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M19.90
M19.90

M19.90: Unspecified osteoarthritis, unspecified site

The ICD-10-CM code for arthritis documented without a named joint or a stated type, carrying the FY2027 inclusion terms Arthritis NOS, Arthrosis NOS and Osteoarthritis NOS.

Billable
FY2027

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At a glance

Code Family

M19: Other and unspecified osteoarthritis.

DRG Grouping

MS-DRG 553 or 554, bone diseases and arthropathies with or without MCC, under the FY2027 MS-DRG v44 grouper.

HCC Mapping (v28)

None. No code in the M15-M19 osteoarthritis block maps to a CMS-HCC v28 category.

Condition

Osteoarthritis

Family Specificity

Category M19 splits on two axes at once: the type of osteoarthritis and the joint involved. M19.90 is the only code in the family that leaves both open.

Billable

Yes. M19.90 is a valid billable code requiring no further characters.

Which M19 code do I assign?

Category M19 resolves two axes at the same time: the type of osteoarthritis and the joint involved. M19.90 is the residual code for the encounter that settles neither axis.

When documentation says…
Code
Arthritis", "DJD" or "osteoarthritis" recorded with no joint and no type
M19.90
Unspecified osteoarthritis, unspecified site. The FY2027 tabular carries Arthritis NOS, Arthrosis NOS and Osteoarthritis NOS as inclusion terms at this code. The note must document a degenerative joint diagnosis. It must name no joint and state no type.
Primary osteoarthritis" with no joint named
M19.91
Primary osteoarthritis, unspecified site. The type is documented and the joint is not. This is the nearest wrong choice to M19.90. The record only has to say primary or idiopathic to move here.
Post-traumatic arthritis of the joint after an old injury", joint not named
M19.92
Post-traumatic osteoarthritis, unspecified site. The record must tie the degeneration to a prior injury of that joint. Where the cause is documented but is not trauma, M19.93 applies instead.
Primary osteoarthritis of the right shoulder
M19.011
Primary osteoarthritis, right shoulder. A joint named inside the M19 range moves the encounter out of subcategory M19.9. Subcategories M19.0, M19.1 and M19.2 each carry the joint and the side. The Index sends Osteoarthritis, shoulder with no type stated to the M19.01 codes.
Osteoarthritis of the knee
M17.9
Osteoarthritis of knee, unspecified. The knee has its own category and never appears in M19. Category M16 does the same for the hip. Category M18 does the same for the first carpometacarpal joint.
Osteoarthritis of multiple joints
M15.9
Polyosteoarthritis, unspecified. Category M19 carries an Excludes1 note for polyarthritis. Multiple joint osteoarthritis is never reported from M19. Category M15 includes arthritis of multiple sites.
Rheumatoid arthritis" with no serostatus stated
M06.9
Rheumatoid arthritis, unspecified. Rheumatoid arthritis sits in the inflammatory polyarthropathy block M05-M14, outside M15-M19 entirely. M19.90 is not a substitute when the record documents an inflammatory diagnosis. The Index sends seropositive rheumatoid arthritis to M05.9.

Tabular notes

EXCLUDES1

Category M19 carries one Excludes1 note: polyarthritis (the M15 codes). Excludes1 means the two are not reported together for the same condition. Osteoarthritis involving multiple joints is classified to the M15.- codes, not to M19. Category M15 in turn carries an Excludes1 note for bilateral involvement of a single joint (M16-M19). Both knees or both hips therefore stay in M16-M19 and are not polyosteoarthritis.

EXCLUDES2

Category M19 carries three Excludes2 notes: arthrosis of spine (M47.-), osteoarthritis of spine (M47.-) and hallux rigidus (M20.2). The M15-M19 block repeats osteoarthritis of spine (M47.-) at block level. Excludes2 means the patient may carry both conditions at once. A patient with documented spinal spondylosis and documented peripheral osteoarthritis may be assigned a code from M47.- alongside M19.90.

USE ADDITIONAL

Chapter 13 carries a chapter-level instruction: use an external cause code following the code for the musculoskeletal condition, if applicable, to identify the cause of the musculoskeletal condition. Category M19 itself carries no Use Additional instruction. It carries no Code Also and no Code First instruction either.

