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The spine is the most common site of bony metastases in the human body, with approximately 18,000 new cases diagnosed annually in North America [1–3]. At least half of all spinal metastases are from breast, lung, prostate, or renal carcinoma [3, 4]. Most of these patients present to the spine surgeon with pain or weakness. The pain may be caused by destruction or collapse of the vertebral body with frank instability [5]. Weakness or paralysis may be caused by direct invasion of the spinal canal with tumor or by pathologic fracture with deformity and spinal cord compression [4]. Radiologic evidence of metastases does not become apparent on plain radiographs until approximately 30% to 50% of the bone is destroyed [3, 6]. Typically, these radiographs demonstrate either uniform vertebral collapse or ventral wedge compression with ensuing kyphotic deformity [2].

With improvements in chemotherapy, hormonal manipulation, and radiotherapy, survival times of many patients with metastatic disease have improved dramatically [7]. As a result of this lengthened survival, a shift in the management strategy for treatment of spinal metastatic disease has occurred, with some authors advocating an aggressive approach, including prophylactic stabilization to prevent pathologic fractures and their associated morbidity [7]. Identification of appropriate candidates for surgical intervention, both prophylactic and symptomatic, requires a firm understanding by the spine surgeon of the biomechanical changes initiated within the spine