Design of an In-situ Spinal Rod Cutter for Orthopaedic Surgeons
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Date
2017-09-20
Authors
Bodo, Andre
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
As spine deformities scoliosis and kyphosis progress in severity, surgical treatment
is often required. Implant rods are attached by bone screws to the spinal vertebrae to
correct these deformities and stabilize the spine. It can be difficult to cut these rods to the
ideal length before implantation and sometimes these rods are too long and must be cut
in-situ. Also, when revision surgery is performed to replace a rod section, in-situ rod
cutting must be performed. The rods are difficult to cut and only manual rod cutting tools
are available. These rod cutters are physically demanding to use and difficult to position
while avoiding any spurious with the exposed spine. There is a clear need for an improved
in-situ rod cutter. Thus, the objective of this thesis is to develop a new and improved
design for an in-situ rod cutter.
Experimental work was done to show that shear cutting and bolt-cutting techniques
produced the most desirable results for cutting spinal rods in-situ. The shear cutting
techniques required slightly less force than bolt cutting techniques and produced a
cleaner rod cut with less deformation. It was found that cutting force increased with the
diameter of the spinal rod, regardless of the rod material. Constraints and criteria were
established to guide the design of a new in-situ rod cutter. It was decided that any attempt
at designing a new in-situ cutter must include a non-manual power source for operation.
Two design alternatives, a shear cutting design and bolt-cutting design were presented
and scored in an engineering design process. A shear cutter design was initially chosen
and work was done to implement the shear cutter design. However, the prototype
fractured in initial testing and the shear cutter design was abandoned. A bolt-cutter design
was then developed and a 3D printed prototype was made to demonstrate the mechanism
involved. Analysis was performed to estimate the mechanical advantage of the
mechanism used to amplify the force applied by a pneumatic cylinder used as the power
source. Further development was required to implement the bolt-cutting design but initial
progress in this design project was achieved. It is recommended that stress analysis,
prototyping and testing be done to move this design towards application in spinal surgery.
Description
Keywords
Surgical Tool, Rod Cutter, Engineering Design, Spinal Rod Cutter, Mechanical Design