As part of my Masters program, I took a course called EECE 542 – Computer Integrated Surgery, which focused on image segmentation/registration techniques, surgical interface design, and computer assisted surgery systems. My term project was focused on Femoral Head (Hip) resurfacing, a bone-preserving procedure used to treat early-stage cartilage degeneration of the femoral head. The procedure initially gained traction with surgeons as it was believed to be easier to revise to a total hip replacement (THR) (due to the preservation of healthy bone), and preserved normal hip kinematics better than a THR. As long-term studies became published, it would become suggested that the poor survival rate of the FHR made it an inferior procedure and when coupled with the high level of technical difficulty, the adoption rate would drop off. But that wasn’t clear at the time, so I soldiered on.
Through discussions with colleagues who have published in the area, I learned that one of the most difficult parts of the surgery is drilling a hole along the femoral neck axis. Deviations from this axis would impact the implant’s kinematics and ultimately its survival, so accuracy was at a premium.
It was originally planned that I would work with one of my labmates who was also in this course. I would handle the preoperative planning and postoperative analysis and he would integrate my imaging and trajectory planning into an IGSTK-based tracking system and perform mock surgery. Unfortunately we couldn’t get the DICOM files from our lab’s C-Arm to show up in the IGSTK tracker program, and attempting to load the trajectory data would crash the program, so we had to abandon our combined project plan and go off on our own.
My project goal was to determine the effects that removing a mechanical guidance jig would have on femoral neck axis drilling accuracy. I didn’t have access to the mechanical jig in question, one from Biomet, but their protocol required a certain amount of freehand interoperative planning that seemed redundant with the jig in place. I figured I could test freehand versus freehand with Biomet’s planning protocol to see if there were any effects.
I imaged smoked pig femurs (smoked because then I could perform the drilling on my kitchen table and not worry about contaminating everything) using a Siemens Arcadis Orbic 3D C-Arm and segmented them using ITKSnap after converting the filetype with 3D Slicer. This was done because I find the 3D marching snakes segmentation algorithm in ITKSnap more effective than the threshold-based options in Slicer, especially when dealing with noisy C-Arm images.
I then loaded the 3D model of the femur into Paraview, and plotted the femoral neck axis by slicing the model in the A/P plane and aligning a vector parallel to each side of the femoral neck. This seems arbitrary but I was assured that many surgeons use freehand neck-axis targeting in their surgeries, so I went with it.
As I mentioned before, I used two groups of femurs for the study. The first group, used as a control, were completely manually drilled, using the expert intuition of the guy with the cordless drill. The second group used the preliminary A/P and M/L Biomet targeting lines, and were drilled in an identical fashion.
Long story short, elimination of the drill guidance jig resulted in worse surgical outcomes than the control group. Since elimination isn’t possible, a movement towards simplification of the surgical workflow should be the goal and a group from Queen’s is using rapid prototyping to create custom drilling templates for each patient. I wanted to try this but was severely hampered by the lack of access to the very expensive Mimics software suite they used.
One of the main problems with this study was the guy doing the drilling. I know my way around tools, but wood is much different than bone, and my drill handling skills reflect this. In the case of the biomet targeting, I had to keep the drill perpendicular to both the A/P and M/L lines. This caused me to hesitate, manifesting itself in a lower drill rotation speed. This resulting in the drill tip wandering from it’s intended entrance site, greatly impacting accuracy. Several months after I completed the course, I learned from my supervisor, working with his startup company, that the tip wandering from guidance hesitation is a problem reported by surgeons. This was perhaps the most important finding from this study, far outside my original hypothesis.
You can read the full report here: EECE 542 Final Report