# Recurrent Instability of the Patella (RIP)

RIP

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/rip`
HTML: https://magentlab.com/docs/rip
Markdown: https://magentlab.com/docs/rip.md

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

## What it computes

Sum the Hevesi 2019 Recurrent Instability of the Patella (RIP) score after first-time patellar dislocation from age, caller-assigned skeletal immaturity, trochlear dysplasia, and TT-TG/PL ratio, and return the published 0–5 point total and 10-year recurrent-instability band.

## When to use

When an agent has already assigned Hevesi 2019 RIP factors after a first-time patellar dislocation and needs the published point total and 10-year recurrent-instability band, not a surgical order and not a later PIP model.

## When not to use

- Not a medical device. magent does not read radiographs, assign Dejour grade, or measure TT-TG or patellar length.
- Trochlear dysplasia is a caller-assigned present/absent flag for Dejour A–D; magent does not grade trochlea.
- Age <25 scores 2; age ≥25 scores 0. Age 8–80 and TT-TG/PL 0.1–2.0 are magent clamps, not published ranges.
- This is Hevesi 2019 RIP only. Not Balcarek 2013 and not a later patellar-instability predictor (PIP) model. Does not use contralateral dislocation as a factor.
- Bands 0–1 low (10-year recurrent instability 0.0%), 2–3 intermediate (30.6%), and 4+ high (79.2%) follow Hevesi 2019. Not a reconstruction order.

## Formula

```
RIP = age_points (<25 → 2, ≥25 → 0) + skeletal_immature 1 + trochlear_dysplasia 1 + (tt_tg_pl_ratio ≥ 0.5 → 1); Hevesi 2019; max 5; risk 0-1 low, 2-3 intermediate, 4+ high (10-year recurrent instability 0.0% / 30.6% / 79.2%)
```

## Citation

[The Recurrent Instability of the Patella Score: A Statistically Based Model for Prediction of Long-Term Recurrence Risk After First-Time Dislocation](https://doi.org/10.1016/j.arthro.2018.09.017)
Hevesi M, Heidenreich MJ, Camp CL, Hewett TE, Stuart MJ, Dahm DL, Krych AJ
Arthroscopy. 2019;35(3):953-960
DOI: [10.1016/j.arthro.2018.09.017](https://doi.org/10.1016/j.arthro.2018.09.017)

## Worked example

### Adult, no RIP factors

Given: `age=40, skeletal_immature=false, trochlear_dysplasia=false, tt_tg_pl_ratio=0.3`

1. age 40 ≥ 25 → 0; skeletal_immature false → 0; trochlear_dysplasia false → 0; tt_tg_pl_ratio 0.3 < 0.5 → 0
2. Score = 0 (max 5); risk low (0–1; 10-year 0.0%)


### Age <25 with all three additional factors

Given: `age=16, skeletal_immature=true, trochlear_dysplasia=true, tt_tg_pl_ratio=0.5`

1. age 16 < 25 → 2; skeletal_immature true → 1; trochlear_dysplasia true → 1; tt_tg_pl_ratio 0.5 ≥ 0.5 → 1
2. Score = 5 (max 5); risk high (4+; 10-year 79.2%)


## Also searched as

- RIP score
- Recurrent Instability of the Patella
- Hevesi RIP
- first-time patellar dislocation
- patellar instability recurrence
- TT-TG/PL ratio
- trochlear dysplasia Dejour
- skeletal immaturity physes
- Hevesi 2019

## Parameters

- `age` (integer, required): Age in years (integer 8-80; magent clamp, not a published range). Hevesi 2019: age <25 → 2 points; age ≥25 → 0. magent does not assign age.
- `skeletal_immature` (boolean, required): Caller-assigned skeletal immaturity / open physes (Hevesi 2019). true scores 1. magent does not read radiographs or assign physeal status. true or false.
- `trochlear_dysplasia` (boolean, required): Caller-assigned trochlear dysplasia Dejour A–D present (Hevesi 2019). true scores 1. magent does not grade trochlea or read radiographs. true or false.
- `tt_tg_pl_ratio` (number, required): Caller-assigned tibial tubercle–trochlear groove / patellar length (TT-TG/PL) ratio (Hevesi 2019). ≥0.5 inclusive scores 1. Magent clamp 0.1-2.0, not a published range. magent does not measure TT-TG or patellar length.

## Bulk (POST)

POST the same path with a JSON items array. The first item is the GET unit; each additional item is $0.002. Invalid items return HTTP 400 before settlement.

