Abstract
It remains unclear what is the real safe limit of torque magnitude during Bilateral Apical Vertebral Derotation (BAVD) in thoracic curve correction. Up to author’s knowledge there is no study except this one, to reproduce in–vivo real measurements and intraoperative conditions during BAVD maneuver. The objective of this study was to evaluate the torsional strength of the instrumented thoracic spine under axial rotation moment as well as to define safety limits under BAVD corrective maneuver in scoliosis surgery. 10 fresh, full-length, young and intact human cadavers were tested. After proper assembly of the apparatus, the torque was applied through its apical part, simulating thoracic curve derotation. During each experiment the torque magnitude and angular range of derotation were evaluated. For more accurate analysis after every experiment the examined section of the spine was resected from the cadaver and evaluated morphologically and with a CT scan. The average torque to failure during BAVD simulation was 73,3 ± 5,49Nm. The average angle of BAVD to failure was 44,5 ± 8,16°. The majority of failures were in apical area. There was no significant difference between the fracture occurrence of left or right side of lateral wall of the pedicle. There was no spinal canal breach and/or medial wall failure in any specimen. The safety limits of thoracic spine and efficacy of BAVD for axial plane correction in the treatment of Adolescent Idiopathic Scoliosis (AIS) were established. It provided qualitative and quantitative information essential for the spinal derotation under safe loading limits.
Highlights
Derotation of the spine maneuver has recently gained popularity as it provides efficient control of the spine in the transverse plane creating better 3 –dimensional correction of the curve [1,2,3]
A Direct Vertebral Rotation (DVR) system introduced by Suk in 2004, applies direct rotational force on Apical Vertebrae (AV) in the opposite direction to the rod rotation maneuver and to that of the deformity
A Bilateral Apical Vertebral Derotation (BAVD) introduced by Chang and Lenke [6] came into practice
Summary
Derotation of the spine maneuver has recently gained popularity as it provides efficient control of the spine in the transverse plane creating better 3 –dimensional correction of the curve [1,2,3]. For the effective DVR or BAVD maneuvers, a device with large lever arms has to be attached to the pedicle screws at multiple levels of the spine through which surgeon can apply significant torsional loads to the curve The safety of these procedures has not been established yet and has been questioned due to possible pedicle fractures or other serious intraoperative complications such as deterioration of neural structures in the spinal canal or aortic abutment due to plowing of pedicle screws [17,18,19]. Up to author’s knowledge despite the large variations amongst the biomechanical studies of derotation of the spine, there is no study except this one, where fresh, young and intact cadavers were used for BAVD critical torque testing This helped us to reproduce in–vivo real measurements and intraoperative conditions. What is even more important, the clinical applicability of this preclinical biomechanical study could lead to the invention of Apical Derotator, which would be used routinely during scoliosis surgery in the clinical field
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