Predictors of Malreduction in Zone II and III 5th Metatarsal Fractures Fixed with an Intramedullary Screw: A Retrospective Analysis

CATEGORY: Midfoot/Forefoot; Sports INTRODUCTION/PURPOSE: Percutaneous fixation of 5th metatarsal fractures may lead to malreduction due to improper implant selection and placement. Our aim was to test the effects of screw entry, length, and diameter on malreduction, delayed union, non-union, or refracture. METHODS: We retrospectively reviewed zone II and proximal zone III 5th metatarsal fractures managed with intramedullary screw fixation. Comparisons were made between plantar cortex distraction/lateral cortex distraction and ratios of screw length, diameter, and entry point using multiple regression analysis. A further analysis was carried out between time to union and distraction in the lateral and plantar cortices. RESULTS: Plantar and lateral gap were both correlated with entry point ratio on lateral and AP view respectively (p<0.001 for both views). We did not see an association between plantar and lateral gap with screw diameter ratio (p=0.393 for AP and p=0.981 for lateral) or screw length ratio (p=0.966 for AP and p=0.740 for Lateral). Ratio of postop/preop apex height on AP and lateral showed correlation to presence of lateral and plantar fracture gap respectively (p<0.0001). Presence of a plantar gap did have a slight influence on time to union (p=0.044). Most fractures showed radiographic union at 12 weeks (38/44 that were followed until union). There were no refractures or nonunions as per available records. CONCLUSION: Our study shows that screw length and diameter did not lead to significant plantar or lateral fracture site distraction. However, entry point had a significant effect on plantar and lateral gap on post-operative x-ray. Patients with a plantar gap did have an increased risk of delayed union. Entry point should be given more significance rather than screw diameter and length in managing zone 2/3 fifth metatarsal base fractures. This is contradictory to existing radiologic studies.