New Techniques and MIS: The Interspinous Fixation Devices

Abstract

The treatment of vertebral instability has evolved over the years with the aim of searching and developing the most effective and less invasive procedure to reduce and to neutralize dynamically the metameric hypermobility; pedicle screw fixation (PSF) has been widely employed to reach vertebral fixation and fusion and still remains the “gold standard” technique [1, 2]. PSF is associated with well-known risks [3, 4] such as increased rates of cerebrospinal fluid leakage, fracture of the pedicles during screw insertion, transient/permanent injury to nervous structures, and deep wound infections. Furthermore, as a result of muscle dissection and long operative times, some disadvantages can be evident, such as postoperative back pain and long postoperative recovery time [5]. There are risks of exposure to ionizing radiations for the surgeon and the whole operating room staff, other than for the patient, due to the use of fluoroscopic guidance for the implantation of pedicle screws (PS) [4, 6]. The muscle dissection related to surgical exposure leaded to the development of minimally invasive procedures, at the cost of increased exposure to ionizing radiations. This has led to the development of a lot of different devices, some of them used indiscriminately in recent years but with questionable long-term results. In this context, a major role was played by interspinous devices, generally used in degenerative lumbar spine disease. Interspinous posterior device (IPD) is a term used to identify a relatively recent group of implants employed in the treatment of lumbar spinal degenerative disease. This kind of device is classified as part of the group of the dynamic stabilization systems of the spine. The concept of dynamic stabilization has been actually replaced by the principle of dynamic neutralization of the hypermobility, with the intention of clarifying that the primary aim of this kind of systems is not the preservation of the movement but the dynamic neutralization of the segmental hypermobility, which is at the base of the pathological condition. The surgical indications for the implantation of an IPD are the spinal stenosis and neurogenic claudication, assuming that its function is the enlargement of the neural foramen and the decompression of the roots forming the cauda equina in the central part of the vertebral canal. Recently, it has been noticed that those devices have significant problems in terms of clinical follow-up, since the action exercising on the vertebral body has an appreciable effect on the biomechanics of the lumbar spine. This is why in the last few years new devices have been introduced, the so-called interspinous anchors (IA) or interspinous fusion devices (IFD). Those differ from the IPD as their aim is the fusion of the spinous processes on which they are anchored, and therefore the target is spinal stabilization by arthrodesis and not the dynamic neutralization of the hypermovement. The question that requires response is: are those devices able to replace arthrodesis with plates and screws in lumbar instability?