M85.059 Fibrous dysplasia (monostotic), unspecified thigh

ICD-10-CM Diagnosis Code M85.059: Fibrous dysplasia (monostotic), unspecified thigh

ICD-10-CM code M85.059 represents fibrous dysplasia (monostotic), unspecified thigh, classifying it as a Disease or Syndrome. Fibrous dysplasia is a benign bone lesion where fibro-osseous tissue replaces normal bone, and the monostotic form affects a single bone. This active code resides within the musculoskeletal chapter under parent concept M85.05. 1 2 3

Plain-language overview

Fibrous dysplasia is a benign bone lesion characterized by fibro-osseous tissue replacing normal bone due to altered osteogenesis, which can occur in a monostotic form affecting a single bone. 2

The monostotic form of fibrous dysplasia affects a single bone and accounts for 75 to 80 percent of fibrous dysplasia cases, with patients often presenting without symptoms. 2

What this code represents

The active ICD-10-CM code M85.059 designates the diagnosis of fibrous dysplasia (monostotic), unspecified thigh, and is categorized with the semantic type of Disease or Syndrome. 1

Code M85.059 is a narrower concept under the parent code M85.05, which broadly classifies fibrous dysplasia (monostotic) of the thigh region in the ICD-10-CM terminology. 1 3

Coding details

Code M85.059 falls under subcategory M85.0 for monostotic fibrous dysplasia, within category M85 for other disorders of bone density and structure in Chapter 13 covering musculoskeletal diseases. 3

Documentation considerations

The official terminology record for M85.059 establishes the active diagnosis label as fibrous dysplasia (monostotic), unspecified thigh, and notes that the concept has narrower descendant concepts within the hierarchy. 1

Clinical context

Although monostotic fibrous dysplasia is often asymptomatic, the replacement of normal bone with fibro-osseous tissue can result in complications including fractures or compression of adjacent soft tissues. 2

What the sources add

While the terminology record establishes M85.059 as an active code for unspecified thigh involvement, the clinical reference explains that monostotic radiologic appearance can mimic other bone lesions like simple bone cysts. 1 2

The terminology record provides the official code hierarchy and active status for M85.059, whereas the coding reference details its placement within the broader M80-M85 disorders of bone density and structure grouping. 1 3

Sources

1. ICD-10-CM M85.059 terminology record — National Cancer Institute Enterprise Vocabulary Services; accessed 2026-07-27.
2. Bookshelf — ncbi.nlm.nih.gov; accessed 2026-07-27.
3. ICD-10-CM Code M85.05 | Vero — veroscribe.com; accessed 2026-07-27.