The Development of a Newly Designed Expandable Cage for Spinal Fusion Surgery

This study aims to develop an expandable spinal fusion cage that is modular in nature. With use of such expandable spinal cage, the spinal curvature is physiologically maintained, and the increase of successful rate in spinal fusion is expected. The spinal column of bones is highly complex, housing and protecting critical elements of the nervous system that have innumerable peripheral nerves and circulatory bodies in close proximity. Additionally, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction. The vertebral bodies of the spine are not all equal in length or identical in shape. Potentially, it is necessary for the treatment of a given spinal injury to use a fusion cage having a specific angle, depending on the location of the spinal injury along the spine, to effectively immobilize those vertebral bodies to achieve clinically desirable results. When installing interbody devices, such as fusion cage, a surgeon may find that it is necessary to have more anterior expansion than was initially anticipated in order to correct spinal curvature. Consequently, it is often desirable to be able to increase the expansion in increments that allow the surgeon to determine whether expansion is sufficient. Therefore, it is desirable to have modular expansion device which can each be screwed into and secured in place in the cage so as to resist inadvertent removal during use. Practically, it is desirable for the fusion cages to not expand sideways, while the cages are expanding vertically. Sideways expansion may interface with positioning of bone chips for grafting. Some prior art devices expand radically which expands the devices vertically, but also sideways. This study is thus designed to develop a new expandable spinal fusion cage with modular design to solve the following two clinical problems: (1). Prevention of loosening of fusion cage or over stress of cage/bone contact surface, and (2). Restoration of physiological spinal curvature. The comparison of the mechanical characteristics between the conventional and newly expandable spinal fusion cage will be performed by using MTS test machine. Both static and cyclic tests involving compression, shear, subsidence and torsion tests will be performed according to ASTM F 2077-03 and ASTM F 2267-04 testing standard. The expandable spinal fusion cage is designed with the following features: (1) modular design in nature; the same body can be used with different degrees of expansion, (2) vertical expansion without sideways and (3) easy-to-operate. Summarily, the specific aims of this study are listed as follows: (1) provide surgeons with an easy-to-operate implant, (2) increase the successful rate in spinal fusion, (3) reduce the costs for spinal fusion, (4) establish close cooperation between medical professionals and engineers, (5) gain experience in the development of medical devices for engineers and surgeons, (6) become familiar with the requirements for official approval of a medical instrument.

Project ID:PB10006-1023
External Project ID:NSC100-2622-E182-002-CC3