{ "@context": "../../../../../spec/context/v0.5.jsonld", "id": "https://uofa.net/nagaraja/cou1", "type": "UnitOfAssurance", "conformsToProfile": "https://uofa.net/vocab#ProfileComplete", "name": "Nagaraja COU1 — Non-cannulated pedicle screw compression-bending credibility assessment", "description": "V&V 40 credibility assessment for FEA prediction of ASTM F1717 static compression-bending performance of a non-cannulated 7.5 mm pedicle screw construct. COU1 is the validation activity itself — the FEA model ensemble (FDA, Ansys, DePuy Synthes) is compared against N=11 experimental constructs across two laboratories. All 13 V&V 40 factors assessed; one factor (Test conditions) below required level due to single test condition.", "bindsRequirement": "https://uofa.net/nagaraja/req/mechanical-integrity", "bindsClaim": "https://uofa.net/nagaraja/claim/cou1-noncannulated-adequacy", "bindsModel": "https://uofa.net/nagaraja/model/ansys-abaqus-ensemble", "bindsDataset": [ "https://uofa.net/nagaraja/data/f1717-bench", "https://uofa.net/nagaraja/data/e8-ti6al4v" ], "hasContextOfUse": { "id": "https://uofa.net/nagaraja/cou/cou1-noncannulated", "type": "ContextOfUse", "name": "COU1: Non-cannulated construct compression-bending prediction", "description": "FEA predicts construct stiffness, yield force, and force at 40 mm displacement for the non-cannulated 7.5 mm pedicle screw design under ASTM F1717 static compression-bending. Validated by direct comparison to bench testing (N=11 constructs across two laboratories). Model influence MEDIUM (testing confirms results); decision consequence MEDIUM (pedicle screw fracture leads to revision surgery, not death).", "intendedUse": "Demonstrate that the FEA modeling framework reproduces experimental compression-bending behavior of a non-cannulated pedicle screw construct within pre-established acceptance bounds (<10% QoI difference, E/uval < 1.96).", "deviceClass": "Class II", "modelInfluence": "Medium", "decisionConsequence": "Medium" }, "hasValidationResult": [ "https://uofa.net/nagaraja/validation/mesh-convergence", "https://uofa.net/nagaraja/validation/numerical-solver-error", "https://uofa.net/nagaraja/validation/level1-qoi-comparison", "https://uofa.net/nagaraja/validation/level2-asme-vv20-comparison", "https://uofa.net/nagaraja/validation/sensitivity-analysis", "https://uofa.net/nagaraja/validation/monte-carlo-uq" ], "wasDerivedFrom": "https://doi.org/10.1016/j.ymeth.2024.03.003", "wasAttributedTo": "https://uofa.net/org/nagaraja-grau-inc", "generatedAtTime": "2024-03-08T00:00:00Z", "hash": "sha256:c0c3c30b766833b5581cea440871dfeae07e4745dbd6d55fd47797fff27e2727", "signature": "ed25519:6492cb6e175eba273a22cd3a5f905c8932b93686fe3aa61ce092aa3cf95443c834f694c0f5e54f57aae6149d13615e383bf06a09839f6d9f075307074e7e7e04", "signatureAlg": "ed25519", "canonicalizationAlg": "json-sortkeys/v1", "hasCredibilityFactor": [ { "id": "https://uofa.net/nagaraja/cou1/factor/software-quality-assurance", "type": "CredibilityFactor", "factorType": "Software quality assurance", "requiredLevel": 3, "achievedLevel": 3, "factorStatus": "assessed", "acceptanceCriteria": "Goal (c): commercial FEA solvers (Ansys 2019R1, Abaqus 6.14) widely used in medical device industry with active SQA documentation; anomaly lists reviewed by each lab. [Nagaraja Table 1, SQA]", "rationale": "Three labs (FDA, Ansys, DePuy Synthes) used commercial solvers with documented SQA processes. No major anomalies relevant to compression-bending simulation reported in vendor anomaly lists.", "factorStandard": "ASME-VV40-2018" }, { "id": "https://uofa.net/nagaraja/cou1/factor/numerical-code-verification", "type": "CredibilityFactor", "factorType": "Numerical code verification", "requiredLevel": 3, "achievedLevel": 3, "factorStatus": "assessed", "acceptanceCriteria": "Goal (c): each lab ran benchmark verification problems (cantilever beam bending, contact-pair convergence) before producing COU results. [Nagaraja Table 1, NCV]", "rationale": "All three labs verified solver performance against analytical benchmarks within their internal verification suites prior to model application.", "factorStandard": "ASME-VV40-2018" }, { "id": "https://uofa.net/nagaraja/cou1/factor/discretization-error", "type": "CredibilityFactor", "factorType": "Discretization error", "requiredLevel": 2, "achievedLevel": 2, "factorStatus": "assessed", "acceptanceCriteria": "Goal (b): grid convergence observed via three mesh refinement levels per lab; QoI variation <2% between fine and finest