Published 1/1/2014
Margaret M. Maley BSN, MS

ICD-10 Coding of Osteoarthritis

Start with the common things

With just a few months left before the International Classification of Diseases, 10th Edition (ICD-10) goes into effect, it is time to begin focused, orthopaedic-specific training in earnest.

Under ICD-9, most diagnosis codes used by orthopaedic surgeons were in the musculoskeletal section, and categories were numbers from 710 to 739. Injury and poisoning diagnostic categories, including traumatic fractures, were reported with codes that ranged from 800 to 999.

In ICD-10, most orthopaedic codes will begin with the letters M or S. These codes will be found in Chapter 13 (M00-M99), Diseases of the Musculoskeletal & Connective Tissue, and in Chapter 19 (S00-T88), Injury, Poisoning and Certain Other Consequences of External Causes.

Coding osteoarthritis
The range of codes for osteoarthritis (OA) runs from M15 through M19 (excluding OA of the spine, which is found in the category M47). OA codes, as other codes, are further divided into specific locations, laterality, and types of OA.

For example, M15, Polyosteoarthritis, requires the addition of a fourth character to provide specific details as follows:

  • M15.0—Primary generalized (osteo) arthritis
  • M15.1—Heberden’s nodes (with arthropathy)
  • M15.2—Bouchard’s nodes (with arthropathy)
  • M15.3—Secondary multiple arthritis
  • M15.4—Erosive OA
  • M15.8—Other polyosteoarthritis
  • M15.9—Other polyosteoarthritis, unspecified, or generalized OA not otherwise specified (NOS)

The term “not otherwise specified (NOS)” in ICD-10 is defined the same way as it was in ICD-9. This notation indicates that the documentation does not provide enough detail to allow the use of a more specific code. This differs from the “other” code, such as M15.8, which refers to the fact that a specific ICD-10 code to describe the “type” of OA documented in the record does not exist.

Coding hip OA
In categories M16 through M18, the fifth character, when required, addresses laterality. For example, when coding hip OA (M16), the fourth character describes the type of hip OA and whether it is bilateral or unilateral, and the fifth character indicates laterality (
Table 1). Within the M16 category, specific codes also describe OA due to hip dysplasia and posttraumatic OA; in both cases, a fifth character is required to address the issue of laterality.

Coding knee OA
The architecture of the ICD-10 codes describing OA of the knee under category M17 is similar to that of OA of the hip, minus the section on dysplasia (
Table 2). Again, when the condition is unilateral, a fifth character is required to specify which side is affected.

Coding thumb (CMC joint) OA
Category M18 covers OA of the first carpometacarpal (CMC) joint; again, the architecture of the ICD-10 codes follows a similar pattern (
Table 3) and will require a fifth character to specify laterality in situations when only one hand is affected.

OA in other joints
The codes under block M19 describe primary (M19.0), posttraumatic (M19.1), secondary (M19.2), and unspecified (M19.3) OA in joints other than the hip, knee, and first CMC joint. In this block, the fifth character is used to describe the location of the other joint (such as shoulder, elbow, or wrist) and the sixth character describes laterality (
Table 4). As in ICD-9, the word “and” in a descriptor should be read as “and/or.”

It is unclear at this time what payers will do if orthopaedic surgeons submit unspecified codes after October 2014. Reviewing the architecture of the OA code set in ICD-10 also illustrates that orthopaedic surgeons and coders cannot assume that the sixth character will always be used to describe laterality. For example, laterality is addressed by the fifth character in codes for OA of the hip, knee, and first CMC joint. In other joints, however, the sixth character addresses laterality.

Studying ICD-10 architecture by taking an in-depth look at the codes which describe OA, the most common orthopaedic diagnosis, provides a sense of the level of specific documentation required to support ICD-10 codes and how new additional characters are used to describe location, laterality, and type of a disease or illness. This exercise also offers insight into the work that will be required to educate providers, coders, and billing personnel to be ready for the “go-live” date in October of 2014.

Margaret M. Maley, BSN, MS, is a senior consultant with KarenZupko & Associates, Inc., who focuses on CPT and ICD-10 coding education for orthopaedic practices.

For more information…
The AAOS has produced a three-webinar series to help practices with the successful planning and implementation of ICD-10. Although the series has been concluded, members can access the recordings and syllabus materials for each of the three 75-minute webinars in the series. Additional information and links to other ICD-10 resources can be found on the AAOS website at