Abstract
Introduction: Back pain affects much of the population, no one structure within the spine is responsible for this symptom. However some structures play a larger role in back pain than others. The facet joints of the spine are synovial joints that guide and limit the spine’s movements and are the largest single source of pain in the back. The facet joint has a synovial cavity which is associated with many pain producing structures and also the source of certain types of spinal cyst.
The facet joint has been the subject of much anatomical study, and has been described in great detail over the years. Little if any research has had the facet joint cavity as its main focus. Previous work focused on the articular surfaces of the facet joint. The facet joint cavities are assumed to be organised and determined by the articular surfaces. However, a facet joint cavity consists of two elements, the first element is the space between the articular cartilages of two opposing facets, named the facet space in this thesis, and the second element is the facet recesses around the facets. Some of the previous research demonstrated that the joint cavity was larger than the articular surface in small joints, but no real insight has been given regarding the facet joint cavity. The regional differences of the facet joint cavities along the spine have not been broached. An understanding of the detail of the anatomy of the facet joint cavity will greatly facilitate facet joint arthrography and interpretation of its medical images, as well as injection procedures targeting the facet joint for diagnostic or therapeutic purposes. It is also conceivable that the size and shape of the facet joint cavity are the key determinates for the mobility of a facet joint. Thus, the overall goal of this study was to investigate the 3-D configuration of the facet joint cavity and clarify its regional differences along the whole spine.
In addition to this primary goal, the incidental finding of type II meningeal spinal cysts during the preliminary experiment created the secondary aim which was to identify the nature of the three incidentally found cysts and define the in situ macro/microscopic analysis of the cysts with their surrounding structures.
Material and Methods: A total of 21 spines were observed for this study (3 cadaver, 16 E12 plastinated slice sets and 2 cryogenic section sets). For the study of the facet joint cavities the cadavers were dissected and micro-injected with contrast medium for µ-CT scanning to create 3D rendered models, the scanned cadaveric specimens were then used for corroborative photography during further dissection. The E12 plastinated slice sets were used to help describe the facet joint cavities and produce maps of these spaces, with the use of dissection and confocal microscopes alongside high definition dual lens scanning. The Three Type II meningeal cysts were identified in an E12 plastinated sheet set and were analysed using the same tools.
Results: (1) The incidentally found spinal cysts: The three Type II cysts were in the thoracic spine and all had a common feature of a clearly identifiable cysts neck that connected the cyst body to the subarachnoid space. The dorsal root was centred in the cysts neck but was spread over the cyst body or traversed the cyst cavity, the cyst body was halted laterally by the dorsal root ganglion. The meningeal opening of the cyst neck was superior to the inferior border of the vertebral pedicle, thus it hugged around it and sharply turned inferolaterally into the intervertebral foramen.
(2) The facet joint cavity: The facet space between the facet surfaces and the surrounding recesses were present in larger numbers and volumes in the cervical and lumbar regions than the thoracic region. The C1-C2 facet joint cavity had extensive recesses all around especially anterolaterally, the recesses extended superiorly and inferiorly. The C2-C7 facet joint cavities had recesses lipping around the facet spaces minimally on the medial aspects and maximally at the antero and posterolaterally edges of the facet spaces. The thoracic spine had few recesses and small sized facet spaces. The lumbar spine facet joint cavities had large facet spaces with recesses superiorly, inferiorly and along their posterior borders. The characteristics of the facet joint cavities changed between regions, and did not follow the same rate of transition as the articular surfaces.
Conclusion: (1) This study reveals the in situ macro/microscopic configuration of the Type II cyst and its anatomic relationship with the meninges, spinal nerve roots and ganglion, vertebral pedicle, epidural space and intervertebral foramen in the thoracic spine. The results constitute a novel contribution to the understanding of the anatomy of Type II meningeal cysts (Tarlov cysts), suggesting that it may be feasible to localize and ligate the cyst neck for surgical management of Type II cysts.
(2) In the first qualitative description of the facet joint cavities the results differ from the previous assumptions regarding their characteristics and transition between regions, and led to the proposal of more anatomically considered approaches for targeting the facet joint cavities for diagnostic or therapeutic purposes.