Spinal Decompression Force Calculator
ANA›Life Services Authority›National Calculator Authority›Spinal Decompression Force Calculator
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Spinal Decompression Force Calculator
Estimates the traction force needed to decompress spinal segments, accounting for body weight, spinal region, table friction, and patient position. Results are for educational purposes only — always follow a licensed clinician's protocol.
Body Weight (kg)
Spinal Region
Lumbar (L1–L5) Cervical (C1–C7)
Patient Position
Supine (lying on back) Prone (lying face down)
Table Friction Coefficient (μ)
Typical split-table: 0.4–0.6 | Frictionless (motorised): 0
Table / Traction Angle (°)
0° = horizontal; positive = head-end elevated (lumbar) or declined (cervical)
Calculate
function spiCalc() { var resultDiv = document.getElementById('spi-result');
// --- Inputs --- var weight = parseFloat(document.getElementById('spi-weight').value); var region = document.getElementById('spi-region').value; var position = document.getElementById('spi-position').value; var mu = parseFloat(document.getElementById('spi-friction').value); var angleDeg = parseFloat(document.getElementById('spi-angle').value);
// --- Validation --- if (isNaN(weight) || weight 300) { resultDiv.innerHTML = 'Please enter a valid body weight between 20 and 300 kg.'; return; } if (isNaN(mu) || mu 1) { resultDiv.innerHTML = 'Friction coefficient (μ) must be between 0 and 1.'; return; } if (isNaN(angleDeg) || angleDeg 45) { resultDiv.innerHTML = 'Traction angle must be between 0° and 45°.'; return; }
var g = 9.81; // m/s² var W = weight * g; // Total body weight force (N)
// --- Segment weight fraction --- // Lumbar traction acts on the lower body (~45% of BW for supine lumbar) // Cervical traction acts on the head (~6–8% of BW) var segmentFraction; if (region === 'lumbar') { segmentFraction = 0.45; // lower body below L1 ≈ 45% BW } else { segmentFraction = 0.07; // head ≈ 7% BW }
var Wseg = W * segmentFraction; // Weight of segment being tractioned (N)
// --- Angle correction --- // When the table is angled, the component of segment weight along the table surface changes. // For lumbar supine: gravity component along table = Wseg * cos(angle) // Friction force = μ * Normal force = μ * Wseg * cos(angle) // Net traction force needed = Wseg * cos(angle) * (1 + μ) [distraction + overcome friction] // For cervical: no table friction (head hangs or harness used), friction term = 0 var angleRad = angleDeg * Math.PI / 180; var cosA = Math.cos(angleRad); var sinA = Math.sin(angleRad);
var frictionForce, distractionForce, totalForce;
if (region === 'lumbar') { // Normal force on table surface (perpendicular component) var N = Wseg * cosA; frictionForce = mu * N; // Friction opposing traction (N) distractionForce = Wseg * cosA; // Force needed to distract segment (N) totalForce = distractionForce + frictionForce; // Total traction force (N) } else { // Cervical: patient seated or supine with head off table; friction negligible frictionForce = 0; distractionForce = Wseg * cosA; totalForce = distractionForce; }
// Convert to kg-force for clinical display (1 kgf = 9.81 N) var totalKgf = totalForce / g; var totalLbs = totalKgf * 2.20462;
// --- Clinical starting dose (typically 50% of calculated force) --- var startKgf = totalKgf * 0.50; var startLbs = startKgf * 2.20462;
// --- Intradiscal pressure reduction estimate --- // Nachemson (1981): traction reduces intradiscal pressure ~30–50% at therapeutic force var pressureReduction = (totalKgf >= (weight * 0.25)) ? '30–50%' : '10–25%';
// --- Output --- resultDiv.innerHTML = '### Results ' + '' + 'ParameterValue' + 'Segment Weight (Wseg)' + (Wseg/g).toFixed(1) + ' kgf (' + Wseg.toFixed(1) + ' N)' + 'Friction Force' + (frictionForce/g).toFixed(1) + ' kgf (' + frictionForce.toFixed(1) + ' N)' + 'Total Traction Force' + totalKgf.toFixed(1) + ' kgf | ' + totalLbs.toFixed(1) + ' lbs | ' + totalForce.toFixed(1) + ' N' + 'Recommended Starting Force (50%)' + startKgf.toFixed(1) + ' kgf | ' + startLbs.toFixed(1) + ' lbs' + 'Estimated Intradiscal Pressure Reduction' + pressureReduction + '' + '' + '⚠️ These values are estimates for educational use. Traction therapy must be prescribed and supervised by a qualified healthcare professional.
'; }
#### Formulas Used
1. Segment Weight: Wseg = BW × g × fseg where fseg = 0.45 (lumbar, lower body) or 0.07 (cervical, head)
2. Normal Force on Table: N = Wseg × cos(θ)
3. Friction Force (lumbar only): Ffriction = μ × N = μ × Wseg × cos(θ)
4. Total Traction Force: Ftraction = Wseg × cos(θ) + Ffriction = Wseg × cos(θ) × (1 + μ) [lumbar] = Wseg × cos(θ) [cervical, μ = 0]
5. Clinical Starting Dose: Fstart = 0.50 × Ftraction
#### Assumptions & References
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