ICD-10-CM · Hip

M16.6

M16.6 classifies bilateral hip osteoarthritis that is secondary in origin but does not arise from hip dysplasia or prior trauma — the two secondary causes assigned their own dedicated codes (M16.2 and M16.4).

Verified May 8, 2026 · 5 sources ↓

Status: Billable
Chapter: 13
Related CPT: 9
Region: Hip

Drawn from CDCicd10data.com 2026CMSAAPC

Documentation tips

What should appear in the chart to support M16.6.

Source · Editorial brief grounded in 5 cited references ↓

Document both hips as affected — M16.6 is explicitly bilateral; a single-hip finding requires M16.7 instead.
Identify and code the underlying secondary cause (e.g., metabolic disorder, systemic disease) as an additional diagnosis to substantiate the 'secondary' classification.
Specify why the OA is not post-traumatic and not dysplasia-related; if either of those etiologies applies, the correct code shifts to M16.4 or M16.2.
Include bilateral hip imaging results (joint space narrowing, osteophytes, subchondral sclerosis) with Kellgren-Lawrence grade or equivalent radiographic description for both sides.
Record prior conservative treatment history (PT, NSAIDs, intra-articular injections) when M16.6 supports surgical authorization such as bilateral total hip arthroplasty.

Related CPT procedures

Procedure codes commonly billed with M16.6. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

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.

27132 $1,504.04

Conversion of a previously operated hip — any prior surgery except total hip arthroplasty — to a complete total hip arthroplasty, replacing both femoral and acetabular components, with or without bone graft.

27134 $1,695.43

Revision of total hip arthroplasty involving replacement of both the femoral and acetabular components in a single operative session.

27236 $1,089.87

Open treatment of a proximal femoral fracture at the femoral neck, using internal fixation hardware or prosthetic replacement to stabilize the fracture site.

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.

20610 $68.81

Aspiration and/or injection of a major joint or bursa (shoulder, hip, knee, or subacromial bursa) performed without ultrasound guidance.

27000 $362.40

Percutaneous tenotomy of the hip adductor muscle, performed through a small puncture rather than an open incision.

27299 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M16.6 and adjacent codes.

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

Defaulting to M16.6 when the OA is actually post-traumatic (use M16.4) or dysplasia-related (use M16.2) — each has its own bilateral code and must not be collapsed into M16.6.
Using M16.6 for unilateral secondary OA of unknown laterality — if only one hip is documented or laterality is unclear, M16.7 (unilateral) or M16.9 (unspecified) applies, not M16.6.
Failing to code the underlying systemic or metabolic condition that makes this OA 'secondary,' leaving the claim without clinical justification for the secondary classification.
Upcoding from M16.9 to M16.6 without documentation of a specific secondary etiology — the secondary designation requires a documentable causative condition, not just severity.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Use M16.6 when the patient has degenerative joint disease in both hips and the osteoarthritis is attributable to a secondary cause other than hip dysplasia or post-traumatic injury. Common underlying etiologies captured here include metabolic conditions (e.g., acromegaly, hemochromatosis), inflammatory arthropathy sequelae, avascular necrosis, or other systemic conditions that accelerate cartilage breakdown bilaterally. The 'other' qualifier is what separates M16.6 from M16.2 (bilateral dysplasia-related) and M16.4 (bilateral post-traumatic).

Within the M16 category, the secondary codes (M16.6 and M16.7) sit between the post-traumatic codes and M16.9 (unspecified). If only one hip is involved with this 'other secondary' etiology, use M16.7 instead. If the secondary cause is documented as trauma, use M16.4; if dysplasia, use M16.2. M16.6 requires that both hips are affected — do not use it when documentation supports only unilateral involvement.

Because M16.6 is a catch-all for secondary bilateral hip OA outside of two named etiologies, payer scrutiny is higher than for primary OA codes. The underlying condition driving the secondary OA should be coded additionally where possible. Thorough documentation of the causative condition, bilateral imaging findings, and the clinical link between the underlying disease and joint degeneration is essential for audit defense and accurate risk adjustment.

Sibling codes

Other billable codes under M16 (laterality / anatomic variants).

M16.7

Other unilateral secondary osteoarthritis of hip

M16.9

Osteoarthritis of hip, unspecified

M16.4

Bilateral post-traumatic osteoarthritis of hip

M16.0

Bilateral primary osteoarthritis of hip

M16.2

Bilateral osteoarthritis resulting from hip dysplasia

Frequently asked questions

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

01What makes hip OA 'secondary' for M16.6 versus primary (M16.0)?

Secondary OA results from an identifiable underlying condition — metabolic disease, inflammatory arthropathy, avascular necrosis, or similar — that accelerates joint degeneration. Primary OA (M16.0) is idiopathic; no specific causative condition is identified. The provider must document the secondary etiology to support M16.6.

02If the bilateral secondary OA is from a prior hip fracture on both sides, should I still use M16.6?

No. Post-traumatic bilateral hip OA has its own code: M16.4. M16.6 is explicitly for secondary causes other than trauma and other than dysplasia. Misassigning M16.6 when trauma is the documented cause is a coding error.

03Can M16.6 be used when one hip is worse than the other but both are involved?

Yes. Bilateral means both joints are affected, not that they are equally severe. Document the severity in each hip separately; M16.6 still applies as long as both hips have secondary OA of this type.

04Should I code the underlying condition separately when using M16.6?

Yes. Code the causative condition (e.g., acromegaly, hemochromatosis, or another systemic disease) as an additional diagnosis. This substantiates the secondary classification and reduces audit risk. The ICD-10-CM tabular may include a 'code also' or 'code first' instruction at the parent category level.

05Is M16.6 appropriate when the provider documents 'bilateral hip OA' without specifying primary or secondary?

No. Unspecified bilateral hip OA without a documented secondary cause maps to M16.9 (osteoarthritis of hip, unspecified) or M16.0 if the context clearly supports primary OA. Use M16.6 only when the secondary etiology is explicitly documented.

06What CPT codes commonly pair with M16.6 in an orthopedic setting?

Bilateral total hip arthroplasty (27130 per side, or 27132 for revision), diagnostic hip X-rays (73521, 73523), and therapeutic joint injections (20610) are the most common procedural pairings when M16.6 supports surgical or interventional management.

Sources & references

Editorial content was developed using the following public sources. Last verified May 8, 2026.

01CDC ICD-10-CM Tabular List 2026 — https://www.cdc.gov/nchs/icd/icd-10-cm/index.html
02icd10data.com 2026 ICD-10-CM Diagnosis Code M16.6 — https://www.icd10data.com/ICD10CM/Codes/M00-M99/M15-M19/M16-/M16.6
03CMS ICD-10 Clinical Concepts for Orthopedics — https://www.cms.gov/medicare/coding/icd10/downloads/icd10clinicalconceptsorthopedics1.pdf
04CMS FY2025 ICD-10-CM Official Coding Guidelines — https://www.cms.gov/files/document/fy-2025-icd-10-cm-coding-guidelines.pdf
05AAPC Codify ICD-10 Code M16.6 — https://www.aapc.com/codes/icd-10-codes/M16.6

Mira AI Scribe

The Mira AI Scribe captures bilateral hip involvement, the identified secondary causative condition (metabolic, inflammatory, or systemic), bilateral imaging findings with graded joint space narrowing, and history of conservative management — all from the encounter note. This prevents downcoding to M16.9 (unspecified), eliminates audit exposure from undocumented secondary etiology, and supports payer authorization for bilateral hip procedures.

See how Mira captures M16.6 documentation