Characterization Of First Metatarsal Regeneration After New Modern Minimally Invasive Bunion Surgery. A Retrospective Radiographic Review Of 172 Cases.

Abstract

Introduction First metatarsal regeneration (FMR) is a new phenomenon that occurs as a result of new minimally invasive bunion surgery (MIBS) and has yet to be studied. The goal of this investigation is to characterize bone healing and introduce a new classification system (3 Types). Methods A retrospective radiographic review between January 2018 to June 2021 was performed, identifying 172 feet (122 patients). A minimum of four months of follow-up was required to be included. We classified the extent of callus formation based on the relationship to the primary “anchor” screw. A FMR Type I involved callus medial to the screw, FMR Type II involved callus medial and lateral to the screw, and FMR Type III had robust callus with first metatarsal regeneration. Results Mean age was 46.6±14.6 years; 117 (95.9%) females and 5 (4.1%) males. Mean follow-up was 8.2±5.7 months. The FMR bone healing distributions were Type I (17.4%, 30 feet), Type II (42.4%, 73 feet), and Type III (40.1%, 69 feet). There was a statistically significant overall difference in both IMA and HVA, (P<0.001), which was maintained across all FMR types (I-III, p<0.0001 for all comparisons). No statistical significant correlation between FMR type and age, sex, laterality, operation on both or one foot, length of follow-up, and pre- and postop radiographic angles. The same FMR type occurred in bilateral surgery in 28% when performed on the same day, and 20% on different days; and these differences were not statistically significant. Conclusion This is the first investigation to provide patterns of healing after MIBS, and evidence that FMR does occur for all bunion severities. Surgeons considering performing MIBS should no longer fear that bone healing is not possible. Our classification will help guide future studies by comparing the FMR with different techniques, fixation types/constructs and/or weight bearing protocols.