Maintenance of Correction of the Modified Lapidus Procedure With a First Metatarsal to Second Metatarsal Screw With "Spot Weld" Technique: A Retrospective and Radiographic Analysis.

Lapidus first tarsometatarsal (TMT) arthrodesis gained popularity for its ability to correct large deformities especially in cases of medial column instability. Despite solid first TMT fusion, instability between the first and second columns can result in loss of intermetatarsal (IM) angle correction over time. A "spot weld" or fusion between the first and second metatarsal may improve maintenance of correction. This retrospective study reviewed cases of Lapidus arthrodesis with first to second metatarsal base screw fixation for maintenance of IM correction and determine whether a "spot weld" is predictive of maintenance. A total of 90 cases (77 patients) performed by a single surgeon met inclusion with average follow-up of 309 days. First TMT fusion occurred in 87/90 (96.7%) cases with 76 dorsal plate, 10 dorsal staple, and 4 all screws. No incidence of complications related to the 1-2 screw was noted. Mean preoperative IM 1-2 angle 14.90°, mean correction to 6.22° post-operative and final maintained correction at 7.10°, mean loss of correction 0.87°. There were "spot welds" in 65/90 (72.2%) with mean loss of 0.48° versus loss of 1.88° in "no spot weld" subgroup (p < .001). Cases with no spot weld and screw lucency lost 2.25° (p < .001). Loss of IM 1-2 correction can occur due to first and second ray intra-column instability even in cases of solid first TMT arthrodesis. Incorporating a completed "spot weld" with bone grafting and first to second metatarsal screw was found to maintain correction with minimal loss (0.87°).