Development of a Computer-Aided Design and Finite Element Analysis Combined Method for Affordable Spine Surgical Navigation With 3D-Printed Customized Template

Abstract

Introduction: Revision surgery of a previous lumbosacral non-union is highly challenging, especially in case of complications, such as a broken screw at the first sacral level (S1). Here, we propose the implementation of a new method based on the CT scan of a clinical case using 3D reconstruction, combined with finite element analysis (FEA), computer-assisted design (CAD), and 3D-printing technology to provide accurate surgical navigation to aid the surgeon in performing the optimal surgical technique by inserting a pedicle screw at the S1 level.Materials and Methods: A step-by-step approach was developed and performed as follows: (1) Quantitative CT based patient-specific FE model of the sacrum was created. (2) The CAD model of the pedicle screw was inserted into the sacrum model in a bicortical convergent and a monocortical divergent position, by overcoming the geometrical difficulty caused by the broken screw. (3) Static FEAs (Abaqus, Dassault Systemes) were performed using 500 N tensile load applied to the screw head. (4) A template with two screw guiding structures for the sacrum was designed and manufactured using CAD design and 3D-printing technologies, and investment casting. (5) The proposed surgical technique was performed on the patient-specific physical model created with the FDM printing technology. The patient-specific model was CT scanned and a comparison with the virtual plan was performed to evaluate the template accuracyResults: FEA results proved that the modified bicortical convergent insertion is stiffer (6,617.23 N/mm) compared to monocortical divergent placement (2,989.07 N/mm). The final template was created via investment casting from cobalt-chrome. The template design concept was shown to be accurate (grade A, Gertzbein-Robbins scale) based on the comparison of the simulated surgery using the patient-specific physical model and the 3D virtual surgical plan.Conclusion: Compared to the conventional surgical navigation techniques, the presented method allows the consideration of the patient-specific biomechanical parameters; is more affordable, and the intraoperative X-ray exposure can be reduced. This new patient- and condition-specific approach may be widely used in revision spine surgeries or in challenging primary cases after its further clinical validation.

Commentary: Development of a Computer-Aided Design and Finite Element Analysis Combined Method for Affordable Spine Surgical Navigation With 3D-Printed Customized Template

“…The methodology provided by Eltes et al is a sound design; however, follow up data on this patient's surgical outcomes would benefit further understanding the reliability of utilizing a 3D printed template. Given the nature of recurrent spinal pathology, this patient may have external factors which could contribute to the post-operative stress applied to the new screw (i.e., osteoporosis) ( 1 , 3 , 4 ).…”

“…The recent publication by Eltes et al ( 3 ) outlines a therapeutic attempt on a patient with a history significant for multiple spinal surgeries presenting with acute broken S1 left pedicle screw in addition to associated failure of solid fusion between the L5 and S1 vertebrae. In summary, this study utilized Quantitative Computed Tomography (QCT) scans and segmentation to generate a three-dimensional geometric model of the patient's sacrum.…”

“…From a standpoint of pedicle screw placement, there is a growing amount of literature outlining similar methodologies which utilize a patient-specific spine template for placement. In addition, a future direction which Eltes et al ( 3 ) indirectly contributes to is in utilizing 3D printing in other areas in orthopedics such as oncologic tumors ( 4 , 6 ). Given the patient-specific approach of the 3D-printed templates, it may be possible to stereotactically navigate surgical resection of a tumor utilizing QCT as outlined earlier, which can potentially cause a dramatic improvement in patient outcomes if resection margins can be obtained ( 5 ).…”

“…Current literature on 3D printed templates have long been dominated by its use in congenital heart and vascular pathologies ( 7 , 8 ). Upon observation, the methodology by Eltes et al could be used in further decreasing pre-operative preparation among cardiovascular procedures through similar computer-aided-designs to lessen the intraoperative CT imaging discussed in aforementioned study ( 3 ).…”

Complicated Postoperative Flat Back Deformity Correction With the Aid of Virtual and 3D Printed Anatomical Models: Case Report

“…The virtual geometries are then integrated in the clinical communication as a 3DPDF document. (16). The document was accessible by clinicians from any institutional desktop PC or mobile device.…”