2027 ICD-10-CM Diagnosis Code M85.661Other cyst of bone, right lower leg

ICD-10-CM Codes›M00–M99›M80-M85›M85

ICD-10-CM M85.661
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

M85.661 is a billable ICD-10-CM diagnosis code for other cyst of bone, right lower leg. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 553 through 554. Coders also document this condition as bilateral tibia bone cyst. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified bone disease and musculoskeletal deformities.

Code Identity

ICD-10-CM Code
M85.661
Billable Status
Yes — Valid for Submission
Code Describes
Other cyst of bone, right lower leg
Short Description
Other cyst of bone, right lower leg
Same as the full description in the CMS dataset.
Parent Code
M85.66
Other cyst of bone, lower leg

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM80-M85Disorders of bone density and structure
CategoryM85Other disorders of bone density and structure
This CodeM85.661Other cyst of bone, right lower leg

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Bilateral tibia bone cyst
  • Bone cyst of left tibia
  • Bone cyst of right fibula
  • Bone cyst of right tibia
  • Bone cyst of tibia

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to M85.661: its own notes plus those printed at M85.6, M85, and Chapter 13. A note printed at a category, block or chapter applies to every code under it.

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From M85.6 Other cyst of bone applies to 24 codes
  • cyst of jaw NEC (M27.4)
  • osteitis fibrosa cystica generalisata [von Recklinghausen's disease of bone] (E21.0)
From M85 Other disorders of bone density and structure applies to 169 codes
  • osteogenesis imperfecta (Q78.0)
  • osteopetrosis (Q78.2)
  • osteopoikilosis (Q78.8)
  • polyostotic fibrous dysplasia (Q78.1)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 13 (M00-M99) Diseases of the musculoskeletal system and connective tissue applies to 6,687 codes
  • arthropathic psoriasis (L40.5-)
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • compartment syndrome (traumatic) (T79.A-)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

Notes

General instructions on how these codes are used.

From Chapter 13 (M00-M99) Diseases of the musculoskeletal system and connective tissue applies to 6,687 codes
  • Use an external cause code following the code for the musculoskeletal condition, if applicable, to identify the cause of the musculoskeletal condition

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR MUS028
Other specified bone disease and musculoskeletal deformities
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Bone Diseases

Your bones help you move, give you shape and support your body. They are living tissues that rebuild constantly throughout your life. During childhood and your teens, your body adds new bone faster than it removes old bone. After about age 20, you can lose bone faster than you make bone.

Read the full article at MedlinePlus

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

Convert M85.661 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
733.29 Bone cyst NEC
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About M85.661Overview

What is the ICD-10 code for other cyst of bone, right lower leg?

The ICD-10-CM code for other cyst of bone, right lower leg is M85.661 (sometimes written as M85661). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is M85.661 (Other cyst of bone, lower leg) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other cyst of bone, right lower leg on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does M85.661 group to?

When other cyst of bone, right lower leg is the principal diagnosis on an inpatient stay, it groups to MS-DRG 554, 553, with relative weights from 0.8328 to 1.2492 depending on complications. Higher weights mean higher Medicare reimbursement.

Can M85.661 be reported with M27.4?

Not as a rule. The Excludes1 note at M85.6, which applies to M85.661, lists "cyst of jaw NEC (M27.4)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).

What is the ICD-9 equivalent of M85.661?

Under the General Equivalence Mappings, other cyst of bone, right lower leg converts to ICD-9-CM 733.29 (bone cyst NEC). The mapping is approximate, so confirm the match fits the documentation.