.
CMS recognizes M43.28 as a covered diagnosis supporting medical necessity for sacroiliac joint injections and related procedures (CPT 27096, 64451, HCPCS G0260) per CMS Article A59246. It frequently appears alongside other sacral-region pathology codes in spinal procedure claims and should be paired accurately with the operative or interventional CPT codes to avoid NCCI bundling conflicts.
Sibling codes
Other billable codes under M43.2 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 5 cited references ↓
01Can M43.28 be used as the diagnosis code supporting a sacroiliac joint injection claim?
02What is the difference between M43.28 and Z98.1 for spinal fusion?
03Is M43.28 appropriate when ankylosing spondylitis causes sacral fusion?
04Does M43.28 require a 7th character?
05What imaging documentation is needed to support M43.28?
06What is the parent code for M43.28 and when would I use it instead?
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-/M43.28
- 03aapc.comhttps://www.aapc.com/codes/icd-10-codes/M43.28
- 04cms.govhttps://www.cms.gov/medicare-coverage-database/view/article.aspx?articleid=59246
- 05cms.govhttps://www.cms.gov/medicare-coverage-database/view/article.aspx?articleId=59154
Mira AI Scribe
Mira's AI scribe captures the treating physician's documentation of acquired bony ankylosis at the sacral or sacrococcygeal spinal level, including relevant imaging findings (CT/MRI evidence of joint fusion, trabecular bridging, or loss of joint space), confirmation that the fusion is pathological rather than surgical, and the clinical distinction from ankylosing spondylitis or congenital fusion. Capturing these elements prevents downcoding to a nonspecific dorsopathy code and protects against medical necessity denials on sacroiliac joint procedure claims.
See how Mira captures M43.28 documentation