Impact of anchor type on porcine lumbar biomechanics: Finite element modelling and in-vitro validation.
BACKGROUND
Rigid posterior implants used for spinal stabilization can be anchored to the vertebrae using pedicle screws or screws combined with transverse process hooks. In the present study, a finite element model of a porcine lumbar spine instrumented with screws and hooks is presented and validated.


METHODS
The porcine lumbar spine model was validated using in-vitro measurements on six porcine specimens. Validation metrics included intervertebral rotations (L1 to L6) and nucleus pressure in the topmost cranial instrumented disc. The model was used to compare the biomechanical effect of anchor types.


FINDINGS
Good agreement was observed between the model and validation experiments. For upper transverse hooks construct, intervertebral rotations increased at the upper instrumented vertebra and decreased at the adjacent level. Additionally, nucleus pressures and stress on the annulus decreased in the adjacent disc and increased in the upper instrumented disc. The pull-out forces predicted for both anchor configurations were significantly lower than the pull-out strength found in the literature.


INTERPRETATION
These numerical observations suggest that upper transverse process hooks constructs reduce the mobility gradient and cause less stress in the adjacent disc, which could potentially reduce adjacent segment disease and proximal junction kyphosis incidence without increasing the risk of fixation failure. Future work needs to assess the long-term effect of such constructs on clinical and functional outcomes.
['Brummund|Martin|M|', 'Brailovski|Vladimir|V|', 'Petit|Yvan|Y|', 'Facchinello|Yann|Y|', 'Mac-Thiong|Jean-Marc|JM|']
D000818:Animals D001696:Biomechanical Phenomena D001863:Bone Screws D020342:Finite Element Analysis D006801:Humans D007738:Kyphosis D008159:Lumbar Vertebrae D023421:Models, Animal D065289:Pedicle Screws D011312:Pressure D013123:Spinal Fusion D053441:Suture Anchors D013552:Swine
Finite element modelling Pedicle screws Transverse process hooks Porcine lumbar spine Proximal junction kyphosis Spinal fusion