meshes. Formal Richardson extrapolation not performed. [Nagaraja §2.3, Table 1]", "rationale": "Each lab independently ran mesh-convergence sweeps. Construct stiffness and yield force converged to within 2% across the two finest mesh densities. Richardson extrapolation deferred per V&V 40 (b) gradation.", "factorStandard": "ASME-VV40-2018" }, { "id": "https://uofa.net/nagaraja/cou1/factor/numerical-solver-error", "type": "CredibilityFactor", "factorType": "Numerical solver error", "requiredLevel": 3, "achievedLevel": 3, "factorStatus": "assessed", "acceptanceCriteria": "Goal (c): convergence-tolerance sensitivity studies performed; nonlinear solver iterations checked for residual decay. [Nagaraja Table 1, NSE]", "rationale": "Each lab tightened convergence tolerances by an order of magnitude as a sensitivity check; QoI changes were below experimental measurement noise.", "factorStandard": "ASME-VV40-2018" }, { "id": "https://uofa.net/nagaraja/cou1/factor/use-error", "type": "CredibilityFactor", "factorType": "Use error", "requiredLevel": 3, "achievedLevel": 3, "factorStatus": "assessed", "acceptanceCriteria": "Goal (c): independent peer review of inputs/outputs by a second engineer at each laboratory before submission to the round-robin comparison. [Nagaraja §2.5]", "rationale": "Round-robin comparison across three independent labs provides cross-validation of input setup and output extraction. Discrepancies between labs were reconciled via shared input files and joint review.", "factorStandard": "ASME-VV40-2018" }, { "id": "https://uofa.net/nagaraja/cou1/factor/model-form", "type": "CredibilityFactor", "factorType": "Model form", "requiredLevel": 2, "achievedLevel": 2, "factorStatus": "assessed", "acceptanceCriteria": "Goal (b): influence of key assumptions explored — frictional contact between rod-screw, bonded threads vs frictional threads, elastoplastic Ti-6Al-4V material model. [Nagaraja §2.3-2.4]", "rationale": "Three contact assumptions evaluated. Bonded-thread approximation produced QoIs within 3% of frictional thread; elastoplastic material model with measured Ti-6Al-4V stress-strain curve used.", "factorStandard": "ASME-VV40-2018" }, { "id": "https://uofa.net/nagaraja/cou1/factor/model-inputs", "type": "CredibilityFactor", "factorType": "Model inputs", "requiredLevel": 2, "achievedLevel": 2, "factorStatus": "assessed", "acceptanceCriteria": "Goal (b): four-parameter sensitivity analysis (yield strength, modulus, friction coefficient, mesh refinement) plus 30-point Latin-hypercube Monte Carlo UQ on three parameters. [Nagaraja §2.4.1.3]", "rationale": "Sensitivity ranking: yield strength (highest), elastic modulus, friction coefficient. Monte Carlo UQ on three parameters produced output uncertainty (Uval) ~3.7% of construct stiffness across the three QoIs.", "factorStandard": "ASME-VV40-2018" }, { "id": "https://uofa.net/nagaraja/cou1/factor/test-samples", "type": "CredibilityFactor", "factorType": "Test samples", "requiredLevel": 2, "achievedLevel": 2, "factorStatus": "assessed", "acceptanceCriteria": "Goal (b): N=11 construct samples; nominal geometric range only (no intentional variation in screw diameter, rod diameter, polyaxial angle). [Nagaraja §2.4.1.2, Table 1]", "rationale": "Eleven non-cannulated constructs assembled to nominal dimensions and tested per ASTM F1717. Sample count exceeds typical N≥6 recommended for spinal device testing.", "factorStandard": "ASME-VV40-2018" }, { "id": "https://uofa.net/nagaraja/cou1/factor/test-conditions", "type": "CredibilityFactor", "factorType": "Test conditions", "requiredLevel": 3, "achievedLevel": 1, "factorStatus": "assessed", "acceptanceCriteria": "Goal (c) intended; Goal (a) achieved: single test condition (ASTM F1717 static compression-bending at 25 mm/min, room temperature, dry). Range, repeats, and uncertainty quantification of test conditions limited. [Nagaraja Table 1, §2.4.1.2]", "rationale": "BELOW TARGET. Authors acknowledge in §4: 'the sample size chosen for experimental testing may not meet a statistically relevant sample size' — encoded as a factor-level shortfall here. The N=11 sample size partly compensates per ASTM spinal device convention. The shortfall is documented in the decision rationale rather than blocking acceptance.", "factorStandard": "ASME-VV40-2018" }, { "id": "https://uofa.net/nagaraja/cou1/factor/equivalency-of-input-parameters", "type": "CredibilityFactor", "factorType": "Equivalency of input parameters", "requiredLevel": 3, "achievedLevel": 