Influence of the screw augmentation technique and a diameter increase on pedicle screw fixation in the osteoporotic spine: pullout versus fatigue testing

Purpose For posterior spinal stabilization, loosening of pedicle screws at the bone-screw interface is a clinical complication, especially in the osteoporotic population. Axial pullout testing is the standard pre-clinical testing method for new screw designs although it has questioned clinical relev...

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Bibliographic Details
Published in:European spine journal 2014-10, Vol.23 (10), p.2196-2202
Main Authors: Kueny, Rebecca A., Kolb, Jan P., Lehmann, Wolfgang, Püschel, Klaus, Morlock, Michael M., Huber, Gerd
Format: Article
Language:English
Subjects:
Aged
Aged, 80 and over
Biomechanical Phenomena
Bone Cements
Equipment Failure Analysis
Female
Humans
Lumbar Vertebrae - physiology
Lumbar Vertebrae - surgery
Male
Materials Testing
Medicine
Medicine & Public Health
Neurosurgery
Original Article
Osteoporosis - surgery
Pedicle Screws - adverse effects
Spinal Fusion - adverse effects
Spinal Fusion - instrumentation
Spinal Fusion - methods
Surgical Orthopedics
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Summary:Purpose For posterior spinal stabilization, loosening of pedicle screws at the bone-screw interface is a clinical complication, especially in the osteoporotic population. Axial pullout testing is the standard pre-clinical testing method for new screw designs although it has questioned clinical relevance. The aim of this study was to determine the fixation strength of three current osteoporotic fixation techniques and to investigate whether or not pullout testing results can directly relate to those of the more physiologic fatigue testing. Methods Thirty-nine osteoporotic, human lumbar vertebrae were instrumented with pedicle screws according to four treatment groups: (1) screw only (control), (2) prefilled augmentation, (3) screw injected augmentation, and (4) unaugmented screws with an increased diameter. Toggle testing was first performed on one pedicle, using a cranial-caudal sinusoidal, cyclic (1.0 Hz) fatigue loading applied at the screw head. The initial compressive forces ranged from 25 to 75 N. Peak force increased stepwise by 25 N every 250 cycles until a 5.4-mm screw head displacement. The contralateral screw then underwent pure axial pullout (5 mm/min). Results When compared to the control group, screw injected augmentation increased fatigue force (27 %, p  = 0.045) while prefilled augmentation reduced fatigue force (−7 %, p  = 0.73). Both augmentation techniques increased pullout force compared to the control ( p s 
ISSN:0940-6719
1432-0932
DOI:10.1007/s00586-014-3476-7