Lower Extremity Functional Scale

Status: stable Category: function Added: 2026-04-20 Last reviewed: 2026-04-21

Summary

The Lower Extremity Functional Scale (LEFS) is Trinity's lower-limb function instrument. Twenty items, each scored 0–4, summing to a 0–80 total. Higher scores indicate better function. This is the opposite sign convention from oswestry, neck_disability, and quick_dash, where higher means more disability.

⚠ Sign convention: higher = better

Unlike most disability instruments in the catalog, the LEFS is a function instrument — the maximum score (80) represents full function, and 0 represents total loss of function.

This matters for callers who consume multiple function scores and apply rules like "flag subjects whose function score exceeds a threshold." A threshold of 40 against ODI means subjects with severe disability; against LEFS it means subjects with moderate-to-severe disability (since 41–60 is mild on LEFS). Flipping that sign will produce the wrong set.

Read the band field when mixing instruments — band names (minimal, mild, moderate, severe) have consistent meaning across instruments, so they are the safer cross-instrument signal than the raw numeric score.

Resource identity

Field	Value
Category	function
Resource	lower_extremity_function
Instrument ID	lower_extremity_function
Rubric version	1.0.0
Path prefix	/api/function/lower_extremity_function

Operations

Operation	Method	Path	Contract
Questions	GET	/api/function/lower_extremity_function/questions	patterns-questions.md
Score	POST	/api/function/lower_extremity_function/score	patterns-score.md

Items

Twenty items, each on a 0–4 scale.

ID	Prompt (paraphrased)
item_1	Usual work, housework, or school activities.
item_2	Usual hobbies, recreational, or sporting activities.
item_3	Getting into or out of the bath.
item_4	Walking between rooms.
item_5	Putting on your shoes or socks.
item_6	Squatting.
item_7	Lifting an object from the floor.
item_8	Performing light activities around the home.
item_9	Performing heavy activities around the home.
item_10	Getting into or out of a car.
item_11	Walking two blocks.
item_12	Walking a mile.
item_13	Going up or down 10 stairs.
item_14	Standing for 1 hour.
item_15	Sitting for 1 hour.
item_16	Running on even ground.
item_17	Running on uneven ground.
item_18	Making sharp turns while running fast.
item_19	Hopping.
item_20	Rolling over in bed.

Answer choices per item (note: 0 is the worst response):

Value	Label
0	Extreme difficulty / unable
1	Quite a bit of difficulty
2	Moderate difficulty
3	A little bit of difficulty
4	No difficulty

Scoring

Field	Value
Method	simple_sum over all twenty items.
Score range	0 – 80.

Bands

Band	Range (inclusive)	Clinical meaning
severe	0 – 20	Severe functional limitation.
moderate	21 – 40	Moderate functional limitation.
mild	41 – 60	Mild functional limitation.
minimal	61 – 80	Minimal functional limitation.

Note the band order: severe is at the low end, minimal is at the high end — consistent with the "higher = better function" sign convention.

Required items

All twenty items are required for a strict /score call.

Worked example

Every item answered with 2 ("moderate difficulty"). See quickstart.md for per-language scaffolding and patterns-score.md for the shared /score contract.

Send:

POST /api/function/lower_extremity_function/score HTTP/1.1
Host: engine.tripod-health.com
apikey: $ENGINE_API_KEY
Content-Type: application/json
X-Request-ID: docs-lower_extremity_function-score-basic

{
  "responses": {
    "item_1": 2, "item_2": 2, "item_3": 2, "item_4": 2, "item_5": 2,
    "item_6": 2, "item_7": 2, "item_8": 2, "item_9": 2, "item_10": 2,
    "item_11": 2, "item_12": 2, "item_13": 2, "item_14": 2, "item_15": 2,
    "item_16": 2, "item_17": 2, "item_18": 2, "item_19": 2, "item_20": 2
  }
}

Receive (200 OK):

{
  "instrument": "lower_extremity_function",
  "category": "function",
  "finding": {
    "algorithm_id": "lower_extremity_function",
    "algorithm_version": "1.0.0",
    "score": 40,
    "band": "moderate",
    "raw": {
      "rubric_version": "1.0.0",
      "responded_items": 20
    },
    "context": null,
    "imputed": false,
    "sd": null,
    "prior_source": null
  },
  "confidence": {
    "overall": 1,
    "tier": "high",
    "breakdown": {
      "input_completeness": 1,
      "imputation_variance": null,
      "model_certainty": null
    }
  },
  "recommendations": null,
  "depth": "basic",
  "catalog_version": "0.13.0",
  "request_id": "docs-lower_extremity_function-score-basic",
  "timestamp": "2026-04-21T23:14:55.913104+00:00"
}

Computation: sum = 20 × 2 = 40, top of the moderate band (21–40). Every item at 4 (no difficulty) yields 80 (minimal); every item at 0 yields 0 (severe). Remember LEFS is higher = better; the band semantics invert compared to disability-index instruments.

