Electroactive Spinal Instrumentation for Targeted Osteogenesis and Spine Fusion: A Computational Study

Model pedicle screws: (A) simplified and (B) threaded.

Electrical field distribution of electroactive pedicle screws implanted in the trabecular bone: (A) simplified screw and (B) threaded screw. Osteogenic electrical amplitude is concentrated in the elliptical region surrounding screws. The amplitude rapidly declined with increasing orthogonal distance from midpoint of each screw (C) in saline and (D) in trabecular bone.

Electrical fields generated via electroactive simplified pedicle screws in trabecular bone. Osteogenic electrical field (>1 mv/cm) is represented as dark red on colorimetric scale surrounding the screw. (A–E) Electrical fields created by stimulation from 20 to 100 µA amplitudes. (F) Larger stimulus amplitude increased electrical field amplitude and distance orthogonal to midpoint of screw.

Effect of selective anodization with a uniform layer of 400 nm on electrical field distribution at constant stimulus amplitude of 40 µA around the pedicle screw. Osteogenic electrical field (>1 mv/cm) is represented as dark red on colorimetric scale surrounding the screw. (A) Without anodization. (B–D) Increasing anodization from 50% to 95% of the screw.

Effects of graded anodization of the screw body on electrical field distribution. (A) Gradient anodization (100% linear) and (B) gradient anodization limited to distal half of screw (50% linear). (C) Gradient anodization limited to distal half of screw (100% exponential). (D) Gradient anodization limited to distal half of screw (50% exponential). Osteogenic electrical field (>1 mv/cm) is represented as dark red on colorimetric scale surrounding the screw.

The osteogenic electrical field distribution in regions of interest of L4-L5 level (A) by varying percentage of anodization and (B) gradient vs exponential anodization of electroactive pedicle screws at constant electrical stimulation amplitude of 40 µA. Increasing anodization to 50% focused osteogenic electrical field within the intervertebral (IV) space, vertebra, and instrumented pedicles. Screw anodization of >50% further focused osteogenic electrical field in the intervertebral space, anterior vertebral body, however, reduced in the instrumented pedicles. Similarly, increasing gradient anodization (both linear and exponential) resulted in osteogenic electric fields within the intervertebral space, vertebra, and instrumented pedicles.