Biomechanical Effects of Pedicle Screw Positioning on the Surgical Segment in Models After Oblique Lumbar Interbody Fusion: An in-silico Study

Abstract

Chen Xu,1,* Chenyi Huang,2,* Ping Cai,3 Zhongxin Fang,4 Zhangchao Wei,2 Fei Liu,2 Jingchi Li,1,2 Yang Liu1 1Department of Spine Surgery, Shanghai Changzheng Hospital, Naval Medical University, Shanghai, 200003, People’s Republic of China; 2Department of Orthopedics, Hospital (T.C.M) Affiliated to Southwest Medical University, Luzhou, 646000, Sichuan, People’s Republic of China; 3Department of Orthopedics, Affiliated Hospital of Nanjing University of Chinese Medicine, Nanjing, Jiangsu, People’s Republic of China; 4Fluid and Power Machinery Key Laboratory of Ministry of Education, Xihua University, Chengdu, People’s Republic of China*These authors contributed equally to this workCorrespondence: Yang LiuDepartment of Spine Surgery, Shanghai Changzheng Hospital, Naval Medical University, 415th Fengyang Road, Shanghai, 200003, People’s Republic of China, Email [email protected] LiDepartment of Orthopedics, Hospital (T.C.M) Affiliated to Southwest Medical University, No. 182, Chunhui Road, Luzhou, Sichuan Province, 646000, People’s Republic of China, Email [email protected]: Bilateral pedicle screw (BPS) is the “gold standard” of fixation methods for patients with lumbar interbody fusion. Biomechanical deterioration initially triggers complications in the surgical segment. Studies proved that BPS positions and trajectory changes affect the local biomechanical environment. However, no study illustrates the biomechanical effect of insertional screw positions’ change on the surgical segment.Methods: Oblique lumbar interbody fusion (OLIF) with different BPS insertional positions has been simulated in a well-validated lumbo-sacral model. Fixation stability and stress responses on the surgical segment were evaluated under identical loading conditions.Results: There is no clear variation tendency for the risk of BPS failure and the change of strain energy density of the grafted bone. However, shifting the insertional screw position close to the surgical segment will increase the range of motions (ROM) in the surgical segment and lead to stress concentration of bony structures, especially in the caudal side of the surgical segment.Conclusion: Adjusting the insertional position of BPS close to the surgical segment in OLIF models will lead to stress concentration of bony structures and surgical segmental instability. Therefore, reducing BPS’s fixation length was not recommended, which may increase the risk of segmental instability, non-union, and cage subsidence.Keywords: oblique lumbar interbody fusion, bilateral pedicle screw, cage subsidence, insertional screw positions, non-union

Keywords

• oblique lumbar interbody fusion
• bilateral pedicle screw
• cage subsidence
• insertional screw positions
• non-union.