ICD-10-CM · Spine

M51.A2

A large defect in the annulus fibrosus of an intervertebral disc at the lumbar level, typically documented post-discectomy and confirmed on MRI imaging.

Verified May 8, 2026 · 5 sources ↓

Status: Billable
Chapter: 13
Related CPT: 8
Region: Spine

Drawn from CDCMedcentralCMSICD10DataNIH

Documentation tips

What should appear in the chart to support M51.A2.

Source · Editorial brief grounded in 5 cited references ↓

Record the measured dimensions of the annular defect from MRI (width ≥6 mm and height ≥4 mm confirms 'large' per the original CDC committee criteria).
Specify that the defect is lumbar, not lumbosacral — if it involves the L5-S1 junction, M51.A5 is the correct code.
Document the clinical context: post-discectomy status, date of prior surgery, and whether the annular defect was assessed, treated, or closed during the current encounter.
Note the absence of herniation or radiculopathy if applicable — M51.A2 is not the right code when herniation with nerve compression is the primary finding.
Include the MRI report or operative findings in the record to support the size classification and distinguish large from small defects.

Related CPT procedures

Procedure codes commonly billed with M51.A2. 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.

63030 $898.15

Single-interspace lumbar laminotomy with nerve root decompression, including partial facetectomy, foraminotomy, and/or herniated disc excision performed via open surgical technique.

63047 $1,065.49

Lumbar laminectomy at a single vertebral segment that also includes facetectomy and foraminotomy for decompression of the spinal cord, cauda equina, and/or nerve roots — unilateral or bilateral.

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.

99213 $95.19

Established patient office or outpatient visit requiring 20–29 minutes of total time or low-complexity medical decision-making.

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.

72149 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M51.A2 and adjacent codes.

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

Using M51.A2 when the defect is at the lumbosacral region — that's M51.A5; lumbar means L1-L5 disc levels, not L5-S1.
Defaulting to M51.A0 (unspecified size) when imaging actually documents measurable defect dimensions — size-specific codes are available and preferred.
Stacking M51.A2 with an active disc herniation/radiculopathy code (e.g., M51.16) without confirming the conditions are separately documented and clinically distinct.
Applying M51.A2 to pre-discectomy presentations — this code family was designed for post-discectomy annular defect assessment, not primary disc herniation diagnosis.
Confusing M51.A2 with M51.36 (other intervertebral disc degeneration, lumbar) — annular defects with documented size belong in the M51.A subcategory, not the degeneration series.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

M51.A2 codes a large annular defect in the lumbar region — defined as ≥6 mm wide and ≥4 mm high per the CDC committee recommendations that drove creation of this code family. These codes were introduced in FY2023 specifically to let spine surgeons document the size of annular defects identified or addressed after discectomy. Before M51.A, coders had no size-specific option for this condition.

Use M51.A2 when imaging (typically MRI) confirms a large lumbar annular defect and the treating provider documents that the defect was assessed or treated. If the defect falls below the large threshold — or imaging is inconclusive about size — drop to M51.A1 (small) or M51.A0 (unspecified size). If the defect is at the lumbosacral junction rather than purely lumbar, use M51.A5 instead.

M51.A2 appears on the CMS LCD supporting list for lumbar MRI (Article A57207), making it a valid medical necessity anchor for imaging orders. It should not be used as a stand-alone code when disc herniation with radiculopathy is the primary finding — code the herniation directly (e.g., M51.16) and reserve M51.A2 for the annular defect when it is separately identified and clinically addressed.

Sibling codes

Other billable codes under M51.A (laterality / anatomic variants).

M51.A4

Intvrt annulus fibrosus defect, small, lumbosacral region

M51.A1

Intervertebral annulus fibrosus defect, small, lumbar region

M51.A0

Intvrt annulus fibrosus defect, lumbar region, unsp size

M51.A3

Intvrt annulus fibrosus defect, lumbosacr region, unsp size

M51.A5

Intvrt annulus fibrosus defect, large, lumbosacral region

Frequently asked questions

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

01What defect size qualifies as 'large' for M51.A2?

The CDC committee criteria that drove these codes define large as ≥6 mm wide and ≥4 mm high. Both dimensions must meet the threshold. A defect measuring 7 mm wide but only 3 mm high would not meet the large criteria — use M51.A1 (small) or M51.A0 (unspecified) in that scenario.

02Is M51.A2 only used after discectomy?

The code family was created specifically to document annular defects following discectomy, and the clinical context is almost always post-surgical. The code itself does not require a prior procedure code, but documentation should reflect the clinical basis for identifying and treating the defect.

03Can M51.A2 and M51.16 (lumbar disc disorder with radiculopathy) be reported together?

Only if the provider documents them as distinct, separately addressed conditions in the same encounter. If the annular defect is the structural basis for the radiculopathy, M51.16 is the more specific code. Do not use both unless the record clearly supports two separate diagnoses.

04Does M51.A2 support medical necessity for a lumbar MRI order?

Yes. CMS LCD Article A57207 explicitly lists M51.A2 among ICD-10-CM codes that support medical necessity for lumbar MRI. Include it as the primary or supporting diagnosis on the imaging order when the clinical indication is a documented large lumbar annular defect.

05What is the difference between M51.A2 and M51.A5?

M51.A2 is a large annular defect in the lumbar region (L1-L5 disc levels). M51.A5 is a large annular defect in the lumbosacral region (L5-S1). Check the operative or imaging report for the specific disc level before selecting between these two codes.

06When should M51.A0 (unspecified size) be used instead of M51.A2?

Use M51.A0 only when imaging does not document defect dimensions or the provider cannot classify the defect as small or large. If the MRI report includes measurable dimensions that meet the large threshold, M51.A2 is the correct code — unspecified is a fallback, not a default.

Sources & references

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

Mira AI Scribe

The Mira AI Scribe captures MRI-reported defect dimensions (width and height in mm), lumbar level involved, post-discectomy status, and whether the defect was assessed or treated at the encounter. This prevents the coder from dropping to the unspecified-size code M51.A0 or the wrong region code M51.A5, and it gives the MRI ordering provider the documented medical necessity anchor required by CMS LCD A57207.

See how Mira captures M51.A2 documentation