The degeneration of the lumbar spine begins with the loss of intervertebral disc height, secondary to dehydration of the nucleus pulposus. This overloads the facet joints whose anatomy is not designed to bear weight thus leading to the development of spondyloarthritis and posterior hypertrophy [2,3]. Voltage loss and structural damage to the ligaments of the spine, which produce instability, also appear [4-6].
This instability is compensated due to hypertrophy of other structures like yellow ligament that eventually results in the narrowing of the canal and the foramina of conjunction.
The most common outcome of all this cascade of pathophysiological events is chronic low back pain, which is very disabling and has a difficult medical management [7,8].
The conventional surgical treatment for chronic low back pain causes the fusion of degenerative spinal segment, thus irreversibly eliminating movement. However, despite the fact that the perfection of the technique has achieved fusion rates of 100%, not comparable to clinical outcomes of pain relief have been obtained and, on the contrary, the possibility of developing disease in the adjacent segment means that alternative therapies [9,10] are being sought.
The management of the lumbar spine without causing fusion and maintaining movement stems from this need. This dynamic stabilization theoretically would prevent disease in the adjacent segment, especially in young patients.
Multiple previous dynamic systems as well developed, trying to replace the intervertebral disc, based on experience with joint prosthetic hip and knee replacements. The problem of THA vertebral disc is replacing the former component of the motion segment, but not stabilized and requires facet joints without degeneration; therefore maintains the movement but does not stabilize, it is really wanted: to stabilize motion preservation.
The action mechanism of these systems is through the separation of the spinous processes between each vertebra the spinal canal increase.
The management of the lumbar spine without causing fusion and maintaining movement stems from this need. This dynamic stabilization theoretically would prevent disease in the adjacent segment, especially in young patients.
Thus, multiple prior dynamic systems were also developed, in an attempt to replace the intervertebral disc, based on experience with joint prosthetic hip and knee replacements. The problem with the THA vertebral disc is that it replaces the anterior component of the motion segment, but does not stabilize and requires facet joints with no degeneration; it therefore maintains the movement but does not stabilize, which is what we really want: to stabilize while, at the same time, maintaining mobility.
The action mechanism of these systems is carried out by using the separation of the spinous processes between each vertebra to expand the spinal canal.
Recent biomechanical analyses have concluded that when one of these procedures is carried out, overlying segmental instability is generated over time, which is why the use of a semi-rigid interspinous spacer is recommended [11,12].
We can then take into account that their indication is limited to the narrow spinal canal and lumbar facet disorders in lumbar segments between L3-L4-L5, with very limited indications in the lumbosacral transition (L5-S1) [13]. Since the development of this new device all that has changed, and constitutes the best find in our clinical study: to allow the placement of a device which prevents instability after Lumbar discectomy in almost all patients operated.
The degree of success of the use of the UN6 device in terms of reoperation rate and implant survival did not depend on the number of segments treated. This contrasts with the failure rate of lumbar fusion, which is reported to increase with the number of fused segments. The observed absence of a difference between the actuarial survivorship of single-level implants and multiple-level implants also supports the safety and efficacy of each segment of these multi-level dynamic constructs. Should there be any flaws inherent in the system, one would expect a poorer outcome in a series of double-level implants, not to mention that in patients with three or four instrumented levels. Moreover, the patients operated on two, three or four levels arguably had more advanced degenerative lesions than those operated on one level. The lack of difference between the outcomes of the two groups should be highlighted.
Despite limitations related to the high attrition rate, this first long-term analysis of an interspinous dynamic lumbar stabilization system provides promising information. The primary relevance of this study was that it demonstrated the long-term safety of the system.
The aim of the study was not to demonstrate the superiority of the device over fusion. The goal was to delay a relatively invasive fusion procedure for as long as possible (even definitively) with a simple superficial device that preserved the segmental anatomy [14,15]. By achieving this goal in around 80% of the patients for 7 years, the coflex implants demonstrated efficacy in delaying fusion (historical group 2004-2011) due to the fact that they presented no clinical symptoms or Rx signs.
When revision was necessary, there were no implant-related complications and the surgical procedure was quite straightforward. In terms of reoperation rates, the long-term outcomes of the UN6 implants indicate that they may be a valuable addition to our therapeutic armamentarium for degenerative lumbar segments, notably after decompressive procedures for certain cases of herniated disc occurring in segments with advanced changes and instability. With the endpoint ‘any subsequent lumbar operation’, the actuarial survivorship analysis compares favourably with that of revision operations adjacent to lumbar fusion procedures recently reported in the literature [16-19]. This might reflect long-term protective action against adjacent-level degeneration by motion preservation. More importantly, this was not a fusion procedure. Contrary to fusion, the vertebrae, discs, facet joints and ligaments except for the interspinous ligament were left intact and functional during surgery so that all therapeutic options remained open [20-22]. This is a safe device that can be used without great risk when a decompressive procedure is being carried out, thus possibly reducing the need for a further operation.
This semi-rigid device is appropriate for patients with severe low back pain (Baastrup syndrome) whose symptoms are exacerbated in extension and relieved in flexion, implanted between the spinous processes without disrupting the normal anatomical structures [23,24].
Interspinous implants are used for motion-preserving stabilization of primarily posterior lumbar spinal pathologies like spinal stenosis or facet joint arthritis [25-27]. In the interspinous “U” device, the height of the same distracts the foraminal opening; the “U” shape is designed to allow controlled movement in forward and backward bending [28-30]. This implant has only a transient effect on the postoperative restoration of disc height and reduction of slip in spondylolisthesis. This cannot be used as a substitute for a rigid fusion in cases of marked instability [31-33]. As we all know and, because of the anatomical characteristics of the space L5-S1, the chances of placing these implants is reduced by configuration of the same (size and design) because they do not adapt to the specific characteristics of the anatomical region [34-36]. The development and use of this UN6 device has allowed us to place it in 90% of the cases studied, by opening the anterior third of the vertebral body.
To date, monitoring by means of Rx (Figure 4) at 3-6 months and 1-2 years has allowed us to objectively observe the absence of any kind of movement of the device once put into place.
Figure 4: F-Up.
Unlike other authors [37-39] who have started to use this technique for the treatment of stenosis and although our experience is also proven, we wanted to advance the possibilities of this spacer by using it in surgery for virgin herniated lumbar disc.
As we move forward towards our goal, we try to avoid a process of instability that requires more aggressive treatment (transpedicular fixation). We, of course, rely on the idea of the triad which determines that on occasion radiographic abnormalities are detected from a clinical point of view.
From the idiosyncrasies of our own study based on the arthritic degenerative process of human beings that can be exacerbated by the surgical technique to produce an overload segment and accelerate the osteoarthritic process and, although our study has a follow-up ranging from a maximum of 10 years to a minimum of 1 year (historical group 2004 to present), and, although preliminary data obtained allows us to be optimistic about the use of the implant to the delay of the instability of the segment after single discectomy. In relation to the use of the UN6 device, this has proved to be effective as has its versatility for segment L5-S1.