2026 ICD-10-CM Diagnosis Code M66Spontaneous rupture of synovium and tendon

ICD-10-CM Codes›M00–M99›M65-M67›M66

ICD-10-CM M66
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M66 is a non-billable ICD-10-CM category code for spontaneous rupture of synovium and tendon, so it cannot be submitted on claims. Use a more specific code from this category instead, such as M66.0, M66.10, M66.111, and M66.112.

Code Identity

ICD-10-CM Code
M66
Billable Status
No — Non-Billable Category
Code Describes
Spontaneous rupture of synovium and tendon
Short Description
Spontaneous rupture of synovium and tendon
Same as the full description in the CMS dataset.
Chapter
M65-M67
Disorders of synovium and tendon

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM65-M67Disorders of synovium and tendon
CategoryM66Spontaneous rupture of synovium and tendon
This CodeM66Spontaneous rupture of synovium and tendon

Specific Coding for Spontaneous rupture of synovium and tendonOverview

Non-specific codes like M66 require more characters. Use one of these billable codes instead:

  • Use M66.0 for Rupture of popliteal cyst

  • M66.1 for Rupture of synovium

  • Use M66.10 for Rupture of synovium, unspecified joint

  • M66.11 for Rupture of synovium, shoulder

  • M66.12 for Rupture of synovium, elbow

  • M66.13 for Rupture of synovium, wrist

  • M66.14 for Rupture of synovium, hand and fingers

  • M66.15 for Rupture of synovium, hip

  • M66.17 for Rupture of synovium, ankle, foot and toes

  • Use M66.18 for Rupture of synovium, other site

  • M66.2 for Spontaneous rupture of extensor tendons

  • Use M66.20 for Spontaneous rupture of extensor tendons, unspecified site

  • M66.21 for Spontaneous rupture of extensor tendons, shoulder

  • M66.22 for Spontaneous rupture of extensor tendons, upper arm

  • M66.23 for Spontaneous rupture of extensor tendons, forearm

  • M66.24 for Spontaneous rupture of extensor tendons, hand

  • M66.25 for Spontaneous rupture of extensor tendons, thigh

  • M66.26 for Spontaneous rupture of extensor tendons, lower leg

  • M66.27 for Spontaneous rupture of extensor tendons, ankle and foot

  • Use M66.28 for Spontaneous rupture of extensor tendons, other site

  • Use M66.29 for Spontaneous rupture of extensor tendons, multiple sites

  • M66.3 for Spontaneous rupture of flexor tendons

  • Use M66.30 for Spontaneous rupture of flexor tendons, unspecified site

  • M66.31 for Spontaneous rupture of flexor tendons, shoulder

  • M66.32 for Spontaneous rupture of flexor tendons, upper arm

  • M66.33 for Spontaneous rupture of flexor tendons, forearm

  • M66.34 for Spontaneous rupture of flexor tendons, hand

  • M66.35 for Spontaneous rupture of flexor tendons, thigh

  • M66.36 for Spontaneous rupture of flexor tendons, lower leg

  • M66.37 for Spontaneous rupture of flexor tendons, ankle and foot

  • Use M66.38 for Spontaneous rupture of flexor tendons, other site

  • Use M66.39 for Spontaneous rupture of flexor tendons, multiple sites

  • M66.8 for Spontaneous rupture of other tendons

  • Use M66.80 for Spontaneous rupture of other tendons, unspecified site

  • M66.81 for Spontaneous rupture of other tendons, shoulder

  • M66.82 for Spontaneous rupture of other tendons, upper arm

  • M66.83 for Spontaneous rupture of other tendons, forearm

  • M66.84 for Spontaneous rupture of other tendons, hand

  • M66.85 for Spontaneous rupture of other tendons, thigh

  • M66.86 for Spontaneous rupture of other tendons, lower leg

  • M66.87 for Spontaneous rupture of other tendons, ankle and foot

  • Use M66.88 for Spontaneous rupture of other tendons, other sites

  • Use M66.89 for Spontaneous rupture of other tendons, multiple sites

  • Use M66.9 for Spontaneous rupture of unspecified tendon

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Includes

  • rupture that occurs when a normal force is applied to tissues that are inferred to have less than normal strength

Type 2 Excludes

  • rotator cuff syndrome M75.1
  • rupture where an abnormal force is applied to normal tissue - see injury of tendon by body region

Patient EducationClinical

Joint Disorders

Your joints are places where two or more bones come together. Your shoulders, elbows, hips, knees, and knuckles are all joints. Your spine has joints, too.

The full article covers:

  • What are joints?
  • What are joint disorders?
  • What diseases can affect the joints?
  • What types of joint disorders happen from sudden injuries?
  • What types of joint disorders happen from overuse?
  • How can I keep my joints healthy?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About M66Overview

Is M66 (Spontaneous rupture of synovium and tendon) a billable code?

No. This is a category header that groups the codes for spontaneous rupture of synovium and tendon, and headers cannot be submitted on claims. Claims for spontaneous rupture of synovium and tendon need a more specific code from this category, such as M66.0, M66.10, and M66.111.