Method: `POST /api/calc/rip`
Max items: 25
Price: unit_amount + extra_item_amount * (n - 1) (unit 5000 atomic, extra 2000 atomic)
Status: PREVIEW

- 1 to 25 items. Each item uses the same keys as the GET query parameters.
- POST of 1 item costs the same as GET. Lists longer than 25: chunk into multiple POSTs. Extra items still execute; do not pad dummy rows.
- 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:

```json
{
  "items": [
    {
      "age": "40",
      "skeletal_immature": "false",
      "trochlear_dysplasia": "false",
      "tt_tg_pl_ratio": "0.3"
    },
    {
      "age": "40",
      "skeletal_immature": "false",
      "trochlear_dysplasia": "false",
      "tt_tg_pl_ratio": "0.3"
    }
  ]
}
```

Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/rip

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/rip",
  "items": [
    {
      "components": [
        {
          "value": 40,
          "factor": "age",
          "points": 0,
          "present": false
        },
        {
          "factor": "skeletal_immature",
          "points": 0,
          "present": false
        },
        {
          "factor": "trochlear_dysplasia",
          "points": 0,
          "present": false
        },
        {
          "value": 0.3,
          "factor": "tt_tg_pl_ratio",
          "points": 0,
          "present": false
        }
      ],
      "age": 40,
      "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": "Hevesi M, Heidenreich MJ, Camp CL, Hewett TE, Stuart MJ, Dahm DL, Krych AJ",
        "doi": "10.1016/j.arthro.2018.09.017",
        "id": "hevesi-2019",
        "pmid": "30612768",
        "source": "Arthroscopy. 2019;35(3):953-960",
        "title": "The Recurrent Instability of the Patella Score: A Statistically Based Model for Prediction of Long-Term Recurrence Risk After First-Time Dislocation"
      },
      "formula": "rip",
      "formula_expression": "RIP = age_points (<25 → 2, ≥25 → 0) + skeletal_immature 1 + trochlear_dysplasia 1 + (tt_tg_pl_ratio ≥ 0.5 → 1); Hevesi 2019; max 5; risk 0-1 low, 2-3 intermediate, 4+ high (10-year recurrent instability 0.0% / 30.6% / 79.2%)",
      "max_score": 5,
      "score": 0,
      "risk": "low",
      "skeletal_immature": false,
      "trochlear_dysplasia": false,
      "tt_tg_pl_ratio": 0.3
    },
    {
      "components": [
        {
          "value": 40,
          "factor": "age",
          "points": 0,
          "present": false
        },
        {
          "factor": "skeletal_immature",
          "points": 0,
          "present": false
        },
        {
          "factor": "trochlear_dysplasia",
          "points": 0,
          "present": false
        },
        {
          "value": 0.3,
          "factor": "tt_tg_pl_ratio",
          "points": 0,
          "present": false
        }
      ],
      "age": 40,
      "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": "Hevesi M, Heidenreich MJ, Camp CL, Hewett TE, Stuart MJ, Dahm DL, Krych AJ",
        "doi": "10.1016/j.arthro.2018.09.017",
        "id": "hevesi-2019",
        "pmid": "30612768",
        "source": "Arthroscopy. 2019;35(3):953-960",
        "title": "The Recurrent Instability of the Patella Score: A Statistically Based Model for Prediction of Long-Term Recurrence Risk After First-Time Dislocation"
      },
      "formula": "rip",
      "formula_expression": "RIP = age_points (<25 → 2, ≥25 → 0) + skeletal_immature 1 + trochlear_dysplasia 1 + (tt_tg_pl_ratio ≥ 0.5 → 1); Hevesi 2019; max 5; risk 0-1 low, 2-3 intermediate, 4+ high (10-year recurrent instability 0.0% / 30.6% / 79.2%)",
      "max_score": 5,
      "score": 0,
      "risk": "low",
      "skeletal_immature": false,
      "trochlear_dysplasia": false,
      "tt_tg_pl_ratio": 0.3
    }
  ]
}
```

## Response fields

- `formula` (string): rip
- `formula_expression` (string): Exact expression used
- `score` (integer): Hevesi 2019 RIP points 0-5. Not a surgical order.
- `max_score` (integer): 5
- `risk` (string): Hevesi 2019 10-year recurrent-instability band: low (0-1, 0.0%), intermediate (2-3, 30.6%), or high (4+, 79.2%). Not a reconstruction order.
- `age` (integer): Age in years used (8-80)
- `skeletal_immature` (boolean): Caller-assigned skeletal immaturity / open physes used
- `trochlear_dysplasia` (boolean): Caller-assigned trochlear dysplasia (Dejour A–D present) used
- `tt_tg_pl_ratio` (number): Caller-assigned TT-TG/PL ratio used
- `components` (array): Per-factor Hevesi 2019 RIP points
- `citation` (object): Hevesi et al. Arthroscopy 2019 citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "components": [
    {
      "value": 40,
      "factor": "age",
      "points": 0,
      "present": false
    },
    {
      "factor": "skeletal_immature",
      "points": 0,
      "present": false
    },
    {
      "factor": "trochlear_dysplasia",
      "points": 0,
      "present": false
    },
    {
      "value": 0.3,
      "factor": "tt_tg_pl_ratio",
      "points": 0,
      "present": false
    }
  ],
  "age": 40,
  "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": "Hevesi M, Heidenreich MJ, Camp CL, Hewett TE, Stuart MJ, Dahm DL, Krych AJ",
    "doi": "10.1016/j.arthro.2018.09.017",
    "id": "hevesi-2019",
    "pmid": "30612768",
    "source": "Arthroscopy. 2019;35(3):953-960",
    "title": "The Recurrent Instability of the Patella Score: A Statistically Based Model for Prediction of Long-Term Recurrence Risk After First-Time Dislocation"
  },
  "formula": "rip",
  "formula_expression": "RIP = age_points (<25 → 2, ≥25 → 0) + skeletal_immature 1 + trochlear_dysplasia 1 + (tt_tg_pl_ratio ≥ 0.5 → 1); Hevesi 2019; max 5; risk 0-1 low, 2-3 intermediate, 4+ high (10-year recurrent instability 0.0% / 30.6% / 79.2%)",
  "max_score": 5,
  "score": 0,
  "risk": "low",
  "skeletal_immature": false,
  "trochlear_dysplasia": false,
  "tt_tg_pl_ratio": 0.3
}
```

