Background First metatarsophalangeal (MTP-1) joint fusion is a reliable method for the correction of various deformities including hallux valgus and hallux rigidus. Ideal constructs provide high rates of fusion in desired alignment. The present study examines the union rates, as well as the change in dorsiflexion angle during the follow up period in patients who underwent MTP-1 fusion with a dorsal locking plate and a lag screw, versus patients fused with a dorsal locking plate alone. Methods This is a retrospective review of 99 feet undergoing MTP-1 fusion. Joints were fused using either a dorsal locking plate alone or a lag screw plus a dorsal locking plate. Union was determined radiographically during the follow up period. Suspected nonunions were confirmed with CT. Dorsiflexion angles were radiographically measured at first post-operative visit and at final follow up. Results There were 36 patients in the lag screw plus dorsal plate group, and 63 in the dorsal plate group. Mean follow up was 12.9 months (Range: 12–33.5 months). The dorsal plate plus lag screw group had a significantly lower change in mean dorsiflexion angle (0.57° ± 5.01°) during the post-operative period compared to the dorsal plate group at final follow up versus the dorsal plate group (6.73° ± 7.07°). Conclusion The addition of a lag screw to a dorsal locking plate for MTP-1 arthrodesis may offer improved stability of the joint in the sagittal plane over time compared to a dorsal plate alone. Level of evidence Retrospective level III evidence.