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Comparing the fixation of a novel hollow screw versus a conventional solid screw in human sacra under cyclic loading.

Abstract：

STUDY DESIGN:The loosening rates of two monocortical pedicle screw designs (hollow and solid) were compared in a cadaveric sacrum model subjected to cyclic loading. OBJECTIVE:To determine if a hollow screw would be more resistant to loosening than a solid pedicle screw when placed into the pedicles of S1 and tested under stair-cased cyclic loading. SUMMARY OF BACKGROUND DATA:Screw loosening is a clinical problem for lumbosacral fusions. No previous literature has evaluated the use of a monocortical hollow screw within the sacrum; however, in other vertebral bodies, results of using this screw have been varied. METHODS:Seven fresh-frozen cadaveric sacra were thawed and stripped of soft tissues. Solid and hollow screws were inserted contralaterally into the pedicles of S1. A materials testing machine applied alternating flexion and extension bending moments at 1 Hz, to each screw independently, via a standard connecting rod. Flexion moments were applied starting at 0.5 Nm and increased by 0.5 Nm after every 1000 cycles until the screw had visibly failed. Extension moments were maintained at 0.5 Nm. Screw rotation (flexion) relative to the sacrum was recorded using a custom optical tracking system, and analyzed using 2-way repeated measures analyses of variances and post hoc Student-Newman-Keuls tests (alpha = 0.05). RESULTS:Screw rotation tended to gradually increase to six degrees, after which the screw was grossly loose. Overall, the hollow screw required fewer loading cycles (P = 0.004) and less applied moment (P = 0.003) to achieve the same magnitude of screw rotation as the solid screw. To achieve 6 degrees of screw rotation, the number of loading cycles were 6301 +/- 2161 and 11151 +/- 4221 for hollow and solid screws, respectively. The corresponding applied moments were 3.5 +/- 1.0 Nm and 5.8 +/- 2.0 Nm. CONCLUSION.: The novel hollow screw was less resistant to loosening when compared with a conventional solid pedicle screw in this sacral model under cyclic loading.

journal_name

Spine (Phila Pa 1976)

journal_title

Spine

authors

McLachlin SD,Beaton BJ,Sabo MT,Gurr KR,Bailey SI,Bailey CS,Dunning CE

doi

10.1097/BRS.0b013e3181808c75

subject

Has Abstract

pub_date

2008-08-01 00:00:00

pages

1870-5

issue

eissn

0362-2436

issn

1528-1159

pii

00007632-200808010-00010

journal_volume

pub_type

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Comparing the fixation of a novel hollow screw versus a conventional solid screw in human sacra under cyclic loading.