Biomechanical analysis of anterior versus circumferential spinal reconstruction for various anatomic stages of tumor lesions

Study Design. Spinal reconstruction procedures for metastasis were evaluated biomechanically using human cadaver specimens. Objective. To investigate the stiffness of anterior versus circumferential spinal reconstructions for different anatomic stages of tumor lesions. Summary of Background Data. Metastatic tumors predominantly involve the vertebral bodies. Although anterior instrumentation and strut grafts provide excellent stability, it remains unclear to what extent vertebral destruction requires anterior reconstructions alone versus combined anterior and posterior procedures. Methods. Ten human cadaveric thoracolumbar spines were used. The L1 vertebral body and posterior elements were resected sequentially based on Weinstein's anatomic zone classification for tumor lesions. Anterior reconstruction was performed between T12 and L2 using an iliac strut graft and the Kaneda SR system (AcroMed, Cleveland, OH). For circumferential reconstruction, the Cotrel-Dubousset hook and rod system was combined with the anterior reconstruction procedure. Experimental groups included the intact condition and five reconstruction stages: anterior reconstructions for corpectomy, subtotal and total spondylectomies, and circumferential reconstructions for subtotal and total spondylectomies. Nondestructive biomechanical testing was performed under four different loading modes. Results. All the reconstruction groups except anterior instrumentation alone for total spondylectomy returned stiffness to a level equivalent or higher to that of the intact spine. There were no statistical differences observed between anterior and circumferential reconstruction for subtotal spondylectomy, Anterior instrumentation alone for total spondylectomy did not restore stiffness to the intact level, and demonstrated significantly lower stiffness than that of circumferential reconstruction. Conclusions, For corpectomy or subtotal spondylectomy, anterior reconstruction alone can provide stiffness equivalent to circumferential reconstruction. However, total spondylectomy significantly reduces the anterior reconstruction stiffness, suggesting the need for combined anterior and posterior procedures.