The effects on calcaneofibular ligament function of differences in the angle of the calcaneofibular ligament with respect to the long axis of the fibula: a simulation study

Background: In the present study, CFLs harvested from cadavers were categorized according to the differences in the angle of the CFL with respect to the long axis of the fibula and their shape, and then three-dimensional reconstructions of the CFLs were used to simulate and examine the differences in the angles of the CFLs with respect to the long axis of the fibula and how they affect CFL function. Methods: The study sample included 81 ft from 43 Japanese cadavers. CFLs were categorized according to their angle with respect to the long axis of the fibula and the number of fiber bundles. Five categories were subsequently established: CFL20 degrees (angle of the CFL with respect to the long axis of the fibula from 20 degrees to 29 degrees); CFL30 degrees (range 30-39 degrees); CFL40 degrees (range 40-49 degrees); CFL50 degrees (range 50-59 degrees); and CFL2 (CLFs with two crossing fiber bundles). Three-dimensional reconstructions of a single specimen from each category were then created. These were used to simulate and calculate CFL strain during dorsiflexion (20 degrees) and plantarflexion (30 degrees) on the talocrural joint axis and inversion (20 degrees) and eversion (20 degrees) on the subtalar joint axis. Results: In terms of proportions for each category, CFL20 degrees was observed in 14 ft (17.3%), with CFL30 degrees in 22 ft (27. 2%), CFL40 degrees in 29 ft (35.8%), CFL50 degrees in 15 ft (18.5%), and CFL2 in one foot (1.2%). Specimens in the CFL20 degrees and CFL30 degrees groups contracted with plantarflexion and stretched with dorsiflexion. In comparison, specimens in the CFL40 degrees, CFL50 degrees, and CFL2 groups stretched with plantarflexion and contracted with dorsiflexion. Specimens in the CFL20 degrees and CFL2 groups stretched with inversion and contracted with eversion. Conclusions: CFL function changed according to the difference in the angles of the CFLs with respect to the long axis of the fibula.