Augmented Bridge Spinal Fixation: A New Concept for Addressing Pedicle Screw Pullout via a Steerable Drilling Robot and Flexible Pedicle Screws

To address the screw loosening and pullout limitations of rigid pedicle screws in spinal fixation procedures, and to leverage our recently developed Concentric Tube Steerable Drilling Robot (CT-SDR) and Flexible Pedicle Screw (FPS), in this paper, we introduce the concept of Augmented Bridge Spinal Fixation (AB-SF). In this concept, two connecting J-shape tunnels are first drilled through pedicles of vertebra using the CT-SDR. Next, two FPSs are passed through this tunnel and bone cement is then injected through the cannulated region of the FPS to form an augmented bridge between two pedicles and reinforce strength of the fixated spine. To experimentally analyze and study the feasibility of AB-SF technique, we first used our robotic system (i.e., a CT-SDR integrated with a robotic arm) to create two different fixation scenarios in which two J-shape tunnels, forming a bridge, were drilled at different depth of a vertebral phantom. Next, we implanted two FPSs within the drilled tunnels and then successfully simulated the bone cement augmentation process.

Towards the Feasibility Analysis and Additive Manufacturing of a Novel Flexible Pedicle Screw for Spinal Fixation Procedures

In this paper, we explore the feasibility of developing a novel flexible pedicle screw (FPS) for enhanced spinal fixation of osteoporotic vertebrae. Vital for spinal fracture treatment, pedicle screws have been around since the early 20th century and have undergone multiple iterations to enhance internal spinal fixation. However, spinal fixation treatments tend to be problematic for osteoporotic patients due to multiple inopportune variables. The inherent rigid nature of the pedicle screw, along with the forced linear trajectory of the screw path, frequently leads to the placement of these screws in highly osteoporotic regions of the bone. This results in eventual screw slippage and causing neurological and respiratory problems for the patient. To address this problem, we focus on developing a novel FPS that is structurally capable of safely bending to fit curved trajectories drilled by a steerable drilling robot and bypass highly osteoporotic regions of the vertebral body. Afterwards, we simulate its morphability capabilities using finite element analysis (FEA). We then additively manufacture the FPS using stainless steel (SS) 316L alloy through direct metal laser sintering (DMLS). Finally, the fabricated FPS is experimentally evaluated for its bending performance and compared with the FEA results for verification. Results demonstrate the feasibility of additive manufacturing of FPS using DMLS approach and agreement of the developed FEA with the experiments.

Spatial Spinal Fixation: A Transformative Approach Using a Unique Robot-Assisted Steerable Drilling System and Flexible Pedicle Screw

Spinal fixation procedures are currently limited by the rigidity of the existing instruments and pedicle screws leading to fixation failures and rigid pedicle screw pull out. Leveraging our recently developed Concentric Tube Steerable Drilling Robot (CT-SDR) in integration with a robotic manipulator, to address the aforementioned issue, here we introduce the transformative concept of Spatial Spinal Fixation (SSF) using a unique Flexible Pedicle Screw (FPS). The proposed SSF procedure enables planar and out-of-plane placement of the FPS throughout the full volume of the vertebral body. In other words, not only does our fixation system provide the option of drilling in-plane and out-of-plane trajectories, it also enables implanting the FPS inside linear (represented by an I-shape) and/or non-linear (represented by J-shape) trajectories. To thoroughly evaluate the functionality of our proposed robotic system and the SSF procedure, we have performed various experiments by drilling different I-J and J-J drilling trajectory pairs into our custom-designed L3 vertebral phantoms and analyzed the accuracy of the procedure using various metrics.