ICD-10-CM · Spine

M43.26

M43.26 identifies ankylosis or pathological fusion of the lumbar spinal joints, representing a fixed, non-mobile state of one or more lumbar vertebral articulations due to disease or prior surgical intervention.

Verified May 8, 2026 · 4 sources ↓

Status: Billable
Chapter: 13
Related CPT: 14
Region: Spine

Drawn from CDCICD10DataAAPC

Documentation tips

What should appear in the chart to support M43.26.

Source · Editorial brief grounded in 4 cited references ↓

Specify the lumbar region explicitly in notes — document the affected vertebral levels (e.g., L4-L5) to support medical necessity for adjacent-level workup or intervention.
Distinguish between pathological fusion (M43.26) and surgical arthrodesis status (Z98.1); the note must make clear whether this is a disease finding or a post-op anatomical status.
Document the underlying etiology driving the fusion — degenerative disc disease, spondylolisthesis, inflammatory arthropathy — so the primary diagnosis can be coded alongside M43.26.
If ankylosing spondylitis is the cause, do not use M43.26; the M45.0- series is correct and the documentation must reflect the inflammatory diagnosis.
Record imaging findings (X-ray, CT, or MRI) that confirm fusion or ankylosis — bridging osteophytes, loss of disc space, bony trabeculation across the joint — to support the diagnosis on audit.

Related CPT procedures

Procedure codes commonly billed with M43.26. Linking the right diagnosis to the right procedure is what establishes medical necessity.

Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis

22612 $1,467.64

Posterior or posterolateral lumbar arthrodesis of a single interspace, performed via a posterior approach with bone graft and typically pedicle screw fixation to achieve vertebral segment fusion.

22630 $1,510.72

Posterior interbody arthrodesis of a single lumbar interspace, including laminectomy and/or discectomy performed to prepare the interspace for fusion rather than for decompression.

22633 $1,700.11

Single-level lumbar arthrodesis combining posterior or posterolateral technique with posterior interbody technique, including laminectomy and/or discectomy sufficient to prepare the interspace — performed as one surgical session at one lumbar interspace.

22614 $349.37

Add-on code for each additional interspace treated by posterior or posterolateral arthrodesis beyond the first level billed with a primary fusion code.

22840 $668.35

Posterior non-segmental instrumentation placed during spinal surgery, using rods, hooks, or wires that span multiple vertebral levels without anchoring at each intervening segment.

22842 $680.04

Posterior segmental spinal instrumentation spanning 3 to 6 vertebral segments, reported as an add-on to the primary spinal procedure code.

22843 $728.47

Posterior segmental spinal instrumentation spanning 7 to 12 vertebral segments, reported as an add-on to the primary fusion or decompression procedure.

72148 $191.72

Non-contrast MRI of the lumbar spine used to evaluate disc pathology, spinal stenosis, nerve root compression, and other structural abnormalities without administration of contrast material.

72158 $318.31

MRI of the lumbar spinal canal and its contents performed first without contrast, then repeated after contrast administration for enhanced visualization.

72100 $40.42

Radiologic examination of the lumbosacral spine capturing two or three views, used to evaluate the lumbar vertebrae and sacrum for injury, degeneration, or structural abnormality.

72110 $53.44

Radiologic examination of the lumbar spine (lumbosacral) with a minimum of four views, including oblique and/or bending views.

27279 $758.53

Minimally invasive arthrodesis of the sacroiliac joint using a transfixing implant device placed percutaneously across the joint.

72131 View procedure details

72132 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M43.26 and adjacent codes.

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

Using M43.26 as a post-surgical status code: if the documentation reflects arthrodesis status after a prior fusion procedure, Z98.1 is correct — M43.26 is for pathological or clinically established fusion, not routine post-op status.
Failing to apply the congenital fusion exclusion: lumbar fusion present from birth maps to Q76.4, not M43.26 — review patient history before assigning.
Coding M43.26 for ankylosing spondylitis: the tabular explicitly excludes ankylosing spondylitis at the M43.2 level; use M45.06 (lumbar region) instead.
Assigning M43.26 for pseudoarthrosis after fusion: nonunion following a prior arthrodesis is M96.0, not M43.26.
Selecting M43.20 (site unspecified) when lumbar involvement is clearly documented — always use M43.26 when the lumbar region is specified to avoid unspecified-code audit flags.

