Failure analysis of broken pedicle screws on spinal instrumentation.
Revised spinal surgery is needed when there is a broken pedicle screw in the patient. This study investigated the pedicle screw breakage by conducting retrieval analyses of broken pedicle screws from 16 patients clinically and by performing stress analyses in the posterolateral fusion computationally using finite element (FE) models. Fracture surface of screws was studied by scanning electron microscope (SEM). The FE model of the posterolateral fusion with the screw showed that screws on the caudal side had larger axial stress than those on the cephalic side, supporting the clinical findings that 75% of the patients had the screw breakage on the caudal side. SEM fractography showed that all broken screws exhibited beach marks or striations on the fractured surface, indicating fatigue failure. Screws of patients with spinal fracture showed fatigue striations and final ductile fracture around the edge. Among the 16 patients who had broken pedicle screws 69% of them achieved bone union in the bone graft, showing that bone union in the bone graft did not warrant the prevention of screw breakage.
Institute of Rehabilitation Science and Technology, National Yang-Ming University Taipei, Taiwan.
Chen-Sheng
CS
Chen
Wen-Jer
WJ
Chen
Cheng-Kung
CK
Cheng
Shyh-Hua Eric
SH
Jao
Shan-Chang
SC
Chueh
Chang-Chih
CC
Wang
D000328:Adult; D001863:Bone Screws; D003198:Computer Simulation; D019544:Equipment Failure Analysis / Q000379:methods*; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology* / Q000601:surgery; D008159:Lumbar Vertebrae / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008954:Models, Biological; D011379:Prognosis; D011475:Prosthesis Failure; D013123:Spinal Fusion / Q000295:instrumentation*; D013499:Surface Properties; D016896:Treatment Outcome