Augmented PMMA distribution: improvement of mechanical property and reduction of leakage rate of a fenestrated pedicle screw with diameter-tapered perforations

Abstract

<jats:sec> <jats:title>OBJECTIVE</jats:title> <jats:p>This study investigated the optimum injection volume of polymethylmethacrylate (PMMA) to augment a novel fenestrated pedicle screw (FPS) with diameter-tapered perforations in the osteoporotic vertebral body, and how the distribution characteristics of PMMA affect the biomechanical performance of this screw.</jats:p></jats:sec> <jats:sec> <jats:title>METHODS</jats:title> <jats:p>Two types of FPSs were designed (FPS-A, composed of 6 perforations with an equal diameter of 1.2 mm; and FPS-B, composed of 6 perforations each with a tapered diameter of 1.5 mm, 1.2 mm, and 0.9 mm from tip to head. Each of 28 human cadaveric osteoporotic vertebrae were randomly assigned to 1 of 7 groups: FPS-A1.0: FPS-A+1.0 ml PMMA; FPS-A1.5: FPS-A+1.5 ml PMMA; FPS-A2.0: FPS-A+2.0 ml PMMA; FPS-B1.0: FPS-B+1.0 ml PMMA; FPS-B1.5: FPS-B+1.5 ml PMMA; FPS-B2.0: FPS-B+2.0 ml PMMA; and conventional pedicle screws (CPSs) without PMMA. After the augmentation, 3D CT was performed to assess the cement distribution characteristics and the cement leakage rate. Axial pullout tests were performed to compare the maximum pullout force thereafter.</jats:p></jats:sec> <jats:sec> <jats:title>RESULTS</jats:title> <jats:p>The CT construction images showed that PMMA bone cement formed a conical mass around FPS-A and a cylindrical mass around FPS-B. When the injection volume was increased from 1.0 ml to 2.0 ml, the distribution region of the PMMA cement was enlarged, the PMMA was distributed more posteriorly, and the risk of leakage was increased. When the injection volume reached 2.0 ml, the risk of cement leakage was lower for screws having diameter-tapered perforations. The pullout strengths of the augmented FPS-A groups and FPS-B groups were higher than that of the CPS group (p &lt; 0.0001). All FPS-B groups had a higher pullout strength than the FPS-A groups.</jats:p></jats:sec> <jats:sec> <jats:title>CONCLUSIONS</jats:title> <jats:p>The diameter of the perforations affects the distribution of PMMA cement. The diameter-tapered design enabled PMMA to form larger bone-PMMA interfaces and achieve a relatively higher pullout strength, although statistical significance was not reached. Study results indicated 1.5-ml of PMMA was a conservative volume for PMMA augmentation; more cement injection would significantly increase the risk of cement leakage.</jats:p></jats:sec>

An innovative technique for osteoporotic vertebral compression fractures &ndash; vertebral osteotome with side-opening cannula

“… 24 Previous studies showed that a larger bone–cement interface would achieve a relatively higher vertebral strength and reduce leakage rate. 25 It was suggested that the cement should spread through the vertebral body in a controlled manner that appeared fluoroscopically as a “uniformly expanding cloud” 26 . Insufficient cement distribution in the fractured area might lead to unrelieved pain after PVP.…”

Comparison of unilateral and bilateral polymethylmethacrylate-augmented cannulated pedicle screw fixation for the management of lumbar spondylolisthesis with osteoporosis

“…The PMMA powder and water agent were mixed, and then injected using a special device once the mixture had reached a dough-like consistency. The amount of PMMA (not more than 2 mL) was determined by intraoperative monitoring of intravertebral PMMA dispersion [16]. The surrounding tissue of the intervertebral disk space was loosened after the injection procedure was completed.…”

Comparison of Unilateral and Bilateral Polymethylmethacrylate-augmented Cannulated Pedicle Screw Fixation for Management of Lumbar Spondylolisthesis with Osteoporosis

“…PMMA powder and water agent were mixed, and then, injected by a special device during a dough-like mass viscosity. The amount of PMMA not more than 2 ml was determined by intraoperative monitoring of intravertebral PMMA dispersion (16). The surrounding tissue of intervertebral disc space was loosened after the injection procedure completed.…”