ICD-10-CM · Knee

M17.31

Post-traumatic osteoarthritis of the right knee arising as a sequela of prior joint injury, coded as a unilateral condition with confirmed right-side laterality.

Verified May 8, 2026 · 6 sources ↓

Status: Billable
Chapter: 13
Related CPT: 17
Region: Knee

Drawn from CDCICD10DataAAPCCMSAAHKS

Documentation tips

What should appear in the chart to support M17.31.

Source · Editorial brief grounded in 6 cited references ↓

Explicitly name the inciting traumatic event (e.g., 'OA right knee secondary to ACL tear sustained in 2018') — a vague history of 'prior knee injury' is insufficient to distinguish M17.31 from primary OA.
Record Kellgren-Lawrence grade or describe radiographic findings (joint space narrowing, osteophytes, subchondral sclerosis) to support medical necessity for any planned procedure.
Document laterality by name ('right knee') every encounter — do not rely on prior notes or problem-list entries to carry the specificity.
If the patient had prior knee surgery (meniscectomy, ACL reconstruction, ORIF), state the surgical history and the provider's clinical judgment linking that surgery to current degenerative changes.
For injection encounters, document current pain level, functional limitation, and conservative care history (PT, NSAIDs) to support medical necessity alongside M17.31.

Related CPT procedures

Procedure codes commonly billed with M17.31. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

27447 $1,159.35

Knee replacement surgery addressing both the medial and lateral tibiofemoral compartments, with or without resurfacing of the patella.

27446 $1,047.45

Arthroplasty of the knee involving resurfacing of the condyle and tibial plateau in a single tibiofemoral compartment — medial OR lateral, not both.

27487 $1,574.52

Revision total knee arthroplasty with replacement of both the femoral and tibial components, with or without the use of allograft tissue.

27486 $1,274.91

Revision of a total knee arthroplasty involving a single component, performed with or without the use of donor bone graft material.

27440 $745.84

Surgical reconstruction of the tibial component of the knee joint to relieve pain and restore function in patients with a damaged or deteriorated knee.

27331 $459.60

Open arthrotomy of the knee joint for exploration, biopsy, or removal of loose or foreign bodies.

27332 $614.91

Open arthrotomy of the knee with excision of the medial or lateral semilunar cartilage (meniscectomy) through a formal open incision.

27333 $564.48

Open arthrotomy with removal of one or both semilunar cartilages (menisci) from the medial and/or lateral compartments of the knee joint.

20610 $68.81

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

73564 $49.43

Radiologic examination of the knee consisting of four or more views, including oblique and tunnel projections, for a complete diagnostic workup.

73562 $42.42

Three-view radiographic examination of the knee joint, capturing anteroposterior, lateral, and a third angle such as a sunrise or oblique view.

73560 $34.40

Radiologic examination of the knee joint, one or two views, unilateral.

27570 $149.97

Manipulation of the knee joint performed under general anesthesia, including application of traction or other fixation devices as needed to restore range of motion.

29877 $586.85

Knee arthroscopy with surgical debridement or shaving of articular cartilage (chondroplasty) — does not include meniscal work.

29881 $515.71

Knee arthroscopy with surgical removal of the medial or lateral meniscus, including any associated cartilage shaving or debridement performed in the same or a separate compartment.

29880 $533.08

Arthroscopic knee surgery removing both the medial and lateral menisci, including any meniscal shaving and chondroplasty of articular cartilage in any compartment when performed.

27370 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M17.31 and adjacent codes.

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

Assigning M17.11 (primary OA, right knee) when the note documents a trauma history — if the provider links the OA to prior injury, M17.31 is required, not M17.11.
Using the non-billable parent code M17.3 instead of drilling to the fifth character M17.31; M17.3 will reject for specificity on most payer edits.
Coding M17.31 when the provider documents bilateral post-traumatic OA — bilateral involvement requires M17.2, not two units of M17.31.
Omitting the causal trauma link in the note and then coding M17.31 anyway — without documented etiology the audit trail does not support post-traumatic classification.
Confusing M17.31 with M17.5 (other unilateral secondary OA) — secondary OA from non-traumatic causes (inflammatory arthritis, metabolic disease) belongs in M17.5, not M17.31.

