Abnormal anterior curvature (hyperlordosis or loss of normal curve) affecting the thoracolumbar junction — the transitional zone where the thoracic and lumbar spine meet — with etiology not further specified in the clinical record.

Documentation tips

What should appear in the chart to support M40.55.

Source · Editorial brief grounded in 5 cited references ↓

• Specify 'thoracolumbar region' or 'thoracolumbar junction' explicitly in the note — vague terms like 'low back lordosis' may not map clearly to M40.55 vs. M40.56.
• State the etiology if known; 'unspecified' is a last resort. Postural, secondary, or post-surgical etiologies all have more specific codes that reduce audit risk.
• Document imaging findings that confirm the deformity — X-ray Cobb angle measurement, vertebral levels involved, and any adjacent segment changes support medical necessity.
• If an underlying disease (e.g., neuromuscular disorder, osteoporosis) is causing the lordosis, document that relationship explicitly so the 'code first' instruction for M40 can be followed.
• Record functional impact (pain severity, range-of-motion limitation, gait changes) to support medical necessity for physical therapy, imaging, or surgical consultation claims.

Related CPT procedures

Procedure codes commonly billed with M40.55. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

Common coding pitfalls

The recurring mistakes coders make with M40.55 and adjacent codes.

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

• Using M40.55 when the lordosis is postural — if posture is the documented cause, M40.45 (postural lordosis, thoracolumbar region) is the correct code.
• Defaulting to M40.50 (site unspecified) when the provider clearly identified the thoracolumbar junction in the note — that under-specifies and increases denial risk.
• Applying M40.55 to post-surgical flatback or hyperlordosis after spinal instrumentation — postprocedural spinal deformities belong in M96.- not M40.-.
• Forgetting the 'code first' instruction: when an underlying disease drives the lordosis, listing M40.55 as the primary diagnosis without first coding the causative condition violates tabular sequencing rules.
• Confusing the thoracolumbar region (T10–L2 junction) with the lumbar region; if the apex of the curve is squarely lumbar, M40.56 is more precise.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Sibling codes

Other billable codes under M40.5 (laterality / anatomic variants).