ICD-10 Code for OA (Osteoarthritis)

When you look up “ICD-10 code for OA,” what you really want is clarity. Osteoarthritis (OA) has several ICD-10 codes, and each one depends on the type of OA, the joint involved, and whether the condition is generalized, localized, primary, secondary, or post-traumatic. Coding correctly matters because it impacts clinical accuracy, insurance claims, and research data.

This guide explains the ICD-10 codes for OA in detail, with tables, examples, and practical tips to help you choose the correct one.

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Understanding ICD-10 and OA Codes

The ICD-10-CM system (International Classification of Diseases, 10th Revision, Clinical Modification) organizes osteoarthritis under the M15 to M19 category.

• M15: Polyosteoarthritis or generalized OA affecting multiple joints.

• M16: OA (osteoarthritis) of the hip.

• M17: OA (osteoarthritis) of the knee.

• M18: OA (osteoarthritis) of the first carpometacarpal joint (thumb base).

• M19: Other and unspecified osteoarthritis.

Each of these categories breaks down further into specific codes that describe whether the OA is primary, secondary, post-traumatic, unilateral, bilateral, or unspecified. This level of detail ensures that the diagnosis reflects the real condition of the patient.

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Deciding Primary vs. Secondary OA

A key step in coding osteoarthritis is deciding if it is primary or secondary.

• Primary OA: This is the most common type, linked to aging and natural joint wear. It occurs without a clear underlying cause. For example, an elderly patient with knee pain and no injury history is usually coded as primary OA.

• Secondary OA: This results from another condition. It can follow a fracture, joint injury, congenital defect, or another disease such as rheumatoid arthritis. For example, a patient who develops hip OA after a past trauma would be coded under secondary OA.

If the documentation does not specify, coders are advised to assume primary OA, since it is more common. This default keeps coding accurate and consistent, but it also shows why detailed documentation from physicians is essential.

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Step-by-Step: How to Choose the Right Code

Because ICD-10 codes are so specific, it helps to follow a structured process. Here is a simple method to avoid mistakes:

1. Check the documentation thoroughly
   Look for the type of OA, the joint affected, and any history of trauma or disease.

2. Identify the joint
   Each major joint (hip, knee, thumb, etc.) has its own category. Always choose the joint-specific code when possible.

3. Check for laterality
   If the condition is on the left, right, or both sides, select the corresponding code. For example, M17.11 is for unilateral primary OA of the right knee.

4. Determine if it is primary or secondary
   If the record mentions an old fracture, trauma, or another condition, select a secondary OA code.

5. See if it is generalized
   If multiple joints are affected and the physician documents it as generalized, use M15.0.

6. Use unspecified codes only as a last resort
   Codes such as M19.90 (unspecified OA, unspecified site) should only be used when the record does not provide enough detail.

By following these steps, you can select the most accurate ICD-10 code for osteoarthritis in every case.

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ICD-10 Codes for Osteoarthritis (M15–M19)

Here is a breakdown of the main ICD-10 codes used for osteoarthritis.

Generalized Osteoarthritis (M15)

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Hip Osteoarthritis (M16)

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Knee Osteoarthritis (M17)

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First Carpometacarpal (Thumb) OA (M18)

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Other and Unspecified OA (M19)

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Real Coding Scenarios

1: A 72-year-old man with age-related pain in both knees.

Correct code: M17.0 (bilateral primary osteoarthritis of knee).

2: A 60-year-old woman with right hip OA following a fracture 10 years ago.

Correct code: M16.31 (unilateral secondary osteoarthritis of right hip).

3: A 55-year-old man with OA in the left thumb carpometacarpal joint, no injury history.

Correct code: M18.12 (unilateral primary OA of left first carpometacarpal joint).

4: Patient record says “OA, site not specified.”

Correct code: M19.90 (unspecified osteoarthritis, unspecified site).

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FAQs

Q1. What is the ICD-10 code for unspecified osteoarthritis?
The general code is M19.90, which is used when the site and type are not documented.

Q2. Should I always code primary if the physician does not specify?
Yes, unless there is clear evidence of trauma or another underlying condition, primary OA is the default.

Q3. How do I code bilateral knee osteoarthritis?
Use M17.0 for bilateral primary OA or M17.2 for bilateral secondary OA.

Q4. What if the OA is documented as “degenerative joint disease”?
Degenerative joint disease is another name for osteoarthritis. Use the same OA codes based on site and type.

Q5. Can obesity or other conditions affect OA coding?
No, obesity is coded separately. OA coding still depends only on joint, laterality, and type.

Q6. How do I code post-traumatic osteoarthritis?
Use the post-traumatic subcode under the relevant joint, such as M17.4 for knee or M16.4 for hip.

Q7. What is the ICD-10 code for generalized OA?
Use M15.0 when multiple joints are affected and the condition is described as generalized.

Q8. Should I avoid unspecified codes like M19.9?
They are valid but should be used only if the physician’s notes do not provide enough detail. Specific codes are always better for accuracy and billing.

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Final Thoughts

The ICD-10 code for OA is not a single number but a structured system that reflects the complexity of osteoarthritis. To code correctly, you need to:

• Identify the joint.

• Check if it is unilateral, bilateral, or generalized.

• Decide if it is primary, secondary, or post-traumatic.

• Use unspecified codes only when no other information is available.

By following this process, coders can ensure accuracy, reduce claim denials, and support better medical records. With practice, these steps become second nature, making osteoarthritis coding straightforward and reliable.