| Pullout Strength of the Cervical Expansion Screws: Biomechanical Study |
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Koang Hum Bak, M.D., Kyu Seok Lee, M.D., Seong Hoon Oh, M.D., Jin Hwan Cheong, M.D., |
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Department of Neurosurgery, School of Medicine, Hanyang University, Seoul, Korea |
| 경추부 확장성 나사못의 인장 항력: 생체역학적 연구 |
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백광흠·이규석·오성훈·정진환·김재민·김충현 |
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한양대학교 의과대학 신경외과학교실 |
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| Abstract |
Objective
Many factors have been studied to increase the pullout strength of spinal screws. Expansive screws from many manu- facturers have been developed to increase the pullout strength in cervical and thoracolumbar screw fixation. The objective of this study is to determine how much an expansive cervical screw design could improve biomechanical fixation in cervical spine.
Methods
There were 72 DOC (Depuy Acromed, Cleveland, USA) cervical screws that have a configuration of 12 mm in length and 4.0mm in diameter: There were 36 expansive screws and 36 regular non-expansive screws for control group.
After pilot holes were either drilled or awled, the 36 screws in each group were inserted into the synthetic cancellous material in either 0 , 20 , 30 angle. The screws were extracted axially at a rate of 2.4mm/min using a servohydraulic machine. Pullout strength was recorded with a digital oscilloscope. The synthetic bone was underwent macroscopic examination after pullout.
Results
The mean pullout force of the expansive screws was 371.42N±94.87 and the non-expansive screws was 362.99N ±78.55. There was no statistical significance in pullout resistance between two groups. Also there was an evidence of crack in grain structure of synthetic bone that expansive screws were inserted.
Conclusion
Expansive screw design does not increase pullout strength in cervical screws. The data represent only the primary stability of the screw because the present study design precluded any cycling testing.
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| Keywords:
Biomechanics, Bone screw, Spine fusion, Tensile strength |
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