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 the desired alignment. The present study examined the union rates and the change in dorsiflexion angle during the follow-up period in patients who had undergone MTP-1 fusion with a dorsal locking plate and a lag screw compared with patients who had undergone fusion with a dorsal locking plate alone. We performed a retrospective review of 99 feet undergoing MTP-1 fusion. The 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 by computed tomography. The dorsiflexion angles were radiographically measured at the first postoperative visit and at the final follow-up visit. Of the 99 feet, 36 (36.4%) were in the lag screw plus dorsal plate group and 63 (63.6%) in the dorsal plate group. The mean follow-up period was 12.9 (range 12 to 33.5) months. The dorsal plate plus lag screw group had a significantly lower change in the mean dorsiflexion angle (0.57° ± 5.01°) during the postoperative period compared with the dorsal plate group (6.73° ± 7.07°). The addition of a lag screw to a dorsal locking plate for MTP-1 arthrodesis might offer improved stability of the joint in the sagittal plane over time compared with a dorsal plate alone.