The Invention of New Anterior Spinal Instrumentation Prototype: A Structural Analysis of KKU Expandable Cage
Surachai Sae-Jung MD*, Kitti Jirarattanaphochai MD*, Sukit Saengnipanthkul MD*
Affiliation : * Department of Orthopedics, Faculty of Medicine, Khon Kaen University, Khon Kaen
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 simulta-
neously stabilize the upper vertebra with the lower vertebra, to tolerate the thoracolumbar physiologic load
and augment the interbody arthrodesis of the spine.
Materials and Methods : The new model of expandable anterior spinal instrumentation, named KKU expand-
able 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 thora-
columbar physiologic compression load (1250N) is between 11692.7 N/m2 to 94.7266 x106 N/m2, less than
compression strength of the 316L stainless steel (170 x106 N/m2).
Conclusion : The stainless steel 316 L KKU expandable cage for anterior spinal instrumentation can with-
stand 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.
Keywords : Anterior instrumentation, Spine surgery, Expandable cage
