Intervertebral Foramen Variation Following Dynamic L4−L5 Interspinal Device Implantation

Abstract

This is a biomechanical study. Measuring changes in foraminal size after L4-L5 interspinous devices implantation. Low-back pain aetiologies include foraminal stenoses. A niche is developing for interspinal implants that are minimally invasive with few harmful side effects. At present, we do not have sufficient understanding about their impact on the foraminal opening. Six fresh L2-S1 columns were prepared with preservation of the capsuloligamentary and discal structures. The L4-L5 foramen was particularly carefully prepared. A 2-dimensional photographic analysis measured the length and width of the foramen and the extraforaminal surface, both before and after the implantation of a supple interspinal device that preserves the supraspinal ligaments. Photographic calibration and the use of precise and identical photographic landmarks (pixels) permitted the calculation of the foraminal deformity. A Wilcoxon test was performed for statistical analysis with P<0.05 for significance. The average foraminal length was 15.7±2.8 mm and the average width was 9.4±1.2 mm. After the implantation of an interspinal device, it was 16.8±2.5 and 10.1±1.3 mm, respectively. The increase in the average foraminal opening was 7.45% and 7.63%, respectively (P=0.02). The average foraminal surface area was 150.4±35.8 mm and following intervention, this was 165.1±28.3 mm, that is an average gain of 14.65 mm (5.3-26.9) (P=0.03). Few interspinal devices have been the subject of studies on the foraminal opening after implantation. Among the initial strict indications on root compressions for which conventional surgery is too invasive, these implants could present a true therapeutic alternative. This supple implant significantly opened the L4-L5 foramen on the cadavers. Nevertheless, biomechanical data are lacking on its effects on the 3 planes following stress. Even if the impact on the foraminal opening is of interest, kinematic studies are needed to determine the exact effects before clinical implantation.