Meniscoids of the intervertebral joints

PURPOSE OF THE STUDY: A large amount of material was used to study the distribution, location and shape of meniscoids in intervertebral joints of the human spine, from the atlanto-occipital joint to the sacrum, in order to find out how many of intervertebral joints had mobile meniscoids. These might be regarded as possible causes of spinal blockade or other vertebrogenous complaints. MATERIAL: The materials provided by the Department of Anatomy and Department of Forensic Medicine at the Faculty of Medicine of Charles University in Pilznen included 20 cadaverous spines from humans aged 20 to 80 years. METHODS: Access to each joint was provided by dissection of the articular capsule from the lower articular processes of the vertebra situated above. In the orthograde view, all meniscoids were described in terms of shape, size, consistence and location. Their structure was ascertained by histological examination of cross sections stained with haematoxylin and eosin. RESULTS: Meniscoids varying in shape and size were found in all of the intervertebral joints. They were classified by their histological structure as synovial, fat and fibrous meniscoids. The first category was observed frequently, the last only rarely. A total of 29 mobile meniscoids were recorded, most of them in the lumbar spine. Most of the meniscoids present in the cervical spine were of synovial and less frequently of fat types. Meniscoids found in the thoracic spine were poorly developed synovial ones and those present in the lumbar spine were of all types and were also largest in size. The most conspicuous meniscoids were seen in the spines that showed degenerative changes in intervertebral joints. Large fat pads were found in atlanto-occipital and atlanto-axial joints. Mobile meniscoids, most of them present in the lumbar spine (6.4% of all joints.), were connected with the capsule by a thin pedicle and it was possible to move them over a half of the articular surface. Some inter-individual changes were also found; in some spines, the most developed meniscoids were fat pads, in the others, these were synovial meniscoids. Spines of younger individuals showed a predominance of synovial meniscoids with smooth surfaces that arched against the articular cavity. In spines of elderly individuals, meniscoids were rough, in some cases fibrous in structure, and had a lobulated or frayed edge. DISCUSSION: The shape, location of meniscoids and their presence in every joint indicate their definite role for the spine: they compensate the incongruence of articular surfaces, fill in empty spaces and facilitate spread of synovial fluid during translation movements. Variability in shape, size and location of meniscoids give support to the view that meniscoids developed secondarily in relation to the morphogenesis of articular surfaces and that they are fully adapted to the shape and function of the joint. Mobile meniscoids, particularly fibrous ones, can get wedged between articular surfaces due to a sudden, rush movement (entrapment theory) or can be caught between the edge of an articular surface and the articular capsule attachment (extrapment theory). This situation may result in either mechanical or functional blockade of the spine and a subsequent painful condition due to compression of nerves and reflex contraction of muscles. Direct evidence of such blockade and the validity of either hypothesis can today be provided by magnetic resonance imaging. CONCLUSIONS: All intervertebral joints, along the length of spine, possess capsule processes, i.e., meniscoids, which can be classified as synovial, fat and fibrous. Meniscoids are most developed in the lumbar and cervical spine. They serve to compensate for the incongruence of articular surfaces and to fill in empty spaces. Mobile, peduncular meniscoids can, at sudden or non-physiological movements, be caught between articular surfaces and cause spinal blockade and painful conditions. Manipulative treatment is, therefore, justified in indicated cases.