M17.0: Bilateral primary osteoarthritis of knee

The ICD-10-CM code for primary osteoarthritis of both knees, assigned when the record names the right knee and the left knee with no prior injury and no other underlying cause.

Billable

FY2027

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At a glance

Code Family

M17: Osteoarthritis of knee.

Condition

Knee osteoarthritis

Billable

Yes. M17.0 is a four character leaf code with no children and requires no fifth character.

HCC Mapping (v28)

None. No code in category M17 appears in the diagnosis to condition category crosswalk distributed with the CMS-HCC Version 28 model software.

DRG Grouping

MS-DRG 553 or 554, bone diseases and arthropathies with or without MCC, in MDC 08 under the FY2027 MS-DRG v44 grouper. A knee arthroplasty moves the case to a surgical MS-DRG.

Family Specificity

Eleven billable codes in category M17, split on two axes at once: laterality and etiology. M17.0 is the bilateral primary code.

Which M17 code do I assign?

Category M17 splits on two axes at once: which knees the record names, and how the osteoarthritis arose. M17.0 sits where the first axis reads bilateral and the second reads primary.

When documentation says…

Code

Bilateral primary osteoarthritis of the knees

M17.0

Primary degenerative change documented in the right knee and in the left knee. The note must name both knees. It must record no prior injury and no other underlying cause.

Osteoarthritis of both knees, cause not stated

M17.0

The FY2027 Alphabetic Index routes the subterm bilateral under Osteoarthritis, knee to M17.0. The word primary is not required once the record names both knees and names no cause.

Primary osteoarthritis of the right knee, left knee uninvolved

M17.11

Unilateral primary osteoarthritis of the right knee. The left knee counterpart is M17.12. Where one knee is involved but the side is never named, the code is M17.10.

Osteoarthritis of both knees following an earlier injury to each knee

M17.2

Bilateral post-traumatic osteoarthritis of knee. The note must tie the degeneration in both knees to a documented prior injury. The unilateral post-traumatic codes are M17.30 for an unstated side, M17.31 for the right knee and M17.32 for the left knee.

Osteoarthritis of both knees secondary to a named underlying condition

M17.4

Other bilateral secondary osteoarthritis of knee. The record must name the underlying cause that makes the osteoarthritis secondary. The unilateral counterpart is M17.5, which carries the inclusion term Secondary osteoarthritis of knee NOS.

Osteoarthritis of the knee, side not stated, cause not stated

M17.9

Osteoarthritis of knee, unspecified. The Alphabetic Index routes the subterm knee under Osteoarthritis to M17.9. Adding the word bilateral moves the encounter to M17.0.

Arthritis, no joint named

M19.90

Unspecified osteoarthritis, unspecified site. This is the fallback where the record names no joint. Naming both knees displaces it and lands the encounter on M17.0.

Tabular notes

EXCLUDES2

Excludes2 at the Osteoarthritis block (M15-M19): osteoarthritis of spine (the M47 codes). Apart from the Chapter 13 Excludes2 list, that is the only Excludes note reaching M17.0. Category M17 prints no Excludes note of its own. Code M17.0 prints none either. An Excludes2 note means the patient may carry both conditions at once. A record documenting bilateral knee osteoarthritis and spinal spondylosis takes M17.0 alongside a code from the M47.- series. The note that governs bilateral disease sits one category away. Category M15, polyosteoarthritis, carries an Excludes1 note for bilateral involvement of single joint (M16-M19). Excludes1 means the two are not reported together for the same condition. Osteoarthritis of both knees and no other joint is therefore not polyosteoarthritis. It stays in M17.

USE ADDITIONAL

Chapter 13 carries an instruction at the head of the chapter: use an external cause code following the code for the musculoskeletal condition, if applicable, to identify the cause of the musculoskeletal condition. Category M17 carries no Use additional instruction of its own. Code M17.0 carries none either. The FY2027 tabular prints no Code also and no Code first instruction anywhere in category M17. Secondary osteoarthritis is the one place a coder looks for a Code first note. Neither M17.4 nor M17.5 carries one. Sequencing of the underlying cause therefore follows the circumstances of the encounter.

FY2027: EFFECTIVE 1 OCTOBER 2026

M17.0 is unchanged in the FY2027 update, effective 1 October 2026. The FY2027 codes addenda add, delete or revise no code in category M17 or elsewhere in the M15-M19 block. The FY2027 tabular addenda revise no note at category M17 or at the M15-M19 block. M17.0 is in the FY2027 billable code list.

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+)

M17.0 carries no CMS-HCC v28 mapping.

No code in the M15-M19 osteoarthritis block appears in the diagnosis to condition category crosswalk distributed with the CMS-HCC Version 28 model software. The three v28 categories nearest 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.

Moving from M17.9 to M17.0 changes nothing in a Medicare Advantage risk score. Neither does moving from M17.0 to M17.2 or M17.4.

Where the record documents rheumatoid arthritis rather than osteoarthritis, M06.9 maps to HCC 93.

