Technology of pre-operative digitalized simulation of osteotomy in degenerative spinal deformity with sagittal malalignment

Abstract

Objective To assess the availability of applying pre-operative digitalized simulation of osteotomy in degenerative scoliosis by comparing the sagittal parameters of pre-operative simulation and post-operative results. Methods A retrospective study of 16 degenerative scoliosis patients who underwent posterior PSO surgeries in our center from June 2012 to June 2014, 15 cases (2 male and 13 female) of which successfully underwent pre-operative digitalized simulation of osteotomy. Long-cassette standing upright posterior-anterior and lateral radiographs of the spine and pelvis were taken before and two weeks after surgery. The sagittal radiographic parameters including pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), lumbar lordosis (LL), thoracic kyphosis (TK), and sagittal vertical axis (SVA) were measured. PT setting method and ratio control method were used in pre-operative lateral radiographs for digital design of osteotomy, and the sagittal parameters were measured after osteotomy simulation. Pared-samples t test was conducted to assess difference in terms of sagittal parameters between the 2 methods of osteotomy simulation and post-operative results. Results LL was 43.33°±12.55° according to PT setting method and 40.67°±6.79° based on ratio control method, both of which showed no significant difference compared to actual post-operative LL (34.16°±8.52°). Regarding SVA, significant difference was observed between ratio control method (-24.78±31.44) mm and actual post-operative value (13.38±37.83) mm. Smaller PT was found as a result of PT setting method (11.33°±0.47°) compared to that of post-operative result vs. (20.33°±5.37°) while similar PT was simulated by ratio control method. Conclusion The present study confirmed that the pre-operative digital simulation of osteotomy can predict post-operative sagittal restoration. The combination of PT setting method and ratio control method may be a better solution for simulation. Meanwhile, the angle of osteotomy, the close ratio, and the thoracic kyphosis compensation should be taken into consideration during simulation. Key words: Preoperative period; Osteotomy; Scoliosis; Signal processing, computer-assisted