The Occurrence Parallelism of the 1st and 2nd Ray in Mid Foot Fracture Dislocations. A Review of 234 Cases

CATEGORY: Trauma INTRODUCTION/PURPOSE: The parallel nature of the 1st and 2nd metatarsal has been reported in Lisfranc type injuries to the midfoot, reportedly the result of the lateral and dorsal subluxation of the 2nd metatarsal base. In this study, our aim was to explore the prevalence of parallelism in midfoot injuries and the associated features. METHODS: SETTING: Multicentre observational study Methods: Data was retrospectively collected from three centres on surgically treated midfoot fracture dislocations between 2011 and 2021. Radiographs were analysed using departmental PACS. Parallelism was defined as a 1/2 intermetatarsal angle of less than 6. All statistics was performed using SPSS 26. RESULTS: A total of 234 cases were included in the study. All 234 had undergone non-weightbearing (NWB) radiographs, with 80 patients who had also undergone (WB) weightbearing radiographs. The prevalence of parallelism was 21.3% (17/80) in the WB radiographs and 20.1% (47/234) in the NWB radiographs. The average IMA in the non-parallel group was 9.45 (95% CI 9.12,9.77) and 4.18 (95% CI 3.78, 4.57) in the parallel group. Concomitant lateral column injury was the only factor with a significant association with parallelism (p=.015). Other factors such as bone or ligamentous injury (p=.657), medial column injury (p=.085) and central column injury (p=.323) did not have a significant association. CONCLUSION: Parallelism in midfoot fracture dislocations occurs in approximately 20% of cases. If present, a high index of suspicion to the presence of a lateral column injury should be maintained due to its significant association.