The Optimal Insertion Position of the Lumbar Interspinous Dynamic Stabilization Device: A Biomechanical Evaluation

Abstract

Introduction To evaluate the optimal insertion position of the Coflex lumbar interspinous dynamic stabilization device, a biomechanical study was conducted. Materials and Methods Six fresh adult human cadaveric lumbar spine specimens (L1-L5) were mounted in a materials testing machine (MTS) by embedding to clamps with L1 and L5 vertebrae. L3/4 motion segment of each specimen was operated by selective decompression and Coflex interspinous device insertion. The L3 and L4 vertebrae was inserted one needle attached with four marker points, respectively, which were used to record the range of motion (ROM). Each lumbar spine specimen was tested according to the loading sequence at five condition models: intact (keeping lumbar ligamenta and facet joints intact); partial destabilized (resection of L3/4 interspinous ligamenta, ligamentum flavum, facet capsule, and bilateral resection 50% of L3 inferior facets); 10 mm insertion (distance between apex of U-shaped Coflex and dural sac was 10 mm), 5 mm insertion (the distance was 5 mm), and 0 mm insertion (the distance was 0 mm). Each lumbar spine specimen was tested according to a loading sequence consisting of flexion, extension, left/right lateral bending, left/right axial rotation, loaded with pure moments of 8 Nm, and was recorded the ROM of operative segment at the third time. ROM of five condition models in six directions, respectively, was analyzed with one-way ANOVA test and multiple comparisons are based on LSD method. Results The ROMs of the 5 and 0 mm group were on significant differences ( p > 0.05) comparing with the intact group in flexion (F = 8.472), extension (F = 18.310), left (F = 16.809), and right axial rotation (F = 6.624), but they were significantly different comparing with the partial destabilized group in the same directions ( p < 0.01). There were significant differences ( p < 0.01) in the ROM of left lateral bending (F = 7.700) and right lateral bending (F = 12.473) between the 5 and 0 mm group and the intact group, but there was no difference comparing with the partial destabilized group in the same directions ( p > 0.05). The 10 mm group had significant high ROM in six directions than the intact group ( p < 0.01), but were no differences comparing with the partial destabilized group ( p > 0.05). Conclusion The insertion of Coflex interspinous dynamic stabilization device can maintain the stability of a partially destabilized specimen back to an intact one in flexion, extension, and axial rotation when distance between apex of U-shaped Coflex and dural sac was 5 mm or less, but cannot return the stability in lateral bending. The Coflex cannot return the stability of a partially destabilized specimen back to an intact one in six directions when distance between apex of U-shaped Coflex and dural sac was or more 10 mm. Disclosure of Interest None declared