|Year : 2016 | Volume
| Issue : 2 | Page : 72-74
Interfacetal intra-articular spacers: Emergence of a concept
Department of Neurosurgery, King Edward Memorial Hospital and Seth Gordhandas Sunderdas (GS) Medical College, Mumbai, Maharashtra, India
|Date of Web Publication||5-May-2016|
Department of Neurosurgery, King Edward VII Memorial Hospital and Seth Gordhandas Sunderdas (GS) Medical College, Parel, Mumbai - 400 012, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Goel A. Interfacetal intra-articular spacers: Emergence of a concept. J Craniovert Jun Spine 2016;7:72-4
The concept of introduction of metal spacer within the articular cavity or in the interfacetal region of spine was first described for atlantoaxial joint in the year 2004.  The technique of introduction of spacer within the joint was discussed as a mode of treatment for the patients with basilar invagination, who were conventionally treated by transoral surgical decompression. The basis of treatment was the understanding that instability of the region was the cause of basilar invagination and distraction of the facets using intra-articular spacers along with bone graft after appropriately preparing the host bone by wide decortication resulted in reduction of basilar invagination and stabilization of the joint. The procedure ultimately resulted in arthrodesis of the region. The concept that instability of the region was the primary etiological issue dramatically revolutionized the treatment of basilar invagination, and transoral surgery has slowly but surely slipped into the realm of history.  The observation that impaction of intra-articular spacers resulted in remarkable stability of the joint has widened the scope of its deployment to cases having all kinds of atlantoaxial instability. The impaction of metallic spacer within the atlantoaxial joint after distraction of the facets was termed as "joint jamming."  The spacers are introduced after overdistracting the facets so that the spacers are impacted in situ by the elasticity of the region. The wide, circular, and flat joint surface provided space and safety to the process of introduction of the spacer. The technique of joint jamming was used to provide a supplemental stabilization in association with the primary or the principal technique of fixation by lateral mass plate/rod screw method as described by us. , The combination of fixation methods provided remarkable stability to the region and resulted in craniovertebral realignment. In situations where plate/rod and screw fixation were not possible for some reason, joint jamming was found by itself to be a strong, safe, and simpler method of surgical stabilization. 
Atlantoaxial joint instability can be identified by facetal malalignment or even by direct observation and bone handling during surgery. We have recently classified the diagnosis of atlantoaxial instability and basilar invagination on the basis of facetal malalignment and instability. , We observe that there may be instability even when the atlantodental interval is not affected and even when there is no evidence of cord alterations or changes. Atlantoaxial instability that is diagnosed only by clinical evaluation and by manual manipulations and without any radiological abnormality has been termed by us as central or axial atlantoaxial instability. , Intra-articular spacers can be deployed for all forms of atlantoaxial instability.
Degenerative arthritis involving the craniovertebral junction is common but has only infrequently been studied or analyzed in the literature.  We identified that atlantoaxial joint that is the most mobile joint of the body is most likely to undergo "degenerative" changes.  Our studies have concluded that disc degeneration or reduction in its water content is not the primary issue in the pathogenesis of spinal degeneration. ,,,, We currently use the terms "degenerative changes" and "instability" in parallel. This is because we have realized that degenerative spinal changes are initiated and progress due to the instability of the facet joints and are secondary to muscle weakness related to their disuse or misuse. , Essentially, facetal instability is the primary point of pathogenesis and all other alterations of ligaments, soft tissues, bones, and discs are secondary in nature and possibly protective in their function. Like reduction in subaxial intervertebral body spaces in spinal degeneration (instability), there is reduction in the atlantoaxial joint space in the craniovertebral junctional region degeneration (instability). This reduction in joint space results in subtle basilar invagination and atlantoaxial dislocation. Reduction in the joint space also results in circumferential buckling of the atlantoaxial ligaments and osteophyte formation. Para- or retro-odontoid osteophyte or bone formation is an indication of instability of the atlantoaxial joint, and when symptoms are significant such alterations are highly suggestive of the need for surgical stabilization.  We identified that intra-articular spacers distracted the facets, restored the joint space, and affected the reduction of both atlantoaxial dislocation and basilar invagination. More importantly, the distraction reversed or has the potential of reversing the circumferential buckling of ligaments in the region of the atlantoaxial joint. By restoring the taut on the ligaments, it reverses the trend of osteophyte formation around the bone-ligament junctions. , Essentially, the aim of the intra-articular spacers is to restore the bone and soft tissue anatomy toward normalcy. Plate/rod and screw fixation provides additional stabilization and the combination of fixation procedures provides a ground for arthrodesis of the region.
