Biomechanical Effects Of X-Stop Interspinous Distracting Device On Kinematics Of The Implanted And Adjacent Levels In Elderly Patients With Lumbar Spinous Stenosis As Well As Clinical Outcomes Evaluation

ObjectivesTo explore the biomechanical efficacy of X-Stop interspinous distraction device on the implanted and adjacent segments during various functional activities in elderly patients with degenerative lumbar spinal stenosis and to evaluate the clinical outcomes of X-Stop interspinous distraction device surgeries.Summary of Background DataRecently, the X-stop interspinous process (ISP) distraction device has been introducing to treat elderly patients with lumbar spinal stenosis (LSS) and has reported promising outcomes in short-medium term. However only limited in-vitro experiments and two-dimensional (2D) in-vivo studies have evaluated the biomechanical efficiency of the X-Stop ISP distraction device, it is still not clear how the X-Stop ISP distraction device works and if disturbs the kinematics of the cranio-caudal adjacent levels in-vivo. In this study, we quantified the in-vivo biomechanical efficiency of the X-Stop ISP distraction surgeries during various functional activities using novel dual-fluoroscopy imaging system (DFIS) coupled with3dimensional-2dimensional digital matching techniques in elderly patients with degenerative LSS. MethodsTen patients with LSS scheduled for X-Stop surgeries were recruited. Eight subjects completed all the biomechanical tests and nine subjects finished clinical outcomes evaluateion using Oswenstry disability index (ODI), EuroQol-5dimensions (EQ-5D), and Short form-12items survey (SF-12). Prior to surgery, patients were computed tomography/magnetic resonance imaging (CT/MRI) scanned in order to construct three dimensional (3D) L2to S1vertebral models. The lumbar spines of the enrolled subjects were imaged using dual orthogonal fluoroscopes while they performed seven functional activities before and average7months postoperatively. The in-vivo3D vertebral positions were determined in the dual fluoroscopic images using an established3D-2D matching method. The shortest distances of the interspinous processes at the operated and the adjacent segments were measured using iterative closest point (ICP) method and were dissected into vertical (gap) and horizontal (lateral translation) components. The vertebral3D ranges of motion (ROM) of the implanted and cranial-caudal adjacent levels were measured using6degree of freedom (6-DOF), which consisted of the primary rotations and the coupled translations and rotations. In order to quantify the’flexion’effect caused by the X-Stop ISP device implantation, the flexed angle also were measured during various torso functional positions. At the X-Stop ISP device implanted segments and the cranio-caudal adjacent segments, the intervertebral foreman (IVF) mean dimensions (area, width and height), segmental spinal canal length (SSCL), anterior and posterior disc heights were measured pre-and post-operatively. In addition, we retrospectively compared the clinical outcomes between20patients treated with X-Stop devices and25patients with laminectomy in conjunction with posterolateral fusions using Prolo functional status at different postoperative intervals.ResultsAt the operated levels, the shortest vertical ISP distances (gap) significantly (p<0.05) increased by1.5mm during standing,1.2mm during left twist,1.3mm during extension and1.1mm during flexion. The lateral translations were not significantly affected. Primary ROM of the implanted segment was significantly decreased (p<0.05) by50.2%only at torso extension, yet not significantly (p>0.05) at flexion, twisting and lateral bending. The flexed angles of the X-Stop implanted levels were significantly (p<0.05) increased by1.7±1.7°,2.8±3.2°and1.9±2.0°at standing, extension and right bending respectively. The postoperative IVF area was significantly increased by32.9%(or32mm2)(p<0.05) and the IVF width was increased by24.4%(or1.1mm, p=0.06) during extension, but with minimal change in standing and flexion. The IVF heights were significantly (p<0.05) increased at standing (1.2mm) and extension (1.8mm), but not at flexion. The SSCL were significantly (p<0.05) increased by1.1mm during standing and1.2mm during extension as well as0.9mm in flexion. Anterior disc space of the implanted level was significantly decreased from8.0to6.6mm during standing.At the both cephalad and caudad adjacent levels, the ISP distances (vertical and horizontal), primary ROM and the coupled translations and rotations, the IVF dimensions (area, width and height) and SSCL as well as disc space were also not significantly affected (p>0.05) after X-Stop ISP distraction device surgeries.At the half year follow-up, the ODI scores were significantly (p<0.05) reduced by29.7%, and the EQ5D-VAS scores were also significantly (p<0.05) improved by21.4%. Patients who underwent X-Stop interspinous devices implantations had similar Prolo functional status with patients who underwent traditional laminectomy surgeries at all postoperative intervals during the examination time. And both of surgeries can significantly improve clinical outcomes of LSS patients.ConclusionsX-Stop ISP distraction devices can effectively enlarge the IVF dimensions, through vertically distracting the ISP and creating approximate2°-3°flexed angle at the implanted segment. However, it does reduce anterior disc space. The cranio-caudal adjacent levels were not significantly disturbed, which also implicated X-Stop ISP distraction devices probably will not lead increased degeneration. Long term follow up is warranted to evaluate if the biomechanical efficiency can remain. X-Stop ISP distraction device can effectively treat elderly patients with degenerative lumbar spine stenosis and can become an alternative treatment to the traditional laminectomy surgery. The current combined dual-orthogonal fluoroscopy imagining system and3D-2D digital matching technique can provide accurate in vivo biomechanical information.