Impact of Screw Diameter and Length on Pedicle Screw Fixation Strength in Osteoporotic Vertebrae: A Finite Element Analysis

Matsukawa Keitaro,Yato Yoshiyuki,Imabayashi Hideaki 대한척추외과학회 2021 Asian Spine Journal Vol.15 No.5

Study Design: Biomechanical study. Purpose: To quantitatively investigate the effect of screw size on screw fixation in osteoporotic vertebrae with finite element analysis (FEA) Overview of Literature: Osteoporosis poses a challenge in spinal instrumentation; however, the selection of screw size is directly related to fixation and is closely dependent on each surgeon’s experience and preference. Methods: Total 1,200 nonlinear FEA with various screw diameters (4.5–7.5 mm) and lengths (30–50 mm) were performed on 25 patients (seven men and 18 women; mean age, 75.2±10.8 years) with osteoporosis. The axial pullout strength, and the vertebral fixation strength of a paired-screw construct against flexion, extension, lateral bending, and axial rotation were examined. Thereafter, we calculated the equivalent stress of the bone-screw interface during nondestructive loading. Then, using diameter parameters (screw diameter or screw fitness in the pedicle [%fill]), and length parameters (screw length or screw depth in the vertebral body [%length]), multiple regression analyses were performed in order to evaluate the factors affecting various fixations. Results: Larger diameter and longer screws significantly increased the pullout strength and vertebral fixation strength; further, they decreased the equivalent stress around the screws. Multiple regression analyses showed that the actual screw diameter and %length were factors that had a stronger effect on the fixation strength than %fill and the actual screw length. Screw diameter had a greater effect on the resistance to screw pullout and flexion and extension loading (β=0.38–0.43, p<0.01); while the %length had a greater effect on resistance to lateral bending and axial rotation loading (β=0.25–0.36, p<0.01) as well as mechanical stress of the bone-screw interface (β=−0.42, p<0.01). Conclusions: The screw size should be determined based on the biomechanical behavior of the screws, type of mechanical force applied on the corresponding vertebra, and anatomical limitations.

Incidences and Risk Factors for Postoperative Non-Union after Posterior Lumbar Interbody Fusion with Closed-Box Titanium Spacers

Tsunehiko Konomi,Akimasa Yasuda,Kanehiro Fujiyoshi,Yoshiyuki Yato,Takashi Asazuma 대한척추외과학회 2020 Asian Spine Journal Vol.14 No.1

Study Design: A retrospective, single-center clinical study with follow-up of more than 24 months. Purpose: To evaluate the union rates and relevant risk factors for non-union after posterior lumbar interbody fusion (PLIF) using porous-coated closed-box titanium spacers. Overview of Literature: Although the use of a closed-box interbody spacer for PLIF could avoid potential complications associated with the harvesting of autologous bone, few studies have reported detailed follow-up of fusion progression and risk factors for non-union in the early postoperative period. Methods: PLIF using closed-box spacers without filling the autologous bone was performed in 78 (88 levels) consecutive patients. Surgical procedures included PLIF using traditional pedicle screw fixation (PLIF, n=37), PLIF using cortical bone trajectory screw fixation (CBT-PLIF, n=30), and transforaminal lumbar interbody fusion with traditional pedicle screw fixation (TLIF, n=11). Lateral dynamic radiography and computed tomography findings were investigated, and the relationship between the union status and variables that may be related to the risk of non-union was tested statistically. Results: The overall bone union rates at 12 and 24 months were 68.0% and 88.5%, respectively. Incidences of bone cyst formation, subsidence, and retropulsion of spacers were 33.3%, 47.4%, and 14.1%, respectively. Union rates at 24 months were 94.6% in PLIF, 80.0% in CBT-PLIF, and 90.9% in TLIF. Multivariate logistic regression analyses showed that at 12 months postoperatively, the risk factor for non-union was age >75 years (p=0.02). In contrast, no significant risk factor was observed at 24 months. Conclusions: These findings demonstrated the efficacy of interbody closed-box spacers for PLIF without the need to fill the spacer with autologous bone. However, the risk of non-union should be considered in elderly patients, especially intra-operatively and during the early postoperative stage.

