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Types of Pedicle Screws

Pedicle screws are spinal fusion tools, which surgeons use to grip on to segments of the spine. The screws are responsible for anchoring rods, which surgeons stretch across the spinal column in order to apply pressure and help fusion. Pedicle screw and bracing rod assemblies also help prevent the fusing spine segments from shaking and otherwise moving.

  1. Monoaxial Pedicle Screws

    • A monoaxial pedicle screw has one axis, which means that its top segment, or arm, forms a continuous, linear, rigid structure with its bottom, threaded segment.

      According to the Burton Report, surgeons first began experimenting with monoaxial pedicle screws in the 1960s. However, they would not successfully insert the screws into a spine in conjunction with bracing structures until the late 1970s. Instead of the modern, more flexible bracing rods scientists would later develop, they used rigid, heavy plates of metal. These plates sometimes exerted unnecessary stress on the spinal column and on the monoaxial pedicle screws, which commonly resulted in complications.

    Polyaxial Pedicle Screws

    • According to Spine Universe, polyaxial, or multiaxial, pedicle screws are the modern standard when it comes to spinal fusion surgery. Unlike their monoaxial counterparts, polyaxial screws have mobile arms, which can swivel freely of their threaded bottom segments. This helps reduce stress on the spinal column, as bracing rods stretching between two screws can flex and adapt more easily to body movements. The majority of polyaxial pedicle screws consist of titanium, which manufacturers utilize for its strength, its resistance to corrosion and its compatibility with MRI (magnetic resonance imaging) machines.

    Conical Pedicle Screws

    • The majority of pedicle screws that surgeons use for spinal fusion are long, skinny and have a uniform cylindrical shape. This is true both of monoaxial and polyaxial screw varieties. However, according to the National Institutes of Health, the National Taiwan University of Science and Technology published a study in 2008, which showed that conical pedicle screws might be a better option when it comes to spinal fusion surgery. The study pitted 10 different types of pedicle screws against each other, all of which had varying shapes and tapering. The conical screws proved to be the strongest and most reliable.

    Arm Length

    • You can also identify pedicle screws according to their arm lengths. Both monoaxial and polyaxial varieties can come with short or long arms. While surgeons use the former for bridging smaller sections of spine, they use the latter on larger sections, as the longer arms give them more surface area for connecting the rods, which must also be correspondingly longer.

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