MS-DRG v44 (FY2027)

MS-DRG 461: bilateral or multiple major joint procedures of lower extremity with MCC.

MS-DRG 462: bilateral or multiple major joint procedures of lower extremity without MCC.

A simultaneous bilateral knee arthroplasty admission with M17.0 as the principal diagnosis groups to MS-DRG 461 or 462, in MDC 08 under the FY2027 MS-DRG v44 grouper. That pair is reached through a procedure code combination rather than through any single procedure code.

MS-DRG 469: major hip and knee joint replacement or reattachment of lower extremity with MCC or total ankle replacement.

MS-DRG 470: major hip and knee joint replacement or reattachment of lower extremity without MCC.

A staged admission that replaces one knee groups to MS-DRG 469 or 470, in the same MDC.

An admission with M17.0 as the principal diagnosis and no major joint procedure groups to MS-DRG 553 or 554, bone diseases and arthropathies with or without MCC.

All three pairs split on MCC alone. None of them carries a CC tier.

Medicare and commercial payers

M17.0 is a billable code and is valid for HIPAA covered transactions.

No National Coverage Determination governs osteoarthritis diagnosis coding.

The FY2027 ICD-10-CM Official Guidelines, section I.B.13, direct that where no bilateral code is provided and the condition is bilateral, separate codes are assigned for the left and the right side. Category M17 does provide bilateral codes. M17.11 and M17.12 are therefore not reported together to describe bilateral primary disease.

Section I.B.13 also states that when laterality is not documented by the patient's provider, code assignment for the affected side may be based on medical record documentation from other clinicians.

Section I.B.13 governs staged bilateral surgery directly. It directs assignment of the bilateral code for a bilateral condition treated in separate encounters, including for the encounter that treats the first side. For the second encounter, after one side has been treated and the condition no longer exists there, it directs the unilateral code for the side where the condition still exists. A patient whose right knee has been replaced therefore moves from M17.0 to M17.12.

M17.0 asserts disease in both knees. A procedure code carries its own laterality. Where a claim pairs M17.0 with a single sided procedure, the operative note has to show which knee was treated at this encounter.

WHERE SPECIFICITY IS LOST

M17.9 gives up both axes at once. It records osteoarthritis of the knee without the laterality or the etiology the chart already holds.

M17.10 records a unilateral primary case without naming the knee. It is never the right choice for documented bilateral disease.

M19.90 gives up the joint as well. Naming both knees displaces it.

Reporting M17.11 and M17.12 together in place of M17.0 puts two diagnoses on the claim. It still fails to state that the disease is bilateral.

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

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

Documentation checklist to support M17.0

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

A documented diagnosis of osteoarthritis, arthrosis or degenerative joint disease of the knee.

Both knees named as involved. The Alphabetic Index reaches M17.0 through the subterm bilateral under Osteoarthritis, knee.

No documented prior injury to either knee. Documented trauma to both knees moves the encounter to M17.2.

No documented underlying condition driving the degeneration. A named underlying cause moves the encounter to M17.4.

Imaging or examination findings supporting degenerative change in the right knee and in the left knee.

Separate documentation for every other joint involved, because each joint carries its own code. Osteoarthritis of both knees and no other joint is not polyosteoarthritis.

Arthroplasty status where a knee has already been replaced. The status code is Z96.651 for the right knee, Z96.652 for the left knee and Z96.653 for both, and the diagnosis steps down to the knee that still has disease.

Provider documentation of the obesity diagnosis itself where obesity is reported as a comorbidity. Section I.B.14 of the ICD-10-CM Official Guidelines allows the body mass index value to come from another clinician. It requires the associated diagnosis to come from the patient's provider.

For an outpatient encounter, a confirmed diagnosis rather than suspected osteoarthritis. Unconfirmed bilateral knee pain is reported with M25.561 and M25.562 together, because no bilateral knee pain code exists.

FAQ

What does ICD-10-CM code M17.0 mean?

M17.0 is bilateral primary osteoarthritis of knee. It records primary degenerative arthritis in the right knee and the left knee on one code. It is billable at four characters and requires no fifth character.

Should I report M17.11 and M17.12 together instead of M17.0?

No. Section I.B.13 of the FY2027 ICD-10-CM Official Guidelines directs separate left and right codes only where no bilateral code is provided. Category M17 provides M17.0 for bilateral primary disease. One code carries both knees.

Does the note have to say primary for M17.0 to apply?

No. The FY2027 Alphabetic Index routes the subterm bilateral under Osteoarthritis, knee straight to M17.0. Primary is the default reading of documented bilateral knee osteoarthritis. It holds unless the record documents a prior injury or names an underlying cause.

What moves the case off M17.0 to M17.2 or M17.4?

Documentation of a cause moves the case. M17.2 requires the degeneration in both knees to be tied to a documented prior injury, such as an old tibial plateau fracture or a torn cruciate ligament. M17.4 requires a documented underlying condition driving the degeneration, such as a prior septic arthritis or a hemophilic arthropathy. Absent either, the case is primary and stays on M17.0.