Clinical context

Source · Editorial summary grounded in 6 cited references ↓

M17.31 is the correct code when degenerative joint disease of the right knee is directly attributable to a prior traumatic event — fracture, ligament tear, meniscal injury, dislocation, or surgical trauma — rather than idiopathic degeneration. The etiology must be documented explicitly; the provider must link the current arthritic condition to a specific past injury or procedure. If that causal link is not stated, default to primary OA (M17.11 for right knee) or unspecified OA (M17.9).

Laterality is locked at the fifth character: M17.31 = right, M17.32 = left, M17.30 = unspecified. Never use M17.30 when the operative or clinical note identifies the right knee — specificity is both achievable and required. For bilateral post-traumatic OA, step up to M17.2 instead.

This code groups into MS-DRG 553/554 (Bone Diseases and Arthropathies with/without MCC) for inpatient claims. On the outpatient side it supports medical necessity for procedures ranging from viscosupplementation injections to total knee arthroplasty. Secondary OA codes (M17.4, M17.5) cover non-traumatic causes such as metabolic or inflammatory conditions; M17.31 is reserved strictly for trauma-origin arthritis.

Sibling codes

Other billable codes under M17.3 (laterality / anatomic variants).

M17.32

Unilateral post-traumatic osteoarthritis, left knee

M17.30

Unilateral post-traumatic osteoarthritis, unspecified knee

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 6 cited references ↓

01What makes OA qualify as 'post-traumatic' for M17.31 rather than primary OA coded as M17.11?

The provider must document a direct causal link between a prior injury (fracture, ligament tear, meniscal damage, dislocation) or surgical trauma and the current degenerative changes. If the note says 'OA, no prior trauma,' use M17.11. If it says 'OA following 2019 tibial plateau fracture,' use M17.31.

02Can M17.31 and M17.11 be coded together on the same claim?

Only if the patient has post-traumatic OA in one knee and primary OA in the other. You cannot assign both codes for the same right knee on the same encounter — pick the type supported by the documented etiology.

03The patient has post-traumatic OA in both knees. Which code do I use?

Use M17.2 (Bilateral post-traumatic osteoarthritis of knee) instead of M17.31. M17.31 is strictly unilateral right-knee; bilateral disease has its own code at M17.2.

04Is a prior arthroscopy or meniscectomy sufficient to justify M17.31?

Yes, provided the treating provider documents that the post-surgical joint changes are the cause of the current OA. Surgical trauma counts as trauma for coding purposes, but the causal statement must appear in the current note — not just in old operative reports.

05Does M17.31 require an external cause code for the original injury?

No. External cause codes are voluntary for most payers when coding established OA. However, some trauma registries and workers' compensation payers may require an external cause code documenting the mechanism of the original injury.

06What is the fallback code if laterality for post-traumatic knee OA is not documented?

Use M17.30 (Unilateral post-traumatic osteoarthritis, unspecified knee). Query the provider for laterality before claim submission if at all possible — M17.30 is a documentation deficiency, not a preferred code.

07Does M17.31 support medical necessity for total knee arthroplasty (CPT 27447)?

Yes. AAHKS and CMS cross-reference materials list post-traumatic OA codes, including M17.31, as accepted diagnoses supporting CPT 27447. Confirm with the specific payer's LCD/NCD, as coverage criteria can vary.

Sources & references

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

Mira AI Scribe

Mira captures the right-knee laterality, the provider's explicit causal statement linking current OA to a prior traumatic event or surgery, imaging findings (KL grade or descriptive X-ray/MRI findings), and conservative care history from the encounter note. This prevents assignment of the less-specific M17.30 or incorrect use of primary OA code M17.11, both of which create audit exposure and can trigger medical-necessity denials for arthroplasty or injection procedures.

See how Mira captures M17.31 documentation