Introduction Lateral access surgery has seen an increase in popularity among spine surgeons since its initial introduction (1-3). The transpsoas approach provides access to the lumbar spine with relatively predictable anatomy and obviates the need for an access surgeon (4,5). Lateral access surgery is performed in the lateral decubitus position and the discectomy, endplate preparation, and interbody insertion are all performed while the patient remains in the lateral position. Once the interbody has been inserted, traditionally, the wounds are closed and the patient is repositioned prone for pedicle screw fixation (1). The repositioning requires completing a second round of prepping, draping, and room positioning, which may add significant time to the case and increase the risk of contamination. The lateral position tends to be better tolerated by the patient compared to prone surgery and avoids many of the major concerns that exist with prone positioning including but not limited to: postoperative vision loss, cardiovascular complications, hypovolemia, reduced pulmonary compliance, and cardiac arrest (6-8). Concern exists

Cancellous screws are designed to optimize fixation in metaphyseal bone environments; however, certain clinical situations may require the substitution of cortical screws for use in cancellous bone, such as anatomic constraints, fragment size, or available instrumentation. This study compares the biomechanical properties of commercially available cortical and cancellous screw designs in a synthetic model representing various bone densities. Commercially available, fully threaded, 4.0-mm outer-diameter cortical and cancellous screws were tested in terms of pullout strength and maximum insertion torque in standard-density and osteoporotic cancellous bone models. Pullout strength and maximum insertion torque were both found to be greater for cancellous screws than cortical screws in all synthetic densities tested. The magnitude of difference in pullout strength between cortical and cancellous screws increased with decreasing synthetic bone density. Screw displacement prior to failure and total energy absorbed during pullout strength testing were also significantly greater for cancellous screws in osteoporotic models. Stiffness was greater for cancellous screws in standard and osteoporotic models. Cancellous screws have biomechanical advantages over cortical screws when used in metaphyseal bone, implying the ability to both achieve greater compression and resist displacement at the screw-plate interface. Surgeons should preferentially use cancellous over cortical screws in metaphyseal environments where cortical bone is insufficient for fixation. [Orthopedics.2016; 39(5):e828-e832.].

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