ICD-10-CM · Spine

M40.36

Flatback syndrome localized to the lumbar region — loss of the normal lumbar lordosis resulting in a straightened or hypolordotic lumbar spine segment.

Verified May 8, 2026 · 5 sources ↓

Status: Billable
Chapter: 13
Related CPT: 15
Region: Spine

Drawn from CDCICD10DataAAPCCMS

Documentation tips

What should appear in the chart to support M40.36.

Source · Editorial brief grounded in 5 cited references ↓

Provider must specify 'lumbar region' by name — documentation that says only 'flatback syndrome' without a spinal region defaults to M40.30 (unspecified), which is a weaker code.
Record imaging findings explicitly: lumbar lordosis angle (Cobb method), segmental hypolordosis, and any sagittal imbalance measurement on full-length standing radiographs or MRI.
If an underlying disease drives the flatback (e.g., degenerative disc disease, AS), document it clearly so it can be sequenced first per the 'Code first' instruction at M40.
Note whether prior spinal surgery is in the patient's history — if the flatback is a complication of instrumentation, the correct code shifts to M96.- (Excludes1 applies), not M40.36.
Document functional impact: inability to stand erect without hip or knee flexion, gait disturbance, or pain with prolonged standing — supports medical necessity for advanced imaging and treatment.

Related CPT procedures

Procedure codes commonly billed with M40.36. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

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.

72114 $61.79

Radiologic examination of the lumbosacral spine, complete series with bending (flexion/extension) views — minimum of 6 views total.

72120 $42.09

Radiologic examination of the lumbosacral spine using bending views only, minimum of four views, to assess spinal flexibility and alignment.

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.

22800 $1,312.99

Posterior spinal arthrodesis for deformity correction spanning up to 6 vertebral segments, with or without application of a body cast.

22802 $1,936.25

Posterior spinal arthrodesis for deformity correction spanning 7 to 12 vertebral segments, with or without body cast application.

22804 $2,222.50

Posterior spinal arthrodesis for deformity correction spanning 13 or more vertebral segments, performed with or without application of a body cast.

72149 View procedure details

95925 View procedure details

95926 View procedure details

95927 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M40.36 and adjacent codes.

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

Using M40.36 after prior spinal surgery when the flatback is a direct postprocedural complication — that scenario belongs to M96.- per the Excludes1 note at M40.
Defaulting to M40.30 (site unspecified) when the provider documented the lumbar region — always assign the most specific site code available.
Failing to sequence the underlying disease first when the flatback is secondary to a documented systemic or degenerative condition, violating the 'Code first' tabular instruction.
Confusing M40.36 (lumbar) with M40.37 (lumbosacral) — if the deformity involves L5-S1 or the sacral articulation, M40.37 is correct; lumbar-only pathology uses M40.36.
Coding M40.36 alongside M41.- (kyphoscoliosis) for the same region — these are Excludes1 conditions and cannot be reported together.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

M40.36 codes flatback syndrome when the pathology is confined to the lumbar region (approximately L1–L5). Flatback syndrome is a spinal deformity characterized by reduction or reversal of the normal lumbar lordotic curve, typically causing forward-pitched posture, difficulty standing upright, and progressive low back and hip pain. Use M40.36 when imaging and clinical documentation confirm lumbar-level hypolordosis and the provider has specified the lumbar region as the site of deformity.

The tabular note at M40 requires you to 'Code first underlying disease.' If the flatback is attributable to a degenerative disc process, ankylosing spondylitis, or prior spinal instrumentation-related deformity, sequence that condition before M40.36. However, postprocedural kyphosis and lordosis (M96.-) is an Excludes1 — if the flatback is a direct complication of a prior spinal procedure, use the M96 code instead of M40.36. Similarly, congenital lordosis/kyphosis (Q76.4) and kyphoscoliosis (M41.-) are Excludes1 conditions and cannot be reported alongside M40.36 for the same spinal segment.

CMS has explicitly listed M40.36 as a supporting medical necessity code for lumbar MRI (CMS LCD Article A57207) and somatosensory testing (A57041), which means payers will expect this code on the claim when those services are billed for flatback-related evaluation. If the deformity spans the thoracolumbar junction, use M40.35; if it extends into the lumbosacral segment, use M40.37. When the region is unspecified in documentation, fall back to M40.30 — but push the provider to specify.

Sibling codes

Other billable codes under M40.3 (laterality / anatomic variants).

M40.30

Flatback syndrome, site unspecified

M40.37

Flatback syndrome, lumbosacral region

M40.35

Flatback syndrome, thoracolumbar region

Frequently asked questions

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

01What is the difference between M40.36 and M40.30?

M40.36 specifies the lumbar region; M40.30 is the unspecified-site fallback. Use M40.30 only when the provider's documentation genuinely does not identify a spinal region. If 'lumbar' is documented, M40.36 is required.

02Can I use M40.36 after a patient has had lumbar spinal fusion?

Only if the flatback is not a direct complication of the surgery. The Excludes1 note at M40 directs postprocedural kyphosis and lordosis to M96.-. If the operative report or clinical notes attribute the deformity to the instrumentation or fusion, use the appropriate M96 code instead.

03Do I need to code the underlying disease separately when using M40.36?

Yes. The tabular 'Code first underlying disease' instruction at M40 requires the causative condition — such as degenerative disc disease or ankylosing spondylitis — to be sequenced before M40.36 on the claim.

04Which lumbar MRI CPT codes does CMS recognize M40.36 as supporting for medical necessity?

CMS LCD Article A57207 explicitly lists M40.36 as a supporting diagnosis for lumbar MRI services. Confirm the specific CPT codes covered under your MAC's local coverage determination before billing.

05What adjacent codes should I consider if the flatback spans multiple regions?

Use M40.35 for the thoracolumbar region, M40.37 for the lumbosacral region, and M40.30 only when the site is truly unspecified. If deformity spans two named regions, assign the code that best reflects the primary site of pathology per the provider's documentation, or query the provider.

06Is M40.36 valid for FY2026 billing dates?

Yes. M40.36 has been stable without change since it was introduced in FY2016 and remains valid for dates of service on or after October 1, 2025 under the FY2026 ICD-10-CM code set.

Sources & references

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

Mira AI Scribe

Mira AI Scribe captures lumbar region specification, standing radiograph or MRI findings (Cobb angle, sagittal imbalance, hypolordosis measurement), any underlying diagnosis driving the deformity, and prior spinal surgery history. That data locks in M40.36 over the unspecified fallback M40.30, satisfies the 'Code first' sequencing rule, and flags the M96.- Excludes1 conflict before the claim is submitted.

See how Mira captures M40.36 documentation