Biomechanical evaluation of Caspar cervical screws: comparative stability under cyclical loading. Neurosurgery 1993 Dec;33(6):1045-50; discussion 1050-1
Date
12/01/1993Pubmed ID
8133990DOI
10.1227/00006123-199312000-00013Scopus ID
2-s2.0-0027373248 (requires institutional sign-in at Scopus site) 26 CitationsAbstract
Anterior cervical instrumentation is used as an adjunct to bone fusion; however, definitive biomechanical data to support some applications and techniques are lacking. In the absence of supportive experimental data, posterior cortical penetration has been recommended with the Caspar system. Previously, we compared the axial pull-out strength of Caspar screws with and without posterior cortical penetration. This study compares the stability of unicortical versus bicortical screw penetration groups under cyclical loading simulating physiological flexion-extension. Caspar screws were placed in human cadaveric vertebrae with or without posterior cortical purchase. Each screw was separately tested, simulating flexion-extension to 200 cycles. Deformation time data allowed a direct comparison of screw "wobble" with and without posterior cortical purchase. The mean deformation differences between subcortical and bicortical groups were statistically significant and increased over time within both groups. Enhanced stability was noted with bicortical purchase throughout most of the examined range, becoming more pronounced over longer periods of cyclical loading. Significant (P < 0.05) increases in deformation over time were noted for both groups, suggesting potentially significant deterioration at the screw-bone interface, despite bicortical purchase. Such deterioration with repeated flexion-extension loading may be of concern in the use of Caspar plates in the presence of multicolumn instability.
Author List
Gallagher MR, Maiman DJ, Reinartz J, Pintar F, Yoganandan NAuthors
Frank A. Pintar PhD Chair, Professor in the Biomedical Engineering department at Medical College of WisconsinNarayan Yoganandan PhD Professor in the Neurosurgery department at Medical College of Wisconsin
MESH terms used to index this publication - Major topics in bold
Absorptiometry, PhotonBiomechanical Phenomena
Bone Screws
Cervical Vertebrae
Equipment Design
Equipment Failure
Humans
Stress, Mechanical