2027 ICD-10-CM Diagnosis Code M84.421KPathological fracture, right humerus, subsequent encounter for fracture with nonunion
ICD-10-CM Codes›M00–M99›M80-M85›M84
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- 7th Character K — Subsequent, Nonunion
- Not Chronic
M84.421K is a billable ICD-10-CM diagnosis code for pathological fracture, right humerus, subsequent encounter for fracture with nonunion. The 7th character K means subsequent encounter for fracture with nonunion. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 564 through 566. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 5,561 closely related codes. Coders also document this condition as pathological fracture - upper arm. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Pathological fracture, subsequent encounter.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Pathological fracture - upper arm
- Pathological fracture of right humerus
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to M84.421K: its own notes plus those printed at M84.4, M84, 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.
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.
- personal history of (healed) pathological fracture (Z87.311)
- traumatic fracture of bone-see fracture, by site
- 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.
- Use an external cause code following the code for the musculoskeletal condition, if applicable, to identify the cause of the musculoskeletal condition
7th Character
Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.
- The appropriate 7th character is to be added to each code from subcategory M84.4:
- Ainitial encounter for fracture
- Dsubsequent encounter for fracture with routine healing
- Gsubsequent encounter for fracture with delayed healing
- Ksubsequent encounter for fracture with nonunion this code
- Psubsequent encounter for fracture with malunion
- Ssequela
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name M84.421K, its category, or a range that includes it.
Excludes1 4
These codes carry an Excludes1 note naming M84.421K: they are not reported together with it, unless the two conditions are unrelated.
- M48.4 Fatigue fracture of vertebrapathological fracture NOS (M84.4-) names M84.4-, which includes this code
- M48.5 Collapsed vertebra, not elsewhere classifiedpathological fracture NOS (M84.4-) names M84.4-, which includes this code
- M80 Osteoporosis with current pathological fracturepathological fracture NOS (M84.4) names M84.4, which includes this code
- M84.3 Stress fracturepathological fracture NOS (M84.4.-) names M84.4.-, which includes this code
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Fractures, Spontaneous
fractures occurring as a result of disease of a bone or from some undiscoverable cause, and not due to trauma. (dorland, 27th ed)
Patient EducationClinical
Arm Injuries and Disorders
Of the 206 bones in your body, three of them are in your arm: the humerus, radius, and ulna. Your arms are also made up of muscles, joints, tendons, and other connective tissue. Injuries to any of these parts of the arm can occur during sports, a fall, or an accident.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert M84.421K to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About M84.421KOverview
Is M84.421K (Pathological fracture, right humerus) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report pathological fracture, right humerus, subsequent encounter for fracture with nonunion on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What does the 7th character K in M84.421K mean?
The final character K reports a subsequent encounter where the pathological fracture, right humerus has failed to heal, called a nonunion. In this category the CMS Tabular List defines K as "subsequent encounter for fracture with nonunion".
What MS-DRG does M84.421K group to?
When pathological fracture, right humerus, subsequent encounter for fracture with nonunion is the principal diagnosis on an inpatient stay, it groups to MS-DRG 564, 566, 565, with relative weights from 0.7374 to 1.4909 depending on complications. Higher weights mean higher Medicare reimbursement.
Is M84.421K a CC or MCC?
CMS lists M84.421K as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 5,561 closely related codes in its exclusion list.
Can M84.421K be reported with M48.5?
Not as a rule. The Excludes1 note at M84.4, which applies to M84.421K, lists "collapsed vertebra NEC (M48.5)". 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).