Clinical context

Source · Editorial summary grounded in 4 cited references ↓

M43.26 captures lumbar spinal fusion as a clinical condition — not a surgical procedure code. Use it to describe the current state of the lumbar spine when joints have become fused or ankylosed, whether from inflammatory disease, degenerative processes, or as the result of prior arthrodesis that is now an established anatomical finding. The parent code M43.2 (Fusion of spine) carries an 'Applicable To' note that includes ankylosis of spinal joint, making M43.26 appropriate for lumbar ankylosis regardless of etiology.

Critical exclusions apply at the M43.2 level. Do NOT use M43.26 for ankylosing spondylitis (use M45.0-), congenital fusion of the spine (use Q76.4), or pseudoarthrosis after fusion or arthrodesis (use M96.0). If the patient has a documented arthrodesis status post-surgical fusion and you are reporting that status — not a pathological finding — Z98.1 is the correct code. M43.26 is reserved for fusion as a pathological or established clinical condition, not merely as a post-op status designator.

This code groups under MS-DRG v43.0 DRGs 551 (Medical back problems with MCC) and 552 (Medical back problems without MCC). It is commonly coded alongside the underlying condition driving the fusion (e.g., degenerative disc disease, spondylolisthesis, spinal stenosis) and may appear on encounters for imaging review, pain management, or pre-operative planning for adjacent-level pathology.

Sibling codes

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

M43.22

Fusion of spine, cervical region

M43.23

Fusion of spine, cervicothoracic region

M43.24

Fusion of spine, thoracic region

M43.27

Fusion of spine, lumbosacral region

M43.21

Fusion of spine, occipito-atlanto-axial region

M43.20

Fusion of spine, site unspecified

M43.25

Fusion of spine, thoracolumbar region

M43.28

Fusion of spine, sacral and sacrococcygeal region

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 4 cited references ↓

01What is the difference between M43.26 and Z98.1 for a patient who had a prior lumbar fusion surgery?

Z98.1 (Arthrodesis status) is the correct code when documenting the post-surgical status of a successfully fused spine. M43.26 applies when fusion or ankylosis is identified as a pathological clinical finding — not simply as a history-of-surgery status. If the chart says 'history of L4-L5 fusion' with no active pathological finding, use Z98.1.

02Can M43.26 be used for ankylosing spondylitis causing lumbar fusion?

No. The M43.2 tabular entry explicitly excludes ankylosing spondylitis and directs coders to M45.0-. For lumbar involvement in ankylosing spondylitis, use M45.06. M43.26 is not appropriate even if lumbar fusion is radiographically present.

03Should M43.26 be the primary or secondary diagnosis?

M43.26 is typically a secondary or coexisting diagnosis. The condition responsible for the fusion — degenerative disc disease, spondylolisthesis, prior trauma — should generally lead the claim, with M43.26 providing additional anatomical specificity about the current lumbar state.

04Is M43.26 appropriate for congenital lumbar fusion?

No. Congenital fusion of the spine is excluded from M43.2 and maps to Q76.4. Review developmental history before assigning M43.26; if the fusion was present at birth, Q76.4 is correct.

05What imaging documentation supports M43.26 on audit?

X-ray, CT, or MRI findings showing bridging osteophytes, complete loss of disc height with bony continuity, or trabecular bridging across a lumbar facet or disc level support the diagnosis. Document the modality, the specific levels visualized, and the radiologist's or treating physician's interpretation confirming fusion or ankylosis.

06What is M96.0 and how does it differ from M43.26?

M96.0 is pseudoarthrosis after fusion or arthrodesis — meaning the fusion failed and a false joint formed. M43.26 describes successful or pathological fusion where the joint is truly ankylosed. These are mutually exclusive; document whether bony union is confirmed or absent before selecting.

07Which MS-DRGs does M43.26 group to?

M43.26 groups to MS-DRG 551 (Medical back problems with MCC) or 552 (Medical back problems without MCC) under MS-DRG v43.0, per the ICD-10-CM tabular grouping logic.

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 Oct 1, 2025)
02
icd10data.com
https://www.icd10data.com/ICD10CM/Codes/M00-M99/M40-M43/M43-/M43.26
03
icd10data.com
https://www.icd10data.com/ICD10CM/Codes/M00-M99/M40-M43/M43-/M43.2
04
aapc.com
https://www.aapc.com/codes/icd-10-codes/M43.26

Mira AI Scribe

Mira AI Scribe captures lumbar region specificity, documented vertebral levels, imaging confirmation of fusion or ankylosis, the underlying condition driving the fusion, and whether this is a pathological finding versus post-surgical status — preventing conflation of M43.26 with Z98.1 (arthrodesis status) or M96.0 (pseudoarthrosis), either of which triggers claim denials or audit flags.

See how Mira captures M43.26 documentation