Legg-Calvé-Perthes disease of the femoral head in a skeletally immature patient where the operative or clinical note does not specify right or left side.
Verified May 8, 2026 · 4 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 14
- Region
- Hip
Documentation tips
What should appear in the chart to support M91.10.
Source · Editorial brief grounded in 4 cited references ↓
- Record laterality by name (right or left hip) in every encounter note — even screening visits — so M91.11 or M91.12 can be used instead of the unspecified M91.10.
- Document the patient's skeletal age or Tanner stage alongside chronological age to support the 'juvenile' component of the diagnosis.
- Include imaging findings that confirm avascular necrosis of the femoral head: X-ray findings (Herring lateral pillar grade, Catterall classification), MRI signal changes, or bone scan results.
- If both hips are involved, document each side independently with its own laterality designation and disease stage; bilateral LCP is uncommon and reviewers may query unspecified coding.
- Note prior conservative treatment (bracing, activity restriction, physical therapy) when the encounter is for escalating surgical management — this contextualizes medical necessity.
Related CPT procedures
Procedure codes commonly billed with M91.10. 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 M91.10 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Defaulting to M91.10 on surgical claims when the operative report clearly identifies a single hip — payers cross-reference site-of-service and will deny or downcode laterality mismatches.
- Confusing M91.1x (LCP disease) with M93.0x (slipped upper femoral epiphysis); the Excludes1 note at M91 prohibits using both on the same encounter, and the conditions have different clinical presentations.
- Using M91.10 for an adult patient with residual hip deformity from childhood LCP — the active-disease code is inappropriate once skeletal maturity is reached; code the resulting structural condition instead.
- Omitting the laterality query when the note says 'hip pain' without specifying side — do not assume unspecified; query the provider before submitting M91.10.
- Applying a 7th-character extension to M91.10 — M-codes in this section do not use 7th-character designators (A/D/S are for S-code injury encounters only).
Clinical context
Source · Editorial summary grounded in 4 cited references ↓
M91.10 captures Legg-Calvé-Perthes disease (LCP) — avascular necrosis of the developing femoral head — when laterality is not documented. It is the fallback code under parent M91.1; use M91.11 for the right hip and M91.12 for the left hip whenever the treating provider's note names a side. LCP is a pediatric diagnosis; encounters for adults with residual deformity from childhood LCP are coded differently (typically under late-effect or post-procedural sequelae categories).
M91.10 is appropriate at initial evaluation when the chart is incomplete pending imaging, or in rare genuine bilateral cases where both hips are affected symmetrically and the provider documents unspecified laterality. Do not default to M91.10 simply because the intake form lacks a laterality checkbox — query the provider. The Excludes1 note at M91 blocks simultaneous use of M93.0- (slipped upper femoral epiphysis, nontraumatic); these are distinct conditions and must not be coded together on the same encounter.
For surgical encounters — femoral or acetabular osteotomy, containment procedures, total hip arthroplasty in late-stage disease — payers expect a laterality-specific code (M91.11 or M91.12). Submitting M91.10 on a surgical claim will often trigger a laterality mismatch denial when the operative report and facility site-of-service data specify a side.
Sibling codes
Other billable codes under M91.1 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 4 cited references ↓
01When is M91.10 actually correct to use versus M91.11 or M91.12?
02Can M91.10 be used alongside M93.0- for slipped capital femoral epiphysis on the same claim?
03Is M91.10 appropriate for an adult who had Perthes disease as a child and now presents with hip arthritis?
04What CPT codes are most commonly paired with M91.10 on claims?
05Does M91.10 require a 7th-character extension?
06How does the Herring lateral pillar classification affect coding for LCP?
07If a child is diagnosed with LCP in both hips, how should the coding be handled?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026 (FY2026, effective Oct 1, 2025)
- 02aapc.comhttps://www.aapc.com/codes/icd-10-codes/M91.10
- 03aapc.comhttps://www.aapc.com/codes/icd-10-codes/M91.1
- 04cms.govhttps://www.cms.gov/medicare/coordination-benefits-recovery/overview/icd-code-lists
Mira AI Scribe
Mira AI Scribe captures the affected hip side by name, the patient's age and skeletal maturity indicators, imaging modality and findings (Herring grade, MRI avascular signal, bone scan uptake pattern), and any prior containment or conservative treatment documented in the visit note. Capturing this during the encounter prevents laterality-unspecified coding (M91.10) when a side-specific code (M91.11 or M91.12) is warranted, eliminating the most common surgical claim denial for this diagnosis.
See how Mira captures M91.10 documentation