Legg-Calvé-Perthes disease affecting the right hip: avascular necrosis of the right capital femoral epiphysis in a skeletally immature patient, classified under juvenile osteochondroses of the hip and pelvis.
Verified May 8, 2026 · 5 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 7
- Region
- Hip
Documentation tips
What should appear in the chart to support M91.11.
Source · Editorial brief grounded in 5 cited references ↓
- Explicitly document the affected side as 'right' — laterality is required to assign M91.11 over the unspecified M91.10.
- Record imaging findings that confirm avascular necrosis of the right capital femoral epiphysis: X-ray (AP and frog-leg lateral views), MRI signal changes, or bone scan results, including Herring lateral pillar classification or Catterall staging if assessed.
- Document the patient's skeletal maturity or age at diagnosis, as LCP is a juvenile (pediatric) condition; assignment of this code to an adult without documented history of childhood onset may trigger an audit flag.
- If containment surgery is planned or performed, note the stage of disease (fragmentation, reossification, remodeling) and any associated deformity such as coxa magna or coxa plana, which have separate codes under M91.4x and M91.2x respectively.
- When bilateral involvement is present, document each side independently so both M91.11 and M91.12 can be reported accurately.
Related CPT procedures
Procedure codes commonly billed with M91.11. 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 M91.11 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Defaulting to M91.10 (unspecified leg) when the operative report, imaging report, or provider note clearly states 'right hip' — this downcodes specificity and can trigger payer queries.
- Confusing LCP disease with slipped upper femoral epiphysis (SUFE): SUFE maps to M93.0- and carries an Excludes1 note at M91, meaning M91.11 and M93.0x cannot be reported for the same hip at the same encounter.
- Assigning M91.11 for avascular necrosis of the femoral head in an adult without documented history of childhood LCP — adult AVN maps to M87.05x (idiopathic aseptic necrosis of femur) rather than the juvenile osteochondrosis codes.
- Failing to add a second LCP code (M91.12) when bilateral disease is documented, because no single bilateral code exists in this subcategory.
Clinical context
Source · Editorial summary grounded in 5 cited references ↓
M91.11 is the billable code for Legg-Calvé-Perthes (LCP) disease of the right hip — idiopathic avascular necrosis of the femoral head occurring in children, typically between ages 4 and 10. The right-leg specificity is encoded in the 6th character (1 = right). Use this code when the treating provider has documented LCP disease or juvenile osteochondrosis of the right femoral head based on clinical presentation and imaging. Do not assign this code for slipped upper femoral epiphysis (SUFE), which maps to M93.0-; that condition carries an Excludes1 note at the M91 category level, making the two codes mutually exclusive.
The M91.1x family has three options: M91.10 (unspecified leg), M91.11 (right leg), and M91.12 (left leg). Always assign M91.11 when laterality is documented as right — do not default to M91.10 when the chart clearly identifies the affected side. If bilateral LCP is documented, both M91.11 and M91.12 should be reported; there is no single bilateral code in this subcategory.
For inpatient encounters, M91.11 groups to MS-DRG 553 (Bone diseases and arthropathies with MCC) or 554 (without MCC) under MS-DRG v43.0. Sequencing depends on the primary reason for the encounter — whether the visit is for diagnosis, conservative management, or surgical intervention such as femoral osteotomy or containment procedure.
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 ↓
01Can M91.11 be used for an adult patient with a history of Perthes disease as a child?
02Is there a bilateral code for Legg-Calvé-Perthes disease?
03What is the Excludes1 note at category M91, and why does it matter?
04Which MS-DRGs does M91.11 group to for inpatient claims?
05What CPT codes are commonly paired with M91.11?
06When should M91.10 (unspecified leg) be used instead of M91.11?
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)
- 02icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M91-M94/M91-/M91.11
- 03aapc.comhttps://www.aapc.com/codes/icd-10-codes/M91.11
- 04aapc.comhttps://www.aapc.com/codes/icd-10-codes/M91.1
- 05MS-DRG v43.0 Grouper (CMS)
Mira AI Scribe
Mira's AI scribe captures laterality ('right hip'), the patient's age or skeletal maturity, imaging modality and findings (X-ray Herring grade, MRI signal change, bone scan), current disease stage, and any prior conservative treatment or surgical intervention. Capturing these specifics prevents downgrade to M91.10 (unspecified leg) and provides the clinical detail needed to defend the code on audit and support MS-DRG assignment.
See how Mira captures M91.11 documentation