The effect of spinal shortening after total en bloc spondylectomy: a biomechanical study in the thoracic spine.

STUDY DESIGN: A biomechanical study using human cadaveric thoracic spine specimens. OBJECTIVE: To evaluate and compare the biomechanical effects of spinal shortening and cross-links in reconstruction after total en bloc spondylectomy (TES). SUMMARY OF BACKGROUND DATA: There have been no studies that have examined the biomechanical effects of spinal reconstruction after multilevel TES or the biomechanical effects of spinal shortening in reconstruction after TES. METHODS: Eight human cadaveric spines (T2-T9) were used. After the intact specimen had been biomechanically tested to determine the stiffness in compression, flexion, extension, left and right lateral bending, and left and right axial rotation, a TES at T5-6 was carried out. Three reconstruction methods were tested biomechanically (same as for the intact specimen) for their ability to restore stiffness to the specimen: (1) anterior short cage and multilevel posterior instrumentation at T3-8 with 2 cross-links (S2C), (2) anterior short cage and multilevel posterior instrumentation at T3-8 with 1 cross-link (S1C), and (3) anterior long cage and multilevel posterior instrumentation at T3-8 with 2 cross-links (L2C). A cage that was 6-10 mm shorter in height than the space created by the TES at T5-6 was selected as the "short cage" and a cage 10 mm taller in height than the short cage was selected as the "long cage" in each specimen. RESULTS: All 3 reconstruction methods using an anterior cage and multilevel posterior instrumentation provides a stiffer construct than that shown by the intact specimen. The reconstruction method using the 10-mm shorter cage (S2C vs. L2C) provided more stiffness than the one using the longer cage. The reconstruction using 2 cross-links (S2C vs. S1C) did not provide a stiffer construct than the one using 1 cross-link. CONCLUSIONS: The reconstructions using an anterior cage and multilevel posterior instrumentation provided a stiffer construct than that shown by the intact specimen. The reconstruction using a 10-mm shorter cage provided a stiffer construct than the reconstruction using the longer cage.