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Abstract
BackgroundWith the properties of three-column fixation and anterior-approach-only procedure, anterior transpedicular screw (ATPS) is ideal for severe multilevel traumatic cervical instabilities. However, the accurate insertion of ATPS remains challenging. Here we constructed a patient-specific biocompatible drill template and evaluated its accuracy in assisting ATPS insertion.MethodsAfter ethical approval, 24 formalin-preserved cervical vertebrae (C2–C7) were CT scanned. 3D reconstruction models of cervical vertebra were obtained with 2-mm-diameter virtual pin tracts at the central pedicles. The 3D models were used for rapid prototyping (RP) printing. A 2-mm-diameter Kirschner wire was then inserted into the pin tract of the RP model before polymethylmethacrylate was used to construct the patient-specific biocompatible drill template. After removal of the anterior soft tissue, a 2-mm-diameter Kirschner wire was inserted into the cervical pedicle with the assistance of drill template. Cadaveric cervical spines with pin tracts were subsequently scanned using the same CT scanner. A 3D reconstruction was performed of the scanned spines to get 3D models of the vertebrae containing the actual pin tracts. The deviations were calculated between 3D models with virtual and actual pin tracts at the middle point of the cervical pedicle. 3D models of 3.5 mm-diameter screws were used in simulated insertion to grade the screw positions.FindingsThe patient-specific biocompatible drill template was constructed to assist ATPS insertion successfully. There were no significant differences between medial/lateral deviations (P = 0.797) or between superior/inferior deviations (P = 0.741). The absolute deviation values were 0.82±0.75 mm and 1.10±0.96 mm in axial and sagittal planes, respectively. In the simulated insertion, the screws in non-critical position were 44/48 (91.7%).ConclusionsThe patient-specific drill template is biocompatible, easy-to-apply and accurate in assisting ATPS insertion. Its clinical applications should be further researched.
Highlights
Surgical interventions are common for degenerative cervical spine diseases [1,2,3]
For a successful $2-level corpectomy or operation for severe traumatic three-column instabilities, a combined anterior and posterior approach was found to be desirable [14,15,16] but it would require a secondary posterior approach procedure that might lead to a significant increase in morbidity
The Kirschner wires were inserted into the cervical pedicle with the assistance of the patient-specific biocompatible drill template
Summary
Due to the three-column fixation property, transpedicular screw fixation via the posterior approach has been shown to have superior stabilization capabilities in several biomechanical and clinical surveys [4,5,6,7]. Since the screws in the anterior approach are anchored in the cancellous vertebral body, the biomechanical stability of anterior plate fixation is limited, leading to significant failure rates [13]. For a successful $2-level corpectomy or operation for severe traumatic three-column instabilities, a combined anterior and posterior approach was found to be desirable [14,15,16] but it would require a secondary posterior approach procedure that might lead to a significant increase in morbidity. With the properties of three-column fixation and anterior-approach-only procedure, anterior transpedicular screw (ATPS) is ideal for severe multilevel traumatic cervical instabilities. We constructed a patient-specific biocompatible drill template and evaluated its accuracy in assisting ATPS insertion
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