Radiographic Assessment of Relative First Metatarsal Length Following Modified Lapidus Procedure

Background: The modified Lapidus is a surgical procedure for managing moderate to severe hallux valgus, especially in the presence of first tarsometatarsal joint arthritis or hypermobility. It has good long-term results but reportedly can lead to transfer metatarsalgia due to inherent shortening of the first metatarsal. Methods: A retrospective analysis of all adult patients who underwent a modified Lapidus procedure during a 3-year period was performed. Clinical notes were evaluated to look for nonunion or any other complications related to the surgery. Pre- and postoperative standard weightbearing radiographs were used to establish the relative metatarsal length (RML), intermetatarsal angle (IMA), hallux valgus angle (HVA), and distal metatarsal articular angle (DMMA). A total of 69 modified Lapidus procedures were identified, with 32 included in the study. Results: The mean pre- and postoperative RMLs were -0.8 and -4.9 mm, respectively. The average RML shortening due to the procedure was -4.1 (P< .0001). The mean pre- and postoperative IMAs were 15 and 5 degrees, respectively (P< .0001). The mean pre- and postoperative HVAs were 33 and 9 degrees, respectively (P< .0001). One patient reported transfer metatarsalgia, which was attributed to elevation of the first metatarsal. Conclusion: We found a statistically significant degree of shortening of the relative length of the first metatarsal without any clinically significant metatarsalgia. The low rate of transfer metatarsalgia following the modified Lapidus procedure could be attributed to the sagittal plane correction and stability obtained by performing a first tarsometatarsal fusion.