Glossary · Clinical

Spondylolysis

Spondylolysis is a stress fracture or defect of the pars interarticularis—the bony bridge connecting the superior and inferior articular facets of a vertebra—most commonly occurring at L5. It is distinct from spondylolisthesis, which occurs when the defect allows one vertebral body to slip forward on the one below.

Verified May 8, 2026 · 7 sources ↓

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Definition

Source · Editorial summary grounded in 7 cited references ↓

Spondylolysis represents a failure of the pars interarticularis, the narrow isthmus of bone in the posterior neural arch. The defect is most frequently a fatigue fracture caused by repetitive hyperextension loading, making it especially prevalent in young athletes engaged in gymnastics, football linemen, and overhead throwing sports. The L5 level accounts for roughly 90% of cases; L4 is the next most common site. The condition can be unilateral or bilateral; bilateral defects carry a higher risk of progressing to isthmic spondylolisthesis (M43.1x).

Clinically, patients typically present with activity-related low back pain that worsens with lumbar extension. Imaging workup often begins with plain radiographs, but a SPECT scan or MRI with thin-cut sequences provides greater sensitivity for early stress reactions before a frank defect is visible. CT remains the gold standard for characterizing established bony defects and planning surgical repair.

Treatment ranges from activity restriction and physical therapy for acute stress reactions to direct pars repair (e.g., Buck's screw technique) or spinal fusion for chronic, symptomatic defects unresponsive to conservative care. Accurate documentation of the vertebral level, acuity (stress reaction versus established defect), and presence or absence of associated listhesis drives both clinical management and ICD-10-CM code selection.

Why it matters

Spondylolysis and spondylolisthesis share a parent category (M43) but are distinct billable concepts: conflating them—or defaulting to the unspecified site code M43.00 when the operative or imaging report clearly identifies the lumbar level—undermines specificity and can trigger a claim rejection under MS-DRG grouping rules. Lumbar spondylolysis (M43.06) maps to MS-DRG 551/552 (Medical Back Problems); if the coder mistakenly assigns spondylolisthesis codes or selects a nonspecific site, the DRG weight and reimbursement may change, and a payer audit that uncovers the mismatch between the documented level and the submitted code creates a compliance exposure. Additionally, if a congenital etiology is documented, the correct code shifts entirely to Q76.2, which is a Type 1 Excludes note under M43.0—an automatic claim error if both are reported together.

Common mistakes

Where people most often go wrong with this concept.

Source · Editorial brief grounded in cited references ↓

Assigning M43.06 (lumbar spondylolysis) when the provider also documents forward vertebral slippage—at that point spondylolisthesis (M43.16) is the correct code, and ICD-10-CM explicitly excludes spondylolisthesis from the M43.0 subcategory.
Using the nonspecific parent code M43.00 (site unspecified) when the operative report, MRI, or radiology read clearly identifies the vertebral level—failing to drill down to the level-specific code is an addressable specificity gap that payers can flag.
Coding M43.06 for a congenital pars defect; the ICD-10-CM Type 1 Excludes note directs congenital spondylolysis to Q76.2, and reporting both codes on the same claim is incorrect.
Treating 'pars fracture,' 'pars defect,' and 'spondylolysis' as always interchangeable for coding purposes without querying the provider—AHA Coding Clinic guidance notes that pars fracture documentation alone does not automatically equate to spondylolysis and may require clarification before code assignment.
Omitting a separate spondylolisthesis code when both conditions are documented and both are clinically active; each is a separately billable diagnosis when clearly supported in the record.

Related codes

Codes commonly involved when this concept appears in practice.

CPT

ICD-10

M43.00 M43.01 M43.02 M43.03 M43.04 M43.05 M43.06 M43.07

Modifiers

59 Distinct procedural service LT Left side RT Right side 22 Increased procedural services

Frequently asked questions

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

01What is the ICD-10-CM code for lumbar spondylolysis?

M43.06 is the site-specific code for spondylolysis of the lumbar region. It has been valid since the ICD-10-CM go-live date of October 1, 2015, and remains active through the 2026 code year.

