StabilimaxNZ® versus simulated fusion: evaluation of adjacent-level effects

Abstract

Rationale behind motion preservation devices is to eliminate the accelerated adjacent-level effects (ALE) associated with spinal fusion. We evaluated multidirectional flexibilities and ALEs of StabilimaxNZ and simulated fusion applied to a decompressed spine. StabilimaxNZ was applied at L4-L5 after creating a decompression (laminectomy of L4 plus bilateral medial facetectomy at L4-L5). Multidirectional Flexibility and Hybrid tests were performed on six fresh cadaveric human specimens (T12-S1). Decompression increased average flexion-extension rotation to 124.0% of the intact. StabilimaxNZ and simulated fusion decreased the motion to 62.4 and 23.8% of intact, respectively. In lateral bending, corresponding increase was 121.6% and decreases were 57.5 and 11.9%. In torsion, corresponding increase was 132.7%, and decreases were 36.3% for fusion, and none for StabilimaxNZ ALE was defined as percentage increase over the intact. The ALE at L3-4 was 15.3% for StabilimaxNZ versus 33.4% for fusion, while at L5-S1 the ALE were 5.0% vs. 11.3%, respectively. In lateral bending, the corresponding ALE values were 3.0% vs. 19.1%, and 11.3% vs. 35.8%, respectively. In torsion, the corresponding values were 3.7% vs. 20.6%, and 4.0% vs. 33.5%, respectively. In conclusion, this in vitro study using Flexibility and Hybrid test methods showed that StabilimaxNZ stabilized the decompressed spinal level effectively in sagittal and frontal planes, while allowing a good portion of the normal rotation, and concurrently it did not produce significant ALEs as compared to the fusion. However, it did not stabilize the decompressed specimen in torsion.

Non-fusion instrumentation of the lumbar spine with a hinged pedicle screw rod system: an in vitro experiment

“…additional axial preload). However, related to other studies [20,25] the present results indicate that the cosmicMIA system is likely to decrease the ROM in axial rotation to a greater extent than other non-fusion devices. Normalised to the intact state the results in axial rotation for the Dynesys published by Schmoelz et al [25] showed a comparable increase in ROM for the defect model (approximately 220%) and no reduction of the ROM to the range of the intact specimen after instrumentation with the Dynesys.…”

“…Therefore, one might speculate that the motion restricting effect of the rigid instrumentation is underestimated. However, the ROM for the rigid instrumentation in the present study is comparable with the ROM reported for rigid instrumentation in the literature [20,25]. Meyers et al evaluated the load sharing in posterior dynamic stabilisation devices using instrumented pedicle screws [17].…”

“…However, the defect model of the Dynesys study included dissection of the ligament supraspinous, ligament interspinous, ligament flavum, tenotomy of facet joint and nucleotomy, while in the present study the decompression was comprised of a laminectomy L4 and hemifacetectomy of L3-4 and L4-5. In an in vitro study of the Stabilimax posterior dynamic stabilisation device, Panjabi et al, [20] reported an increase of 120-130% of the intact ROM after decompression (dissection of ligament supraspinous, ligament interspinous, ligament flavum and 50% medial facetectomy L4-5) and a reduction of ROM after dynamic instrumentation to approximately 60% of the intact state in flexion/extension and lateral bending, while in axial rotation the device was not effective in reducing the ROM of the treated motion segment [20].…”

“…Biomechanical studies have shown, that interspinous devices have a stabilising effect on decompressed segments in extension, but are hardly capable of stabilising a decompressed segment in axial rotation [7,13,23,26,29]. Laboratory in vitro studies of various posterior devices also mainly show a stabilising effect in flexion/extension and lateral bending and only a limited stabilising effect in axial rotation [3,18,20,[24][25][26]32].…”

Kinematic evaluation of one- and two-level Maverick lumbar total disc replacement caudal to a long thoracolumbar spinal fusion

“…Stiffness or hybrid protocols, rather than flexibility protocols, must be used to study the effects of surgical interventions on the biomechanics of the adjacent (non-operated) spinal levels [28,40]. With these methods, segmental kinematics are evaluated for the intact nonfusion, fusion, and TDR situations at an identical spinal posture [14,26,27,29,36,40,41]. However, some of the studies that have been performed to study TDR's adjacent to fusions [10,25,34] did not apply hybrid testing methods [10,34], or applied bending using an offset shear force that resulted in combined bending and shear loading [25].…”