Listract test: a Standardized Assessment Method for Isolated Lisfranc Instability in Cadaver Models

Abstract

Background: The gold standard for diagnosis of Lisfranc instability is direct visualization in the operation room while the examination techniques is still unstandardized and non-reproducible. We aimed to introduce a novel reproducible intraoperative mechanical testing method (Listract test) for intraoperative isolated Lisfranc instability assessment. Methods: The Lisfranc ligament between the first cuneiform (C1) and second metatarsus (M2) in eight lower leg cadaveric specimens were dissected to replicate C1-M2 Lisfranc instability by eight foot and ankle surgeons. The 50N distraction force was applied in the direction of the C1-M2 ligament. Three methods of fixation - flexible fixation, metal screw, and bio-absorbable screw- were used to fix the injury, and Listract test was applied again after fixation. Besides intraoperative assessment, C1-M2 diastasis and area were measured using radiographs for assessment of Lisfranc instability. Results: The sensitivity and specificity of the Listract test for detection of C1-M2 instability were 100% and 100% intraoperatively, 33.3% and 95.2% using radiographic diastasis measurement, and 63.2% and 38% using area measurement, respectively. The Listract test had a specificity and sensitivity of 100% and 96% for intraoperative assessment, 87.5% and 64.3 for radiographic C1-M2 diastasis, and 48% and 50% for radiographic area. Conclusion: The Listract test is a simple, reproducible, and replicable intraoperative method for evaluating the Lisfranc joint for instability. Developing a device with this mechanism can help clinicians confirm the diagnosis and provide appropriate treatment particularly for equivocal diagnoses.