02Is spondylolysis the same as spondylolisthesis?

No. Spondylolysis is a defect or fracture of the pars interarticularis. Spondylolisthesis is the forward displacement of one vertebra on the one below, which may or may not result from a spondylolysis. ICD-10-CM treats them as separate conditions with separate codes under the M43 category, and the M43.0 subcategory explicitly excludes spondylolisthesis.

03Can spondylolysis and spondylolisthesis be coded together?

Yes, when both are independently documented as active diagnoses. Assign the level-specific spondylolysis code (e.g., M43.06) and the corresponding spondylolisthesis code (e.g., M43.16) separately. The ICD-10-CM excludes note under M43.0 means spondylolisthesis is not included in the spondylolysis code—both must be reported when both are present.

04When should a coder use Q76.2 instead of M43.06?

Q76.2 covers congenital spondylolysis. If the provider documents or the history establishes a congenital origin, Q76.2 is the correct code. M43.06 is for acquired defects. ICD-10-CM lists a Type 1 Excludes note under M43.0 pointing to Q76.2, so assigning both codes together on the same claim is a coding error.

05Does spondylolysis always require surgical coding?

No. Most spondylolysis cases are managed conservatively with activity modification, bracing, and physical therapy, which are captured through E/M codes and therapy codes rather than surgical CPT codes. Surgical CPT codes such as spinal fusion (22612, 22630) or direct pars repair are relevant only when operative intervention is performed.

06Which MS-DRGs does M43.06 map to?

Under MS-DRG version 43.0, M43.06 groups to DRG 551 (Medical Back Problems with MCC) or DRG 552 (Medical Back Problems without MCC), depending on the presence of a major complication or comorbidity.

Sources & references

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

Mira AI Scribe

When Mira detects documentation language such as 'pars defect,' 'pars fracture,' 'pars stress reaction,' or 'spondylolysis' in a spine note, it flags the following code-selection logic: 1. LEVEL SPECIFICITY: Confirm the vertebral level from imaging or operative findings. Lumbar = M43.06; lumbosacral = M43.07; thoracic = M43.04; unspecified only if no level is documented anywhere in the encounter. 2. CONGENITAL VS. ACQUIRED: If the note or history indicates a congenital origin, route to Q76.2—do not assign M43.0x alongside Q76.2 (Type 1 Excludes). 3. LISTHESIS CHECK: Scan the impression and clinical assessment for any mention of vertebral slippage, percent listhesis, or Meyerding grade. If present and separately documented as an active condition, a spondylolisthesis code (M43.1x at the corresponding level) should accompany—not replace—the spondylolysis code, unless the spondylolisthesis is the only condition being treated this encounter. 4. PROCEDURE PAIRING: When a lumbar fusion (e.g., 22612, 22630, 22633) is billed alongside a decompression code (e.g., 63012, 63030), flag for NCCI PTP edit review before finalizing. Modifier 59 may apply only when the procedures are performed at clearly distinct levels or anatomic sites per CMS NCCI Chapter 4 guidance. 5. QUERY TRIGGER: If documentation uses only 'pars fracture' without also stating 'spondylolysis' or 'pars defect,' Mira will prompt a provider query before auto-assigning M43.06, consistent with AHA Coding Clinic guidance on terminology equivalence.

See Mira's approach

Related terms

Spondylolisthesis Clinical

Spondylolisthesis is a spinal condition in which one vertebra slips forward (anterolisthesis) or, less commonly, backward (retrolisthesis) relative to the vertebra below it. It most often occurs at L4–L5 or L5–S1 and ranges in severity from mild instability to frank neurologic compromise.

Stress fracture Clinical

A stress fracture is a small crack or severe bruising within a bone caused by repetitive mechanical load rather than a single traumatic event. It is coded under ICD-10-CM category M84.3-, with specificity required for anatomical site, laterality, and encounter type.

Lumbar fusion Clinical

Lumbar fusion (arthrodesis) is a surgical procedure that permanently joins two or more lumbar vertebrae using bone graft material, with or without instrumentation, to eliminate painful motion at a diseased spinal segment.