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World Neurosurg. 2018 Aug 6. pii: S1878-8750(18)31733-9. doi: 10.1016/j.wneu.2018.07.253. [Epub ahead of print]

Biomechanical fixation properties of the cortical bone trajectory in the osteoporotic lumbar spine.

Author information

1
Department of Orthopedics, the First Affiliated Hospital of Anhui Medical University, 210 Jixi Road, Hefei, Anhui 230022, China.
2
Department of Orthopedics, the First Affiliated Hospital of Anhui Medical University, 210 Jixi Road, Hefei, Anhui 230022, China. Electronic address: shencailiang1616@163.com.

Abstract

OBJECTIVE:

Selecting optimal strategies for improving fixation in the osteoporotic lumbar spine remains an important issue in clinical research. Cortical bone trajectory (CBT) screws have been proven to enhance screw pullout strength. However, the biomechanical efficacy of these screws remains understudied. The aim of this study was to evaluate the biomechanical efficacy of CBT screws in the osteoporotic lumbar spine.

METHODS:

A total of 31 vertebrae from 14 cadaveric lumbar spines were obtained. All specimens were measured by computed tomography, while the diameter of their pedicles, excluding those of vertebral bodies with very small pedicle developments, was calculated. After measuring bone mineral density (BMD), the CBT screw was randomly inserted into one side, while the traditional trajectory (TT) screw was inserted into the contralateral side. The maximum insertional torque was recorded after the screw insertion. A total of 21 vertebrae were subjected to a pullout testing at a rate of 5 mm/min, while 10 vertebrae were subjected to a cyclic fatigue testing. Each construct was loaded until exceeding 5 mm.

RESULTS:

The average BMD was 0.567±0.101 g/cm2. The CBT screw had a higher maximum insertional torque (t=5.78, p<0.001, 0.333 Nm vs. 0.188 Nm) and higher axial pullout strength than the TT screw (t=7.41, p<0.001, 394 N vs. 241 N). Increased BMD was not significantly associated with a higher pullout load. Compared with the TT screw, the CBT screw showed better resistance to fatigue testing and required more cycles to exceed 5 mm (t=5.62, p<0.001, 6161 cycles vs. 3639 cycles). The failure load for displacing the screws was also significantly greater for the CBT screw than for the TT screw (t=5.75, p<0.001, 443 N vs. 317 N).

CONCLUSION:

The CBT screw had a better biomechanical fixation performance in the osteoporotic lumbar spine compared with the standard pedicle screw.

KEYWORDS:

Cortical screw; Pedicle screw; biomechanics; cortical bone trajectory; lumbar spine; osteoporosis; traditional trajectory

PMID:
30092463
DOI:
10.1016/j.wneu.2018.07.253

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