M87.373 Other secondary osteonecrosis, unspecified ankle

Billable ICD-10-CM code, FY2026. Acts as a Complication or Comorbidity (CC) as a secondary diagnosis.

Applies from M87 Osteonecrosis

Includes

• avascular necrosis of bone

Excludes1 (never code together)

• juvenile osteonecrosis (M91-M92)
• osteochondropathies (M90-M93)

Use additional code

• code to identify major osseous defect, if applicable (M89.7-)

Risk adjustment (HCC)

• CMS-HCC V28: HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
• CMS-HCC V22: HCC 39 — Bone/Joint/Muscle Infections/Necrosis
• RxHCC V08: HCC 80 — Aseptic Necrosis of Bone
• ESRD V24: HCC 39

MS-DRG index

Defines the logic of DRG(s) 553-554 in MDC 08.

Approximate ICD-9-CM (GEMs)

• 733.49 Aseptic necrosis of bone, other (approximate)

Medicare Code Edits (MCE v43.1 (April 2026))

• Unspecified code (laterality): Unspecified codes for which a more specific code identifying laterality (right, left, bilateral) exists within the same code family.

Code annotations containing back-references to M87.373

Back-references to M87

• Code First: M89.7 Major osseous defect ("aseptic necrosis of bone (M87.-)")
• Code First: M89.7 Major osseous defect ("osteonecrosis (M87.-)")

Nearby codes

• M87.365 Other secondary osteonecrosis, left fibula
• M87.366 Other secondary osteonecrosis, unspecified fibula
• M87.37 Other secondary osteonecrosis, ankle and foot
• M87.371 Other secondary osteonecrosis, right ankle
• M87.372 Other secondary osteonecrosis, left ankle
• M87.373 Other secondary osteonecrosis, unspecified ankle (this code)
• M87.374 Other secondary osteonecrosis, right foot
• M87.375 Other secondary osteonecrosis, left foot
• M87.376 Other secondary osteonecrosis, unspecified foot
• M87.377 Other secondary osteonecrosis, right toe(s)
• M87.378 Other secondary osteonecrosis, left toe(s)