Summary: In the Cotrel-Dubousset and Texas Scottish Rite Hospital spinal implants systems, the upper hook on the convex rod is usually clawed to prevent posterior pull out. A transverse process hook and an upwardly directed pedicle hook are usually inserted on the same lamina level. However, clawing two levels instead of one is a simpler surgical procedure. We biomechanically compared the posterior pull-out strength of a one-level versus two-level construct. The average load of failure of the double-level construct was significantly greater (p <0.05) as compared with the single level. Thus, the two-level construct is not only easier to insert, it is also stronger.
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