=====Anchored screw=====
Anchor sleeves with 6.5-mm-diameter pedicle screws provided markedly higher resistance to screw pullout than 7.5-mm-diameter revision screws and fixation statistically equivalent to 8.5-mm-diameter screws, possibly because of medial-lateral expansion within the vertebral space and/or convex filling of the pedicle. AS results had the lowest SD, indicating minimal variability in bone-screw purchase
((Manon J, Hussain MM, Harris J, Moldavsky M, La Marca F, Bucklen BS.
Biomechanical Investigation of a Novel Revision Device in an Osteoporotic Model: 
Pullout Strength of Pedicle Screw Anchor Versus Larger Screw Diameter. J Spinal
Disord Tech. 2015 Aug 19. [Epub ahead of print] PubMed PMID: 26301731.
)).