Designs and Techniques That Improve the Pullout Strength of Pedicle Screws in Osteoporotic Vertebrae: Current Status

Abstract

Osteoporosis is a medical condition affecting men and women of different age groups and populations. The compromised bone quality caused by this disease represents an important challenge when a surgical procedure (e.g., spinal fusion) is needed after failure of conservative treatments. Different pedicle screw designs and instrumentation techniques have been explored to enhance spinal device fixation in bone of compromised quality. These include alterations of screw thread design, optimization of pilot hole size for non-self-tapping screws, modification of the implant's trajectory, and bone cement augmentation. While the true benefits and limitations of any procedure may not be realized until they are observed in a clinical setting, axial pullout tests, due in large part to their reproducibility and ease of execution, are commonly used to estimate the device's effectiveness by quantifying the change in force required to remove the screw from the body. The objective of this investigation is to provide an overview of the different pedicle screw designs and the associated surgical techniques either currently utilized or proposed to improve pullout strength in osteoporotic patients. Mechanical comparisons as well as potential advantages and disadvantages of each consideration are provided herein.

Effect of various factors on pull out strength of pedicle screw in normal and osteoporotic cancellous bone models

“…A detailed discussion regarding these factors can be read in a review paper by Shea et al . [68] . The current study is limited by the absence of cadaver experiments.…”

Cement leakage in pedicle screw augmentation: a prospective analysis of 98 patients and 474 augmented pedicle screws

“…Second, there are numerous different pedicle screw types, varying in core diameter and size and number and location of radial holes. 42 The screw used in the present study has about 20 radial holes in its distal third (hole diameter 1.2 mm) and has a core diameter of 1.68 mm. High cement application pressure as well as low cement viscosity are directly related to an increased cement leakage rate.…”

Predictive validity of preoperative CT scans and the risk of pedicle screw loosening in spinal surgery

“…The previous investigations have demonstrated an incidence of screw loosening of up to 60 % in osteoporotic bones [7] compared to 1-27 % in nonosteoporotic patients treated with rigid posterior stabilization [12,13,24]. Based on this, newer techniques and materials have been developed to prevent this kind of complication [19].…”