Fibrous dysplasia (monostotic), unspecified thigh

This code describes a benign, non-hereditary bone disorder characterized by the replacement of normal bone with fibrous tissue and immature woven bone, specifically affecting a single bone (monostotic) in an unspecified thigh. This leads to weakened bone, which can result in pain, deformity, or pathological fractures.

Use this code when documentation confirms a diagnosis of monostotic fibrous dysplasia located in the thigh, and the specific thigh (right or left) is not documented. This diagnosis is typically made based on imaging studies (X-ray, CT, MRI) and sometimes confirmed by biopsy.

• Ensure documentation clearly specifies "monostotic" involvement; polyostotic fibrous dysplasia uses different codes.
• Avoid using this code if the laterality of the thigh is specified; instead, use M85.051 (right thigh) or M85.052 (left thigh).
• Code any associated pathological fractures separately, linking them to the fibrous dysplasia as the underlying cause.