Article

Pedicle screw fixation, the standard surgical care for posterior
stabilization in the thoraco-lumbar spine has a high rate of failure in
osteoporotic individuals. Screw design factors and insertion techniques have been
shown to influence the biomechanical performance of pedicle screws. Our objective
was to investigate the biomechanical characteristics of pedicle screw fixation in
osteoporotic bone by comparing standard screws with newly designed differential
crest thickness dual lead screws. METHODS: An in-vitro spinal-level paired
factorial study design was used to examine thoraco-lumbar spine biomechanical
outcomes for differential pedicle screw thread designs. Six cadaveric human
spines (T8-L5) were tested for six groups (n=20) consisting of 2 different crest
thickness and 3 different insertion techniques. Bone mineral density was assessed
and peak insertion torque measured while placing one screw of new design and
control on the contralateral side. Screw pullout properties were measured from
classical American Society for Testing and Materials protocols. FINDINGS: The
screws designed specifically for osteoporotic bone showed significantly larger
insertion torque compared with the standard screw design irrespective of
insertion technique. Much of the variability in pullout failure and stiffness was
explained by bone mineral density. The osteoporotic screws of different crest
thickness were statistically similar to each other in all outcome measures.
INTERPRETATION: Compared with standard pedicle screws, the dual lead
osteoporotic-specific pedicle screws demonstrated significantly larger insertion
torques and similar pullout properties. Non-significant increased biomechanical
strength was observed for thin crest compared to thick crest dual lead pedicle
screws indicating their enhanced purchase in osteoporotic bone.
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Langue : ANGLAIS