Biomechanical investigation of lumbar hybrid stabilization in two-level posterior instrumentation

Hybrid stabilization with a dynamic implant has been suggested to avoid adjacent segment disease by creating a smoother transition zone from the instrumented segments to the untreated levels above. This study aims to characterize the transition zones of two-level posterior instrumentation strategies for elucidating biomechanical differences between rigid fixation and the hybrid stabilization approach with a pedicle screw-based dynamic implant. Eight human lumbar spines (L1–5) were loaded in a spine tester with pure moments of 7.5 Nm and with a hybrid loading protocol. The range of motion (ROM) of all segments for both loading protocols was evaluated and normalized to the native ROM. For pure moment loading, ROM of the segments cranial to both instrumentations were not affected by the type of instrumentation (p > 0.5). The dynamic instrumentation in L3–4 reduced the ROM compared to intact (p