We used intra-articular atlantoaxial spacers for multiple indications that ranged from rheumatoid arthritis related instability, , tuberculosis , related instability, and tumor related instability.
The success in the use of metal spacer/cage in atlantoaxial instability led us to extend the indications of its use in subaxial spinal instability. We deployed specially designed "Goel facetal spacers" in the cervical and lumbar spinal facetal articulations. ,,, We analyzed and studied the morphometric anatomy of facets of lumbar and cervical spine to evaluate the dimensions of the "Goel facet spacer." , The remarkable stability provided by the spacers and the safety and ease of their insertion, particularly in the cervical spine, opened a new field of spinal stabilization. Intra-articular spacers can be inserted and impacted after the distraction of the facets using specially designed instruments for the purpose. , The ease of insertion and stabilization of the spacers validates the deployment of percutaneous techniques. Several advantages of the use of intra-articular spacers over the other available anterior and posterior surgical techniques has the potential of making this technique the most preferred method of spinal stabilization. Recently, some authors have evaluated their clinical experience of the technique and have used it essentially for cervical radiculopathy  and for symptomatic cervical pseudarthrosis.  Biomechanical studies are now available that evaluate the implant as a treatment modality for atlantoaxial and subaxial stabilization. ,,,
Our hypothesis is that facetal instability is the primary point of genesis of degenerative spinal changes. ,,, Disc degeneration or disc space reduction is not the primary nodal point of pathogenesis but is only a secondary alteration due to facetal instability that leads to telescoping of the facets and reduction in the vertical height of the spinal segment. Facetal distraction results in stabilization of the joint, restores the vertical height of the spinal segments and the intervertebral space, and unbuckles the posterior longitudinal ligaments and ligamentum flavum. In effect, facetal distraction widens the vertical and horizontal dimensions of the spinal canal and intervertebral foramina. Facetal distraction has the potential of restoring the "water content" of the intervertebral discs and can potentially "melt" away the osteophytes. Essentially, facetal distraction can reverse all the known and described changes of spinal degeneration. ,,, The technique can be used for single and multilevel treatment. ,,, Stabilization by facetal distraction can be done by directly visualizing the status and stability of the facets during surgery and thus provides a real-time opportunity to fix unstable segments that can possibly be missed by clinical or even radiological examination. Extension of levels of fixation can be done easily, safely, and quickly. Such multi-level fixation by any other technique is not only time-consuming but can also be wrought with possibility of complications related to retraction and dissection of major blood vessels, aerodigestive tracks, and critical nerves in the vicinity. Our experience with clinical outcome after deployment of spacers for single- and multi-level cervical radiculopathy and myelopathy and lumbar canal stenosis has been remarkably satisfying. , On the basis of our experience, we feel that the technique of intra-articular spacers can have revolutionizing effects on spinal stabilization methods. Considering that no bone or soft tissues are resected during the procedure provides additional advantage to the technique in the fact that it is possible to perform these procedures if the stand-alone technique of insertion of intra-articular spacers does not provide satisfactory clinical outcome. Additionally, the procedure can be used when anterior or posterior midline procedures have failed or have been ineffective. From our experience, it appears that decompression of the neural structures, such as decompressive laminectomy and foraminotomy, can become outdated and historical procedures.
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