ICD-10-CM 2027 diagnosis code
M66.1Rupture of synovium
M66.1 is a header code, so it can't be reported by itself. Choose one of the 8 more specific codes beneath it.
Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data
About M66.1
M66.1 is the ICD-10-CM diagnosis code for rupture of synovium. It belongs to category M66 (spontaneous rupture of synovium and tendon), block M65-M67 (disorders of synovium and tendon) and chapter 13 (diseases of the musculoskeletal system and connective tissue). It is a header code, so it can't be reported by itself; one of its 8 subcodes must be used instead.
Within M66 (spontaneous rupture of synovium and tendon), M66.1 is specifically for rupture of synovium. Related codes cover rupture of popliteal cyst (M66.0), spontaneous rupture of extensor tendons (M66.2), spontaneous rupture of flexor tendons (M66.3), spontaneous rupture of other tendons (M66.8) and spontaneous rupture of unspecified tendon (M66.9).
To report this condition, pick the subcode that matches the documentation: M66.10 (unspecified joint), M66.11 (shoulder), M66.12 (elbow), M66.13 (wrist), M66.14 (hand and fingers), M66.15 (hip), M66.17 (ankle, foot and toes) and M66.18 (other site).
The conditions in its Excludes2 note aren't part of M66.1, but may be coded alongside it if the patient has both: rupture of popliteal cyst (M66.0).
It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.
Specific codes under M66.1
- M66.10Rupture of synovium, unspecified jointBillable
- M66.11Rupture of synovium, shoulder
- M66.12Rupture of synovium, elbow
- M66.13Rupture of synovium, wrist
- M66.14Rupture of synovium, hand and fingers
- M66.141Rupture of synovium, right handBillable
- M66.142Rupture of synovium, left handBillable
- M66.143Rupture of synovium, unspecified handBillable
- M66.144Rupture of synovium, right finger(s)Billable
- M66.145Rupture of synovium, left finger(s)Billable
- M66.146Rupture of synovium, unspecified finger(s)Billable
- M66.15Rupture of synovium, hip
- M66.17Rupture of synovium, ankle, foot and toes
- M66.171Rupture of synovium, right ankleBillable
- M66.172Rupture of synovium, left ankleBillable
- M66.173Rupture of synovium, unspecified ankleBillable
- M66.174Rupture of synovium, right footBillable
- M66.175Rupture of synovium, left footBillable
- M66.176Rupture of synovium, unspecified footBillable
- M66.177Rupture of synovium, right toe(s)Billable
- M66.178Rupture of synovium, left toe(s)Billable
- M66.179Rupture of synovium, unspecified toe(s)Billable
- M66.18Rupture of synovium, other siteBillable
Coding notes
- Rupture of synovial cyst
- rupture of popliteal cyst (M66.0)
Notes that apply from higher levels
Instructions written at a parent level also apply to M66.1.
› From M66 Spontaneous rupture of synovium and tendon
- rupture that occurs when a normal force is applied to tissues that are inferred to have less than normal strength
- rotator cuff syndrome (M75.1-)
- rupture where an abnormal force is applied to normal tissue - see injury of tendon by body region
Broader instructions also apply from Chapter 13: Diseases of the musculoskeletal system and connective tissue.
Codes whose notes reference M66.1
- M71.3Excludes1
Code history
- 2016
- 2017
- 2018
- 2019
- 2020
- 2021
- 2022
- 2023
- 2024
- 2025
- 2026
- 2027
- FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
- No changes since FY2016.
Common questions about M66.1
Is M66.1 billable?
- No. M66.1 is a header code. Report one of its more specific subcodes instead.