The invention of new anterior spinal instrumentation prototype: a structural analysis of KKU expandable cage.

OBJECTIVE: Report the invention and structural analysis of the new model of anterior spinal instrumentation (KKU expandable cage) that is expandable for space filling after vertebral body resection while simultaneously stabilize the upper vertebra with the lower vertebra, to tolerate the thoracolumbar physiologic load and augment the interbody arthrodesis of the spine. MATERIAL AND METHOD: The new model of expandable anterior spinal instrumentation, named KKU expandable cage, was invented and designed using the computer. The structural property of this instrumentation was tested and analyzed using the computer based structural analysis software. RESULTS: The KKU expandable cage made out of 316L stainless steel is 0.0301044 kg in mass and 3.76305 x 10(-6) m3 for volume. The outer diameter of the device is 23 mm and the height can expand from 20 mm to 35 mm for space filling after thoracolumbar vertebrectomy. The stress in the device after applying the maximal thoracolumbar physiologic compression load (1250N) is between 11692.7 N/m2 to 94.7266 x 10(6) N/m2, less than compression strength of the 316L stainless steel (170 x 10(6) N/m2). CONCLUSION: The stainless steel 316 L KKU expandable cage for anterior spinal instrumentation can withstand the maximal thoracolumbar physiologic compression load without failure whereas its expandable property enable it to fill and fit in the space reaching the height of 35 mm. Therefore, the insertion of this device into a space after thoracolumbar or lumbar corpectomy or vertebrectomy for the vertebral osteomyelitis or vertebral metastasis is appropriate. The device can also stabilize the spine and tolerate the maximal physiologic compression load of the thoracolumbar vertebrae. Therefore, the device helps decrease the need for bone graft or bone substitute in these patients.