Interspinous Spacers for Minimally Invasive Treatment of Dynamic Spinal Stenosis and Low Back Pain

Published on 11/04/2015 by admin

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Last modified 11/04/2015

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54 Interspinous Spacers for Minimally Invasive Treatment of Dynamic Spinal Stenosis and Low Back Pain

Introduction: Interspinous Spacers – How Do They Work?

Indirect enlargement of the spinal canal through interspinous distraction devices has become popular for the treatment of dynamic spinal canal stenosis of the lumbar spine.15 Biomechanical data acquired with the first implant on the market (X-Stop, Medtronic, Memphis, TN, USA), could show that interspinous distraction induces segmental slight flexion, reduces segmental lordosis, and limits extension.6 Thus, the spinal canal and neural foramen areas and diameters are enlarged.7 These findings are considered to be the most important primary effects that justify the clinical use of the device for the treatment of dynamic spinal stenosis. Randomized controlled trials could confirm the therapeutic efficiency and proved that the implantation of an interspinous spacer leads to clinical results superior to conservative treatment.5

In ex vivo experiments it could also be demonstrated that interspinous distraction can lead to a significant unloading of the facet joints8,9 and the posterior annulus fibrosus, as well as the nucleus pulposus in neutral position and predominantly in extension.8,10,11 Kinematics of the adjacent segments seem not to be affected.6,12

The “Extension Stoppers”

A variety of these implant types are currently either in routine clinical use or in clinical application studies. Their purpose is to achieve interspinous segmental distraction and to limit extension. They are promoted mainly for the primary treatment of dynamic degenerative lumbar spinal stenosis, as a substitute for open decompression. The main therapeutic goal is to increase the diameter of the spinal canal and foramen as well as to unload the facet joints and the disc.

X – Stop (Medtronic) (Figure 54-1)

The X-Stop has been the prototype of this class of implants. The implant body is made of titanium, and the spacer of PEEK (polyether ether ketone). It has both a fixed and an adjustable wing. The latter is mounted after implantation.

The main indication is neurogenic claudication with leg/buttock pain due to dynamic degenerative lumbar spinal stenosis, which is relieved upon flexion of the lumbar spine.5

Results

In a randomized controlled trial, it could be shown that the results of the treatment of dynamic spinal stenosis are superior to those in conservative therapy .1,5,13 Whereas in initial reports its usefulness was also documented for degenerative spondylolisthesis not greater than grade I, recent data could not confirm this.14

Summary

Although the implantation of the X-Stop device is claimed to be minimally invasive, it occasionally requires a larger skin incision and a wider bilateral muscular dissection as compared to modern microsurgical direct decompression techniques.15,16 Due to the iatrogenic alteration of the dorsolumbar fascia and the paraspinal muscles, it also cannot be considered as a treatment option for discogenic or arthrogenic low back pain. Moreover, bisegmental or multilevel implantations require larger surgical approaches.

InSpace (Synthes, Paoli, PA, USA) (Figure 54-3)

In order to solve the problem of invasiveness, a new cylindrically shaped PEEK interspinous implant with a central titanium screw and four wings that can be deployed once the implant is placed into the interspinous space, has been presented recently. Biomechnical tests have shown that the implant effectively reduces extension without affecting lateral bending of the segment.17,18 Cyclic loading tests have shown that the functionality of the implant is preserved and that the integrity of anatomic structures is not impaired through 15,000 loading cycles.19,20 The effects are thus comparable to the ones described for the X-Stop implant.

The indications are also identical with those described for X-Stop. There are preliminary reports on its potential usefulness for the treatment of discogenic and/or arthrogenic low back pain.21,22

Surgical Technique

The surgical procedure can be performed under local or general anesthesia. The patient is placed in a prone position on a flat soft-frame on an adjustable operating table or on a Wilson frame. Passive distraction of the interspinous space is achieved and adjusted by tilting the foot end of the surgical table until maximum “opening” of the interspinous space is reached (Figure 54-4). The implant is placed through a lateral percutaneous approach (Figure 54-5). Piercing of the interspinous ligament is performed with a K-wire; enlargement of the interspinous space is achieved with blunt distractors of increasing sizes. After removal of the distractors, the implant can be introduced through an application sleeve and the implant wings are deployed under AP fluoroscopic control. Once the wings are deployed completely, the implant is uncoupled from the implant holder, which, together with the application sleeve, is then removed en bloc, leaving the implant in place (Figure 54-6).