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Ottawa knee rule

Apply the Stiell 1995 Ottawa knee rule and return whether a knee x-ray series is indicated from age and caller-assigned bone tenderness, flexion, and weight-bearing findings.

LIVE $0.005 USDC GET /api/calc/ottawa_knee

Markdown: /docs/ottawa-knee.md · Canonical: https://magentlab.com/docs/ottawa-knee

Not a medical device. Not a diagnosis, dose, or listing recommendation.

What it computes

Apply the Stiell 1995 Ottawa knee rule and return whether a knee x-ray series is indicated from age and caller-assigned bone tenderness, flexion, and weight-bearing findings.

When to use

When an agent has caller-assigned findings after blunt knee injury and needs the published knee-series radiography rule, not the Ottawa ankle or Pittsburgh knee rule.

When not to use

• Not a diagnosis of fracture. magent does not examine the knee.
• This tool is the Ottawa knee rule only. It is not the Ottawa ankle or foot rule and not the Pittsburgh knee rule.
• Isolated patellar tenderness is caller-applied. magent does not infer isolation from other flags.
• Inability to bear weight means both immediately after injury and in the emergency department (four steps). One alone is not enough.
• Adult derivation as published (age 18-120). Age 55 or older meets the age criterion; 54 does not.

Formula

Knee x-ray indicated iff age >= 55 or fibular_head_tenderness or isolated_patellar_tenderness or flexion_less_than_90 or (unable_to_bear_weight_immediately and unable_to_bear_weight_in_ed)

Citation

Title

Derivation of a decision rule for the use of radiography in acute knee injuries

Authors

Stiell IG, Greenberg GH, Wells GA, et al.

Source

Ann Emerg Med. 1995;26(4):405-413

DOI

10.1016/S0196-0644(95)70106-0

Worked example

Also searched as

• Ottawa knee rule
• Ottawa Knee Rules
• Stiell knee rule
• knee x-ray decision rule
• OKR knee
• Ottawa radiography knee
• Stiell 1995 knee
• fibular head x-ray rule

Try

Opens the live endpoint. Unpaid browser requests show the paywall; agents should send Accept: application/json.

/api/calc/ottawa_knee?age=40&fibular_head_tenderness=false&isolated_patellar_tenderness=false&flexion_less_than_90=false&unable_to_bear_weight_immediately=false&unable_to_bear_weight_in_ed=false

Full URL: https://api.magentlab.com/api/calc/ottawa_knee?age=40&fibular_head_tenderness=false&isolated_patellar_tenderness=false&flexion_less_than_90=false&unable_to_bear_weight_immediately=false&unable_to_bear_weight_in_ed=false

Call

Expect HTTP 402 until you retry with PAYMENT-SIGNATURE. Incomplete query params return HTTP 400 before any quote or charge.

curl -i -H "Accept: application/json" "https://api.magentlab.com/api/calc/ottawa_knee?age=40&fibular_head_tenderness=false&isolated_patellar_tenderness=false&flexion_less_than_90=false&unable_to_bear_weight_immediately=false&unable_to_bear_weight_in_ed=false"

Parameters

Bulk (POST)

POST the same path with a JSON items array. Price is n times the GET unit. Invalid items return HTTP 400 before settlement.

POST /api/calc/ottawa_knee Max 25 unit_amount * n PREVIEW

• 1 to 25 items. Each item uses the same keys as the GET query parameters.
• The first invalid item fails the whole request (index in the 400 JSON). You are not charged.
• HTTP 200 is {count, path, items}. Each items[i] is the GET 200 body for that row.
• Catalog misses (empty matches, found=false) stay paid 200s inside that slot.
• x402 resource URL is this path plus n and body_sha256. Browsers that prefer text/html get the same paywall as GET; Pay retries POST with the same items.

Example request (fixture)

{
  "items": [
    {
      "age": "40",
      "fibular_head_tenderness": "false",
      "flexion_less_than_90": "false",
      "isolated_patellar_tenderness": "false",
      "unable_to_bear_weight_immediately": "false",
      "unable_to_bear_weight_in_ed": "false"
    },
    {
      "age": "40",
      "fibular_head_tenderness": "false",
      "flexion_less_than_90": "false",
      "isolated_patellar_tenderness": "false",
      "unable_to_bear_weight_immediately": "false",
      "unable_to_bear_weight_in_ed": "false"
    }
  ]
}

Open bulk paywall →

Opens a two-item fixture on the API host. Unpaid browsers get the same MetaMask paywall as GET; Pay retries POST with those items.

