A minimally disruptive model and three-dimensional evaluation of lisfranc joint diastasis

Background: There is no model that can reproduce the diastasis at the Lisfranc joint after isolated transection of the Lisfranc ligament. Prior models required extensive sectioning of ligaments in the midfoot and represent injuries that cause extensive tarsometatarsal fracture-dislocations. They do not represent a subset of injuries that cause subtle or limited disruption at the Lisfranc joint. The purpose of this study was to create a model with the minimum amount of ligamentous disruption and loading necessary to consistently observe diastasis at the Lisfranc joint. Methods: Fourteen fresh-frozen paired cadaver feet were dissected to expose the dorsum. Three screws were inserted into each first cuneiform and second metatarsal to create a pair of registration triads. A digitizer was utilized to record the three-dimensional positions of the screws and their displacement under loaded and unloaded conditions before and after the Lisfranc ligament was cut (intact and cut conditions). The first and second cuneiforms and their metatarsals were removed, and the attachment sites of the dorsal and the Lisfranc ligament were digitized. The three-dimensional positions of the bones and ligament displacement were determined. The significance of differences between conditions was tested with analysis of variance, and linear regression analysis was used to test the correlation between dorsal and plantar displacements. Results: There was a significant difference, of 1.3mm, in themean displacement between the cut loaded and intact loaded conditions (p < 0.0001). A modest correlation (r² = 0.60) was found between dorsal displacement and displacement at the site of the Lisfranc ligament, possibly attributable to rotations between the first cuneiform and second metatarsal. Conclusions: Isolated sectioning of the Lisfranc ligament is sufficient to consistently create diastasis at the Lisfranc joint. Dorsal displacements between the first cuneiform and second metatarsal are a modest predictor of plantar displacements. Clinical Relevance: This model can be used to compare different materials for or methods of fixation used to stabilize the Lisfranc joint, such as screws or sutures with endobuttons or ligament substitutes, in the future.