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Spinous process resistance to different materials and looping techniques for interspinous lumbar vertebropexy
Jonas Widmer1, Anna-Katharina Calek2,3,4, Marie-Rosa Fasser4
1Spine Biomechanics, Department of Orthopedic Surgery, Balgrist University Hospital, University of Zurich, Balgrist Campus, Lengghalde 5, Zurich, 8008, Switzerland. Jonas.Widmer@balgrist.ch.
Purpose:
Semi-rigid spinal stabilization has been explored as an alternative to spinal fusion, and early experience with spinal segment augementation ("vertebropexy") is promising. The main technical challenge is to maintain the integrity of the spinous processes during loading. This study aimed to compare different looping materials and techniques with respect to their performance in maintaining spinous process integrity.
Methods:
One hundred and five thoracolumbar vertebrae were tested with various looping materials and techniques; the "Tunnel-only" double-loop technique was tested with a synthetic tape (FiberTape®), bovine tendon, and a hybrid tape option. Additionally, the performance of the synthetic tape was tested for other augmentation techniques such as the "Figure-of-eight" looping technique, a double-loop combination of tunneling and cortical wrapping, and a double-loop with "Cortical wrapping only". Biomechanical testing was performed by uniaxial caudo-cranial distraction to failure.
Results:
The loads required to cause spinous process failure were lowest with the synthetic tape, followed by tendon and hybrid constructs by tendency (419 N vs. 487 N vs. 519 N) in the "Tunnel-only" double-loop technique. The comparison showed that the "Tunnel + cortical wrapping" technique required significantly higher forces to induce failure compared to other techniques, particularly the "Tunnel only" method (p < 0.001).
Conclusion:
The choice of the looping technique and material in lumbar interspinous vertebropexy significantly affects the resistance of the spinous process to load. Techniques that incorporate cortical bone and use tendinous material demonstrate superior resistance to higher forces, compared to methods that involve passing synthetic tape through a hole solely within trabecular bone. Additionally, the role of trabecular bone density in the spinous process is relatively minor when cortical bone is utilized as an abutment for the loop.