FY2027: EFFECTIVE 1 OCTOBER 2026

M19.90 is unchanged in the FY2027 update, effective 1 October 2026. The FY2027 codes addenda add, delete or revise no code in the M15-M19 block. The FY2027 tabular addenda revise no note in category M19 or at the block. The FY2027 chapter 13 changes sit in categories M04, M67, M72 and M86.

Operational & financial impact

Why specificity matters beyond the chart: risk adjustment, DRG assignment and denial exposure all follow from which code is selected.

CMS-HCC v28 (PY2024+)

M19.90 carries no CMS-HCC v28 mapping.

No code in the M15-M19 osteoarthritis block maps to a CMS-HCC v28 category. The v28 categories in this clinical area are HCC 92 for bone, joint, muscle and severe soft tissue infections and necrosis, HCC 93 for rheumatoid arthritis and other specified inflammatory rheumatic disorders, and HCC 94 for systemic lupus erythematosus and other specified systemic connective tissue disorders. Degenerative osteoarthritis falls in none of the three.

Adding site, side or osteoarthritis type inside M15-M19 therefore changes nothing in the risk score.

Where the record documents rheumatoid arthritis rather than osteoarthritis, M06.9 maps to HCC 93, rheumatoid arthritis and other specified inflammatory rheumatic disorders.

CMS calculates 100 percent of CY2026 risk scores using the 2024 CMS-HCC model, completing the three year phase in, per the CY2026 Medicare Advantage and Part D Rate Announcement.

MS-DRG v44 (FY2027)

MS-DRG 553: bone diseases and arthropathies with MCC.

MS-DRG 554: bone diseases and arthropathies without MCC.

An inpatient admission with M19.90 as the principal diagnosis groups to MS-DRG 553 or 554 under the FY2027 MS-DRG v44 grouper, in MDC 08.

The pair splits on MCC alone. There is no CC tier between 553 and 554.

No code in the M15-M19 block is on the FY2027 CC or MCC list.

Medicare and commercial payers

M19.90 is a billable code and is valid on a claim when the record supports no more specific code.

The FY2027 ICD-10-CM Official Guidelines, section I.B.18, state that unspecified codes have acceptable, even necessary, uses. An unspecified code is appropriate when sufficient clinical information is not known or available to assign a more specific code.

Section I.B.13 directs that where the side is not identified in the medical record, the code for the unspecified side is assigned.

Coverage determinations for joint specific procedures, injections and devices are written against named joints. M19.90 names none. It cannot carry the laterality that a site specific procedure code asserts.

WHERE SPECIFICITY IS LOST

M19.90 gives up the joint and the osteoarthritis type at the same time. No other code in category M19 leaves both open.

The loss does not reach the risk score. No M15-M19 code carries a v28 HCC.

The loss reaches medical necessity review, where a site specific procedure or device has no matching diagnosis on the claim.

Two adjacent choices recover most of it. M19.91 recovers the type as soon as the note states primary osteoarthritis. The M19.0, M19.1 and M19.2 subcategories recover the joint and the side as soon as the note names them.

SEVERITY DESIGNATION (MS-DRG V44.0)

M19.90 carries no severity designation. It appears in neither Appendix G, the CC list, nor Appendix H, the MCC list, of the ICD-10 MS-DRG Definitions Manual Version 44.0. A case reaches the higher tier of its DRG pair on a designation carried by another diagnosis.

Documentation checklist to support M19.90

Chart elements that support code selection and reduce specificity-driven denials.

FAQ

Is M19.90 a billable ICD-10-CM code?

Yes. M19.90 is a valid billable code and requires no further characters. It is the most specific code available when the record documents neither the joint nor the type of osteoarthritis.

Is M19.90 the right code when the note just says arthritis?

Yes. M19.90 is the right code for unqualified or degenerative arthritis with no named joint. The FY2027 tabular lists Arthritis NOS, Arthrosis NOS and Osteoarthritis NOS as inclusion terms at M19.90. An inflammatory diagnosis does not. Rheumatoid arthritis goes to M05.- or M06.-, gout to M10.- or M1A.-, and psoriatic arthritis to the L40.5- codes.