Does M17.0 map to an HCC?

No. M17.0 carries no CMS-HCC v28 mapping. No code in the M15-M19 osteoarthritis block appears in the crosswalk distributed with the CMS-HCC Version 28 model software. Recording the laterality and the etiology does not move a Medicare Advantage risk score.

How does M17.0 group and sequence on a claim?

As the principal diagnosis for a simultaneous bilateral knee arthroplasty, M17.0 groups to MS-DRG 461 or 462 in MDC 08 under the FY2027 MS-DRG v44 grouper. A single knee replacement groups to MS-DRG 469 or 470. An admission with no major joint procedure groups to MS-DRG 553 or 554. Each pair splits on MCC alone. In the outpatient setting only a confirmed diagnosis is coded. An inpatient discharge diagnosis documented as probable or suspected may be coded as confirmed under UHDDS rules.

The right knee was replaced last year and the left knee is still arthritic. Is this still M17.0?

No. Section I.B.13 directs the unilateral code for the side where the condition still exists, once the other side has been treated and the condition no longer exists there. Assign M17.12 for the left knee. Add Z96.651 for the presence of a right artificial knee joint.

Did M17.0 change in FY2027?

M17.0 is unchanged in the FY2027 update, effective 1 October 2026. The update leaves category M17 and its notes unchanged. The FY2026 update, effective 1 October 2025, also left the M17.0 descriptor and the Excludes notes reaching it unchanged. No code was added to or deleted from category M17 that year.

Related codes

Codes in the same family as M17.0. Only codes with a published page render as links.

Sibling codes in the M17 family

M17.10: Unilateral primary osteoarthritis, unspecified knee.
M17.11: Unilateral primary osteoarthritis, right knee.
M17.12: Unilateral primary osteoarthritis, left knee.
M17.2: Bilateral post-traumatic osteoarthritis of knee.
M17.30: Unilateral post-traumatic osteoarthritis, unspecified knee.
M17.31: Unilateral post-traumatic osteoarthritis, right knee.
M17.32: Unilateral post-traumatic osteoarthritis, left knee.
M17.4: Other bilateral secondary osteoarthritis of knee.
M17.5: Other unilateral secondary osteoarthritis of knee.
M17.9: Osteoarthritis of knee, unspecified.

Additional codes to consider

Codes outside the M17 family considered alongside M17.0.

Companion: code alongside when documented

G89.29: Other chronic pain, where the provider documents chronic pain and the encounter is for pain control or pain management. Section I.C.6.b.1 bars a G89 code when the underlying diagnosis is known and the encounter manages that condition.
Z79.1: Long term (current) use of non-steroidal anti-inflammatories (NSAID).

Consider instead

M17.2: Bilateral post-traumatic osteoarthritis of knee, where the record ties the degeneration in both knees to a documented prior injury.
M17.4: Other bilateral secondary osteoarthritis of knee, where the record names an underlying cause.
M17.11: Unilateral primary osteoarthritis, right knee, where only the right knee is involved.
M17.12: Unilateral primary osteoarthritis, left knee, where only the left knee is involved.
M17.10: Unilateral primary osteoarthritis, unspecified knee, where one knee is involved but the side is never named.
M17.9: Osteoarthritis of knee, unspecified, where neither the side nor the etiology is documented.
M15.9: Polyosteoarthritis, unspecified, where osteoarthritis involves multiple joints rather than both knees alone.
M15.0: Primary generalized (osteo)arthritis, where generalized osteoarthritis is documented.
M19.90: Unspecified osteoarthritis, unspecified site, where the record names no joint at all.
M06.9: Rheumatoid arthritis, unspecified, where the record documents an inflammatory rather than a degenerative arthritis.
M47.9: Spondylosis, unspecified, for osteoarthritis of the spine, which the M15-M19 block excludes under an Excludes2 note.
M25.561: Pain in right knee, reported with M25.562 for the left knee, where osteoarthritis is suspected but not confirmed.

Sources

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

National Center for Health Statistics. (2026). International classification of diseases, tenth revision, clinical modification (ICD-10-CM) FY2027 files. https://www.cdc.gov/nchs/icd/icd-10-cm/files.html
Centers for Medicare & Medicaid Services and National Center for Health Statistics. (2026). ICD-10-CM official guidelines for coding and reporting FY2027. https://ftp.cdc.gov/pub/Health_Statistics/NCHS/Publications/ICD10CM/2027/ICD-10-CM-October-1-2026-FY27-Guidelines.pdf
Centers for Medicare & Medicaid Services. (2025). 2026 model software/ICD-10 mappings. https://www.cms.gov/medicare/payment/medicare-advantage-rates-statistics/risk-adjustment/2026-model-software-icd-10-mappings
Centers for Medicare & Medicaid Services. (2026). MS-DRG classifications and software, version 44. https://www.cms.gov/medicare/payment/prospective-payment-systems/acute-inpatient-pps/ms-drg-classifications-and-software