Interspinous devices

     Numerous anatomical studies define the interspinous space as an intervertebral space between spinous processes of great biomechanical significance for spinal movements. It is the insertion site of powerful muscle groups, containing ligament bundles full of elastic fibres and neurosensory fibres that convey the correct tension and balance to the functional spinal unit.
      According to Denis’s three-column theory and studies by Kirkaldy-Willis, much importance has been attributed to the intervertebral disc and, increasingly, to the posterior facet joints as a cause of degenerative disease, but the importance of the interspinous space and its anatomical structures has been neglected.
      With spinal degeneration and, more particularly, a reduction in the space occupied by the intervertebral disc, we observe an inevitable collapse of the interspinous space, which loses its natural elastic movement and its ability to balance the disc-facet joint lever system and the supraspinous ligament, giving rise to anatomical changes that lead to kissing spines and Baastrup’s syndrome.
      These pathological symptoms are often encountered in elderly patients suffering from claudicatio spinalis, but also in young patients suffering from micro-instability of the lumbosacral passage, often complicated by symptomatic disc hernias in phase one and two of degeneration in the Kirkaldy-Willis model.
      If the disease process is not properly treated during the degeneration cascade, over the years it reaches phase three of the K.W. model, with symptoms of neurogenic intermittent claudication when the patient stands upright or walks, with a regression of symptoms when the patient bends.
      Over recent years, the use of interspinous devices implanted by means of minimally invasive surgical access has been increasing in both degenerative disc disease and functional stenosis.
      In this publication it is our aim to put interspinous devices in their rightful place within the field of vertebral surgery. To this end, we open with a thorough historical review of their introduction, with reference to existing publications by the best-known designers and users.
      We then briefly examine the anatomical and anatomopathological aspects of the posterior intervertebral space in the lumbosacral spine, defined as the interspinous space, through a detailed study of imaging.
      We include a discussion of biomechanics and our own clinical and surgical experience in the use of such devices in degenerative diseases of the lumbosacral spine within the Orthopaedics Clinic of Pisa University. We also discuss the topic of patient rehabilitation and, in the appendix, we analyse the best known and most commonly used interspinous devices with their design and biochemical specifications before concluding with a look at interesting perspectives for the future.

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