ICD-10-CM · Spine

M43.20

M43.20 identifies ankylosis of a spinal joint where the specific vertebral region has not been documented. It is the least-specific code in the M43.2 family and should be replaced with a site-specific code whenever the affected region is known.

Verified May 8, 2026 · 5 sources ↓

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

Drawn from CDCICD10DataAetnaAAPCCdek

Documentation tips

What should appear in the chart to support M43.20.

Source · Editorial brief grounded in 5 cited references ↓

Always document the specific vertebral region by name (e.g., lumbar, cervical, thoracolumbar) so a site-specific M43.2x code can be assigned instead of M43.20.
Note whether the fusion is spontaneous/degenerative versus post-surgical — surgical arthrodesis status codes to Z98.1, not M43.2x.
Record imaging findings (plain film, CT, or MRI) that confirm bony or fibrous ankylosis, including the named vertebral levels involved.
Exclude ankylosing spondylitis as the cause before assigning M43.2x — if AS is documented, code to M45.0– instead.
If the fusion involves multiple named regions, evaluate whether M43.29 (multiple sites) is more accurate than M43.20 (site unspecified).

Related CPT procedures

Procedure codes commonly billed with M43.20. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

22548 $1,943.60

Arthrodesis of the clivus-C1-C2 complex via anterior transoral or extraoral approach, with or without odontoid process excision.

22551 $1,604.91

Anterior cervical discectomy and fusion (ACDF) at a single interspace, performed through a front-of-neck approach with removal of disc material and arthrodesis of adjacent vertebral bodies.

22600 $1,282.93

Posterior or posterolateral cervical spinal fusion at a single interspace below C2, performed through a posterior approach to achieve bony arthrodesis.

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.

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.

22853 $228.80

Add-on code for inserting an interbody biomechanical device (e.g., synthetic cage or mesh) with integral anterior anchoring instrumentation into an intervertebral disc space, performed alongside interbody arthrodesis, reported once per interspace.

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.

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.

97016 $12.02

Application of a vasopneumatic (intermittent pneumatic compression) device to one or more extremities to reduce edema or swelling.

Common coding pitfalls

The recurring mistakes coders make with M43.20 and adjacent codes.

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

Assigning M43.20 when the operative report or imaging clearly names the spinal region — this triggers specificity downcoding and may prompt a payer audit.
Confusing M43.20 with Z98.1 (arthrodesis status): M43.20 is for pathological/spontaneous fusion, not for documenting a prior surgical spinal fusion.
Using M43.20 as a secondary code alongside M45.0– (ankylosing spondylitis) — the M43.2 category explicitly excludes ankylosing spondylitis; do not double-code.
Mistaking congenital spinal fusion (Q76.4) for M43.20 — congenital fusions are excluded from M43.2 by a Type 1 Excludes note.
Failing to update M43.20 to a site-specific code after diagnostic imaging results are added to the chart — code to the highest level of specificity available at the time of claim submission.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

M43.20 represents spontaneous or pathological fusion (ankylosis) of a spinal joint at an unspecified level. This is distinct from surgical arthrodesis status (Z98.1), congenital spinal fusion (Q76.4), and ankylosing spondylitis (M45.0–). The code captures a non-congenital, non-surgical bony or fibrous union of adjacent vertebral segments where the clinical record does not specify whether the fusion involves the cervical, thoracic, lumbar, or sacral spine.

Because M43.2 has nine site-specific child codes — M43.21 through M43.28, plus M43.20 for unspecified — payers and RAC auditors treat M43.20 as an incomplete code in most contexts. If imaging, operative report, or clinical notes identify any named spinal region, use the corresponding site-specific code instead: M43.22 (cervical), M43.24 (thoracic), M43.26 (lumbar), etc.

This code appears on payer coverage lists (e.g., Aetna CPB 0009) as a qualifying diagnosis for back braces and related durable medical equipment. For those claims, M43.20 is acceptable only when site documentation is genuinely absent. In orthopedic and spine surgery practice, that scenario is rare — imaging always identifies at least the general region of fusion.

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

M43.26

Fusion of spine, lumbar region

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 5 cited references ↓

01When is it acceptable to use M43.20 instead of a site-specific M43.2x code?

Only when the clinical record genuinely does not specify any vertebral region. If imaging or notes identify any named segment, use the corresponding site-specific code (M43.21–M43.28).

02Does M43.20 cover surgical spinal fusion status?

No. Post-surgical arthrodesis status codes to Z98.1. M43.20 is reserved for pathological or spontaneous ankylosis of a spinal joint, not a prior operative fusion.

03Can M43.20 be used alongside M45.0– for ankylosing spondylitis?

No. The M43.2 category carries a Type 1 Excludes note for ankylosing spondylitis (M45.0–). If AS is the cause of the fusion, code to M45.0– only.

04Is M43.20 accepted by payers for DME or back brace authorization?

Yes — payers such as Aetna list M43.20 through M43.28 as covered diagnoses for back braces when selection criteria are met. However, a site-specific code is preferable whenever documentation supports it.

05What is the difference between M43.20 and congenital spinal fusion (Q76.4)?

Congenital spinal fusion is excluded from M43.2 by a Type 1 Excludes note. Use Q76.4 for fusion present from birth; use M43.20 (or a site-specific M43.2x) for acquired, non-surgical ankylosis.

06If the fusion spans multiple named regions, which code applies?

Use M43.29 (fusion of spine, multiple sites) rather than M43.20. M43.20 should only be selected when no region at all can be identified from the documentation.

07Is pseudoarthrosis after a prior fusion coded with M43.20?

No. Pseudoarthrosis after fusion or arthrodesis has its own code, M96.0, which is explicitly excluded from the M43.2 category.

Sources & references

Editorial content was developed using the following public sources. Last verified May 8, 2026.

01CDC ICD-10-CM Tabular List 2026 — M43.20
02
icd10data.com
https://www.icd10data.com/ICD10CM/Codes/M00-M99/M40-M43/M43-/M43.20
03
aetna.com
https://www.aetna.com/cpb/medical/data/1_99/0009.html
04
aapc.com
https://www.aapc.com/codes/icd-10-codes/M43.20
05
cdek.pharmacy.purdue.edu
https://cdek.pharmacy.purdue.edu/icd10/M43.20/

Mira AI Scribe

Mira AI Scribe captures the specific vertebral region identified on imaging or in the physical exam note — naming the level (e.g., L4–L5 lumbar, C5–C6 cervical) allows the coder to assign a site-specific M43.2x code rather than the unspecified M43.20. This prevents specificity-related claim downgrades and removes the audit risk that accompanies unspecified spinal codes when imaging is on file.

See how Mira captures M43.20 documentation