Unilateral primary osteoarthritis affecting one knee where the specific side (right or left) has not been documented or identified by the treating provider.
Verified May 8, 2026 · 5 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 14
- Region
- Knee
Documentation tips
What should appear in the chart to support M17.10.
Source · Editorial brief grounded in 5 cited references ↓
- Capture laterality explicitly at every encounter — 'right knee' or 'left knee' in the assessment or HPI upgrades this to M17.11 or M17.12 and eliminates the audit flag that unspecified codes attract.
- Record the clinical basis for primary (idiopathic) OA: age-related wear, absence of prior significant trauma, absence of inflammatory or systemic arthritis — this distinguishes M17.1x from M17.3x (post-traumatic) or M17.5x (secondary).
- Document imaging findings that support OA: joint space narrowing, osteophyte formation, subchondral sclerosis, or Kellgren-Lawrence grade when available — payers routinely require these for injection or surgical pre-authorization.
- Note conservative care history (NSAIDs, PT, bracing, prior injections) when billing for viscosupplementation or surgical procedures, as many LCDs require documented failure of conservative treatment.
- If the encounter is a referral or triage note and laterality truly isn't known yet, flag the chart for coder follow-up once the provider completes the exam — don't let M17.10 sit permanently in the problem list.
Related CPT procedures
Procedure codes commonly billed with M17.10. 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 M17.10 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Using M17.10 when laterality is documented elsewhere in the note: if 'right knee' or 'left knee' appears anywhere in the assessment, HPI, or imaging report, M17.11 or M17.12 is required — M17.10 is not a safe default.
- Stacking M17.11 + M17.12 for bilateral OA instead of using M17.0: ICD-10-CM provides a dedicated bilateral code (M17.0); combining two unilateral codes is incorrect and can trigger claim edits.
- Confusing M17.10 with M17.9 (osteoarthritis of knee, unspecified): M17.9 is non-specific as to primary vs. secondary and bilateral vs. unilateral — M17.10 at least confirms unilateral primary OA, making it the more specific choice when those facts are known.
- Applying M17.10 to post-traumatic knee OA: if there is a documented history of prior knee injury causing the degeneration, the correct code is M17.31 (right), M17.32 (left), or M17.30 (unspecified) — primary OA is idiopathic by definition.
- Failing to update M17.10 after laterality is established: once the treating provider documents a specific side, the code must be updated in the active problem list and on subsequent claims.
Clinical context
Source · Editorial summary grounded in 5 cited references ↓
M17.10 is the fallback code within the M17.1 (unilateral primary osteoarthritis of knee) subcategory when the provider has confirmed OA is present in one knee but has not specified which side. It also covers "Primary osteoarthritis of knee NOS" per the Applicable To annotation at M17.1. Use it only when laterality is genuinely absent from the clinical record — not as a shortcut when the note mentions a side but you haven't read far enough.
In practice, M17.10 should be a rare code in an orthopedic setting. If the provider documents "right knee" or "left knee," move immediately to M17.11 or M17.12. If both knees have primary OA, use M17.0 — do not stack M17.11 + M17.12. M17.10 exists for edge cases: telephone triage notes, referral orders, or initial intake encounters where laterality hasn't yet been confirmed.
This code sits under Chapter 13 (M00–M99) and the M15–M19 Osteoarthritis block. Note the Type 2 Excludes at M15–M19: osteoarthritis of the spine routes to M47, not here. Post-traumatic OA routes to M17.3x; secondary OA routes to M17.5x. Primary OA implies idiopathic, age- or wear-related degeneration with no identified traumatic or systemic cause.
Sibling codes
Other billable codes under M17.1 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 5 cited references ↓
01When is it actually correct to use M17.10 instead of M17.11 or M17.12?
02Can I use M17.10 for a patient whose X-ray shows OA in one knee but the radiologist report doesn't name a side?
03Is M17.10 valid for Medicare claims?
04What's the difference between M17.10 and M17.9?
05My provider documented 'knee OA' without specifying primary or secondary. Can I still use M17.10?
06Should I use M17.10 on a total knee arthroplasty claim?
07Can M17.10 and M17.11 appear on the same claim for the same patient?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026 (effective Oct 1, 2025)
- 02icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M15-M19/M17-/M17.10
- 03aapc.comhttps://www.aapc.com/codes/icd-10-codes/M17.10
- 04aapc.comhttps://www.aapc.com/codes/coding-newsletters/my-orthopedic-coding-alert/orthopedic-coding-identify-bilateral-and-unilateral-oa-knee-codes-179433-article
- 05cms.govhttps://www.cms.gov/medicare-coverage-database/view/article.aspx?articleid=57765&ver=24&
Mira AI Scribe
Mira's AI scribe flags laterality at the point of documentation — if the provider dictates or types 'right' or 'left' anywhere in the knee OA assessment, the scribe surfaces M17.11 or M17.12 instead of defaulting to M17.10. It also captures imaging findings (joint space narrowing, osteophyte grade), OA classification (primary vs. post-traumatic), and conservative treatment history, preventing the unspecified-laterality audit flag and supporting payer pre-authorization requirements.
See how Mira captures M17.10 documentation