ABSTRACT
Objective:To develop a specialized clival-cervical plate fixation (CCPF) for anterior surgery to treat craniovertebral instability, and to compare it with a posterior occipitocervical fixation (POCF) in biomechanical validation.Methods:Based on the measurement of 40 adult dry bones and 30 volunteers CT images, the clival-cervical plate was designed and manufactured. 8 cadaveric specimens (occiput-C 3) were tested in five conditions including the intact status, the intact+CCPF status, the injury status, the injury+CCPF status, and the injury+POCF status. Specimens were applied a pure moment of 1.5 N·m in flexion, extension, lateral bending, and axial rotation. Calculating and comparing the range of motion (ROM) and neutral zone (NZ) for the occiput to C 2. The effects of different fixation methods on the distribution of ROMs at the occipitocervical region were compared. Results:The injury+CCPF status constrained ROMs to 1.7° in flexion ( q=4.68, P=0.055) , 1.2° in extension ( q=0.39, P=0.9922) , 2.8° in lateral bending ( q=1.25, P=0.814) , and 4.3° in axial rotation ( q=5.08, P=0.035) , resulted in larger ROM in axial rotation but similar ROMs in other directions ( P>0.05) when compared with the injury+POCF status. There were no significant differences between the above two fixation methods in flexion-extension ( q=1.94, P=0.554) , lateral bending ( q=1.79, P=0.611) and axial rotation ( q=2.14, P=0.478) for the NZs. For the flexion, extension,lateral bendingand axial rotation direction, the proportion of the C 1, 2 ROM to the overall ROM was 28%, 25%, 34% and 56% respectively in the injury+CCPF status, and it was 59%, 53%, 42% and 71% respectively in the injury+POCF status. Conclusion:CCPF is a biomechanically effective alternative or supplemental method of POCF for the craniocervical instability.
ABSTRACT
Objective:To evaluate the feasibility of the screw and plate for clival fixation using a transoral expanded approaches.Methods:The transoral expanded approaches were performed on craniocervical segment specimens obtained from 7 subjects, including transoral approach (TO), transoral with soft (TOP) or hard (TOHP) palate split, mandibulotomy (MO) and mandibuloglossotomy (MLO). The distribution and thickness of soft tissue, the configuration of the vertebral arteries, the distance between the midline and the vertebral arteries, the exposed area of the clivus and cervical spine, and the range of screw angle (the angle between the line from the lower incisor or the central base of the mandible to the exposed area of the clivus and the tangent line of the clivus) were evaluated.Results:The thickness of the soft tissue on the posterior pharyngeal wall above the clival pharyngeal nodules was 3.5±0.6 mm. That on the anterior C 1-C 5 vertebrae was 5.0±0.5 mm. The distances from the bilateral vertebral arteries to the midline was 19.5±1.2 mm at C 1, 2, 14.6±2.7 mm at C 2, 3, 14.0±2.7 mm at C 3, 4, and 13.9±2.7 mm at C 4, 5. For the TO approach, the longitudinal diameter of the exposed clivus was 8.3±3.0 mm. The distance from the lower incisor to the superior margin of the exposed clivus, the lower margin of the exposed clivus, the anterior arch of C 1, the vertebral body of C 2 and C 3 were 104.7±4.3 mm, 99.2±6.8 mm, 81.4±4.3 mm, 75.1±4.0 mm and 68.7±6.5 mm, respectively. Six specimens were exposed to the C 3, while one was exposed to the C 2. For the TOP approach, the longitudinal diameter of the exposed clivus was 18.5±4.8 mm. The distance from the lower incisor to the superior margin of the exposed clivus and the pharyngeal nodules were 107.9±6.7 mm and 104.8±6.7 mm, respectively. For the TOHP approach, the longitudinal diameter of the exposed clivus was 26.3±1.8 mm (the clival length) with distance from the lower incisor to the superior margin of the clivus 112.4±12.6 mm. For the MO/MLO approach, the entire clivus was exposed. The distance from the central base of the mandible to the superior and inferior margin of the exposed clivus and the pharyngeal nodules were 141.8±15.7 mm, 131.0±9.9 mm and 120.5±8.2 mm, respectively. The inferior margin of the exposed cervical vertebra was C 5, 6. The rate of the clival screw placement through anterior occipitocervical fixation using TO, TOP, TOHP, MO and MLO was 0%, 71% (5/7), 86% (6/7), and 100%, respectively. The screw angle was 99.0°±1.8°, 92.6°±7.7°, 92.6°±7.7°, 75.1°±7.7°, and 75.1°±7.7°, respectively. Conclusion:Occipitocervical fixation with clival screw and plate could be conducted in most cases via TOP and TOHP approaches. However, in some cases with small split-mouth or mouth opening limited, smaller clival screw angle caused by basilar impression or basilar invagination, requiring fixation and reconstruction of the lower cervical spine, and the MO/MLO approaches could be still required to achieve the fixation.