Synovial hypertrophy, not elsewhere classified, affecting multiple sites simultaneously — used when thickening of the synovial membrane cannot be attributed to a more specific condition and involves more than one anatomic location.
Verified May 8, 2026 · 4 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 10
- Region
- Multi-region
Documentation tips
What should appear in the chart to support M67.29.
Source · Editorial brief grounded in 4 cited references ↓
- Explicitly list each affected joint or tendon sheath by name and side in the clinical note — 'multiple sites' requires that more than one anatomic location is documented, not merely implied.
- Record imaging findings (MRI, ultrasound) that confirm synovial thickening, including the modality used, the joints evaluated, and descriptive findings such as villous proliferation, joint effusion, or synovial pannus.
- Document that the condition is not villonodular synovitis (pigmented) and not attributable to a systemic inflammatory diagnosis already coded elsewhere — this protects against an Excludes1 conflict with M12.2-.
- If conservative treatment has been attempted (NSAIDs, corticosteroid injections, physical therapy), note the regimen and response to support medical necessity for any planned procedural intervention.
- Specify whether the hypertrophy is bilateral or involves anatomically distinct regions (e.g., both knees vs. knee and wrist) to distinguish polyarticular from multi-region involvement and justify the multiple-sites designation.
Related CPT procedures
Procedure codes commonly billed with M67.29. 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 M67.29 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Assigning M67.29 when only one joint is involved — if imaging or the clinical note identifies a single site, select the site-specific M67.2x subcode with appropriate laterality instead.
- Overlooking the Excludes1 note: pigmented villonodular synovitis must be coded to M12.2-, not M67.29 — using M67.29 when PVNS is documented will trigger an edit.
- Defaulting to M67.29 as a catch-all for any joint swelling without confirming that synovial hypertrophy (not effusion, not synovitis) is the documented pathology — synovitis codes to M65-, not M67.2-.
- Failing to query the provider when imaging shows multi-site synovial thickening but the note only references one joint — underdocumentation of 'multiple sites' leaves M67.29 unsupported on audit.
- Confusing M67.29 (multiple sites, NEC) with M67.28 (other site, NEC) — use M67.28 when a single atypical site is involved, M67.29 only when two or more sites are documented.
Clinical context
Source · Editorial summary grounded in 4 cited references ↓
M67.29 applies when a patient presents with pathological proliferation or thickening of synovial tissue at two or more distinct joints or tendon sheaths, and the condition does not fit a more specific ICD-10-CM category. This 'multiple sites' designation is appropriate only when the provider explicitly documents involvement of more than one anatomic region and no single-site code covers the full clinical picture. If synovial hypertrophy is confined to one region, use the site-specific subcodes under M67.2 (e.g., M67.261/M67.262 for lower leg, M67.271/M67.272 for ankle and foot).
Before assigning M67.29, verify the Excludes1 note at M67.2: villonodular synovitis (pigmented) is excluded and codes to M12.2-. Additionally, the broader M67 category excludes palmar fascial fibromatosis/Dupuytren (M72.0), tendinitis NOS (M77.9-), and xanthomatosis localized to tendons (E78.2). If any of these conditions better explains the synovial pathology, reassign accordingly.
M67.29 is commonly encountered in inflammatory arthropathy workups, post-surgical surveillance, or in patients with systemic connective tissue disorders where synovial proliferation is polyarticular. It is also used when imaging (MRI or ultrasound) demonstrates diffuse synovial thickening across multiple joints and the underlying etiology remains unclassified at the time of the encounter.
Sibling codes
Other billable codes under M67.2 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 4 cited references ↓
01What distinguishes M67.29 from M67.28?
02Can M67.29 be used alongside a systemic inflammatory diagnosis like rheumatoid arthritis?
03Does M67.29 require a 7th character extension?
04Is pigmented villonodular synovitis (PVNS) correctly coded with M67.29?
05What CPT procedures are typically associated with M67.29 in an orthopedic setting?
06When should the coder use M67.20 (unspecified site) instead of M67.29?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026 — https://www.cdc.gov/nchs/icd/icd-10-cm/index.html
- 02icd10data.com 2026 ICD-10-CM M67.29 — https://www.icd10data.com/ICD10CM/Codes/M00-M99/M65-M67/M67-/M67.29
- 03AAPC Codify M67.2 — https://www.aapc.com/codes/icd-10-codes/M67.2
- 04CMS Billing and Coding Article A57079: Injections — Tendon, Ligament, Ganglion Cyst, Tunnel Syndromes and Morton's Neuroma — https://www.cms.gov/medicare-coverage-database/view/article.aspx?articleId=57079
Mira AI Scribe
The Mira AI Scribe captures each affected joint by name and laterality, the imaging modality and key findings (synovial thickening, villous change, effusion), prior treatment attempts, and the provider's explicit statement that multiple anatomic sites are involved. This detail prevents downcoding to the unspecified M67.20 or incorrect assignment of M67.28 (other single site) and closes the documentation gap that most commonly triggers medical necessity denials for synovial pathology claims.
See how Mira captures M67.29 documentation