Ankylosing spondylitis localized to the lumbosacral region of the spine, capturing inflammatory involvement at the junction of the lumbar vertebrae and sacrum.

Documentation tips

What should appear in the chart to support M45.7.

Source · Editorial brief grounded in 5 cited references ↓

• Explicitly name the lumbosacral region in the clinical note — 'lumbar' or 'sacral' alone maps to a different M45 subcategory.
• Document HLA-B27 test result and date, as this supports inflammatory versus degenerative diagnosis distinction.
• Record radiographic or MRI findings: sacroiliitis grade, syndesmophytes, or erosions at the lumbosacral junction.
• Note the duration and pattern of back pain (morning stiffness, nocturnal pain, improvement with activity) to establish inflammatory back pain criteria.
• If multiple spinal regions are involved, document each region explicitly so the coder can determine whether M45.0 or M45.7 applies.
• Record elevated inflammatory markers (CRP, ESR) in the same encounter note to support active inflammatory disease coding.

Related CPT procedures

Procedure codes commonly billed with M45.7. 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 M45.7 and adjacent codes.

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

• Reporting M45 (non-billable parent) instead of M45.7 — the parent code will be rejected; always code to the 4th-character level.
• Confusing M45.6 (lumbar region) with M45.7 (lumbosacral region) — the lumbosacral code applies only when the provider documents involvement at the L5-sacrum junction, not the lumbar spine broadly.
• Using M45.7 when the diagnosis is juvenile ankylosing spondylitis — that maps to M08.1, which is an Excludes1 exclusion at the M45 category level.
• Applying M45.7 when Reiter's disease (reactive arthritis) is the underlying cause of spinal arthropathy — use M02.3- instead.
• Defaulting to M45.9 (unspecified site) when the note documents lumbosacral involvement — M45.9 is a valid code but signals incomplete documentation and may not satisfy LCD specificity requirements.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Sibling codes

Other billable codes under M45 (laterality / anatomic variants).