Solitary bone cyst, unspecified tibia and fibula

This code signifies the presence of a single, non-cancerous, fluid-filled or fibrous lesion within the bone of an unspecified tibia or fibula. These cysts are typically asymptomatic and often discovered incidentally during imaging for other reasons. They represent a localized area of bone destruction or malformation.

Apply this code when documentation confirms a solitary bone cyst located in either the tibia or fibula, but the specific bone (tibia or fibula) is not explicitly stated. This is appropriate for incidental findings on X-rays, CT scans, or MRIs where the lesion is characterized as a simple bone cyst without further specification of the affected lower leg bone.

• Ensure the documentation specifies "solitary" to differentiate from multiple bone cysts.
• Avoid using this code if the specific bone (tibia or fibula) is identified; instead, use the more specific codes for solitary bone cyst of tibia (M85.461, M85.462) or fibula (M85.463, M85.464).
• Do not use this code for aneurysmal bone cysts (M85.5-), which are distinct entities.