Tension Parameters of Junctional Tethers in Proximal Junction Kyphosis: A Cadaveric Biomechanical Study.

OBJECTIVE: Proximal junctional failure following surgical correction for adult spinal deformity significantly impacts quality of life and increases the economic burden of treating underlying spinal deformity. The objective of this cadaver study was to determine optimal tension parameters in junctional tethers for proximal junctional kyphosis prevention. METHODS: Cadaveric specimens were used to establish the optimal tension range in polyethylene tethering devices, such as the VersaTie (NuVasive) used in this study. Three specimens were instrumented to test tether tensions of 0, 75, and 150 Newtons (N) at L1-L2, T9-T10, and T3-T4. An optical tracking system was used to measure when specimens reached proximal junctional kyphosis, experienced instrumentation or tissue failure, or reached a cap of 2500 cycles. Radiographs were obtained before and after testing. RESULTS: At all levels, use of a tether at tension forces of 75 N and 150 N elicited a protective effect. The only level in which a higher tension on the tether resulted in more protection was at T3-T4. When averaged, the use of a tether at tension forces of 75 N and 150 N showed 1000 cycles of protection at L1-L2, 2000 cycles at T9-T10, and 1426 cycles at T3-T4. Radiographic analysis corroborated these findings. CONCLUSIONS: The use of a tether in a cadaveric model prevents the development of proximal junctional kyphosis across all tested levels and an increased tension force of 150 N is protective at the proximal thoracic spine. These data can be used to develop further models for a tether system that reproducibly applies a fixed tension force above the thoracolumbar rod construct.

Mazor X Stealth Robotic Technology: A Technical Note.

BACKGROUND: Minimally invasive techniques in spine surgery have continued to advance as robotic technology has evolved over several generations. Although traditional techniques for placing pedicle screws are still widespread in practice, newer technology has increased the reliability of accurately placing instrumentation with smaller incisions and subsequent decreased length of stay. Additionally, advancements in planning software have improved the ability to align posterior instrumentation to assist with rod placement on multilevel constructs. METHODS: This paper describes the surgical techniques and operative workflow for placing pedicle screws with the latest robotic technology. The robotic platform, registration, surgical planning, and placement of instrumentation are discussed in detail. Advantages of the Mazor X Stealth Edition compared with the previous generation robot include obviating the need for K wires and eliminating the need for a percutaneous pin, as navigation is integrated into the robot. RESULTS: Our use of this new technology has been encouraging. Using the techniques described in this paper, the first 90 pedicle screws placed with the Mazor X Stealth Edition robot yielded 100% grade A accuracy on the Gertzbein-Robbins scale confirmed on immediate postoperative CT. There were no complications experienced in any case. CONCLUSIONS: In our experience, this robotic technology has the potential to improve patient outcomes and is associated with advanced surgical planning compared with more traditional techniques.