Introduction: Lumbar facet joint fusion may be ideal for severe facet arthrosis when facet injections and rhizotomy no longer suffice. In one technique allograft threaded facet dowels (TFD) are placed through the plane of the facet joint. This work compares range of motion (ROM), neutral zone (NZ) and stiffness of TFD implanted segments with Intact and Destabilized conditions.
Methods: Eight L4-L5 segments were subjected to three single-axis (±10Nm) (flexion-extension, lateral bending, axial rotation) and four two-axis (continuous flexion-extension or lateral bending (±7.1Nm) under static left or right axial rotation (7.1Nm) to produce ±10Nm peak resultant moment) tests. Specimens were tested Intact, Destabilized and TFD implanted, then statistically compared.
Results: ROM in flexion, extension, lateral bending, and flexion-extension or lateral bending with or without axial rotation were significantly reduced by TFD compared to Intact or Destabilized (p=0.016 all comparisons). NZ in flexion-extension significantly decreased from Intact or Destabilized to TFD except Intact versus TFD under single-axis flexion-extension (p=0.009 all comparisons). Flexion and extension stiffness increased from Intact or Destabilized to TFD (p=0.015 both comparisons). No other significant changes were observed.
Conclusions: ROM, NZ and segmental stiffness each enhance data interpretation, and together, paint a picture of how TFD alters segmental biomechanics. Reduced ROM with TFD implantation, is critical to successful fusion. In flexion-extension, NZ and stiffness data suggest that TFD resists facet articulation, while increasing stiffness. However, in lateral bending and axial rotation, NZ and stiffness were not statistically different from the intact spine. Data suggest that TFD may sufficiently reduce motion to promote fusion, while not substantially changing inherent viscoelastic properties of the intact spine. This may be indicative of stabilization without excessive changes in segmental stiffness that may otherwise promote increased adjacent loading. Data underscore the importance of multi-axis, multi-parameter biomechanical evaluation.
Patient Care: Improve the surgeon’s understanding of how best to utilize threaded facet dowels.
Learning Objectives: Understand the biomechanical influence o f threaded facet dowel.