Pull-out strength of patient-specific template-guided vs. free-hand fluoroscopically controlled thoracolumbar pedicle screws: a biomechanical analysis of a randomized cadaveric study

PURPOSE To assess the pull-out strength of thoracolumbar pedicle screws implanted via either a patient-specific template-guided or conventional free-hand fluoroscopically controlled technique in a randomized cadaveric study, and to evaluate the influence of local vertebral bone density, quantified by Hounsfield units (HU), on pedicle screw pull-out strength. METHODS Thoracolumbar pedicles of three spine cadavers were instrumented using either a free-hand fluoroscopically controlled or a patient-specific template-guided technique. Preoperative bone density was quantified by HU measured on CT. Pedicle perforation was evaluated on postoperative CT scans by an independent and blinded radiologist. After dissected vertebrae were embedded in aluminum fixation devices, pull-out testing was initiated with a preload of 50 N and a constant displacement rate of 0.5 mm/s. Subgroup analyses were performed excluding pedicle screws with a pedicle breach (n = 47). RESULTS Pull-out strength was significantly different with 549 ± 278 and 441 ± 289 N in the template-guided (n = 50) versus fluoroscopically controlled (n = 48) subgroups (p = 0.031), respectively. Subgroup analysis limited to screws with an intrapedicular trajectory revealed a tendency toward a higher pull-out strength in the template-guided (n = 30) versus fluoroscopically controlled screws (n = 21) with 587 ± 309 and 454 ± 269 N (p = 0.118), respectively. There was a trend toward a higher pull-out strength (709 ± 418 versus 420 ± 149 N) in vertebrae with a bone density of (>171 HU) versus (<133 HU), respectively (p = 0.061). CONCLUSIONS There was a significantly higher pull-out strength of thoracolumbar pedicle screws when inserted via a patient-specific template-guided versus conventional free-hand fluoroscopically controlled technique, potentially associated with screw trajectory

Antigua and Barbuda

The country of Antigua and Barbuda comprises two islands located in the Lesser Antilles of the Caribbean. While both islands are positioned on the Barbuda Bank, they each consist of a unique geologic setting: Antigua is composed of volcanic rock, clay, and limestone, while Barbuda is largely limestone with prominent cave features. Their unique attributes are not just geologic, as the two islands also have differing histories that developed in part due to environmental constraints—Antigua’s enslaved African population grew sugarcane as a British colony, while enslaved Barbudans raised livestock as a leased entity of the British Codrington family because of shallow soils resulting from the island’s karst topography. Today, Antigua is much more developed relative to Barbuda in terms of tourism and has a greater population density. Barbuda’s population is small and development is limited as a result of Barbuda’s unique land tenure of common property. Still, despite their differences, both islands face similar environmental hazards including drought, hurricanes, soil erosion, flooding, and the long-term risks posed by climate change