To compare radiological and clinical outcomes between lateral locking plate (LLP) and dual-plate fixation (LLP and additional medial buttress plate) for proximal humerus fractures with medial column comminution and varus deformity in patients with osteoporosis. Retrospective. Academic medical center. Overall, 52 patients were enrolled. Of these, 26 patients underwent dual-plate fixation. The control group (LLP) was matched to the dual-plate group for age, sex, injured side, and fracture type. Patients in the dual-plate group were treated with LLP and medial buttress plate, whereas patients in the LLP group were treated with only an LLP. Demographic factors, operative time, and level of hemoglobin of the 2 groups obtained from medical records. Changes in the neck-shaft angle and the development of postoperative complications were recorded. Clinical outcomes were measured based on the visual analog scale; American Shoulder and Elbow Surgeons; Disabilities of the Arm, Shoulder, and Hand; and Constant-Murley scores. The operation time and hemoglobin loss did not differ significantly between the groups. Radiographic evaluation showed a significantly lower change in neck-shaft angle in the dual-=plate group than in the LLP group. The dual-plate group also showed better Disabilities of the Arm, Shoulder, and Hand; American Shoulder and Elbow Surgeons; and Constant-Murley scores than the LLP group. Fixation using additional medial buttress plate with LLP may be considered for treating proximal humerus fractures in patients with an unstable medial column, varus deformity, and osteoporosis. Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.