Effusion, left knee

This code signifies the presence of excess fluid within the joint capsule of the left knee. This accumulation, often referred to as "water on the knee," can result from various underlying conditions such as trauma, inflammation, or degenerative joint disease.

Assign this code when documentation explicitly states effusion of the left knee. This is appropriate for conditions like synovitis, arthritis, or post-traumatic swelling where fluid accumulation is a primary finding in the left knee joint. Supporting documentation includes physician notes detailing physical exam findings (e.g., ballotable patella, swelling), imaging reports (e.g., ultrasound, MRI confirming effusion), or aspiration reports.

• Always specify laterality; do not use unspecified knee effusion codes if left knee is documented.
• Code any underlying cause of the effusion (e.g., osteoarthritis, sprain) as a primary diagnosis if known and documented.
• Distinguish from hemarthrosis (blood in the joint), which has a separate code.