When do I use M19.91 instead of M19.90?

Use M19.91 whenever the record states primary or idiopathic osteoarthritis and names no joint. M19.90 is reserved for the record that leaves the type open as well as the site. M19.91 is the nearest wrong choice to check before assigning M19.90.

Does M19.90 map to a CMS-HCC v28 category?

No. M19.90 carries no CMS-HCC v28 mapping. No code in the M15-M19 osteoarthritis block maps to a v28 category. The v28 categories in this clinical area are HCC 92, HCC 93 and HCC 94. All three sit outside degenerative osteoarthritis. Coding a more specific osteoarthritis code does not change a Medicare Advantage risk score.

What must the note show to support M19.90?

The note must document a degenerative joint diagnosis with no named joint and no stated type. The absence of those two details is what supports the code. Where the assessment names a joint, or states primary, post-traumatic or secondary, a more specific code applies.

How does M19.90 sequence and group on an inpatient claim?

As a principal diagnosis M19.90 groups to MS-DRG 553 or 554 under the FY2027 MS-DRG v44 grouper, bone diseases and arthropathies with or without MCC. The pair splits on MCC alone. There is no CC tier. As a secondary diagnosis M19.90 is reported when the osteoarthritis is documented and addressed during the admission.

Does outpatient reporting treat M19.90 differently from inpatient?

The code selection rule is the same in both settings. The difference is how uncertainty is handled. An outpatient encounter codes only the confirmed diagnosis. An inpatient discharge diagnosis documented as probable or suspected may be coded as though confirmed under UHDDS rules.

Did M19.90 change in FY2027?

M19.90 is unchanged in the FY2027 update, effective 1 October 2026. The update leaves M19.90, its inclusion terms and the M15-M19 block unchanged. The FY2026 update, effective 1 October 2025, also left the descriptor, the inclusion terms and the Excludes notes at M19.90 and M19 unchanged.

Related codes

Codes in the same family as M19.90. Only codes with a published page render as links.

Sibling codes in the M19 family

  • M19.91: Primary osteoarthritis, unspecified site.
  • M19.92: Post-traumatic osteoarthritis, unspecified site.
  • M19.93: Secondary osteoarthritis, unspecified site.
  • M19.09: Primary osteoarthritis, other specified site.
  • M19.19: Post-traumatic osteoarthritis, other specified site.
  • M19.29: Secondary osteoarthritis, other specified site.

Additional codes to consider

Codes outside the M19 family considered alongside M19.90.

Companion: code alongside when documented

  • Z79.1: Long term (current) use of non-steroidal anti-inflammatories (NSAID).

Consider instead

  • M19.91: Primary osteoarthritis, unspecified site, where the note states primary or idiopathic osteoarthritis but names no joint.
  • M15.9: Polyosteoarthritis, unspecified, where osteoarthritis involves multiple joints, which M19 excludes under an Excludes1 note.
  • M15.0: Primary generalized (osteo)arthritis, where generalized osteoarthritis is documented.
  • M17.9: Osteoarthritis of knee, unspecified, where the knee is named and neither the type nor the side is documented.
  • M17.11: Unilateral primary osteoarthritis, right knee.
  • M17.12: Unilateral primary osteoarthritis, left knee.
  • M16.9: Osteoarthritis of hip, unspecified, where the hip is named and neither the type nor the side is documented.
  • M18.9: Osteoarthritis of first carpometacarpal joint, unspecified.
  • M47.9: Spondylosis, unspecified, for osteoarthritis and arthrosis of the spine, which M19 excludes under an Excludes2 note.
  • M06.9: Rheumatoid arthritis, unspecified, where the record documents an inflammatory rather than a degenerative arthritis.
  • M05.9: Rheumatoid arthritis with rheumatoid factor, unspecified.
  • M10.9: Gout, unspecified.
  • M13.80: Other specified arthritis, unspecified site, where a named arthritis is neither osteoarthritis nor a classified inflammatory arthropathy.
  • M12.9: Arthropathy, unspecified.

Sources

All claims on this page derive from government and professional-standards sources.

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