gms | German Medical Science

German Congress of Orthopaedics and Traumatology (DKOU 2016)

25.10. - 28.10.2016, Berlin

Effect of cage design, supplemental posterior instrumentation and approach on primary stability of a lumbar interbody fusion – a biomechanical in vitro study

Meeting Abstract

  • presenting/speaker Werner Schmoelz - Univ.-Klinik für Unfallchirurgie , Medizinisch Universität Innsbruck, Innsbruck, Austria
  • Sabrina Sandriesser - Univ.-Klinik für Unfallchirurgie , Medizinisch Universität Innsbruck, Innsbruck, Austria
  • Oded Loebl - NLT spine, Kafr Saba, Israel
  • Marlies Bauer - Medizinische Universität Innsbruck, Department für Anatomy, Histologie und Embryologie, Innsbruck, Austria
  • Dietmar Krappinger - Univ.-Klinik für Unfallchirurgie , Medizinisch Universität Innsbruck, Innsbruck, Austria

Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2016). Berlin, 25.-28.10.2016. Düsseldorf: German Medical Science GMS Publishing House; 2016. DocWI15-1218

doi: 10.3205/16dkou053, urn:nbn:de:0183-16dkou0537

Published: October 10, 2016

© 2016 Schmoelz et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at



Objectives: There are various techniques and approaches for lumbar interbody fusion differing in access, cage type and type of supplemental posterior instrumentation. While a transforaminal lumbar interbody fusion (TLIF) usually includes a hemifactectomy, the facet joint can be preserved with a more lateral extraforaminal lumbar interbody fusion (ELIF). The type of supplemental posterior instrumentation required for both fusion techniques is also still debated and ranges from none to unilateral internal fixator or bilateral internal fixator. The shape, footprint and surface area of an intervertebral cage can also contribute to the primary stability of a fused spinal segment. The purpose of the present study was to compare the primary stability of an ELIF and TLIF procedure for two different cage types with none, unilateral and bilateral supplemental posterior instrumentation.

Methods: Six lumbar spines were divided in two groups, each composed of monosegmental lumbar FSUs (3xL2-3 and 3xL4-5) and tested for flexibility in a spine tester with pure bending moments of 7.5Nm in flexion/extension, lateral bending and axial rotation. As cages, the newly designed ProwFusion (NLT Spine, Israel), a segmented chain type cage which can be curved in situ to provide a large footprint was compared to a standard TLIF cage (Capstone, Medtronic). FSU flexibility was tested for both cages in the following states: (a)native, (b)stand alone cage, (c)bilateral internal fixator, (d)unilateral internal fixator, (e)unilateral facetectomy+bilateral internal fixator, (f)unilateral facetectomy+unilateral internal fixator and (g)unilateral facetectomy with stand alone cage. For comparison of the flexibility the range of motion (RoM) was normalized to the native state and a general linear model (GLM) with repeated measures was used to compare the effects of the facetectomy, cage type, and supplemental instrumentation.

Results and Conclusion: The within the subject comparison showed a significantly higher RoM for the unilateral facetectomy in all motion directions (p< 0.001). Combination of the effects of facetectomy and supplemental instrumentation was significant with the reduction in RoM being most pronounced for the stand alone cage and declining with increasing stiffness of the supplemental posterior instrumentation (p=0.001).

The in between subject comparison showed a significant effect of the cage type on the RoM (reduced RoM of the ProwFusion compared to the Capstone) in flexion/extension (p=0.002) and lateral bending (p=0.028) but not in axial rotation (p=0.322). The type of supplemental posterior fixation had a significant effect on the RoM in all motion directions (stand alone >unilateral fixator>bilateral fixator).

For both, ELIF and TLIF procedures the in situ curved cage provides a higher primary stability than conventional standard cages, independent of the type of supplemental posterior instrumentation.