Director of Research Musculoskeletal Education and Research Center Audubon, PA, US
Introduction: Proximal junctional kyphosis is a common consequence of long segment instrumented spinal fusion. Here, we evaluate the role of various soft-landing techniques in limiting hypermobility across one level superior to the upper instrumented vertebra (UIV), adjacent to a long lumbar fusion.
Methods: Seven (7) human cadaveric thoracolumbar spine segments were evaluated using a using a six degrees-of-freedom motion simulator (±7.5Nm) to track range of motion (ROM) in flexion/extension (FE), lateral bending (LB), and axial rotation (AR). Four soft-landings, placed at T9-T10, were tested sequentially: Transverse Process Hooks (TP), Untensioned Polyethylene-Terephthalate Cord (U-PET), Tensioned Polyethylene-Terephthalate Cord (T-PET), and a dynamic stabilization device (DSD). All specimens were fused from T10-Pelvis with posterior fixation. Relative motion adjacent to the fusion (T9-T10) for each soft-landing was compared to a control with no soft landing, and the intact spine.
Results: There was a significant difference in ROM, adjacent to the fusion, between groups, in all bending planes (FE p = 0.004; LB p < 0.001; AR p < 0.001). All soft-landing groups had reduced motion, in all bending planes, compared to the control group. Motion of the Control group was greater than intact in all bending planes. FE ROM, for TP (2.77°) and T-PET (2.81°), was similar to Intact (2.79°). FE ROM was lowest for the DSD group (2.06°) and highest for the Control group (3.98°). LB ROM, for TP (4.35°) and T-PET (4.19°), was similar to Intact (4.26°). LB ROM of DSD (3.05°) was significantly less than TP (4.35°) (p = 0.003) and Control (5.60°) (p = 0.021). All soft-landing groups had less AR ROM than Intact. AR ROM of TP (5.59°) was significantly less than Intact (7.16°) (p = 0.038) and Control (7.49°) (p = 0.041).
Conclusion : Single-level soft-landings may be useful in reducing hypermobility of the disc adjacent to long lumbar fusion, compared to control. Motion of the adjacent disc in TP and T-PET groups most resembled Intact, while DSD experienced less motion compared to Intact, in all bending planes. Further analysis is needed to determine if hypermobility is an issue, at the free levels, adjacent to the soft-landing.