Development of percutaneously insertable/removable interspinous process spacer for treatment of posture-dependent lumbar spinal-canal stenosis: preclinical feasibility study using porcine model

Abstract

A procedure using an interspinous process spacer (IPS) was recently developed for the treatment of posture-dependent lumbar spinal-canal stenosis (LSS) patients. We developed a novel IPS which can be inserted with simpler procedures and removed percutaneously. The objectives of this study were: (1) to evaluate the feasibility and safety of this novel technique, and (2) to assess the effectiveness of this spacer in terms of preventing an increase of epidural pressure in lumbar extension using a porcine model. Eight young pigs were used. Under general anesthesia and image guidance, the spacers were inserted. Three months after operation, MR images were taken and all spacers were removed. Blood samples were obtained before and 1, 3, 7days after surgery. After killing the animals, the lumbar spines were observed macroscopically. Another six animals were used. Under general anesthesia and image guidance, a flexible pressure transducer was inserted into the epidural space and epidural pressure was measured in neutral and at maximum extension with and without spacer insertion. Percutaneous insertion and removal of the spacer was successful for all animals through small skin incisions. MR images showed minimal damage to the muscle. No significant up-regulation of Interleukin-6 (IL-6) and CRP was detected. Macroscopic observation of the lumbar spine 3months after the operation revealed that the area of the interspinous process contacting with the inserted spacer showed some bone erosion/remodeling. Insertion of the spacer did not affect the epidural pressure in neutral but significantly prevented an increase of epidural pressure in lumber extension. This study demonstrated that the percutaneous insertion and removal of a novel IPS was feasible and safe using a simple technique. Furthermore, this procedure can be recognized as minimally invasive surgery from the viewpoint of skin incision, short insertion track, inflammatory mediators, and muscle damage. Improvements should be attempted in future studies using softer or more elastic materials for the spacer to lessen bone erosion/remodeling at contacting area of the inserted spacer.