Abstract
Background and Study Aim Cortical screws were proposed as an alternative to the traditional pedicle screws.
Diverse experimental results support the biomechanical superiority of cortical screws
compared to pedicle screws. Laminectomy is often part of multilevel lumbar surgeries.
Laminectomy might weaken the medial bony edge at the entry of the divergently oriented
screw and, thereby, the screw purchase. This study investigated the biomechanical
strength of lumbar cortical screw after laminectomy.
Objective To compare the fixation strength of cortical screws and traditional pedicle screws
after lumbar laminectomy.
Material and Methods A total of 120 pedicles from 60 lumbar vertebrae of 12 cadavers (8 men, 4 women)
were assessed. The mean age of the cadavers was 73.4 ± 6.2 years (range: 62–82 years).
Using a posterior midline approach, we inserted the traditional pedicle screws into
one and the cortical screws into the other side of each vertebra. Laminectomy was
performed after screw insertion. Vertical pullout strength and toggle strength testing
were performed to compare the fixation strength between the two sides.
Results After laminectomy, the pullout strength of the cortical screws was 718.92 ± 340.76 N,
and that of the pedicle screws was 625.78 ± 287.10 N (p = 0.183). The toggle strength of the cortical screws was 544.83 ± 329.97 N; that
of the pedicle screws was 613.17 ± 311.70 N (p = 0.145). No significant difference was found in biomechanical strength between the
two types of screws.
Conclusion Despite laminectomy, lumbar cortical screws offers comparable pullout and toggle
biomechanical strength as traditional pedicle screws.
Keywords
lumbar vertebrae - laminectomy - cortical screws - pullout strength - toggle strength
