M43.27 identifies ankylosis or pathological fusion of the spine specifically at the lumbosacral region — the junction between the fifth lumbar vertebra and the sacrum — as a disease process, not a surgical procedure status.
Verified May 8, 2026 · 4 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 11
- Region
- Spine
Documentation tips
What should appear in the chart to support M43.27.
Source · Editorial brief grounded in 4 cited references ↓
- Specify 'lumbosacral region' or 'L5-S1' explicitly in the assessment — documentation of 'lumbar fusion' alone may support M43.26 (lumbar region) rather than M43.27.
- Distinguish the etiology: document whether ankylosis is degenerative, post-inflammatory, or idiopathic, and confirm it is not ankylosing spondylitis (M45), which is an Excludes 1 condition.
- If the patient has a prior surgical arthrodesis at L5-S1, separately document Z98.1 (Arthrodesis status) alongside M43.27 when both pathological fusion and surgical history are clinically relevant.
- Include imaging evidence: MRI or plain radiograph findings showing bridging osteophytes, complete disc space obliteration, or end-plate fusion at the lumbosacral junction strengthen the diagnosis.
- Note functional impact (range of motion loss, gait changes, neurological symptoms) to support medical necessity for associated imaging or intervention CPT codes.
Related CPT procedures
Procedure codes commonly billed with M43.27. 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 M43.27 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Using M43.27 to document surgical arthrodesis status — the correct code for a prior fusion procedure is Z98.1, not M43.27.
- Confusing the lumbosacral region (L5-S1, M43.27) with the lumbar region (L1-L5, M43.26) — coders should confirm the provider specifies the lumbosacral junction before assigning M43.27.
- Assigning M43.27 when ankylosing spondylitis is the underlying cause — M45.x is the correct category; M43.2x carries an Excludes 1 note for ankylosing spondylitis.
- Failing to add Z98.1 when a patient has both a documented surgical fusion history and active pathological ankylosis — M43.27 does not capture the surgical history, and omitting Z98.1 may misrepresent the clinical picture.
- Selecting M43.28 (sacral and sacrococcygeal region) when the fusion is at the L5-S1 junction — verify the documented spinal level before finalizing the code.
Clinical context
Source · Editorial summary grounded in 4 cited references ↓
M43.27 covers spontaneous or pathological fusion (ankylosis) of the lumbosacral spinal segment. Use it when the clinical record documents loss of mobility at the L5-S1 junction due to a disease process such as degenerative ankylosis, advanced disc disease with end-stage bridging, or inflammatory-origin fusion that does not meet criteria for ankylosing spondylitis (M45). This is a diagnosis code for an active condition — not a status code.
Critical distinction: M43.27 is not the correct code when documenting a patient's history of surgical spinal fusion. Post-operative arthrodesis status is captured by Z98.1 (Arthrodesis status), which carries an Excludes 2 note under M43.2 — meaning both codes can coexist when clinically appropriate, but Z98.1 alone covers the surgical history. If the provider documents both a prior surgical fusion and coexisting pathological ankylosis at the lumbosacral level, dual coding is defensible with supporting documentation.
M43.27 maps to MS-DRG v43.0 groups 551 (Medical back problems with MCC) and 552 (Medical back problems without MCC). The approximate synonyms recognized in the ICD-10-CM index are 'Ankylosis of lumbosacral joint' and 'Fusion of lumbosacral spine.' If the fusion involves the sacral and sacrococcygeal region rather than the lumbosacral junction, use M43.28 instead.
Sibling codes
Other billable codes under M43.2 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 4 cited references ↓
01Is M43.27 the right code after a TLIF or PLIF at L5-S1?
02What is the difference between M43.26 and M43.27?
03Can M43.27 and M45 (ankylosing spondylitis) be coded together?
04Which MS-DRGs does M43.27 map to?
05Does M43.27 require a 7th character extension?
06What ICD-9-CM code did M43.27 replace?
07When should M43.28 be used instead of M43.27?
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-/M43.27
- 03aapc.comhttps://www.aapc.com/codes/icd-10-codes/M43.27
- 04healthnetworksolutions.nethttps://www.healthnetworksolutions.net/images/Comparison_of_Top_100_ICD_9_to_ICD_10.pdf
Mira AI Scribe
Mira AI Scribe captures the spinal level (lumbosacral/L5-S1), imaging findings (bridging osteophytes, disc space obliteration, end-plate fusion on X-ray or MRI), documented loss of segmental mobility, and the provider's stated etiology (degenerative vs. inflammatory). It also flags prior surgical fusion history so Z98.1 can be added when appropriate. This prevents downcoding to the less-specific lumbar region code M43.26, avoids Excludes 1 conflicts with ankylosing spondylitis, and eliminates audit exposure from using a disease code to represent post-surgical status.
See how Mira captures M43.27 documentation