Anatomical variation of Lisfranc mortise has been implicated in the susceptibility of Lisfranc fracture-dislocation. We investigated whether the variations in the dimensions of second metatarsal base makes the joint vulnerable to fracture dislocation.

Patients and Methods: 31 normal (group A) and 23 injured (group B) foot x-rays were compared. The average age of patients was 33(range 16–64) years. Routine AP and 45 degree oblique foot x-rays were used to measure second metatarsal parameters such as L (length of second metatarsal) were measured on x-rays in both groups. Additionally D (height of base of second metatarsal in sagittal plane of foot) was measured in CT scans. Statistical analysis was performed to test the viability of the null hypothesis that states that the relationship of second metatarsal length and height at the base does not correlate with increased susceptibility of Lisfranc injury. Similar analyses of the relevant parameters at the second metatarsal mortice were also calculated.

Results: Mean values of D, L and D/L were obtained in both groups. Statistically the value of D/L was found to be significantly different between injured group and normal group, with a P value of 0.03, while the values of length of second metatarsal itself was not significantly different between two groups (P=0.15). However, no significant correlation was noticed using other parameters of the second metatarsal mortice.

Conclusion: Previously shallowness of the second metatarsal mortice was shown to be significantly correlated with increased risk of Lisfranc injury. However, this study suggests that dimensions of second metatarsal such as, depth/length of the second metatarsal significantly increase the risk of Lisfranc injury. In other words more slender metatarsal dimensions at its base carry increased risk to Lisfranc injury. Thus, anatomical variation at the base of the second metatarsal makes the Lisfranc joint susceptible to injury.