Impact of lumbar pedicle screw positioning on screw stability - A biomechanical investigation.
Pedicle screw
Screw-loosening
Spine
Spondylodesis
Journal
Clinical biomechanics (Bristol, Avon)
ISSN: 1879-1271
Titre abrégé: Clin Biomech (Bristol, Avon)
Pays: England
ID NLM: 8611877
Informations de publication
Date de publication:
04 2020
04 2020
Historique:
received:
08
09
2019
revised:
20
02
2020
accepted:
25
02
2020
pubmed:
8
3
2020
medline:
20
2
2021
entrez:
8
3
2020
Statut:
ppublish
Résumé
Screw loosening is a major complication following spondylodesis. While several modifications increase screw stability, some, such as screw augmentation, are associated with potential complications; new techniques are needed to minimize the risk of screw loosening without increasing complication rates. 13 fresh-frozen human lumbar vertebral bodies (L1 to L5) were dissected. In group 1 (n = 7), pedicle screws were implanted conventionally, while in group 2 (n = 6), the screws were positioned divergent in the sagittal pathway. Screw stability was tested under cyclic axial load; one testing-cycle included 1000 repetitions. The first cycle started with a load of 100 N while the load was increased by +20 N in each following cycle until failure. Failure was defined by either a >5 mm movement of the screw heads or triggering of the switch-off threshold. Average number of cycles until failure was increased in group 2 compared with group 1 (12,046 vs 9761 cycles), as was the average load to failure (Fmax 313 N vs 260 N). Overall, in group 2, the number of cycles until screw loosening or failure increased by 23% (p = 0.28), while the required force increased by 20% (p = 0.3). Statistically significant correlation between BMD and increased number of cycles completed as well as with increased load (p < 0.01) could be observed. The results demonstrate, that divergent screw-drift of pairs of screws in the sagittal plane tends to increase stability, especially in vertebral bodies with lower bone density. Moreover, we could demonstrate a correlation between BMD and stability of screw-fixation.
Sections du résumé
BACKGROUND
Screw loosening is a major complication following spondylodesis. While several modifications increase screw stability, some, such as screw augmentation, are associated with potential complications; new techniques are needed to minimize the risk of screw loosening without increasing complication rates.
METHODS
13 fresh-frozen human lumbar vertebral bodies (L1 to L5) were dissected. In group 1 (n = 7), pedicle screws were implanted conventionally, while in group 2 (n = 6), the screws were positioned divergent in the sagittal pathway. Screw stability was tested under cyclic axial load; one testing-cycle included 1000 repetitions. The first cycle started with a load of 100 N while the load was increased by +20 N in each following cycle until failure. Failure was defined by either a >5 mm movement of the screw heads or triggering of the switch-off threshold.
FINDINGS
Average number of cycles until failure was increased in group 2 compared with group 1 (12,046 vs 9761 cycles), as was the average load to failure (Fmax 313 N vs 260 N). Overall, in group 2, the number of cycles until screw loosening or failure increased by 23% (p = 0.28), while the required force increased by 20% (p = 0.3). Statistically significant correlation between BMD and increased number of cycles completed as well as with increased load (p < 0.01) could be observed.
INTERPRETATION
The results demonstrate, that divergent screw-drift of pairs of screws in the sagittal plane tends to increase stability, especially in vertebral bodies with lower bone density. Moreover, we could demonstrate a correlation between BMD and stability of screw-fixation.
Identifiants
pubmed: 32145671
pii: S0268-0033(20)30077-2
doi: 10.1016/j.clinbiomech.2020.02.013
pii:
doi:
Types de publication
Journal Article
Langues
eng
Sous-ensembles de citation
IM
Pagination
66-72Informations de copyright
Copyright © 2020 Elsevier Ltd. All rights reserved.