Stabilizing potential of anterior, posterior, and circumferential fixation for multilevel cervical arthrodesis -: An in vitro human cadaveric study of the operative and adjacent segment kinematics

Study Design. This is an in vitro biomechanical study. Objective. The current investigation was performed to evaluate the stabilizing potential of anterior, posterior, and circumferential cervical fixation on operative and adjacent segment motion following 2 and 3-level reconstructions. Summary of Background Data. Previous studies reported increases in adjacent level range of motion (ROM) and intradiscal pressure following single-level cervical arthrodesis; however, no studies have compared adjacent level effects following multilevel anterior versus posterior reconstructions. Materials and Methods. Ten human cadaveric cervical spines were biomechanically tested using an unconstrained spine simulator under axial rotation, flexion-extension, and lateral bending loading. After intact analysis, all specimens were sequentially instrumented from C3 to C5 with: (1) lateral mass fixation, (2) anterior cervical plate with interbody cages, and (3) combined anterior and posterior fixation. Following biomechanical analysis of 2-level constructs, fixation was extended to C6 and testing repeated. Full ROM was monitored at the operative and adjacent levels, and data normalized to the intact (100%). Results. All reconstructive methods reduced operative level ROM relative to intact specimens under all loading methods (P < 0.05). However, circumferential fixation provided the greatest segmental stability among 2 and 3-level constructs (P < 0.05). Moreover, anterior cervical plate fixation was least efficient at stabilizing operative segments following C3 - C6 arthrodesis (P < 0.05). Supradjacent ROM was increased for all treatment groups compared to normal data during flexion-extension testing (P < 0.05). Similar trends were observed under axial rotation and lateral bending loading. At the distal level, flexion- extension and axial rotation testing revealed comparable intergroup differences (P < 0.05), while lateral bending loading indicated greater ROM following 2-level circumferential fixation (P < 0.05). Conclusions. Results from our study revealed greater adjacent level motion following all 3 fixation types. No consistent significant intergroup differences in neighboring segment kinematics were detected among reconstructions. Circumferential fixation provided the greatest level of segmental stability without additional significant increase in adjacent level ROM.