Dr. Andrew Kanawati is an Orthopaedic Spine Surgeon at Westmead Hospital, Sydney, who has developed a special interest in clinical and research uses of 3D printing. He has developed several custom 3D printed patient-specific spinal guides to assist in surgery, and uses composite models made of several different materials to plan complex surgeries.
3D Printing Tumors
Historically, research for medical printing has focused on fused deposition modeling (FDM) printers due to their low price point and ubiquitous market penetration in the past. Dr. Kanawati felt there was a huge opportunity to use stereolithography (SLA), due to the superior material properties of the final parts. These material properties, such as being able to print watertight parts (something you can’t do with FDM), meant higher quality medical devices could be printed and tested. One day, Dr. Kanawati was examining a patient who was complaining of leg pain. The patient had been diagnosed with a benign tumor when they were young. A new MRI and CT scan revealed that the tumor was growing into the side of the patient’s spine. Pushing up against nerves, the tumor represented a serious medical challenge. Every tumor is different, and each patient is different. For complex cases involving the spinal cord and nerves, being able to examine human anatomy in 3D space can be the difference between a successful surgery or a failed one. Dr. Kanawati turned to his SLA 3D printer. A full model of the lower spin and tumor used 156ml of resin, the equivalent of only $23. A physical, 360º model of the patient’s spine model and tumor helps surgeons to reduce errors and improve patient outcomes. The models help surgeons visualize and handle the contact points between the tumor and the nerve branches, granting them greater dexterity and confidence when operating. This is a major benefit of 3D printing for spinal surgery. Having SLA printers in-house allows surgeons to scan, segment, and print models within a day. In emergency cases where time is of the essence, a 3D printed model can inform the surgeons’ decisions and grant them extra confidence. Having access to a 3D printed model helps with pre-operative planning, allowing Dr. Kanawati to assess the possibility of conducting a shortening operation. Less time in surgery means reduced spinal cord tension without causing direct neural damage. It also gave the team enhanced insight into which pedicles (a small stalklike structure connecting an organ or other part to the human or animal body) were viable, and how best to conduct the surgery. But Dr. Kanawati wasn’t done creating his patient model. Taking his 3D printing to the next level, he showcased the power of SLA printing for medical applications by printing with multiple materials on a single machine. Dr. Kanawati swapped his build tray for a new one, and started creating replicas of the patient’s nerves in Elastic Resin. This allowed him to overlay the nerves onto his spine model, meaning there were no surprises once the surgery started. He said, “during the operations, we entered the patient from the back. While in surgery, we couldn’t see the nerves, but because of the 3D printed model we knew exactly where they were.” Saving a Limited Resource 3D printing can assist in far more than preoperative planning. Dr. Kanawati wanted to know if he could 3D print patient-specific cutting guides to use for an accurate laminectomy. According to John Hopkins, a laminectomy is a type of surgery in which a surgeon removes part or all of the vertebral bone (lamina). This helps ease pressure on the spinal cord or the nerve roots that may be caused by injury, herniated disk, narrowing of the canal (spinal stenosis), or tumors. According to the Healthcare Cost and Utilization Project (HCUP) Nationwide Inpatient Sample (NIS), “the annual estimate of laminectomy discharges averages around 34 discharges per 100,000 adults from 1998 to 2008”, making them a very common operation. Dr. Kanawati once again turned to his SLS 3D printer, printing both the guides and a spinal model on the same build platform. After removing and post-processing his models, he was able to screw the guides into the spinal model to see if they fit. If any adjustments were needed, they could be easily reprinted. By conducting a full surgical simulation before the cadaveric study, the team is able to find issues with their cutting guides without wasting or risking a fresh cadaver. Given that cadavers are a limited resource, reducing failures in the preoperative testing phase is a source of significant cost savings. The cutting guides have another benefit: they enable the use of high-speed drills. Normally high-speed drills are not allowed in procedures, as if they are misguided they can damage surrounding neural elements. But with a perfect fit 3D printed cutting guide, these drills are usable and greatly improve and speed up surgery. Dr. Kanawati has since published a research paper on this topic, titled The Development of Novel 2-in-1 Patient-Specific, 3D-Printed Laminectomy Guides with Integrated Pedicle Screw Drill Guides.