• Michael Reichl, Rebecca A Kueny, Reza Danyali, Peter Obid, Hüseyin Übeyli, Klaus Püschel, Michael M Morlock, Gerd Huber, Thomas Niemeyer, and Alexander Richter.
• *Spine Center, Asklepios Klinik St. Georg †Institute of Biomechanics, TUHH Hamburg University of Technology ‡Department of Legal Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
• Clin Spine Surg. 2017 May 1; 30 (4): E440-E447.

Study DesignBiomechanical ex vivo study.ObjectiveTo determine if topping off instrumentation can reduce the hypermobility in the adjacent segments when compared with the classic rigid spinal instrumentation.Summary Of The Background DataLong rigid instrumentation might increase the mechanical load in the adjacent segments, the resulting hypermobility, and the risk for adjacent segment disease. Topping off instrumentation intends to reduce the hypermobility at the adjacent level by more evenly distributing segmental motion and, thereby, potentially mitigating adjacent level disease.Materials And MethodsEight human spines (Th12-L5) were divided into 2 groups. In the rigid group, a 3-segment metal rod instrumentation (L2-L5) was performed. The hybrid group included a 2-segment metal rod instrumentation (L3-L5) with a dynamic topping off instrumentation (L2-L3). Each specimen was tested consecutively in 3 different configurations: native (N=8), 2-segment rod instrumentation (L3-L5, N=8), 3-segment instrumentation (rigid: N=4, hybrid: N=4). For each configuration the range of motion (ROM) of the whole spine and each level was measured by a motion capture system during 5 cycles of extension-flexion (angle controlled to ±5 degrees, 0.1 Hz frequency, no preload).ResultsIn comparison with the intact spine, both the rigid 3-segment instrumentation and the hybrid instrumentation significantly reduced the ROM in the instrumented segments (L2-L5) while increasing the movement in the adjacent segment L1-L2 (P=0.002, η=0.82) and in Th12-L1 (P<0.001, η=0.90). There were no ROM differences between the rigid and hybrid instrumentation in all segments.ConclusionsIntroducing the dynamic topping off did not impart any significant difference in the segmental motion when compared with the rigid instrumentation. Therefore, the current biomechanical study could not show a benefit of using this specific topping off instrumentation to solve the problem of adjacent segment disease.

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