A comparative biomechanical study of traditional and in-line plating systems following immediate stabilization of single and bi-level cervical segments.

BACKGROUND

Anterior cervical plate fixation has gained widespread acceptance for treatment of cervical spine pathologies by stabilizing the segment and enhancing fusion rates. While it is generally accepted that multiple fusion levels benefit from plating, few studies have compared plate designs. Wider plates can increase surgical complications and cost and are, therefore, not indicated unless biomechanical benefits exist. In this study, a cervical cadaver model is subjected to physiological loads and stabilized with in-line one-screw, and traditional two-screw per vertebral body plates.

METHODS

Three groups of eight fresh frozen human cadaver cervical spines (C2-C7) were tested by applying pure moments of 1.5 Nm. Motion was obtained at C5-C6, and C4-C5/C5-C6 for single-level and bi-level experiments, respectively, in flexion-extension, lateral bending and axial rotation. Specimens were tested, 1) intact, 2) injured (anterior discectomy), 3) with interbody fusion spacer, 4) in-line one-screw plate+spacer, and 5) two-screw plate+spacer, using four available plate brands.

FINDINGS

Single-level plating with interbody spacer restricted range-of-motion with respect to the spacer-alone construct in flexion-extension, regardless of one-screw or two-screw plate design, or brand. Similar behavior was seen in axial rotation, but not in lateral bending, where significance reductions in motion were achieved only with respect to the intact spine, not the interbody spacer group. In bi-level experiments all plate types restricted range-of-motion below spacer-alone levels in all loading modes.

INTERPRETATION

Anterior plating should be selected based on surgical requirements, as a wide (two-screw) over a narrow (one-screw) plating profile does not appear to provide a tangible biomechanical benefit.