Biomechanical analysis of trivergent, a new posterior lumbar spinal fixation system

Pedicle screw fixation provides stability after posterior lumbar spine surgery. Traditional pedicle screw devices face several complications, including loose and broken screws. A strategy addressing these issues is to eliminate sources of failure and optimize the biomechanical advantage of using a "triangle" in these devices. The purpose of this study was to measure the biomechanical properties of the Trivergent spinal fixation system and compare it to a predicate construct (ie, an FDA approved similar device against which testing is compared), Here, we report the biomechanical results of a new plate-based, triangular fixation device.

The ASTM (American Society for Testing and Materials) protocol included 3 forms of testing: static compression bending, static torsion, and dynamic compression bending. 3 predicate constructs, 3 Trivergent 60° constructs, and 3 Trivergent 75° constructs were tested in both static compression bending and static torsion. 3 predicate constructs, 4 Trivergent 60° constructs, and 7 Trivergent 75° constructs were tested in dynamic compression bending.

In static compression bending, the Trivergent 60°, Trivergent 75°, and predicate constructs tolerated average ultimate loads of 480 N, 550 N, and 400 N, and demonstrated average ultimate moments of 26.5 N-m, 30.2 N-m, and 18.6 N-m, respectively. In static torsion, the Trivergent 60°, Trivergent 75°, and predicate constructs tolerated average yield torques of 44 N-m, 34 N-m, and 20.5 N-m, and demonstrated an average torsional stiffness of 14 N-m/deg, 13 N-m/deg, and 5.22 N-m/deg, respectively. In dynamic compression bending, the Trivergent 60°, Trivergent 75°, and predicate constructs tolerated maximum loads of 300 N (maximum load tested), 230 N, and 160 N, respectively.

Hardware failure in posterior spinal pedicle screw fixation devices is common, and includes issues such as screw migration and rod breakage. The Trivergent device was designed to address these complications by incorporating characteristics such as screw divergence and cortical bone engagement. This study provides evidence of the biomechanical strength of Trivergent, supporting its potential ability to improve outcomes for posterior lumbar fusion surgery. Future cadaveric and human studies would help to substantiate the utility of Trivergent in treating degenerative disc disease, spinal stenosis, and other pathologies of the lumbar spine.