2024 Volume 15 Issue 7 Pages 1008-1018
Introduction: Pedicle screw loosening (PSL) causes bone nonunion; therefore, we aimed to prevent PSL.
Methods: We investigated the process of thoracic bone fusion and the causes of PSL 3 years after circumferential minimally invasive surgery (CMIS) for adult spinal deformity (ASD). The subjects were 52 ASD patients (40 women, 12 men) who had undergone CMIS using LLIF and PPS since 2016 and had been able to undergo FU for >3 years. A comparative study was conducted between a group with PSL (PSL group) and a group without PSL (NPSL group). Various parameters, including preoperative disc condition, angle between the UIV PS and the cranial endplate (PSA), preoperative HU value (UIV), screw malposition in the UIV, depth score, PJK incidence, and pre- and post-operative ODI. Disc status was classified as no degeneration (N), DISH (D), or osteophyte type (O). The screw depth score was 2 points for contact with the cortical bone on both sides, 1 point for contact on one side, and 0 point for no contact.
Results: PSL was administered in 47% of patients (25), and there were no significant differences in age and sex, pre- and post-operative ODI, and HU values between the two groups; PI, postoperative PI-LL, and preoperative SVA were significantly greater in the PSL group, and preoperative TK and PSA were smaller. Screw depth scores were significantly higher in the NPSL group, and multivariate analysis detected PSA levels, screw depth score, and screw malposition as risk factors, with a cutoff value for PSA of 11.7°.
Discussion/Conclusions: There are reports that the HU value is a factor in PSL. However, in this study, PSA and screw depth score were detected as factors for PSL, suggesting that better implant placement at UIV rather than bone quality leads to a reduction in PSL and subsequent spontaneous facet bone fusion involving the thoracic vertebrae.