Association of Continuous Vertebral Bone Bridges and Bone Mineral Density with the Fracture Risk in Patients with Diffuse Idiopathic Skeletal Hyperostosis

Furukawa Mitsuru,Okuyama Kunimasa,Ninomiya Ken,Yato Yoshiyuki,Miyamoto Takeshi,Nakamura Masaya,Matsumoto Morio 대한척추외과학회 2022 Asian Spine Journal Vol.16 No.1

Study Design: Cross-sectional study.Purpose: To examine whether the number of continuous vertebral bone bridges and bone mineral density (BMD) influence the fracture risk in diffuse idiopathic skeletal hyperostosis (DISH) patients.Overview of Literature: Bone bridges connecting through the intervertebral body in DISH create long lever arms that can increase the risk of fractures from minor trauma. DISH patients have a BMD that is higher than or comparable to those of age-matched healthy subjects.Methods: We examined the computed tomography scans from the thoracic vertebra to the sacrum used to diagnose DISH in 140 patients (98 men and 42 women; average age, 78.6 years). We compared patients who did (n=52) and did not have (n=88) fractures at the continuous vertebral bodies fused by bone bridges. The relationship between the vertebral fractures and the maximum number of vertebrae that are bony cross-linked with contiguous adjacent vertebrae (max VB) from the thoracic vertebra to the sacrum or from the lumbar vertebra to the sacrum and proximal femur BMD were analyzed using a logistic regression model.Results: We found that after adjusting for the confounding factors, higher max VB, both from the thoracic vertebrae to the sacrum and the lumbar vertebrae to the sacrum, was associated with a higher risk of vertebral fractures. This difference was statistically significant. The risk was higher when only the lumbar vertebrae to the sacrum was considered (thoracic vertebrae to the sacrum: odds ratio, 1.21; p<0.05; lumbar vertebrae to the sacrum: odds ratio, 2.78; p<0.01). Moreover, low proximal femur BMD in DISH patients raises the fracture risk (odds ratio, 0.47; p<0.01).Conclusions: Many continuous vertebral bone bridges, especially those that extend to the lumbar spine and low proximal femur BMD, are risk factors for fracture in DISH patients.

Effects of Bone Cross-Link Bridging on Fracture Mechanism and Surgical Outcomes in Elderly Patients with Spine Fractures

Furukawa Mitsuru,Fujiyoshi Kanehiro,Okubo Toshiki,Yanai Yoshihide,Matsubayashi Kohei,Kato Takashi,Kobayashi Yoshiomi,Konomi Tsunehiko,Yato Yoshiyuki 대한척추외과학회 2023 Asian Spine Journal Vol.17 No.4

Study Design: This study adopted a cross-sectional study design.Purpose: This study was designed to investigate the effects of bone cross-link bridging on fracture mechanism and surgical outcomes in vertebral fractures using the maximum number of vertebral bodies with bony bridges between adjacent vertebrae without interruption (maxVB).Overview of Literature: The complex interplay of bone density and bone bridging in the elderly can complicate vertebral fractures, necessitating a better understanding of fracture mechanics.Methods: We examined 242 patients (age >60 years) who underwent surgery for thoracic to lumbar spine fractures from 2010 to 2020. Subsequently, the maxVB was classified into three groups: maxVB (0), maxVB (2–8), and maxVB (9–18), and parameters, including fracture morphology (new Association of Osteosynthesis classification), fracture level, and neurological deficits were compared. In a sub-analysis, 146 patients with thoracolumbar spine fractures were classified into the three aforementioned groups based on the maxVB and compared to determine the optimal operative technique and evaluate surgical outcomes.Results: Regarding the fracture morphology, the maxVB (0) group had more A3 and A4 fractures, whereas the maxVB (2–8) group had less A4 and more B1 and B2 fractures. The maxVB (9–18) group exhibited an increased frequency of B3 and C fractures. Regarding the fracture level, the maxVB (0) group tended to have more fractures in the thoracolumbar transition region. Furthermore, the maxVB (2–8) group had a higher fracture frequency in the lumbar spine area, whereas the maxVB (9–18) group had a higher fracture frequency in the thoracic spine area than the maxVB (0) group. The maxVB (9–18) group had fewer preoperative neurological deficits but a higher reoperation rate and postoperative mortality than the other groups.Conclusions: The maxVB was identified as a factor influencing fracture level, fracture type, and preoperative neurological deficits. Thus, understanding the maxVB could help elucidate fracture mechanics and assist in perioperative patient management.