M17.5 captures osteoarthritis of a single knee that developed secondary to an underlying condition — such as prior inflammatory arthritis, obesity, crystal deposition disease, or metabolic disorder — where the etiology is not post-traumatic and does not fit a more specific secondary OA code.

Documentation tips

What should appear in the chart to support M17.5.

Source · Editorial brief grounded in 5 cited references ↓

• Name the underlying condition explicitly (e.g., gout, rheumatoid arthritis, obesity, crystal arthropathy) — 'secondary OA' alone is insufficient to establish medical necessity or justify M17.5 over M17.9.
• Specify which knee is affected (right or left) by name in the assessment; while M17.5 has no laterality sub-character, the note must still identify the affected side to defend against a bilateral claim.
• Include imaging findings that corroborate secondary degenerative change: Kellgren-Lawrence grade, joint space narrowing pattern, osteophytes, and any findings distinguishing secondary from primary OA (e.g., atypical compartment distribution).
• Document the absence of qualifying trauma history to justify M17.5 over M17.31 or M17.32; if trauma is present even historically, the post-traumatic codes take precedence.
• Record functional limitations (range of motion deficits, gait changes, ADL impact) to support medical necessity for associated procedures or DME orders linked to this diagnosis.

Related CPT procedures

Procedure codes commonly billed with M17.5. 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 M17.5 and adjacent codes.

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

• Using M17.5 when a prior knee injury (fracture, ACL tear, meniscal tear) is documented — that scenario requires M17.31 (right) or M17.32 (left), not M17.5.
• Assigning M17.5 for bilateral secondary OA — use M17.4 when both knees are affected by the same secondary process; M17.5 is strictly unilateral.
• Omitting the code for the underlying condition; M17.5 should not stand alone when the secondary etiology is known and codeable.
• Defaulting to M17.9 (osteoarthritis of knee, unspecified) when the provider has documented both the unilateral nature and a secondary cause — M17.5 is more specific and preferred.
• Confusing M17.5 with primary OA codes (M17.11/M17.12) when the record contains an underlying systemic condition that caused the degeneration — type and etiology must match the code selected.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Inclusion & exclusion notes

Per the official ICD-10-CM Tabular List.

Source · CDC ICD-10-CM Official Tabular List · 2026

Sibling codes

Other billable codes under M17 (laterality / anatomic variants).