ObjectiveTo investigate the value of smart phone Scoliometer software in obtaining optimal lumbar lordosis (LL) during L4-S1 fusion surgery. MethodsBetween November 2014 and February 2015, 20 patients scheduled for L4-S1 fusion surgery were prospectively enrolled the study. There were 8 males and 12 females, aged 41-65 years (mean, 52.3 years). The disease duration ranged from 6 months to 6 years (mean, 3.4 years). Before operation, the pelvic incidence (PI) and Cobb angle of L4-S1 (CobbL4-S1) were measured on lateral X-ray film of lumbosacral spine by PACS system; and the ideal CobbL4-S1 was then calculated according to previously published methods [(PI+9°)×70%]. Subsequently, intraoperative CobbL4-S1 was monitored by the Scoliometer software and was defined as optimal while it was less than 5° difference compared with ideal CobbL4-S1. Finally, the CobbL4-S1 was measured by the PACS system after operation and the consistency was compared between Scoliometer software and PACS system to evaluate the accuracy of this software. In addition, value of this method in obtaining optimal LL was validated by comparing the difference between ideal CobbL4-S1 and preoperative one with that between ideal CobbL4-S1 and postoperative one. ResultsThe CobbL4-S1 was (36.17±1.53)° for ideal one, (22.57±5.50)° for preoperative one, (32.25±1.46)° for intraoperative one measured by Scoliometer software, and (34.43±1.72)° for postoperative one, respectively. The observed intraclass correlation coefficient (ICC) was excellent [ICC=0.96, 95% confidence interval (0.93, 0.97)] and the mean absolute difference (MAD) was low (MAD=1.23) between Scoliometer software and PACS system. The deviation between ideal CobbL4-S1 and postoperative CobbL4-S1 was (2.31±0.23)°, which was significantly lower than the deviation between ideal CobbL4-S1 and preoperative CobbL4-S1 (13.60±1.85)° (t=6.065, P=0.001). ConclusionScoliometer software can help surgeon obtain the optimal LL and deserve further dissemination.