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Chapter Summary
• Context: The surgical management of the aging and osteoporotic spine represents one of the most formidable challenges in modern spine surgery. Diminished bone mineral density (BMD), trabecular microarchitectural deterioration, and thinning cortical bone drastically reduce implant purchase, leading to high rates of pedicle screw loosening (up to 60%), pullout, progressive kyphosis, hardware failure, and proximal junctional kyphosis/failure (PJK/PJF). Overcoming these biomechanical vulnerabilities requires a multifaceted approach that integrates advanced surgical techniques with systemic medical optimization. Key surgical strategies include alternative trajectory mechanics such as Cortical Bone Trajectory (CBT) and penetrating endplate screws (PES), polymethylmethacrylate (PMMA) cement augmentation of fenestrated screws, expandable pedicle screws, hydroxyapatite coatings, robust sacropelvic anchoring (S2AI), anterior column load-sharing cages, and junctional transition methods (sublaminar bands, transverse process hooks).
• Chapter Objective: Detail the biomechanical foundations, advanced screw trajectories, cement augmentation protocols, auxiliary anchoring methods, and surgical strategies for fixation in the osteoporotic spine. The reader will master Cortical Bone Trajectory (CBT), PMMA cement augmentation of fenestrated screws, expandable hardware, S2AI pelvic fixation, anterior column support, and junctional failure prevention.
• Biomechanical challenge of the osteoporotic bone-screw interfaceOsteoporosis diminishes cancellous bone trabeculae within the vertebral body while relatively preserving cortical bone. Traditional pedicle screws rely primarily on trabecular core fixation and experience up to 50-70% pullout strength reduction in severe osteopenia. Surgical solutions must redirect purchase toward dense cortical bone or physically expand the bone-implant interface.
• Alternative screw trajectories: Cortical Bone Trajectory (CBT) and PESCortical Bone Trajectory (CBT): The screw starts at the pars interarticularis and travels caudo-cephalad and medio-lateral, engaging 4 cortical surfaces (dorsal cortex, medial pedicle wall, superior pedicle wall, and anterolateral vertebral body cortex). CBT increases pullout strength by 30% and insertional torque by 1.7-fold compared to traditional screws, while allowing smaller incisions and sparing muscle. Penetrating Endplate Screws (PES): Screws penetrate the dense subchondral cortical bone of the superior endplate, achieving multi-cortical stability.
• PMMA cement augmentation, hydroxyapatite, and expandable screwsFenestrated screws with PMMA cement augmentation reduce loosening rates by >60% by creating a broad cement mantle that anchors into surrounding trabeculae. Controlled injection under continuous fluoroscopy (1.5 to 3.0 mL per screw) is vital to avoid cement leakage into the spinal canal or perivertebral venous plexus (pulmonary embolism). Hydroxyapatite-coated screws promote biological bone ingrowth, reducing 1-year loosening to 5.8%. Expandable screws deploy distal radial wings, increasing pullout force by up to 150%.
• Auxiliary anchoring and sacropelvic fixationIn lumbosacral constructs, isolated S1 screws face high pullout failure in osteoporotic bone; S2 alar-iliac (S2AI) pelvic screws cross the SI joint into the dense iliac column, providing stable caudal anchorage. At the proximal upper instrumented vertebra (UIV), auxiliary transition anchors—such as sublaminar polyester bands, laminar hooks, and transverse process hooks (TPH)—distribute stress and prevent proximal junctional kyphosis (PJK).
• Anterior support and multi-column reconstructionIn severe vertebral collapse or burst fractures, anterior column support using wide-footprint interbody cages (ALIF, LLIF, OLIF) spans the dense apophyseal ring, restoring anterior load bearing and protecting posterior instrumentation from fatigue fracture.
• Clinical Application: In clinical decision-making, preoperative CT must measure pedicle diameter and Hounsfield Units (HU <110 indicates osteoporosis) to identify high-risk patients. When performing PMMA cement augmentation through fenestrated screws, the cement must be in the doughy/viscous phase and injected slowly under real-time fluoroscopy, strictly limited to 1.5–3 mL per screw to prevent cement embolization or canal extravasation. In long deformity constructs, topping off the construct with transverse process hooks or sublaminar bands at the UIV softens the rigidity transition, preventing catastrophic proximal junctional failure. Systemic anabolic bone therapy (teriparatide, romosozumab) should be initiated perioperatively in collaboration with endocrinology to optimize fusion and long-term implant survival.
