Thoracolumbar Instrumentation Options: Biomechanical Implications

Pedicle screws and rods are the cornerstone of spine instrumentation. This article focuses on the practical usage of these implants in contemporary spine practice. Furthermore, we discuss strategies to optimize fixation in osteoporotic spine and implant-related considerations in preventing proximal junctional kyphosis. Cross-sectional imaging helps select the longest screws with maximum outer diameter that can be safely placed. Conical inner diameter with V-shaped thread provides best pullout strength. Dual-core, dual-thread screws are biomechanically superior to conventional screws. For pedicle screw placement, undertapping or no tapping and convergent trajectory is recommended. Polyaxial, uniaxial, and monoaxial screws have shown similar clinical and radiologic results. Cortical bone trajectory screws and sublaminar bands can provide alternative fixation options to pedicle screws. Cement augmentation through cannulated fenestrated screws is the most reliable method of pedicle screw augmentation in osteoporotic spine. Alternatively, biodegradable cement augmentation, HA-coated screws, and expandable screws can be used. Both titanium and cobalt-chromium rods have shown similar clinical and radiologic results. Precontoured rods are recommended to prevent notching. Multiple rods are recommended at L5-S1 and osteotomies to prevent complications. "Soft landing" using hooks or sublaminar band, and vertebroplasty at the cranial end of the construct may prevent proximal junctional kyphosis.