## Errors

- HTTP 400 `invalid_rip`: RIP-score inputs must be numeric age plus caller-assigned skeletal immaturity, trochlear dysplasia, and TT-TG/PL as used in Hevesi 2019. Returned before settlement; you are not charged.
- HTTP 400 `invalid_items`: POST body must be a JSON object with only an items array Returned before settlement; you are not charged.
- HTTP 400 `invalid_item_count`: items must be an array of 1 to 25 objects Returned before settlement; you are not charged.
- HTTP 400 `invalid_item`: each items entry must be a JSON object Returned before settlement; you are not charged.

Shared HTTP 402 and 503: https://magentlab.com/docs/payments

## Related tools

- [Mirels](https://magentlab.com/docs/mirels) — Sum the Mirels 1989 score for diagnosing impending pathologic fractures in long-bone metastatic disease from four caller-assigned items and return the published 4–12 integer total and band (≤7 / 8 / ≥9). Not an operative order and not SINS.
- [MESS](https://magentlab.com/docs/mess) — Compute the Johansen 1990 Mangled Extremity Severity Score from caller-assigned skeletal/soft-tissue, limb ischemia, shock, and age integers, doubling ischemia when time exceeds 6 hours, and return the published 0-6 / ≥7 band.

## Payment

Unpaid requests return HTTP 402 even if query parameters or POST items are missing or invalid, so CDP and agents can index the path. After a PAYMENT-SIGNATURE, 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.

- GET the tool with Accept: application/json (do not send Accept: text/html unless you want the human paywall).
- HTTP 402 means you have not paid. Decode the base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote.
- Sign accepts[0] (exact, EIP-3009) with validBefore = now + maxTimeoutSeconds (600 seconds), or accepts[1] (batch-settlement deposit/voucher) on product GET. Ping and POST {items} stay exact. Magent retries transient facilitator 429/5xx before answering.
- Retry the same URL with PAYMENT-SIGNATURE (base64 JSON of accepted and payload). Magent attaches canonical extensions.bazaar on CDP verify/settle; echoing 402 bazaar is optional.
- Success is HTTP 200 JSON plus PAYMENT-RESPONSE. exact settles before the tool. batch-settlement verifies (and deposit-settles) before the tool and commits the charge after HTTP 2xx. HTTP 503: retry the same PAYMENT-SIGNATURE. Mint a new exact nonce only after a new HTTP 402.

- offered `exact` on eip155:8453: Fixed-price USDC on Base. The buyer authorizes the advertised amount (EIP-3009). magent settles before the tool runs (paymentFlow upfront). extra.assetTransferMethod=eip3009 extra.paymentFlow=upfront.
- offered `batch-settlement` on eip155:8453: Payment-channel vouchers claimed later in batches. Exact stays accepts[0]. Same-path POST {items} is still exact. extra.assetTransferMethod=eip3009 extra.paymentFlow=authorization.

- not offered `upto`: Not offered. Usage-based: buyer authorizes a ceiling, seller settles the actual amount after work. Reserved for a future metered tool. Not for current calculators or code search.

Same-path POST {items} is still scheme exact: one EIP-3009 authorization for GET unit plus $0.002 per extra item. That is not x402 batch-settlement (payment channels / vouchers).

Shared HTTP 402 and 503 table: https://magentlab.com/docs/payments

Stdio MCP (one process per host): https://magentlab.com/docs/mcp

## Guarantees

- HTTP 402 is unpaid, including a missing query. After PAYMENT-SIGNATURE, invalid parameters return HTTP 400 before settlement. You are not charged. HTTP 402 never includes the tool JSON.
- exact: settlement finishes before the tool (paymentFlow upfront). batch-settlement: verify/deposit before the tool; chargedCumulativeAmount commits after HTTP 2xx. 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.