ICD-10-CM · Spine

M43.4

Recurrent dislocation at the atlantoaxial joint (C1-C2) that does not fall under the rotatory dislocation category coded at M43.3 — a non-traumatic, repeat instability pattern at the craniocervical junction.

Verified May 8, 2026 · 5 sources ↓

Status: Billable
Chapter: 13
Related CPT: 9
Region: Spine

Drawn from CDCICD10DataAAPCCMS

Documentation tips

What should appear in the chart to support M43.4.

Source · Editorial brief grounded in 5 cited references ↓

Explicitly document 'recurrent' in the note — a single dislocation episode does not support M43.4 and should be coded with the appropriate S-code.
Specify that the dislocation is NOT rotatory; if rotation is present, M43.3 applies instead.
Record the underlying etiology driving instability (e.g., rheumatoid arthritis, Down syndrome, ligamentous laxity) so a secondary diagnosis code can be added for full clinical picture.
Include imaging findings — flexion-extension cervical radiographs, CT, or MRI — confirming atlantoaxial instability or malalignment at C1-C2.
Document symptom burden: neck pain, occipital headache, myelopathic signs, or neurologic deficits, which support medical necessity for advanced imaging and surgical consultation.

Related CPT procedures

Procedure codes commonly billed with M43.4. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

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.

22595 $1,499.03

Posterior arthrodesis of the atlas and axis (C1-C2), surgically fusing the first and second cervical vertebrae through a posterior approach to stabilize the upper cervical spine.

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.

72040 $39.75

Radiologic examination of the cervical spine capturing two or three views (e.g., AP, lateral, oblique).

72050 $55.11

Radiologic examination of the cervical spine capturing a minimum of four views, used to evaluate alignment, fractures, degeneration, or other structural pathology of the neck.

99214 $135.61

Office visit for an established patient requiring moderate-complexity medical decision making (MDM), or 30–39 minutes of total provider time on the date of service.

99215 $192.39

Highest-level office or outpatient E/M visit for an established patient, qualifying via high-complexity medical decision making or 40–54 minutes of total provider time on the date of service.

72125 View procedure details

72127 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M43.4 and adjacent codes.

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

Appending a 7th-character extension (A, D, or S) to M43.4 — this is an M-code with no 7th-character requirement; adding one creates an invalid code.
Using M43.4 for a first-time acute traumatic atlantoaxial dislocation — that episode belongs in the S-code injury chapter with appropriate 7th-character extensions.
Confusing M43.3 (rotatory atlantoaxial dislocation) with M43.4; the provider must document the dislocation type before you assign either code.
Failing to add a secondary code for the systemic condition causing instability (e.g., M05.x for rheumatoid arthritis, Q90.x for Down syndrome), which leaves payer medical-necessity reviews without clinical context.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

M43.4 applies when the atlantoaxial joint repeatedly dislocates or subluxes and the underlying mechanism is classified as 'other' — meaning it is not the rotatory atlantoaxial dislocation captured by M43.3. Common clinical scenarios include recurrent instability secondary to ligamentous laxity (as seen in Down syndrome or Marfan syndrome), inflammatory destruction of the transverse ligament (as in rheumatoid arthritis), or post-surgical instability not attributed to an acute traumatic event. The 'recurrent' qualifier is essential: a single acute traumatic dislocation is an injury-chapter S-code, not M43.4.

Because M43.4 sits within the deforming dorsopathies section (M40–M43) under Chapter 13, it carries no 7th-character extension requirement. Do not append A, D, or S — those extensions apply to injury codes in Chapter 19. If documentation supports an underlying systemic condition driving the instability (e.g., rheumatoid arthritis, Down syndrome), code that condition as an additional diagnosis per sequencing conventions.

Differentiate carefully within the M43 family: M43.3 is rotatory atlantoaxial dislocation; M43.4 is all other recurrent atlantoaxial dislocation. If documentation only says 'atlantoaxial instability' without specifying recurrence or the type of dislocation, query the provider before defaulting to M43.4.

Sibling codes

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

M43.6

Torticollis

M43.9

Deforming dorsopathy, unspecified

M43.3

Recurrent atlantoaxial dislocation with myelopathy

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 5 cited references ↓

01What makes M43.4 'other' recurrent — how does it differ from M43.3?

M43.3 is specifically rotatory atlantoaxial dislocation. M43.4 captures every other pattern of recurrent C1-C2 dislocation or subluxation — translational, anterior, posterior — that isn't rotatory in nature. If the note documents rotatory instability, use M43.3.

02Can I use M43.4 for a patient seen after a car accident with a new atlantoaxial dislocation?

No. An acute traumatic dislocation belongs in the S-code injury chapter (e.g., S13.121A for initial encounter). M43.4 requires a pattern of recurrence and is a disease-chapter code, not a trauma code.

03Does M43.4 need a 7th-character extension?

No. M43.4 is a Chapter 13 musculoskeletal disease code with no 7th-character requirement. Do not append A, D, or S — doing so creates an invalid, unprocessable code.

04Should I code the underlying condition separately when billing M43.4?

Yes. If a systemic condition such as rheumatoid arthritis, Down syndrome, or Marfan syndrome is driving the atlantoaxial instability, add the appropriate secondary diagnosis code. Sequencing follows standard etiology/manifestation rules.

05What imaging is typically needed to support M43.4 in documentation?

Flexion-extension cervical radiographs demonstrating abnormal C1-C2 motion are the standard baseline. CT or MRI may be used to further characterize ligamentous integrity, odontoid position, and spinal cord involvement — all of which strengthen medical necessity documentation.

06Which CPT codes are commonly paired with M43.4?

Evaluation and management codes 99214–99215 for office visits, cervical spine imaging (72040, 72050, 72125, 72127), and surgical procedures such as C1-C2 arthrodesis (22595) or posterior cervical fusion (22600) with instrumentation (22840) when stabilization is indicated.

07If documentation just says 'atlantoaxial instability' without specifying recurrence, can I still use M43.4?

No — query the provider. 'Instability' alone does not confirm recurrent dislocation. The distinction between a single episode, a chronic pattern, and an acute traumatic event changes the correct code entirely.

Sources & references

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

Mira Scribe

The Mira AI Scribe captures documentation of atlantoaxial instability at C1-C2, flags whether the episode is recurrent vs. first-time, records the absence of rotatory mechanism, and pulls in imaging findings (flexion-extension films, CT, MRI) and any documented underlying condition driving the instability. This prevents downcoding to an unspecified cervical diagnosis or miscoding a recurrent M-code condition as an acute S-code injury encounter.

See how Mira captures M43.4 documentation