2026 ICD-10-CM Diagnosis Code M85.561Aneurysmal bone cyst, right lower leg

ICD-10-CM Codes›M00–M99›M80-M85›M85

ICD-10-CM M85.561
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M85.561 is a billable ICD-10-CM diagnosis code for aneurysmal bone cyst, right lower leg. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 553 through 554. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified bone disease and musculoskeletal deformities.

Code Identity

ICD-10-CM Code
M85.561
Billable Status
Yes — Valid for Submission
Code Describes
Aneurysmal bone cyst, right lower leg
Short Description
Aneurysmal bone cyst, right lower leg
Same as the full description in the CMS dataset.
Parent Code
M85.56
Aneurysmal bone cyst, 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 CodeM85.561Aneurysmal bone cyst, right lower leg

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Aneurysmal bone cyst of fibula
  • Aneurysmal bone cyst of right fibula
  • Aneurysmal bone cyst of right tibia
  • Aneurysmal bone cyst of tibia
  • Benign neoplasm of fibula
  • Benign neoplasm of long bone of right lower limb
  • Benign neoplasm of tibia
  • Bone cyst of right fibula
  • Bone cyst of right tibia
  • Bone cyst of tibia
  • Neoplasm of right tibia

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 M85.561 to ICD-9-CMHistory

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

ICD-9-CM
733.22 Aneurysmal bone cyst
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 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About M85.561Overview

Is M85.561 (Aneurysmal bone cyst, lower leg) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report aneurysmal bone cyst, right lower leg on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M85.561 group to?

When aneurysmal bone cyst, right lower leg is the principal diagnosis on an inpatient stay, it groups to MS-DRG 553, 554, with relative weights from 0.8301 to 1.2963 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M85.561?

Under the General Equivalence Mappings, aneurysmal bone cyst, right lower leg converts to ICD-9-CM 733.22 (aneurysmal bone cyst). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.