ICD-10-CM · Hip

M91.22

M91.22 identifies coxa plana of the left hip — a flattening deformity of the femoral head resulting from previous juvenile osteochondrosis (Legg-Calvé-Perthes disease) of the left hip.

Verified May 8, 2026 · 5 sources ↓

Status: Billable
Chapter: 13
Related CPT: 10
Region: Hip

Drawn from CDCICD10DataCMSAAPCCdek

Documentation tips

What should appear in the chart to support M91.22.

Source · Editorial brief grounded in 5 cited references ↓

Specify 'left hip' explicitly — the laterality drives the 6th character (2 = left) and drops M91.20 unspecified from consideration.
Document the history of juvenile osteochondrosis (Legg-Calvé-Perthes disease) to satisfy the Applicable To annotation and establish medical necessity.
Record imaging findings that confirm femoral head flattening — AP pelvis X-ray with Stulberg classification or Kellgren-Lawrence grade for secondary arthritis if present.
Note functional limitations (reduced ROM, gait abnormality, impingement symptoms) to support physical therapy or surgical authorization under medical necessity criteria.
If conservative care has been exhausted, document prior treatments (PT, NSAIDs, activity modification) to support escalation to surgical intervention.

Related CPT procedures

Procedure codes commonly billed with M91.22. Linking the right diagnosis to the right procedure is what establishes medical necessity.

Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis

27120 $1,182.73

Surgical reshaping or reconstruction of the acetabulum (hip socket) to correct deformity, relieve impingement, or address dysplasia — performed without prosthetic joint replacement.

27122 $1,010.71

Acetabuloplasty with resection of the femoral head — the Girdlestone procedure — performed to relieve pain when infection or bone quality precludes joint reconstruction.

27125 $1,035.76

Surgical removal of the femoral head with replacement by a prosthetic implant; the native acetabulum is left in place (hemiarthroplasty).

27130 $1,162.02

Primary total hip arthroplasty replacing both the acetabular socket and proximal femoral components with prosthetic implants, with or without bone graft.

73521 $41.75

Bilateral hip X-ray examination capturing two radiographic views of both hips, including the pelvis when performed.

73523 $61.46

Radiologic examination of both hips, including the pelvis when performed, requiring a minimum of five views captured from multiple projections.

73525 $133.27

Radiologic examination of the hip joint using contrast material, including radiological supervision and interpretation

97110 $29.06

Therapeutic exercise billed per 15-minute unit, targeting strength, endurance, range of motion, or flexibility with direct one-on-one patient contact.

27299 View procedure details

77080 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M91.22 and adjacent codes.

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

Coding M91.20 (unspecified hip) when the operative or clinical report clearly documents the left side — always capture documented laterality.
Confusing coxa plana (M91.22) with pseudocoxalgia (M91.32) — they are sibling subcategories; pseudocoxalgia refers to the active osteochondrosis process, while coxa plana is the residual deformity.
Attempting to code M91.22 alongside M93.00-M93.02 (slipped upper femoral epiphysis) — the Excludes1 at M91 prohibits this combination.
Omitting additional codes for secondary osteoarthritis or femoroacetabular impingement when those conditions are separately documented and treated, leaving reimbursable diagnoses uncaptured.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Coxa plana is the residual structural deformity left after juvenile osteochondrosis of the hip, in which avascular necrosis causes the femoral head to collapse and remodel into a flattened, widened shape. M91.22 is the laterality-specific code for the left hip. Use it when the deformity is the primary reason for encounter — typically in a patient with a history of Perthes disease presenting with pain, reduced range of motion, impingement, or functional limitation attributable to the deformed femoral head.

The parent category M91.2 carries an Applicable To note: 'Hip deformity due to previous juvenile osteochondrosis.' This means M91.22 is appropriate even if the original Perthes episode was decades ago — the code captures the lasting anatomic consequence. Do not confuse M91.22 with pseudocoxalgia (M91.32, left hip) or coxa magna (M91.42, left hip), which are distinct sequelae within the same category.

Note the Excludes1 at the M91 level: slipped upper femoral epiphysis (nontraumatic) is coded to M93.0- and cannot be reported alongside M91.22. If the patient also has femoroacetabular impingement secondary to the coxa plana deformity, that may warrant an additional code from M24.85- depending on documentation.

Sibling codes

Other billable codes under M91.2 (laterality / anatomic variants).

M91.20

Coxa plana, unspecified hip

M91.21

Coxa plana, right hip

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 5 cited references ↓

01Can M91.22 be used for an adult patient whose Perthes disease was diagnosed in childhood?

Yes. M91.22 codes the residual deformity — coxa plana — regardless of when the original osteochondrosis occurred. The Applicable To note at M91.2 explicitly includes 'hip deformity due to previous juvenile osteochondrosis,' making this the correct code for adult sequelae of childhood Perthes disease affecting the left hip.

02What is the difference between M91.22 (coxa plana) and M91.32 (pseudocoxalgia)?

Pseudocoxalgia (M91.32) represents active or ongoing juvenile osteochondrosis of the left hip — the disease process itself. Coxa plana (M91.22) is the fixed structural deformity that remains after the disease has run its course. Use M91.22 when the femoral head is already flattened and remodeled; use M91.32 when the condition is active.

03Is M91.22 valid for outpatient physical therapy billing under Medicare?

Yes. CMS LCD A53065 (Outpatient Physical Therapy) lists M91.22 as a code that supports medical necessity, making it eligible for PT services under Medicare when appropriate documentation of functional limitation is present.

04What CPT codes are most commonly paired with M91.22 in a surgical context?

Femoral head reshaping or acetabular procedures such as CPT 27120 (acetabuloplasty) or 27122 (resection, femoral head) are associated with structural correction of coxa plana. For end-stage cases with secondary arthritis, 27125 (hemiarthroplasty) or 27130 (total hip arthroplasty) may apply. Imaging CPTs 73521–73525 support diagnostic workup.

05Should femoroacetabular impingement (FAI) secondary to coxa plana be coded separately?

If FAI is separately documented and addressed at the encounter, assign an additional code from M24.85- or the appropriate impingement category. Do not assume FAI is bundled into M91.22 — the two conditions reflect different clinical entities and distinct treatment considerations.

06What happens if laterality is not documented — should I default to M91.20?

Yes. If the treating provider's documentation does not specify left or right, use M91.20 (coxa plana, unspecified hip). However, query the provider before submitting — unspecified codes increase audit exposure and may trigger medical necessity review. Laterality is almost always determinable from physical exam, imaging, or operative records.

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)
02
icd10data.com
https://www.icd10data.com/ICD10CM/Codes/M00-M99/M91-M94/M91-/M91.22
03
cms.gov
https://www.cms.gov/medicare-coverage-database/view/article.aspx?articleId=53065&ver=76
04
aapc.com
https://www.aapc.com/codes/icd-10-codes/M91.22
05
cdek.pharmacy.purdue.edu
https://cdek.pharmacy.purdue.edu/icd10/M91.22/

Mira AI Scribe

Mira AI Scribe captures left-hip laterality, documented history of Legg-Calvé-Perthes disease, current symptoms (pain, ROM deficits, impingement), and imaging findings (femoral head flattening, Stulberg grade) from the encounter note — preventing downcoding to M91.20 (unspecified) and eliminating audit risk from missing the Applicable To documentation link between prior juvenile osteochondrosis and the current deformity.

See how Mira captures M91.22 documentation