Investigation and Feasibility of Combined 3D Printed Thermoplastic Filament and Polymeric Foam to Simulate the Cortiocancellous Interface of Human Vertebrae

Abstract

Disorders of the spine are among the most common indications for neurosurgical and orthopedic surgical interventions. Spinal fixation in the form of pedicle screw placement is a common form of instrumentation method in the lower cervical, thoracic, and lumbar spine. A vital principle to understand for the safe and accurate placement of pedicle screws is the palpable difference between the cortical and cancellous bone, both of which have different material properties and compositions. Probing and palpation of the hard cortical bone, also known as the “ventral lamina”, covering the neural elements of the spinal canal during screw placement provides manual feedback to the surgeon, indicating an impending breach if continued directional force is applied. Generally, this practice is learned at the expense of patients in live operating room scenarios. Currently, there is a paucity of human vertebra simulation designs that have been validated based on the in vivo ultrastructure and physical properties of human cortical and cancellous bone. In this study, we examined the feasibility of combining three-dimensionally printed thermoplastic polymers with polymeric foam to replicate both the vertebral corticocancellous interface and surface anatomy for procedural education.

The Place of 3D Printing Preoperative Planning in Upper Thoracic Fractures

“…In the study by William Clifton et al, for 40 C7, 40 T6, and 40 L5 pedicle screws, the rate of agreement between the pedicle positions studied on preoperative models and the postoperative pedicle screw positions was found to be 100% for C7, 100% for T6, and 93% for L5 (26). In our study, 2 (13.3%) of the 15 upper thoracic fracture patients (group 1) were T3, 5 (33.3%) were T4, and 8 (53.3%) were T6 fractures, which were operated on by preoperative planning using 3D modeling.…”

The SpineBox: A Freely Available, Open-access, 3D-printed Simulator Design for Lumbar Pedicle Screw Placement

“…The individual vertebral models in the simulator are designed hollow in order to allow the user to create infill gradients with their chosen slicing software before printing, or to fill with porous foams that accurately replicate the material properties of cancellous bone. Both of these methods have been previously validated as accurate methods of simulating cortical and cancellous bone [12,13,17]. The space around the vertebral models within the housing box can also be easily filled with soft foam, cotton, silicone, or other materials in order to simulate soft tissue structures that can impede visualization during screw placement, and allows the use of retractors during the simulation.…”

“…A: soft polyurethane foam is used in layers to replicate visualization hindrance of the bony posterior elements of the lumbar spine, and can be cut with a scalpel (arrow); B: retractors can be used for exposure of the lumbar spine with similar instrument-working depth, as in a live operative scenario A total of 100 pedicle screws in 50 lumbar levels were placed within the 10 models. Five models were filled with polyisocyanate foam in order to replicate a previously validated method of simulating cancellous bone [17]. The other five models were sliced with a 25% infill in a honeycombed pattern within the vertebrae, which is another validated method of simulating vertebral cancellous bone [18].…”

Orientation Planning in the Fused Deposition Modeling 3D Printing of Anatomical Spine Models

“…One of the most advantageous properties of FDM printing is the ability to manipulate infill or internal density and structures, thus saving material and allowing for variability in models. This is one property that is utilized by our lab to create corticocancellous bone [10].…”

“…To date, these FDM 3D printing techniques have not been explored in great detail, especially in the context of spine modeling. Though many researchers have focused on improving the mechanical properties of the models in order to simulate properties of human bone, methods to preserve the anatomical structure of the model have been investigated to a lesser extent [10][11][12][13][14]. The ability to manipulate the STL file before creating the G-code in order to establish the most efficient printing sequence is not a new concept.…”