Example 200 (fixture)

{
  "count": 2,
  "path": "/api/calc/ottawa_knee",
  "items": [
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Stiell IG, Greenberg GH, Wells GA, et al.",
        "doi": "10.1016/S0196-0644(95)70106-0",
        "id": "stiell-1995",
        "source": "Ann Emerg Med. 1995;26(4):405-413",
        "title": "Derivation of a decision rule for the use of radiography in acute knee injuries"
      },
      "formula": "ottawa_knee",
      "formula_expression": "Knee x-ray indicated iff age >= 55 or fibular_head_tenderness or isolated_patellar_tenderness or flexion_less_than_90 or (unable_to_bear_weight_immediately and unable_to_bear_weight_in_ed)",
      "age_years": 40,
      "criteria": [
        {
          "value": 40,
          "factor": "age_ge_55",
          "met": false
        },
        {
          "factor": "fibular_head_tenderness",
          "met": false
        },
        {
          "factor": "isolated_patellar_tenderness",
          "met": false
        },
        {
          "factor": "flexion_less_than_90",
          "met": false
        },
        {
          "factor": "unable_to_bear_weight_both",
          "met": false,
          "unable_to_bear_weight_immediately": false,
          "unable_to_bear_weight_in_ed": false
        }
      ],
      "xray_indicated": false
    },
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Stiell IG, Greenberg GH, Wells GA, et al.",
        "doi": "10.1016/S0196-0644(95)70106-0",
        "id": "stiell-1995",
        "source": "Ann Emerg Med. 1995;26(4):405-413",
        "title": "Derivation of a decision rule for the use of radiography in acute knee injuries"
      },
      "formula": "ottawa_knee",
      "formula_expression": "Knee x-ray indicated iff age >= 55 or fibular_head_tenderness or isolated_patellar_tenderness or flexion_less_than_90 or (unable_to_bear_weight_immediately and unable_to_bear_weight_in_ed)",
      "age_years": 40,
      "criteria": [
        {
          "value": 40,
          "factor": "age_ge_55",
          "met": false
        },
        {
          "factor": "fibular_head_tenderness",
          "met": false
        },
        {
          "factor": "isolated_patellar_tenderness",
          "met": false
        },
        {
          "factor": "flexion_less_than_90",
          "met": false
        },
        {
          "factor": "unable_to_bear_weight_both",
          "met": false,
          "unable_to_bear_weight_immediately": false,
          "unable_to_bear_weight_in_ed": false
        }
      ],
      "xray_indicated": false
    }
  ]
}

Response

Example JSON

Machine form of the same example. Frozen fixture. Not a live lookup.

{
  "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
  "citation": {
    "authors": "Stiell IG, Greenberg GH, Wells GA, et al.",
    "doi": "10.1016/S0196-0644(95)70106-0",
    "id": "stiell-1995",
    "source": "Ann Emerg Med. 1995;26(4):405-413",
    "title": "Derivation of a decision rule for the use of radiography in acute knee injuries"
  },
  "formula": "ottawa_knee",
  "formula_expression": "Knee x-ray indicated iff age >= 55 or fibular_head_tenderness or isolated_patellar_tenderness or flexion_less_than_90 or (unable_to_bear_weight_immediately and unable_to_bear_weight_in_ed)",
  "age_years": 40,
  "criteria": [
    {
      "value": 40,
      "factor": "age_ge_55",
      "met": false
    },
    {
      "factor": "fibular_head_tenderness",
      "met": false
    },
    {
      "factor": "isolated_patellar_tenderness",
      "met": false
    },
    {
      "factor": "flexion_less_than_90",
      "met": false
    },
    {
      "factor": "unable_to_bear_weight_both",
      "met": false,
      "unable_to_bear_weight_immediately": false,
      "unable_to_bear_weight_in_ed": false
    }
  ],
  "xray_indicated": false
}

Client errors (HTTP 400)

Invalid params return 400 without charge. Shared HTTP 402 and 503 meanings: Payments.

Related tools

• Ottawa ankle rule — Apply the Stiell 1992 Ottawa ankle rule and return whether an ankle x-ray series is indicated from caller-assigned malleolar pain, malleolar bone tenderness, and inability to bear weight.

Payment

Required query parameters must be present and valid. Invalid params return HTTP 400 JSON before settlement. magent does not charge. Fix the params, then request a new 402 quote for that complete URL. Catalog misses (empty matches, found=false) are valid paid 200s. Unpaid valid requests return HTTP 402 with a base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote: retry the same PAYMENT-SIGNATURE. Full handshake and shared payment errors: Payments. Stdio MCP: /docs/mcp.

Guarantees

• Invalid query parameters return HTTP 400 before settlement. You are not charged.
• Settlement finishes before the tool executes (paymentFlow upfront). Uncertain or failed settlement fails closed (HTTP 503). Retry the same PAYMENT-SIGNATURE.
• HTTP 402 is unpaid only. Do not sign a second authorization because of a 503.
• Execution is timeout-bounded and concurrency-capped.
• Calculator inputs are stored encrypted for allowlisted operators (Magent Console). They are not in public logs, SSH lookups, catalog, or rollups. Request logs store path without query.