Abstract： Background:Technical aspects of the correct placement of medial support locking screws in the locking plate for proximal humerus fractures remain incompletely understood.This study was to evaluate the clinical relationship between the number of medial support screws and the maintenance of fracture reduction after locked plating of proximal humerus fractures.Methods:We retrospectively evaluated 181 patients who had been surgically treated for proximal humeral fractures (PHFs) with a locking plate between September 2007 and June 2013.All cases were then subdivided into one of four groups as follows:75 patients in the medial cortical support (MCS) group,26 patients in the medial multiscrew support (MMSS) group,29 patients in the medial single screw support (MSSS) group,and 51 patients in the no medial support (NMS) group.Clinical and radiographic evaluations included the Constant-Murley score (CM),visual analogue scale (VAS),complications,and revision surgeries.The neck-shaft angle (NSA) was measured in a true anteroposterior radiograph immediately postoperation and at final follow-up.One-way analysis of variance or Kruskal-Wallis test was used for statistical analysis of measurement data,and Chi-square test or Fisher's exact test was used for categorical data.Results:The mean postoperative NSAs were 133.46° ± 6.01°,132.39° ± 7.77°,135.17° ± 10.15°,and 132.41° ± 7.16° in the MCS,MMSS,MSSS,and NMS groups,respectively,and no significant differences were found (F =1.02,P =0.387).In the final follow-up,the NSAs were 132.79° ± 6.02°,130.19° ± 9.25°,131.28° ± 1 2.85°,and 127.35° ± 8.50° in the MCS,MMSS,MSSS,and NMS groups,respectively (F =4.40,P =0.008).There were marked differences in the NSA at the final follow-up between the MCS and NMS groups (P =0.004).The median (interquartile range [IQR]) NSA losses were 0.0° (0.0-1.0)°,1.3° (0.0-3.1)°,1.5° (1.0-5.2)°,and 4.0°(1.2-7.1)° in the MCS,MMSS,MSSS,and NMS groups,respectively (H =60.66,P ＜ 0.001).There were marked differences in NSA loss between the MCS and the other three groups (MCS vs.MMSS,Z =3.16,P =0.002;MCS vs.MSSS,Z =4.78,P ＜ 0.001;and MCS vs.NMS,Z =7.34,P ＜ 0.001).There was also significantly less NSA loss observed in the MMSS group compared to the NMS group (Z =-3.16,P =0.002).However,there were no significant differences between the MMSS and MSSS groups (Z =-1.65,P =0.225) or the MSSS and NMS groups (Z =-1.21,P =0.099).The average CM scores were 81.35 ± 9.79,78.04 ± 8.97,72.76 ± 10.98,and 67.33 ± 12.31 points in the MCS,MMSS,MSSS,and NMS groups,respectively (F =18.68,P ＜ 0.001).The rates of excellent and good CM scores were 86.67％,80.77％,65.52％,and 43.14％ in the MCS,MMSS,MSSS,and NMS groups,respectively (x2 =29.25,P ＜ 0.001).The median (IQR) VAS scores were 1 (0-2),1 (0-2),2 (1-3),and 3 (1-5) points in the MCS,MMSS,MSSS,and NMS groups,respectively (H =27.80,P ＜ 0.001).Functional recovery was markedly better and VAS values were lower in the MCS and MMSS groups (for CM scores:MCS vs.MSSS,P ＜ 0.001;MCS vs.NMS,P ＜ 0.001;MMSS vs.MSSS,P =0.031;and MMSS vs.NMS,P＜ 0.001 and for VAS values:MCS vs.MSSS,Z=3.31,P =0.001;MCS vs.NMS,Z =4.64,P ＜ 0.001;MMSS vs.MSSS,Z =-2.09,P =0.037;and MMSS vs.NMS,Z =-3.16,P =0.003).Conclusions:Medial support screws might help enhance mechanical stability and maintain fracture reduction when used to treat PHFs with medial metaphyseal comminution or malreduction.