Biomechanical evaluation of a novel total cervical prosthesis in a single-level cervical subtotal corpectomy model: An in vitro human cadaveric study

Background: Anterior cervical subtotal corpectomy and fusion provides extensive decompression in the treatment of cervical myelopathy. However, early adjacent segment degeneration may arise due to the abnormal kinematics. To the best of our knowledge, this is the first report on a newly-designed total cervical prosthesis (TCP) to preserve the normal kinematics of cervical spine. The purpose of this study was to compare the cervical range of motion (ROM) of TCP with anterior cervical plating (ACP) in a single-level cervical subtotal corpectomy model. Study Design: An in vitro biomechanical study of a novel total cervical prosthesis (TCP) using a cadaveric model. Materials and Methods: After evaluation of the ROM of the 14 human cadaveric cervical spines (C ₂-T ₁) (intact group), single-level subtotal corpectomy models at the C ₅ levels were performed. All specimens were randomized, instrumented with ACP (n = 7) and TCP (n = 7) from C ₄ to C ₆. All specimens were tested for flexion/extension, lateral bending, and axial rotation loading. The ROM of implanted segments (C ₄-C ₆) and adjacent segments (C ₃/C ₄ and C ₆/C ₇) were monitored, respectively. Results: TCP was found to accurately recapitulate the preoperative ROM both in the adjacent segments (C ₃/C ₄ and C ₆/C ₇) and the implanted segments (C ₄-C ₆). In the adjacent segments, no significant difference was found in ROM _C3/C4 between the TCP group and the intact group in flexion, extension, and lateral bending. In the implanted segments, TCP preserved well the ROM _C4-C6, with 5.29° in flexion, 12.27°in extension, 8.95°in right lateral bending, and 7.50°in left lateral bending. In contrast, the mean ROM _C4-C6 in the ACP group was lower than those in the TCP group and the intact group significantly in all directions (P < 0.05). In addition, compared with the ACP group, the mean ROM _C3-C7 in TCP group increased by 32.6% (P = 0.034) in flexion, 62.9% (P = 0.008) in extension, 24.8% (P > 0.05) in lateral bending, and 36.0% (P < 0.01) in rotation. Compared with the intact group, the TCP group showed moderate decrease in flexion and moderate increases in extension, lateral bending, and rotation. But no significant differences were detected (P > 0.05). Conclusions: Biomechanical analyses suggest that TCP preserves ROM in the implanted segments after cervical subtotal corpectomy. TCP will not induce compensatory motion in the adjacent segments, thus may possibly help prevent adjacent segment degeneration.