Legg-Calvé-Perthes disease affecting the left femoral head in a pediatric patient, characterized by avascular necrosis and subsequent reossification of the left capital femoral epiphysis.
Verified May 8, 2026 · 5 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 10
- Region
- Hip
Documentation tips
What should appear in the chart to support M91.12.
Source · Editorial brief grounded in 5 cited references ↓
- Explicitly state 'left hip' or 'left femoral head' — do not rely on laterality inferred from imaging reports alone.
- Record the radiographic stage of LCP (initial, fragmentation, reossification, or remodeling) to support medical necessity for surgical versus conservative management.
- Document the patient's skeletal age or open growth plate status to confirm juvenile classification; adult-onset AVN maps to M87 series, not M91.12.
- Note imaging modality used (X-ray with Kellgren classification, MRI for early-stage disease, or bone scan) and relevant findings such as subchondral lucency, femoral head flattening, or epiphyseal fragmentation.
- If conservative care (abduction bracing, physical therapy, activity restriction) has been trialed, document duration and response — required context for surgical prior authorization.
Related CPT procedures
Procedure codes commonly billed with M91.12. Linking the right diagnosis to the right procedure is what establishes medical necessity.
Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis
Common coding pitfalls
The recurring mistakes coders make with M91.12 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Coding M91.12 alongside M93.0x (slipped upper femoral epiphysis) violates the Excludes1 note at M91 — these diagnoses are mutually exclusive; verify the correct condition before coding.
- Using M91.12 for an adult patient with hip AVN after steroid use or trauma — those cases belong in the M87 category, not M91.
- Defaulting to M91.10 (unspecified leg) when the treating note clearly lateralizes to the left — the specific code is required for clean claim adjudication.
- Reporting only M91.12 when both hips are involved — bilateral LCP requires separate codes M91.11 and M91.12; there is no single bilateral code.
- Confusing the 7th-character extension rules from injury (S-code) encounters with M-code usage — M91.12 carries no 7th-character extension.
Clinical context
Source · Editorial summary grounded in 5 cited references ↓
M91.12 is the left-sided code for Legg-Calvé-Perthes (LCP) disease — idiopathic avascular necrosis of the capital femoral epiphysis occurring in skeletally immature patients. Use it when the diagnosis is confirmed on the left hip and the patient is a child or adolescent whose growth plates remain open. The condition progresses through four radiographic stages (initial, fragmentation, reossification, and remodeling), and laterality must be explicit in the documentation before you can bill this code.
If imaging or the clinical note does not specify left versus right, drop to M91.10 (unspecified leg) — but unspecified codes invite payer scrutiny and can trigger a request for additional documentation. When bilateral involvement is documented, report M91.11 (right) and M91.12 (left) together with a bilateral modifier; there is no single bilateral code under M91.1.
Do not confuse this code with slipped upper femoral epiphysis (SUFE). The Excludes1 note at the M91 category level explicitly prohibits using M91.1x codes alongside M93.0x (nontraumatic SUFE) — they are mutually exclusive conditions. Similarly, avascular necrosis developing in an adult hip after trauma or steroid use maps to M87 series codes, not M91.12.
Sibling codes
Other billable codes under M91.1 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 5 cited references ↓
01Is M91.12 valid for an adult patient diagnosed with Perthes disease as a child who still has residual hip deformity?
02Can I report M91.12 and M91.11 together for bilateral LCP?
03What is the Excludes1 conflict I need to watch for with M91.12?
04Which MS-DRGs does M91.12 group into?
05Does M91.12 require a 7th-character extension?
06What imaging finding best supports the M91.12 diagnosis for audit purposes?
07If only the left hip shows active disease but the right hip shows prior remodeling changes, which codes apply?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026 (effective Oct 1, 2025)
- 02icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M91-M94/M91-/M91.12
- 03aapc.comhttps://www.aapc.com/codes/icd-10-codes/M91.12
- 04icdcodes.aihttps://icdcodes.ai/icd10/M91.12
- 05aaos.orghttps://www.aaos.org/globalassets/quality-and-practice-resources/coding-and-reimbursement/resident-guide/resident-guide_icd10.pdf
Mira AI Scribe
Mira AI Scribe captures left-hip laterality, the patient's age and skeletal maturity status, the radiographic stage of femoral head involvement, and any prior conservative treatment history from the encounter note. This prevents a downcode to unspecified M91.10, blocks an Excludes1 conflict with SUFE codes, and supplies the medical necessity context insurers require for surgical or bracing authorization.
See how Mira captures M91.12 documentation