Objective To investigate the feasibility and efficacy of combinational acetabular quadrilateral surface plates in treating elderly patients with acetabular fractures.Methods A retrospective case series study was conducted on the clinical data of eight elderly patients with acetabular fractures admitted between August 2016 and June 2017.There were five males and three females,with an average age of 64.2 years (range,60-68 years).According to the Letournel-Judet's classification,there were four patients with both column fractures,two T-shaped fractures,two anterior column and posterior hemitransverse fractures,among which three were combined with posterior wall fractures.Before operation,the artificial pelvis model was prepared by 3D printing for simulating the placement of combinational plates in the quadrilateral surface,and the plates were shaped for operation use.During operation,through the high iliac inguinal approach,the infrapectineal plate,pubo-ischiatic plate,and ilio-ischiatic plate were placed successively to fix anterior column," middle column",and posterior column,respectively.The pubo-ischiatic and ilio-ischiatic plates were combined with the infrapectineal plate.After fracture reduction,internal fixation was completed at one time.The incision length,operation time,and intraoperative blood loss were recorded.Postoperative fracture reduction was evaluated by Matta standard,and function of hip joint by modified Merle d'Aubigné and Postel scoring system.The complications were recorded.Results All the patients were followed up for 3 12 months (mean,6.8 months).The average incision length was 10 cm (range,8-12 cm).The average operation time was 130 min (range,100-180 min).The average blood loss was 600 ml (range,350-1 000 ml).According to the Matta standard,six patients got excellent result,one good,and one fair,with an excellent and good rate of 7/8.With respect to the hip joint function at the last follow up,the result was excellent in four patients,good in two,fair in one and bad in one,with an excellent and good rate of 6/8.No iatrogenic vascular injury,inguinal hernia or pulmonary embolism occurred during operation.No traumatic arthritis or avascular necrosis of femoral head occurred after operation.Conclusions The fixation from inside to outside by using combinational quadrilateral surface plates is in accordance with the biomechanical characteristics of hip joint,which enables better function recovery,especially for elderly patients with acetabular fractures involving quadrilateral surface.Combined with 3D printing technique for preoperative planning,it can reduce operation time,blood loss and postoperative complications.