Two-piece ALIF cage optimizes the bone–implant interface in a 360° setting

Clinical research has documented that cage subsidence and the loss of balance correction is a significant complication related to spinal fusion. Subsidence is a multifactorial complication, where implant design is one important element. The aim of the study is to compare the rigidity and bone–implant relative motion of segments treated with either a conventional one-piece ALIF cage versus a two-piece ALIF cage, which adapts in situ and permits 7°–21° of lordosis. Seven lumbosacral (L3-S1) human cadaver specimens were tested in a universal spine tester in the intact condition, the specimens instrumented with a two-piece ALIF cage (Statur®-L, FBC Device, Denmark) and a one-piece ALIF cage (Pezo™-A, Ulrich GmbH & Co. KG., Germany), both supplemented with a pedicle screw system using pure moments of ±7.5 Nm in three principal motion directions. For assessment of the bone–implant interface, fluoroscopic videos were captured during motion and 3D motion was measured using an optical motion capturing system. Significantly less motion at the implant–endplate interface was found for the two-piece cage (1.0° ± 0.6°) in comparison to the one-piece cage (4.2° ± 1.7°) in flexion/extension. No significant differences in segment rigidity were found between the one-piece and two-piece cages in the 360° setup, while both configurations significantly reduced the range of motion compared to the intact condition (p