1. Improvement of Pedicle Screw Placement with First-time Use of Patient Specific Drill Guides by Novice Surgeon
Kyle Walker, MD; Michael Silverstein, MD; David Gurd, MD
Mid-America Orthopaedic Association
2016 Annual Meeting – April 14th, 2016

2. My colleagues and myself have no disclosures to report.
Conflicts of Interest
My colleagues and myself have no disclosures to report.

3. Introduction – PSF with Pedicle Screws
Utilized for over 3 decades
Used to treat multiple spinal pathologies
Small Margin of Error
PSF with pedicle screw placement has been used since the 80s for spinal fixation in multiple pathologies including scoliosis and DDD. Because of the location of the pedicle in relation to the spinal cord, nerve roots and other major structures, accurate placement is critical and there is a small margin of error afforded to avoid poor outcome.

4. Introduction – Current Techniques
Freehand Technique1
Fluoroscopy Aided
Neuromonitoring
10% - 30% “misplacement”2,3
Navigational
i.e. O-Arm™
1% - 8% “misplacement”2,3
The freehand technique as described by Lenke et al, involves choosing starting points on the posterior aspect of the spine that vary based on level of screw placement. A blunt tipped awl is then used to penetrate into the vertebrae through the pedicle and into the vertebral body. A probe is then used to invesitage for breach out of cortex. A measurement of depth is taken, the hole is tapped if necessary, and then a screw is placed. If there is concern for adequate placement, an intraoperative fluoroscopic image can be taken to verify location and trajectory. Navigational techniques using CT scan have improved the percent of “misplacement” (defined by breach of cortex on post operative imaging) however this technique requires extra radiation and expensive equiptment. Furthermore, it changes the overall procedure substantially?

5. Introduction – 3D Printers
Novel technology with high resolution
Pervasive in multiple orthopaedic applications
Shoulder
Knee
Spine
3D printing is a novel technology that is ideal for creating single use patient specific instruments for assistance in surgery. Its high resolution allows printing of complex biological shapes that can interface with different parts of the human body. This technology is currently being used for multiple areas of orthopaedic surgery including shoulder, knee, and spine. Of note, most studies for spine to date have been in the cervical spine.
Sugawara T, Higashiyama N, Kaneyama S, et al. Multistep pedicle screw insertion procedure with patient-specific lamina fit-and-lock templates for the thoracic spine: clinical article. J Neurosurg Spine. 2013;19(2):

6. Study Aims
While some studies have been performed looking at the accuracy of pedicle screw placement with PSIs none have been perform in a first time user or with a novice surgeon
We hypothesize that we can substantially improve thoracolumbar pedicle screw placement in a junior resident using PSI technology who has not utilized this technology previously

7. Methods Pre-operative 59 year old male cadaver
CT Scan and 3D Reconstruction
Randomized T1-L5
Control at each level
Axial slicing and trajectory planning
Canal Alignment and PSI Creation
Print PSI
A 59 year old male without spinal pathology or previous history of spinal surgery was obtained and CT scanned using 0.6mm slicing. The dicom images were imported into proprietary Cleveland Clinic software and reconstructed into an STL surface model. This model was exported into the liscensed CAD software SpaceClaim for trajectory planning. A staff surgeon approved all starting point on the posterior lamina and the second trajectory point was taken by determining the mid point of the small portion of the pedicle screw. A canal developed to accept at 3.0 mm drill bit was aligned to the trajectory and a PSI was created around the canal at each level by subtracting the spine surface to create a negative impression. The PSI was then printed in a FDM printer with durable and sterilixable polycarbonate material.

8. Methods Intraopeartive Exposure Verbal Instruction PSI placed
Craniocaudal direction
3.0mm pilot hole created and tapped
Pedicle Screw Placed
Prechosen Sizing
Freehand Placement T1-L5
After exposure a short, 5 minute, verbal instruction on use of the device was given to the resident surgeron. The PSI grouping was performed first to maximize usable lamina for the PSI. The PSI was placed at each respective level and a 3.0 mm pilot hole was drilled using the canal to guide starting point and trajectory. The screws were placed in order from T1-L5 to avoid PSI interaction with the previous levels’ pedicle screw. Tapping was then performed followed by screw placement. The screws for both the PSI and FH grouping were pre-chosen based on nearest available screw size that was less than 80% of the diameter of the CT scan measurements of the isthmus of the pedicle. After all PSI levels were placed the screws were covered at each level and the SOC freehand placement was performed at each level. The surgeon was able to operate as if he had a first assist for both groupings.

9. Methods Post-Operative CT Scanned Blinded Analysis Segmented Vertebrae
“Anatomic Placement”
Perforation
Poor Outcome
Segmented Vertebrae
Realigned – MeshLab®
Deviation Analysis
Mid-Pedicle Translation
Global Angulation
Post operatively the spines were scanned and analyzed blindly by a staff orthoapedic surgeon. Each pedicle screw placement was labeled by precense of perforation, “anatomic placement” as defined by the need to adjust screw prior to fixation, and by high likelihood of poor outcome. The spine was then 3D reconstructed as before. Each vertebrae was segmented and re-aligned to the preoperative coordinate system using the open source software Meshlab. A secondary analysis was performed on the PSI grouping to measure accuracy of placement based on global angulation deivation from planned trajectory as well as translational deviation at the mid pedicle point.

10. Results PSI FH Perforation 3 8 0.1411 Non-Perforation 14 9
p-value
Perforation 3 8
0.1411
Non-Perforation 14 9
Anatomic Placement 1 6
0.0854
Non-Anatomic 16 11
High Likelihood of Poor Outcome 5
0.0445*
Low/No Likelihood of Poor Outcome 17 12
Avg Screw Placement Time (s)
± 74.42
± 42.97
0.0319*
We had a significant improvement over the FH technique with likelihood of poor outcome and time to placement. No adjustments were made after intial placement so the total time to placement did not include changes that would have been required based off of intraoperative imaging. Of note, the guide used in this study was an early iteration of the design that did not control for tap or screw placement which we believe would have lead to anatomic placement of all 17 levels with the PSI grouping.
PSI
Angular Deviation from Plan (degrees)
± 3.209
Mid-Pedicular Deviation from Plan (mm)
2.012 ± 1.635

11. Study Limitations Small Sample Size
Tap trajectory and screw placement not controlled

12. Conclusions
PSI Technology Improves Screw Placement in Terms of Outcomes
Improves Overall Time to Screw Placement
Easily Utilized by First Time User

13. Future Potential Preoperative Planning to Shorten OR Time
Control for Tapping and Screw Placement
Ability to Optimize Trajectory and Screw Size at Each Level

14. References
1) Gertzbein SD, Robbins SE. Accuracy of pedicular screw placement in vivo. Spine. 1990;15(1): ) Seller, K., Wild, A., Urselmann, L., et al. (2008). Prospektive Schraubenfehllagenanalyse nach konventioneller und navigierter Pedikelschraubenimplantation / Computer Assisted Orthopedic Surgery (CAOS). Biomedizinische Technik/Biomedical Engineering, 50(9), pp ) Lee CH, Hyun SJ, Kim YJ, Kim KJ, Jahng TA, Kim HJ. Accuracy of Free Hand Pedicle Screw Installation in the Thoracic and Lumbar Spine by a Young Surgeon: An Analysis of the First Consecutive 306 Screws Using Computed Tomography. Asian Spine J Jun;8(3):

15. Thank You