Post-traumatic osteoarthritis affecting the first carpometacarpal (CMC1) joint on both the right and left hands, where prior injury is the documented cause of joint degeneration.

Documentation tips

What should appear in the chart to support M18.2.

Source · Editorial brief grounded in 4 cited references ↓

• Explicitly state 'bilateral' CMC1 involvement — if only one side is examined or symptomatic, use M18.11 (right) or M18.12 (left) instead.
• Document the specific prior traumatic event (e.g., Bennett fracture, CMC dislocation, scaphoid fracture with CMC involvement) that precipitates the post-traumatic classification.
• Record imaging findings for both hands separately — joint space narrowing, subchondral sclerosis, osteophyte formation at the trapezio-metacarpal articulation, or Eaton-Littler stage on plain radiograph.
• Note the conservative treatment history for both hands (splinting duration, injection history, therapy) to establish medical necessity before proceeding to surgical intervention.
• Append an external cause code (V00–Y99) when the original injury mechanism can be identified, per the Chapter 13 Use Additional Code instruction.

Related CPT procedures

Procedure codes commonly billed with M18.2. 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 M18.2 and adjacent codes.

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

• Coding M18.2 when only one thumb has documented post-traumatic OA — use M18.11 or M18.12 for unilateral cases; M18.2 requires bilateral documentation.
• Confusing post-traumatic etiology with primary OA: if no prior injury is documented, M18.0 (bilateral primary CMC1 OA) is correct, not M18.2.
• Using the parent code M18 (non-billable) instead of the specific child code M18.2 — M18 is a header and will reject on most payer claims.
• Omitting the external cause code when the precipitating trauma is known — Chapter 13 instructs coders to add an external cause code following the musculoskeletal condition code where applicable.
• Conflating M18.2 with M18.4 (other bilateral secondary CMC1 OA) — M18.4 is for bilateral secondary OA from causes other than trauma (e.g., inflammatory arthropathy sequela); trauma-specific bilateral cases belong at M18.2.

Clinical context

Source · Editorial summary grounded in 4 cited references ↓

Sibling codes

Other billable codes under M18 (laterality / anatomic variants).