“Arthritis” may be common in documentation, but coding it correctly requires more than just identifying the affected joint. 

Not All Osteoarthritis Is the Same 

Osteoarthritis (OA) is one of the most common types of arthritis in medical records, but several distinct types affect code selection. 

Polyosteoarthritis codes in category M15.- are different from other OA codes because they are only four characters and provide less anatomic specificity. Primary OA develops over time, while secondary OA results from an underlying cause or condition. Post-traumatic OA is a subtype of secondary OA associated with a specific injury or trauma, such as a fracture. Dysplastic OA, meanwhile, is specific to the hip and results from abnormal alignment. 

When coding OA, start by identifying three key details: the type of OA, the specific joint or location, and laterality. If the documentation supports secondary OA, remember to also code the underlying or contributing condition when required. 

Look Beyond Osteoarthritis 

Other types of arthritis require their own coding considerations. Rheumatoid arthritis (RA) is primarily found in categories M05-, M06-, and M08-. Pyogenic, or septic, arthritis is caused by infection and is coded from category M00.-. Monoarthritis involves a single joint and is coded from category M13.1-. 

And don’t assume that arthritis documented in multiple joints means each joint should automatically be coded separately. When polyarthritis is documented as involving five or more joints without further specificity, the appropriate code may be M13.0 for unspecified polyarthritis. 

The Takeaway 

Start with the type of arthritis, then work through the documentation for location, laterality, and underlying cause. Taking those extra steps before selecting the code can help prevent a common arthritis diagnosis from becoming a common coding error.