Hayato Futakawa, Hiroto Makino, Shoji Seki, Katsuhiko Kamei, Yushi Yashima, Yasuhito Yahara, Yoshiharu Kawaguchi
Proximity of the screw tip to the anterior and lateral walls, as well as excessive cement injection relative to vertebral body size, significantly increases the risk of leakage. To mitigate this risk, screws should be placed centrally within the vertebral body and at a safe distance from the cortical boundaries. The amount of injected cement should also be determined according to the volume of the individual vertebral body. These findings provide practical guidance for safer screw placement in spinal fusion using fenestrated screws.
INTRODUCTION: Although fenestrated screws enhance pull-out strength, cement leakage into segmental veins carries a risk of pulmonary embolism. This study aimed to identify factors that contribute to cement leakage during posterior spinal fusion with fenestrated screws.
METHODS: We conducted a retrospective analysis of 32 patients who underwent posterior spinal fusion with fenestrated pedicle screws. A total of 147 screws were evaluated using postoperative computed tomography (CT) scans. Risk factors were assessed by measuring vertebral CT values, the volume of injected cement and its ratio to vertebral body volume, and screw positioning parameters, including deviation and distance to the anterior and lateral walls.
RESULTS: Cement leakage occurred in 75% of patients (24 of 32) and in 35% of screws (52 of 147). All leakages were classified as leakage into segmental veins. No symptomatic pulmonary embolism was observed. The thoracic spine exhibited a higher leakage rate than the lumbar spine (47.5% vs. 28.4%, p<0.05). Leakage was significantly associated with shorter distances from the screw tip to the anterior (5.1 mm vs. 7.8 mm) and lateral (4.8 mm vs. 7.3 mm) vertebral walls, as well as a higher cement-to-vertebral-volume ratio (7.1% vs. 4.7%, p<0.01). Leakage also correlated with higher CT values in the posterior vertebral region (126 Hounsfield Unit [HU] vs. 103 HU; p<0.05). Screw deviation showed no association.
CONCLUSIONS: Proximity of the screw tip to the anterior and lateral walls, as well as excessive cement injection relative to vertebral body size, significantly increases the risk of leakage. To mitigate this risk, screws should be placed centrally within the vertebral body and at a safe distance from the cortical boundaries. The amount of injected cement should also be determined according to the volume of the individual vertebral body. These findings provide practical guidance for safer screw placement in spinal fusion using fenestrated screws.