## 1 Introduction  
Lumbar spines have a three-point joint, including a facet joint and spinal disc. Spinal stenosis in the lumbar spine is caused by a hypertrophic facet joint or bulged disc. The hypertrophic ligamentum flavum may also impinge the spinal cord and induce spinal stenosis. The aforementioned scenarios can result in nerve root or spinal cord compression [1]. Decompression laminectomy is employed to open the spinal canal and decompress the spinal cord [2]. Approaches for removing lamina for decompression include partial or total laminectomy. In clinical settings, laminectomy sometimes results in atrogenic spondylictishesis because the surgery involves the removal of excessive posterior elements and the cutting of posterior spinal ligaments, which induce spinal instability [3, 4]. In decompression surgery, the spinal ligament must be retained as much as possible to maintain spinal stability. Laminectomy helps preserve the interspinous and supraspinous ligaments and thus assists in stabilizing spinal motion in flexion [5]. Therefore, partial removal of the lamina, such as in laminotomy, not only decompresses the spinal cord but also allows for the achievement of spinal stability. In addition to the risk of spinal surgery in laminotomy, appropriate reconstruction is critical for strengthening spinal stability. In clinics, many interspinous process devices, such as the DIAM and Coflex, are used to enhance spinal stability and prevent the narrowing of the foramen in extension. In addition, interspinous process devices can effectively reduce the load on facet joints and enable some movement on the motion segment [6]. Compared with rigid devices, such as spinal fixators, interspinous process devices offer enhanced spinal stability. The interspinous process device Coflex exhibited advantages in stabilizingthe surgical level, especially in flexion and extension, but it was too rigid and increased facet joint contact force at the adjacent level by 27% [7]. Additionally, it also caused spinal process fracture in clinical application [8]. The interspinous process DIAMs are made of silicone rubber and provide impact absorption between the interspinous processes in extension. Since the DIAM is not made of metal, its stiffness is less than that of Coflex, which is made of metal. DIAMs lower the risk of spinal process fractures. Therefore, they are used to treat lumbar spine disorders related to neuropathology [9; 10]. However, DIAMs are not as rigid as the traditional metal spinal fixator. Additionally, the DIAM is a V-shape design and offers less stability in torsion [11]. Therefore, a new interspinous process device (NIPD) was developed in this study. The design and efficacy of new orthopaedic implants can be evaluated through in vitro or in vivo experiments. However, the results of these experiments differ according to differences in cadaveric specimens. Finite element (FE) methods are widely used to evaluate the biomechanical behavior of implants [12; 13; 14; 15]. [PERSON] and [PERSON] implemented an FE method with topology optimization to design an interspinous process device [12]. They removed redundant material to redesign the device and evaluated its biomechanical characteristics. This study demonstrated that the new device provided more stability at the instrumented level than the DIAM system, especially in lateral rotation and bending direction. [PERSON] et al. also conducted an FE model of the five-level lumbar spine to analyze the biomechanics of a new interspinous device [15]. They demonstrated that the spinal cage combined with a new interspinous device could reduce range of motion (ROM) of the lumbar spine at least 40% in flexion, extension, torsion, and lateral bending. Many studies have employed FE methods to design or evaluate interspinous process devices, such as soft DIAMs or rigid Coflex. Therefore, this study created a U-shape interspinous process device. Compared to DIAMs, it provides more contact area around the interspinous process to increase spinal stability.