Glossary · Clinical

Subluxation

A subluxation is an incomplete or partial dislocation of a joint in which the articular surfaces lose their normal relationship but retain some contact. In the spinal context used by CMS, it specifically refers to a vertebra that is out of position relative to adjacent vertebrae, producing measurable clinical or radiographic findings.

Verified May 8, 2026 · 7 sources ↓

Drawn from CMSEnlyteMedcoconsultants

Definition

Source · Editorial summary grounded in 7 cited references ↓

Subluxation describes a joint displacement that is partial rather than complete. The bones forming the joint shift out of their normal alignment but do not fully separate, distinguishing the condition from a true dislocation. In peripheral joints—shoulder, patellofemoral, elbow—this partial displacement can result from trauma, ligamentous laxity, neuromuscular imbalance, or congenital variation, and it may reduce spontaneously or require manual or surgical intervention.

In the spinal context, CMS and Medicare coverage policy define subluxation as the incomplete dislocation, off-centering, misalignment, fixation, or abnormal spacing of one or more vertebral or intervertebral units. Spinal subluxations are further classified as acute (e.g., strain or sprain mechanism), chronic (e.g., persistent loss of joint mobility), or nerve-root-related (e.g., radiculopathy from foraminal compromise). Documentation must establish the precise vertebral level and must be supported by physical examination findings—using the PART criteria (Pain, Asymmetry, Range-of-motion restriction, Tissue-tone changes)—or by radiographic evidence.

ICD-10-CM separates subluxation from full dislocation in a clinically meaningful way. Acute traumatic spinal subluxations are reported with S-series codes (e.g., S13.100A for subluxation of an unspecified cervical vertebra, initial encounter), while biomechanical or chiropractic-context subluxation complexes use the M99.1x series. Peripheral joint subluxations carry their own anatomically specific S- and M-series codes. This separation, introduced with ICD-10-CM, replaced the older ICD-9-CM convention in which 'subluxation' was merely a non-essential modifier appended to dislocation codes.

Why it matters

For Medicare chiropractic claims, subluxation is the only covered diagnosis: if the primary diagnosis is not coded to a recognized subluxation level—M99.10–M99.15 or the appropriate S-series traumatic subluxation code—the claim will be denied outright regardless of the services rendered. Orthopedic practices treating peripheral joint subluxations (e.g., shoulder, patella) face a different but equally concrete risk: miscoding a subluxation as a complete dislocation triggers NCCI bundling and payment conflicts, because repair codes for fractures and dislocations are mutually exclusive per CMS NCCI Chapter IV, and the wrong code selection can result in downcoding, overpayment demands, or audit flags. Accurate subluxation coding also drives medical-necessity determinations that separate reimbursable active treatment from non-covered maintenance therapy.

Common mistakes

Where people most often go wrong with this concept.

Source · Editorial brief grounded in cited references ↓

Coding a partial joint displacement with a full-dislocation ICD-10-CM code—ICD-10-CM assigns distinct codes to subluxation and dislocation; using the dislocation code when the joint retained contact is clinically and legally inaccurate.
Omitting the precise vertebral level on Medicare chiropractic claims—CMS requires the exact spinal level as the primary diagnosis; an unspecified or region-only code is insufficient and will trigger denial.
Failing to include a secondary diagnosis—Medicare mandates both a primary subluxation-level code and a secondary neuromusculoskeletal condition code explaining why treatment is necessary.
Billing CPT 98940–98942 without the AT modifier for active treatment—claims submitted without AT are automatically deemed not medically necessary by Medicare and will be denied.
Using maintenance-therapy documentation language ('patient is stable,' 'no expected functional improvement') while still appending the AT modifier—this combination is contradictory and a common CERT audit finding.
Applying M99.1x codes to an acute traumatic event—these codes reflect biomechanical/chiropractic subluxation complexes; a same-day motor-vehicle injury should instead use the S-series traumatic subluxation codes.
Conflating 'subluxation complex' (M99.1x) with a full structural subluxation requiring surgical stabilization—the M99 series is specific to segmental dysfunction and is not appropriate for post-traumatic instability managed operatively.

Related codes

Codes commonly involved when this concept appears in practice.

CPT

ICD-10

M99.10 M99.11 M99.12 M99.13 M99.14 M99.15

Modifiers

59 Distinct procedural service

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 7 cited references ↓

01What is the clinical difference between a subluxation and a dislocation?

In a subluxation the joint surfaces are partially displaced but retain some contact; in a true dislocation all articular contact is lost. This distinction drives separate ICD-10-CM code assignments and different treatment and surgical coding pathways.

02Why does Medicare only cover chiropractic services for subluxation?

Medicare statute limits chiropractic coverage to manual manipulation for the treatment of spinal subluxation. Services beyond that narrow scope—x-rays, physical therapy, orthotics, office visits—are explicitly excluded from Medicare chiropractic coverage regardless of clinical necessity.

03Which ICD-10-CM codes are used for spinal subluxation in chiropractic billing?

CMS recognizes M99.10–M99.15 (subluxation complex of the vertebral column by region) as the primary diagnosis codes for chiropractic claims. Acute traumatic spinal subluxations use the S13, S23, S33, or S43 series depending on spinal level and encounter type.

04What is the AT modifier and when is it required?

The AT modifier tells Medicare that the service is active, corrective treatment—not maintenance therapy. It is required on every Medicare chiropractic claim using CPT 98940, 98941, or 98942 when the chiropractor is providing active treatment. Omitting it results in automatic denial.

05Can the same vertebral subluxation be coded with M99.1x and an S-series code simultaneously?

No. M99.1x codes describe biomechanical or chiropractic-context subluxation complexes and are used for ongoing segmental dysfunction. S-series subluxation codes describe acute traumatic events. The correct series depends on the mechanism and timing; using both for the same level at the same encounter would be duplicative and likely to trigger a claim edit.

06How does a practice document subluxation to satisfy Medicare requirements?

Documentation must establish the precise vertebral level and support findings either through physical examination using the PART criteria (Pain, Asymmetry, Range-of-motion restriction, Tissue-tone changes) or through radiographic evidence. The x-ray, if used, must have been taken within 12 months before or 3 months after initiating treatment.

Sources & references

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

Mira AI Scribe

When Mira detects documentation language suggesting partial joint displacement—phrases such as 'partial dislocation,' 'joint shifted but not fully out,' 'vertebra out of position,' or 'instability without complete separation'—it will prompt the coder to confirm subluxation rather than dislocation before code assignment. For spinal encounters billed to Medicare (CPT 98940–98942), Mira will: 1. Flag if the primary diagnosis is not a recognized subluxation-level code (M99.10–M99.15 or applicable S-series). 2. Prompt for a secondary neuromusculoskeletal diagnosis if one is absent. 3. Alert if the AT modifier is missing on an active-treatment claim. 4. Warn if note language is consistent with maintenance therapy while AT is appended. For peripheral joint encounters, Mira will surface the correct anatomic subluxation code (e.g., S43.004A for initial-encounter glenohumeral subluxation) and flag if a full-dislocation code has been selected when documentation supports only partial displacement. Mira will not auto-populate subluxation codes; it will surface the evidence from the note and present the coder with the correct options and the clinical rationale for choosing between subluxation and dislocation codes. All final code selections remain the responsibility of the credentialed coder or supervising physician.

See Mira's approach

Related terms

Dislocation Clinical

A dislocation is a joint injury in which the articulating bone ends are forcibly displaced out of their normal anatomic position. Treatment is classified as closed, percutaneous, or open, and each classification carries a distinct CPT code family with a 90-day global period.