Abstract： Background:Restoring good alignment after total knee replacement (TKR) is still a challenge globally,and the clinical efficiency of patient-specific instruments (PSIs) remains controversial.In this study,we aimed to explore the value and significance of three-dimensional printing PSIs based on knee joint computed tomography (CT) and full-length lower extremity radiography in TKR.Methods:Between June 2013 and October 2014,31 TKRs were performed using PSIs based on knee joint CT and full-length lower extremity radiography in 31 patients (5 males and 26 females;mean age:67.6 ± 7.9 years;body mass index [BMI]:27.4 ± 3.5 kg/m2).Thirty-one matched patients (4 males and 27 females;mean age:67.4 ± 7.2 years;mean BMI:28.1 ± 4.6 kg/m2) who underwent TKR using conventional instruments in the same period served as the control group.The mean follow-up period was 38 months (31-47 months).Knee Society Score (KSS),surgical time,and postoperative drainage volume were recorded.Coronal alignment was measured on full-length radiography.Results:Twenty-three (74.2％) and 20 (64.5％) patients showed good postoperative alignment in the PSI and control groups,respectively,without significant difference between the two groups (X2 =0.68,P =0.409).The mean surgical time was 81.48 ± 16.40min and 72.90 ± 18.10 min for the PSI and control groups,respectively,without significant difference between the two groups (t =0.41,P =0.055).The postoperative drainage volume was 250.9 ± 148.8 ml in the PSI group,which was significantly less than that in the control group (602.1 ± 230.6 ml,t =6.83,P ＜ 0.001).No significant difference in the KSS at the final follow-up was found between the PSI and control groups (91.06 ± 3.26 vs.90.19 ± 3.84,t =0.95,P =0.870).Conclusions:The use of PSIs based on knee joint CT and standing full-length lower extremity radiography in TKR resulted in acceptable alignment compared with the use of conventional instruments,although the marginal advantage was not statistically different.Surgical time and clinical results were also similar between the two groups.However,the PSI group had less postoperative drainage.