Spinal instrumentation for metastatic disease: in vitro biomechanical analysis

A calf spine corpectomy model was employed to compare the ability of various spinal instrumentation techniques to restore stability after destruction of the anterior and middle columns. The constructs tested were an intact specimen, a Harms titanium cage, a cross-linked rectangular anterior Texas Scottish Rite Hospital construct, posterior segmental Luque rods combined with a cross-linked rectangular anterior TSRH construct, posterior Luque rods alone, cross-linked posterior Luque rods, and posterior Luque rods embedded in polymethyl-methacrylate (PMMA). When compared to the intact state, only the combined anterior/posterior construct and the anterior TSRH construct were able to restore axial, sagittal, and torsional stiffnesses to levels equal to or higher than control levels. Embedding Luque rods in PMMA provided greater stiffness than either Luque rods alone or cross-linked Luque rods. If the anterior and middle columns of the spine are incompetent, as frequently occurs with metastatic disease, the goal of surgical treatment is to restore spinal stability while decompressing the neural elements. Either anterior or posterior techniques may be used. The findings of this study imply that commonly used spinal instrumentation constructs differ in their ability to restore axial, sagittal, and torsional stiffnesses to normal levels.