Dynamic stabilization adjacent to single-level fusion: Part I. Biomechanical effects on lumbar spinal motion

Progression of superior adjacent segment degeneration (PASD) could possibly be avoided by dynamic stabilization of an initially degenerated adjacent segment (AS). The current study evaluates ex vivo the biomechanics of a circumferential fixation connected to posterior dynamic stabilization at the AS. 6 human cadaver spines (L2–S1) were stabilized stepwise through the following conditions for comparison: intact spine (ISP), single-level fixation L5–S1 (SLF), SLF + dynamic AS fixation L4–L5 (DFT), and two-level fixation L4–S1 (TLF). For each condition, the moments required to reach the range of motion (ROM) of the intact whole spine segment under ±10 Nm (WSP10) were compared for all major planes of motion within L2–S1. The ROM at segments L2/3, L3/4, and L4/5 when WSP10 was applied were also compared for each condition. The moments needed to maintain WSP10 increased with each stage of stabilization, from ISP to SLF to DFT to TLF ( p