Calling in your language

curl

curl -sS -X POST "https://engine.tripod-health.com/api/function/lower_extremity_function/score" \
  -H "apikey: $ENGINE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"responses":{"item_1":2,"item_2":2,"item_3":2,"item_4":2,"item_5":2,"item_6":2,"item_7":2,"item_8":2,"item_9":2,"item_10":2,"item_11":2,"item_12":2,"item_13":2,"item_14":2,"item_15":2,"item_16":2,"item_17":2,"item_18":2,"item_19":2,"item_20":2}}'

Python (requests)

# Uses the call() helper from quickstart.md.
responses = {f"item_{i}": 2 for i in range(1, 21)}
result = call("POST", "/api/function/lower_extremity_function/score",
              {"responses": responses})
print(result["finding"]["score"], result["finding"]["band"])

Node.js (native fetch)

// Uses the call() helper from quickstart.md.
const responses = Object.fromEntries(
  Array.from({ length: 20 }, (_, i) => [`item_${i + 1}`, 2]),
);
const result = await call(
  "POST",
  "/api/function/lower_extremity_function/score",
  { responses },
);
console.log(result.finding.score, result.finding.band);

TypeScript

// Uses the typed call<T>() helper from quickstart.md.
const responses = Object.fromEntries(
  Array.from({ length: 20 }, (_, i) => [`item_${i + 1}`, 2]),
);
const result = await call<ScoreResponse>(
  "POST",
  "/api/function/lower_extremity_function/score",
  { responses },
);

Go

// Uses the call() helper from quickstart.md.
responses := make(map[string]int, 20)
for i := 1; i <= 20; i++ {
    responses[fmt.Sprintf("item_%d", i)] = 2
}
result, err := call("POST", "/api/function/lower_extremity_function/score",
    map[string]any{"responses": responses}, 3)
if err != nil {
    panic(err)
}
finding := result["finding"].(map[string]any)
fmt.Printf("LEFS: %v (%v)\n", finding["score"], finding["band"])

Java

// Uses the call() helper from quickstart.md.
StringBuilder body = new StringBuilder("{\"responses\":{");
for (int i = 1; i <= 20; i++) {
    if (i > 1) body.append(",");
    body.append("\"item_").append(i).append("\":2");
}
body.append("}}");
String result = call("POST",
    "/api/function/lower_extremity_function/score", body.toString(), 3);
System.out.println(result);

C# (.NET HttpClient)

// Uses the Call() helper from quickstart.md.
var responses = Enumerable.Range(1, 20)
    .ToDictionary(i => $"item_{i}", _ => 2);
var result = await Call(HttpMethod.Post,
    "/api/function/lower_extremity_function/score",
    new { responses });
var finding = result.GetProperty("finding");
Console.WriteLine($"LEFS: {finding.GetProperty("score").GetDouble()} ({finding.GetProperty("band").GetString()})");

PowerShell

# Uses the Invoke-Engine helper from quickstart.md.
$responses = @{}
1..20 | ForEach-Object { $responses["item_$_"] = 2 }
$result = Invoke-Engine -Method Post -Path "/api/function/lower_extremity_function/score" -Body @{ responses = $responses }
"LEFS: $($result.finding.score) ($($result.finding.band))"

Clinical interpretation

• What it measures. Difficulty with twenty lower-extremity- dependent activities. Total score reflects the sum of remaining function across those activities.
• Score range. 0–80, with 80 representing no limitation.
• Percentage conversion. Some clinical reports express LEFS as a percentage (score / 80 × 100%). Trinity does not compute this; do it client-side if your UI needs it.

Intended use

• Lower-extremity outcome tracking for hip, knee, ankle, or foot conditions.
• Baseline vs. follow-up after intervention targeting the lower limb.
• Feeding the CDRI composite as the lower-extremity function signal.

Mistaken use

• Do not apply an "ODI-like" threshold convention. If you are flagging "function below threshold X," remember that LEFS goes up as function improves. An analogous threshold for concerning function on LEFS is score < 40, not score > 40.
• Do not use for lumbar, cervical, or upper-extremity complaints. Those have their own instruments.
• Do not convert LEFS to ODI-equivalent by subtraction. While 80 - LEFS produces a value between 0 and 80, it does not correspond to any standardized disability scale.
• Do not confuse with LEFS 2.0 or regional short forms. The Trinity implements the original 20-item LEFS.

Debugging

1. Capture request_id. Present in every response body.
2. Scores look inverted compared to other function instruments. Expected — see the sign-convention note above. Consume band for cross-instrument comparisons.
3. 400 ValidationError with missing_items. Send all twenty items.
4. finding.raw.responded_items is less than 20 but the request succeeded. Not possible under the current strict rubric; investigate a proxy between client and API stripping items.

Related

• patterns-questions.md, patterns-score.md — shared contracts.
• instruments-oswestry.md — lumbar; opposite sign convention.
• instruments-quick_dash.md — upper extremity.
• instruments-neck_disability.md — cervical.
• composite-cdri-compute.md — composite.

Change history

Date	Change
2026-04-20	Initial publication.