By combining CT scanning with a Form 2 3D printer, the team were able to fabricate unified patient-specific devices, which proved capable of helping surgeons carry out complex spinal osteotomy procedures. Using the guides, the doctors safely and accurately inserted 30 screws into the vertebrae of 15 test subjects, demonstrating both their efficacy and precision within intricate dorsal operations.
The necessity of surgical guides
A laminectomy is essentially an operation in which surgeons remove a patient’s ‘lamina’ vertebrae, a bone located at the top of the spine. The surgery is necessary for treating conditions such as spinal stenosis or spondylolisthesis which cause lower back pain, but even though it’s a common procedure, it’s not without risk.
Patients can potentially suffer dural tears, damaging their spine’s neural elements, as well as other serious issues like vascular injury or infection. In order to avoid such complications, it’s essential to install pedicle screws accurately, but implantation methods vary wildly from ‘free-hand’ processes to robotic-assisted techniques.
Aside from the method, being able to precisely navigate a patient’s individual anatomy during surgery is also vital to success, making tailor-made guides ideal for the task. Given that existing devices have generally been restricted to pedicle screw guides, the team opted to develop a novel tool that’s specifically designed to optimize laminectomy outcomes.
3D printing the ‘2-in-1’ devices
Leveraging CT scanning and the 3D Slicer CAD software, the doctors constructed 3D models of three cadaver spinal cords, and used them as a basis for their patient-specific guides. The devices were eventually designed to be 2.5mm wide and 14mm deep, and featured modular slots, allowing drill guides to be attached as needed.
Once ready, the templates were fabricated using a standard Formlabs 3D printer and Grey Pro resin, and given to a surgeon, who was tasked with deploying them without pre-surgical planning. In order to assess the efficacy of their design, the team then set up a camera to record the procedure, starting at the time the guide was secured to the bone.
Watching the footage back, and using post-op CT scanning, the clinicians found that all 30 of the screws tested had been successfully fitted without cortical perforation. What’s more, the mean difference between the planned screw position and its actual location was just 1.1mm, and on average, the procedure took just 4 minutes and 46 seconds to complete.
Although the team conceded that their spines were unrealistically clean during testing, they consider their lack of bone breakage to represent a success, especially compared to the perforation rates of 25-43% seen in other studies. As a result, with further R&D and animal trials, the scientists believe that their devices could be deployed in future, as a means of simplifying complex spinal surgical procedures.
Commercial 3D printed spinal implants
While 3D printing is increasingly being utilized to fabricate patient-specific surgical guides, the technology is also widely-used to create end-use spinal implants.
Orthopedic implant firm 4WEB Medical has a large portfolio of spine transplant products, and it added a new Stand-Alone Anterior Spine Truss System to its range in October last year. The device features an enhanced dual-step locking system, which prevents spinal screws from backing out during surgery.
Similarly, Chinese 3D printer and scanner manufacturer Shining 3D has seen its technologies used by Korean medical firm Mantiz to additive manufacture spinal implants. Utilizing a Shining metal 3D printer, the company has been able to provide its PANTHER line of interbody fusion cages with complex mesh-like structures.
Elsewhere, medical device manufacturer Tangible Solutions has conducted a study into the consistency of 3D printed titanium spinal implants. Essentially, the company found that despite some minor center-shifting issues, additive manufacturing’s repeatability was akin to that found elsewhere in the implant industry.
The researchers’ findings are detailed in their paper titled “The Development of novel 2-in-1 patient specific, 3D-printed laminectomy guides with integrated pedicle screw drill guides.”
The research was co-authored by Andrew Kanawati, Renan Jose Rodrigues Fernandes, Aaron Gee, Jennifer Urquhart, Fawaz Siddiqi, Kevin Gurr, Christopher S. Bailey and Parham Rasoulinejad.
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Featured image shows four photos of the doctors’ 3D printed surgical guides. Photos via the World Neurosurgery journal.