3, "factorStatus": "assessed", "acceptanceCriteria": "Goal (c): types and ranges of all inputs (material properties, geometry, boundary conditions, contact) equivalent between FEA model and experimental setup. [Nagaraja Table 1]", "rationale": "FEA inputs match experimental measurements: ASTM E8 stress-strain curve for Ti-6Al-4V, measured construct geometry from CAD, F1717-prescribed boundary conditions and loading rate.", "factorStandard": "ASME-VV40-2018" }, { "id": "https://uofa.net/nagaraja/cou1/factor/output-comparison", "type": "CredibilityFactor", "factorType": "Output comparison", "requiredLevel": 3, "achievedLevel": 3, "factorStatus": "assessed", "acceptanceCriteria": "Goal (c): three QoIs (construct stiffness, yield load, force at 40 mm displacement) compared between FEA and experiment using ASME V&V 20 Level I (E/D ratio) and Level II (E/uval) metrics. [Nagaraja §2.4.1.4, §3]", "rationale": "Level I E/D values: stiffness 1.5%, yield load 1.1%, force at 40 mm 1.3% — all within the pre-established 10% acceptance criterion. Level II E/uval values within ±1.96 (95% confidence) for all three QoIs.", "factorStandard": "ASME-VV40-2018" }, { "id": "https://uofa.net/nagaraja/cou1/factor/relevance-of-the-quantities-of-interest", "type": "CredibilityFactor", "factorType": "Relevance of the quantities of interest", "requiredLevel": 3, "achievedLevel": 3, "factorStatus": "assessed", "acceptanceCriteria": "Goal (c): QoIs (stiffness, yield force, force at 40 mm displacement) are identical between the validation activity and the COU. [Nagaraja §2.2]", "rationale": "Stiffness, yield, and force at 40 mm are the three QoIs the F1717 standard prescribes for static compression-bending. They are mechanically meaningful for rod-screw construct integrity.", "factorStandard": "ASME-VV40-2018" }, { "id": "https://uofa.net/nagaraja/cou1/factor/relevance-of-the-validation-activities-to-the-cou", "type": "CredibilityFactor", "factorType": "Relevance of the validation activities to the COU", "requiredLevel": 3, "achievedLevel": 3, "factorStatus": "assessed", "acceptanceCriteria": "Goal (c): the validation point IS the COU. COU1 evaluates the non-cannulated construct, which is also the experimental construct. Perfect overlap between validation and COU by construction. [Nagaraja §2.2]", "rationale": "COU1 is the validation activity itself. The bench test specimens are exactly the constructs the FEA predicts. Highest credibility level achievable by definition.", "factorStandard": "ASME-VV40-2018" } ], "hasWeakener": [], "hasDecisionRecord": { "id": "https://uofa.net/nagaraja/decision/cou1-overall", "type": "DecisionRecord", "actor": "https://uofa.net/org/nagaraja-grau-inc", "role": "Credibility assessment team", "outcome": "Accepted", "rationale": "Model accuracy met pre-established criterion of <10% difference between FEA and experiment for all three QoIs (stiffness 1.5% E/D, yield load 1.1% E/D, force at 40 mm 1.3% E/D). Critical stress location (rod midshaft) matched experimental failure mode. Test-conditions factor shortfall (achievedLevel 1 vs requiredLevel 3) is acknowledged and offset by N=11 sample size which exceeds typical spinal-device testing recommendations.", "decidedAt": "2024-03-08T00:00:00Z", "hasOffsetRationale": { "id": "https://uofa.net/nagaraja/decision/cou1-overall/offset/test-conditions", "type": "OffsetRationale", "refersToFactor": "https://uofa.net/nagaraja/cou1/factor/test-conditions", "justification": "Test-conditions factor shortfall (achievedLevel 1 vs requiredLevel 3) — single ASTM F1717 static compression-bending condition — is offset by N=11 experimental constructs across two laboratories, which exceeds the typical spinal-device testing sample size convention. Nagaraja et al. (2024) §4 acknowledges the limitation explicitly and treats the larger sample size as compensating evidence for the narrow loading-condition coverage." } }, "assuranceLevel": "Medium", "criteriaSet": "https://uofa.net/criteria/ASME-VV40-2018", "credibilityIndex": { "@value": "0.92", "@type": "xsd:decimal" }, "traceCompleteness": { "@value": "0.92", "@type": "xsd:decimal" }, "verificationCoverage": { "@value": "1.00", "@type": "xsd:decimal" }, "validationCoverage": { "@value": "1.00", "@type": "xsd:decimal" }, "uncertaintyCIWidth": { "@value": "0.037", "@type": "xsd:decimal" }, "modelRiskLevel": 3, "deviceClass": "Class II", "couName": "Non-cannulated F1717 compression-bending", "decision": "Accepted", "hasUncertaintyQuantification": true, "hasSensitivityAnalysis": true }