Enhanced Fixation Strength of Pedicle Screws Using Calcium Phosphate Cement: Development of a Novel Augmentation Technique for Percutaneous Insertion.

Abstract

Introduction: Spinal surgery for osteoporotic vertebral fractures using implants often results in implant failure owing to poor bone quality. We developed a new augmentation technique using calcium phosphate cement (CPC) for percutaneous pedicle screws (PPSs). This study evaluated the reinforcement effect of CPC on the initial fixation strength of PPSs in synthetic bone specimens.

Methods: Using the X-Needle^Ⓡ, developed for screw hole preparation and CPC injection, a 40 mm deep pilot hole was created in 40×40×60 mm bone specimens. A commercially available CPC (BIOPEX-R^Ⓡ) was mixed at a powder-to-liquid ratio of 12 g/3.4 mL, and 0.5 mL was injected into the pilot hole 6 minutes (min) after mixing. Screws were then inserted using the standard PPS technique. Pull-out strength (N) was measured seven times in four groups: without CPC (control group), immediately after CPC injection (CPC0 group), 10 mins after CPC injection (CPC10 group), and 24 hours after CPC injection (CPC24 group). Toggle tests were conducted six times in the control and CPC24 groups to measure the number of cycles/load (N) required to achieve 2 mm screw head displacement.

Results: In the pull-out test, the maximal pull-out strength in the CPC24 group was significantly greater than that in the control and CPC0 groups. Pull-out strength in the CPC10 and CPC24 groups increased to 121.1% and 165.1% of that of the control group, respectively. In the toggle test, the CPC24 group showed significantly higher values for both cycles and load compared to the control group.

Conclusions: The X-Needle^Ⓡ enables simple, minimally invasive CPC injection into the pilot hole, facilitating PPS augmentation. Additionally, screws augmented with CPC showed increased pull-out and toggle strengths. PPS augmentation using CPC may serve as a preventive measure against implant failure in spinal surgery for patients with poor bone quality.