Does a “Spot Weld” with a 1st to 2nd Metatarsal Base Screw Maintain Correction of the Modified Lapidus Procedure? A Retrospective Radiographic Review

CATEGORY: Bunion; Midfoot/Forefoot INTRODUCTION/PURPOSE: The Lapidus 1st tarsometatarsal (TMT) arthrodesis has gained popularity for its ability to correct large deformities especially in cases of medial column instability. Even with solid fusion, instability between the 1st and 2nd columns can result in loss of intermetatarsal (IM) angle correction over time. Anecdotally, a 'spot weld' between the lateral 1stmetatarsal and medial 2nd metatarsal bases seems to predict long term maintenance of IM correction. The purpose of the study is to review cases of Lapidus 1st TMT arthrodesis with supplemental screw fixation from the 1stto 2nd metatarsal base for maintenance of IM correction and determine whether a 'spot weld' is predictive of maintenance and identify an optimum position of the 1st to 2nd metatarsal screw to achieve the 'spot weld. METHODS: A retrospective radiographic review of cases by a single surgeon over the past five years was performed. All cases of tarsometatarsal fusion were queried and reviewed. Inclusion criteria included primary arthrodesis of the 1st TMT joint with supplemental fixation between the 1st and 2nd metatarsal bases, availability of appropriate radiographic image and at least 4 months follow up. Exclusion criteria included 1st TMT fusion without 1st-2nd metatarsal screw fixation, multiple TMT or midfoot fusion, Charcot neuroarthropathy, and revision fusion. A standard surgical technique was utilized with an in situ joint debridement, specific preparation to the medial 2ndmetatarsal base and adjacent lateral 1st metatarsal base, autogenous bone grafting and hardware construct at the 1stTMT joint consisting of compression screw from the 1st metatarsal to the 2nd cuneiform, screw fixation from 1st to 2ndmetatarsal bases and either locking plate or compression staple fixation dorsally across the 1st TMT joint. RESULTS: 90 cases (77 patients) met the inclusion criteria with average follow up of 309 days. Fusion of the 1st TMT occurred in 87/90 (96.7%) cases with 76 dorsal plate, 10 with dorsal staple and 4 with all screws. There was no incidence of complications related to the 1-2 screw. The mean pre-operative IM 1-2 angle was 14.90 degrees, with mean correction to 6.22 degrees post operative and final maintained correction at 7.10 degrees with mean loss of 0.87 degrees. There were 'spot welds' in 65/90 (72.2%) with a mean loss of correction of 0.48 degree versus loss of 1.88 degrees in the 'no spot weld' subgroup (p<0.001). Cases with no spot weld and screw lucency lost 2.25 degrees (p<0.001). CONCLUSION: Loss of IM 1-2 correction can occur due to instability between the 1st and 2nd columns even in cases of solid 1st TMT arthrodesis. The achievement of a 'spot weld' via careful preparation, bone grafting and use of a 1st to 2nd metatarsal base screw as part of a Lapidus construct was found to maintain correction with minimal loss (0.87 degree) versus cases where no 'spot weld' was achieved. Cases with no 'spot weld' that developed screw lucency had the greatest loss of correction. No statistical difference in screw position between groups was found.