The Effects of Depth of Penetration, Screw Orientation, and Bone Density on Sacral Screw Fixation

L5 spinal nerve injury caused by misplacement of outwardly-inserted S1 pedicle screws

“…Bicortical or tricortical methods that penetrate the anterior sacral cortex or cranial S1 endplate are reported to provide stronger stability than monocortical methods that only penetrate the posterior cortex [15][16][17][18]. It is generally agreed that medially oriented placement of S1 pedicle screws provides greater stability than either centrally or laterally oriented positions because the mean bone mineral density in the central region of the sacrum is approximately 30 to 60 % higher than that in the alar region [25,26]. By contrast, several authors have recommended that placement of S1 pedicle screws in a central position should be avoided because of the risk this placement carries of damage to the iliac vessels, the sympathetic chain, and the lumbosacral trunk, which are all close to the sacrum [19][20][21][22][23][24].…”

Surgical Treatment Options in Patients With Impaired Bone Quality

“…Cadaver-based biomechanical studies do offer compelling evidence for a relationship between bone quality and approaches to fracture fixation [3,135,136], instrumentation [48,122,126,146], and rotator cuff repair [69,102]. The paucity of clinical studies, and their limited ability to adequately assess bone quality, limits the prospect for evidence-based treatment recommendations.…”

“…For example, using a screw tap for pilot hole preparation decreases the pullout strength of the screw [16], although this can be partially mitigated by using an undersized tap [48] or instilling polymethylmethacrylate bone cement after pilot hole preparation [126]. In addition, the technique of screw insertion can be altered to maximize screw fixation [7,47,111,122]; for example, directing pedicle screws toward and penetrating the midanterior cortex where optimal bone strength is seen [111,122] or placement of screws in a convergent, triangulated fashion to increase the resistance to pullout in the osteoporotic spine [7,47]. Furthermore, use of a staple to support an anterior thoracolumbar screw increases the pullout strength of the screw [123].…”

The Effect of Sacral Alar Screw on Long-level Fusion Including Lumbosacral Segment

“…Smith et al 28) and Halvorson et al 29) reported that the strength of dual pedicle screws was not greatly increased as compared with a single pedicle screw despite the additional insertion of the screw because the central region of the S1 had a lower degree of the bone mineral density as compared with the sacral ala. According to Smith et al 28) following a comparison of the strength between cases in which a screw was inserted in up to the anteromedial cortical bone in the older sacrum and those in which a screw was inserted in the adjacent area to the cortical bone without being inserted in up to it, the strength was just increased by 4.8% in the former cases. The above authors noted that the strength was not greatly increased because the anterior cortical bone was fragile in the sacrum of elderly patients.…”