title: Cervical anterior transpedicular screw fixation (ATPS)--Part II. Accuracy of manual insertion and pull-out strength of ATPS.
abstract: Reconstruction after multilevel decompression of the cervical spine, especially in the weakened osteoporotic, neoplastic or infectious spine often requires circumferential stabilization and fusion. To avoid the additional posterior surgery in these cases while increasing rigidity of anterior-only screw-plate constructs, the authors introduce the concept of anterior transpedicular screw (ATPS) fixation. We demonstrated its morphological feasibility as well as its indications in a previous study in Part I of our project. Consequently, the objectives of the current study were to assess the ex vivo accuracy of placing ATPS into the cervical vertebra as well as the biomechanical performance of ATPS in comparison to traditional vertebral body screws (VBS) in terms of pull-out strength (POS). Twenty-three ATPS were inserted alternately to two screws into the pedicles and vertebral bodies, respectively, of six cadaveric specimens from C3-T1. For insertion of ATPS, a manual fluoroscopically assisted technique was used. Pre- and post insertional CT-scans were used to assess accuracy of ATPS insertion in the axial and sagittal planes. A newly designed grading system and accuracy score were used to delineate accuracy of ATPS insertion. Following insertion of screws, 23 ATPS and 22 VBS were subjected to pull-out testing (POT). The bone mineral density (BMD) of each specimen was assessed prior to POT. Statistical analysis showed that the incidence of correctly placed screws and non-critical pedicles breaches in axial plane was 78.3%, and 95.7% in sagittal plane. Hence, according to our definition of "critical" pedicle breach that exposes neurovascular structures at risk, 21.7% (n = 5) of all ATPS inserted showed a critical pedicle breach in axial plane. Notably, no critical pedicle perforation occurred at the C6 to T1 levels. Pull-out testing of ATPS and VBS revealed that pull-out resistance of ATPS was 2.5-fold that of VBS. Mean POS of 23 ATPS with a mean BMD of 0.566 g/cm(2) and a mean osseus screw purchase of 27.2 mm was 467.8 N. In comparison, POS of 22 VBS screws with a mean BMD of 0.533 g/cm(2) and a mean osseus screw purchase of 16.0 mm was 181.6 N. The difference in ultimate pull-out strength between the ATPS and VBS group was significant (p < 0.000001). Also, accuracy of ATPS placement in axial plane was shown to be significantly correlated with POS. In contrast, there was no correlation between screw-length, BMD, or level of insertion and the POS of ATPS or VBS. The study demonstrated that the use of ATPS might be a new technique worthy of further investigation. The use of ATPS shows the potential to increase construct rigidity in terms of screw-plate pull-out resistance. It might diminish construct failures during anterior-only reconstructions of the highly unstable decompressed cervical spine.
authors.affiliation: Department for Traumatology and Sport Injuries, Paracelsus Medical University Salzburg, 5020, Salzburg, Austria. heiko.koller@t-online.de
authors.forename: Heiko
authors.initials: H
authors.lastname: Koller
authors.forename: Frank
authors.initials: F
authors.lastname: Acosta
authors.forename: Mark
authors.initials: M
authors.lastname: Tauber
authors.forename: Michael
authors.initials: M
authors.lastname: Fox
authors.forename: Hudelmaier
authors.initials: H
authors.lastname: Martin
authors.forename: Rosmarie
authors.initials: R
authors.lastname: Forstner
authors.forename: Peter
authors.initials: P
authors.lastname: Augat
authors.forename: Rainer
authors.initials: R
authors.lastname: Penzkofer
authors.forename: Christian
authors.initials: C
authors.lastname: Pirich
authors.forename: H
authors.initials: H
authors.lastname: Kässmann
authors.forename: Herbert
authors.initials: H
authors.lastname: Resch
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Hitzl
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D003198:Computer Simulation; D005240:Feasibility Studies; D005260:Female; D005471:Fluoroscopy; D006801:Humans; D016268:Internal Fixators; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000379:methods*; D013122:Spinal Diseases / Q000601:surgery; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery; D014057:Tomography, X-Ray Computed