M91.30 identifies pseudocoxalgia affecting an unspecified hip — a sequela of juvenile osteochondrosis (Legg-Calvé-Perthes disease) in which avascular necrosis of the femoral head produces hip pain and deformity that mimics coxalgia without a primary joint disease cause.

Documentation tips

What should appear in the chart to support M91.30.

Source · Editorial brief grounded in 5 cited references ↓

• Specify laterality (right or left) in every encounter note — this single step lets you bill M91.31 or M91.32 instead of the unspecified M91.30 and prevents laterality-based claim edits.
• Document the patient's Perthes disease history explicitly, including age at diagnosis and prior treatment, to support the causal link between juvenile osteochondrosis and current pseudocoxalgia.
• Record imaging findings — AP pelvis and frog-leg lateral radiographs, MRI if obtained — noting femoral head deformity, flattening, coxa magna, or joint incongruency to substantiate medical necessity for advanced treatment.
• If coxa plana (M91.2x) or coxa magna (M91.4x) coexists, document each structural deformity by name so additional codes in the M91 hierarchy can be assigned alongside M91.30.
• For surgical cases, the operative note must name the affected side in the procedure title and body — a missing laterality in the pre-op diagnosis line is the most common reason a laterality-specific code cannot be assigned post-encounter.

Related CPT procedures

Procedure codes commonly billed with M91.30. 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 M91.30 and adjacent codes.

Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓

• Defaulting to M91.30 when laterality is clearly stated elsewhere in the chart (e.g., imaging report, physical exam) — if the side is documented anywhere in the encounter, use M91.31 or M91.32.
• Confusing M91.30 (pseudocoxalgia, unspecified hip) with M91.10 (Legg-Calvé-Perthes, unspecified leg) — pseudocoxalgia codes the hip pain/deformity sequela, not the active osteochondrosis itself; select the correct subcategory based on disease stage.
• Billing M91.30 on a unilateral surgical claim — most payers auto-edit unspecified laterality codes against laterality-specific procedure codes and will deny or return the claim for correction.
• Omitting co-existing structural deformity codes (coxa plana M91.2x, coxa magna M91.4x) when multiple sequelae are present and documented, resulting in undercoding that may not support the planned procedure's medical necessity.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Sibling codes

Other billable codes under M91.3 (laterality / anatomic variants).