Biomechanical comparison of pedicle screw fixation strength among three different screw trajectories using single vertebrae and one-level functional spinal unit.

Three key factors are responsible for the biomechanical performance of pedicle screw fixation: screw mechanical characteristics, bone quality and insertion techniques. To the best of the authors' knowledge, no study has directly compared the biomechanical performance among three trajectories, i.e.

Improved fixation stability for repairing pedicle screw loosening using a modified cement filling technique in porcine vertebrae.

Polymethylmethacrylate (PMMA) has been applied clinically and biomechanically repair loose pedicle screws. Controversies have arisen over data due to uncontrolled cement properties, various locations and sizes of fenestrated holes in repair screws, irregular holes and different bone densities of specimens. In this study, the pullout strength was compared for two techniques, the modified technique to use PMMA to augment a threaded hole and the traditional technique with retrograde injection of a PMMA filling, for standard loose screws in porcine vertebrae.

Biomechanical Comparison of Different Numbers and Configurations of Cross-Links in Long-Segment Spinal Fixation-An Experimental Study in a Porcine Model.

Study Design: Biomechanical study.

Objective: Cross-links are a type of common clinical spinal instrumentation. However, the effects of the position and number of cross-links have never been investigated in long-segment spinal fixation, and the variables have not been optimized.

Use of longer sized screws is a salvage method for broken pedicles in osteoporotic vertebrae.

Screw loosening due to broken pedicles is a common complication resulting from the insertion of screws either with inadequate diameters or into an osteoporotic pedicle. In this novel in vitro study, we tried to clarify the contribution of the pedicle to screw fixation and subsequent salvage strategies using longer or larger-diameter screws in broken pedicles. Sixty L4 fresh-frozen lumbar vertebrae harvested from mature pigs were designed as the normal-density group (n = 30) and decalcified as the osteoporosis group (n = 30).

Biomechanical comparison of pedicle screw fixation strength in synthetic bones: Effects of screw shape, core/thread profile and cement augmentation.

Pedicle screw loosening resulting from insufficient bone-screw interfacial holding power is not uncommon. The screw shape and thread profile are considered important factors of the screw fixation strength. This work investigated the difference in pullout strength between conical and cylindrical screws with three different thread designs.

Biomechanical study of the fixation stability of broken pedicle screws and subsequent strategies.

Pedicles are often broken when screws are inserted into hard pedicles with small diameters or when the diameter of the screw itself is inadequate. However, there is a lack of biomechanical literature that addresses screw loosening as a result of broken pedicles or the resulting salvage of those screws. We performed a novel in vitro study to compare the pullout strength of screws between intact pedicles and two different types of broken pedicles; strategies to prevent screw loosening were also compared.

Modification of Mechanical Properties, Polymerization Temperature, and Handling Time of Polymethylmethacrylate Cement for Enhancing Applicability in Vertebroplasty.

Polymethylmethacrylate (PMMA) bone cement is a popular bone void filler for vertebroplasty. However, the use of PMMA has some drawbacks, including the material's excessive stiffness, exothermic polymerization, and short handling time. This study aimed to create an ideal modified bone cement to solve the above-mentioned problems.

A Biomechanical Comparison of Expansive Pedicle Screws for Severe Osteoporosis: The Effects of Screw Design and Cement Augmentation.

Expansive pedicle screws significantly improve fixation strength in osteoporotic spines. However, the previous literature does not adequately address the effects of the number of lengthwise slits and the extent of screw expansion on the strength of the bone/screw interface when expansive screws are used with or without cement augmentation. Herein, four designs for expansive pedicle screws with different numbers of lengthwise slits and different screw expansion levels were evaluated.

Biomechanical comparison of different combinations of hook and screw in one spine motion unit--an experiment in porcine model.

Background: The biomechanical performance of the hooks and screws in spinal posterior instrumentation is not well-characterized. Screw-bone interface failure at the uppermost and lowermost vertebrae is not uncommon. Some have advocated for the use of supplement hooks to prevent screw loosening.