BACKGROUND & OBJECTIVES: As the overall health and life expectancy increases in the United States, the incidence of fragility fractures in elderly patients also continues to increase. Given their medical comorbidities and decreased bone mineral density, acetabular fractures in the elderly population present a significant challenge to the orthopaedic trauma surgeon. The anterior column posterior hemitransverse (ACPHT) fracture pattern is a common fracture pattern in this population, and is often associated with central subluxation/dislocation of the femoral head with articular impaction. This study sought to delineate the most stable fixation construct in ACPHT fracture patterns in the elderly population. MATERIALS AND METHODS: The sample consisted of 3 groups of synthetic hemipelves (N=15), which were tested in order to compare stiffness by measuring motion at fracture lines under applied loads. The three groups of unique quadrilateral plate fixation were as follows: a specialty quadrilateral surface plate; 4 long peri-articular screws parallel to the quadrilateral surface into the ischium,; and an 8 hole infrapectineal buttress plate. Digital imaging system measured construct motion under load. Construct stiffness was estimated by linear regression of load between 50 and 850N versus average relative motion (average of relative motion at 200 points along the line of the osteotomy). Permanent deformation was estimated as the magnitude of relative motion upon unloading. RESULTS: Using ANOVA with Tukey's test to determine construct stiffness in loading, the group long peri-articular screws was found to have significantly higher stiffness than either of the other groups. Maximal fracture displacement was located at the intersection of the low transverse fracture line in the posterior column and the free quadrilateral surface fragment. CONCLUSIONS: Results indicate that the best fixation construct for this ACPHT acetabular fracture pattern includes independent lag screws across the anterior column and a pelvic brim plate with long periarticular screws maximizing posterior column fixation and preventing medialization of the free quadrilateral fragment. Although there are potential patient considerations that may complicate the placement of all 4 long screws, in most patients one or more of these screws can be safely placed in order to help prevent secondary displacement.