OBJECTIVES:The use of locked plates in repairing osteopenic 3- and 4-part proximal humerus fractures remains controversial. The purpose of this article was to report the outcomes of open reduction and internal fixation in low-energy proximal humerus fractures treated with locked plating in patients older than 55 years and stratify risk of failure or complication based on initial radiographic features. DESIGN:Retrospective. SETTING:Level I Trauma Center. METHODS:Seventy patients older than 55 years undergoing locked plate fixation for Neer 3- or 4-part proximal humerus fractures were studied retrospectively. All patients had standardized, true size digital radiographs of the injured and normal shoulder in the axillary, scapular Y, and 20-degree external rotation views with a minimum of 18 monthsʼ clinical follow-up. Two groups were identified based on the initial direction of the humeral head deformityvarus or valgus impaction. There were no statistical differences between treatment groups with regard to age, sex, Neer classification, follow-up, or dislocation. Radiographic measurements included humeral head angulation, tuberosity displacement, and length of the intact metaphyseal segment. Clinical outcomes measured Constant scores (CS) using active range of motion at latest follow-up. RESULTS:Twenty-four patients with initial varus fracture patterns healed with an average of 16-degree varus head angulation and an overall CS of 63 at an average of 34 monthsʼ follow-up. Forty-six patients with initial valgus fracture patterns healed with an average of 6 degrees of varus angulation and an overall CS of 71 at an average of 37 monthsʼ follow-up (P < 0.01). Complications of avascular necrosis, humeral head perforation, loss of fixation, tuberosity displacement >5 mm, and varus subsidence >5 degrees were encountered in 19 of 24 (79%) in the varus group compared with 9 of 46 (19%) in the valgus group (P < 0.01). Final CSs for 3-part fractures were 65 versus 72 (P < 0.01) for varus and valgus groups, respectively, and 61 versus 69 (P = 0.19) for 4-part fractures. CONCLUSIONS:Neer 3- and 4-part proximal humeral fractures in older patients with initial varus angulation of the humeral head had a significantly worse clinical outcome and higher complication rate than similar fracture patterns with initial valgus angulation. Two factors had significant influence on final outcome in these fracture patternsinitial direction of the humeral head angulation and length of the intact metaphyseal segment attached to the articular fragment. The best clinical outcomes were obtained in valgus impacted fractures with a metaphyseal segment length of greater than 2 mm, and this was independent of Neer fracture type. Humeral head angulation had the greatest effect on final outcomes (P < 0.001), whereas metaphyseal segment length of less than 2 mm was predictive of developing avascular necrosis (P < 0.001).