Interspinous posterior devices: What is the real surgical indication?

Figure 1 Dynamic X-ray. A: Patient treated for L3-L4 disc herniation (without instability at the dynamic X-rays) with an interspinous posterior device (IPD) implant. The Dynamic X-ray in extension showed a metameric instability at L3-L4 developed 1 year after an IPD implantation; B: Dynamic X-ray in flexion that showed an increase in L3-L4 slipping, developing a I° grade spondylolisthesis, due to the IPD implantation. The patient underwent revision surgery with removal of the IPD, decompressive laminectomy and L3-L4 stabilization with screws and rods.