Biomechanical Testing of an Artificial Cervical Joint and an Anterior Cervical Plate

Abstract

An in vitro biomechanical study was conducted to determine the effects of fusion and nonfusion anterior cervical instrumentation on cervical spine biomechanics in a multilevel human cadaveric model. Three spine conditions were studied: harvested, single-level artificial cervical joint, and single-level graft with anterior cervical plate. A programmable testing apparatus was used that replicated physiologic flexion/extension and lateral bending. Measurements included vertebral motion, applied load, and bending moments. Relative rotations at the superior, implanted, and inferior motion segment units (MSUs) were normalized with respect to the overall rotation of those three MSUs and compared using a one-way analysis of variance (P < 0.05). Application of an anterior cervical plate decreased motion across the fusion site relative to the harvested and artificial joint spine conditions. The reduced motion was compensated for by an increase in motion at the adjacent segments. Use of an artificial cervical joint did not alter the motion patterns at either the instrumented level or the adjacent segments compared with the harvested condition for all modes of testing.

Cervical disc prosthesis versus arthrodesis using one-level, hybrid and two-level constructs: an in vitro investigation

“…Contrary to a number of biomechanical studies previously published [16][17][18], we did not find that implantation of TDR at 1 or 2 levels could restore completely native kinematics of the cervical spine. We noted that ROM after TDR was systematically reduced for the three loading conditions, especially in AR and LB, even if the difference was not always significant.…”

“…They proposed resection of uncinates to restore the extent of 3D motions more completely. In fact, although some authors reported no difference in ROM between intact and instrumented spines [16][17][18], we noted that ROM in some of these studies was most often reduced but the difference was not statistically significant. As an example, Puttlitz et al [17] tested six human cervical spines intact and instrumented with TDR (ProDisc-C, Synthes) by applying 3D pure moments of 1 N m. ROM of instrumented spines was measured to 73 and 72% of intact spines in AR and LB, respectively; however, the authors concluded that there was no difference between the two tested conditions because difference was no statistically significant.…”

“…Because TDR is an emerging technology with the need for evaluation, most laboratory and clinical studies first investigated safety and efficacy of cervical TDR at one-level [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. However, multi-segmental cervical spondylosis is not rare in clinical practice.…”

Reoperation After Cervical Disc Arthroplasty Versus Anterior Cervical Discectomy and Fusion: A Meta-analysis

“…Concerns regarding these issues led to the design and development of the cervical disc arthroplasty. Compared with anterior cervical discectomy and fusion, the cervical disc arthroplasty offers the theoretical biomechanical advantage of preservation of motion at the index level, which reduces stresses at the adjacent levels [12,13]. The equivalency or superiority of the cervical disc arthroplasty as an alternative to anterior cervical discectomy and fusion has been seen in FDA Investigational Device Exemption and other studies [5,7,8,10,22,30,32,34,35,37,38,[42][43][44].…”

“…The cervical disc arthroplasty is designed to maintain disc space height and motion at the index segment and prevent abnormal loading stresses and motion at adjacent segments that theoretically lead to accelerated degeneration [12,13]. During the past decade, the cervical disc arthroplasty has emerged as an alternative to fusion and has been shown to provide the pain relief and functional improvements similar or superior to those of anterior cervical discectomy and fusion in FDA Investigational Device Exemption clinical trials [5,8,10,22,30,32,35,38,44].…”