A Case Series of Synostosis/Blocks Observed in Indian Human Vertebra

Clinical and Developmental Perspective

Abstract

Not just anatomists but also clinicians from a variety of disciplines, including orthopedic doctors, surgeons, neurologists, and neurosurgeons, are interested in vertebral abnormalities. Numerous morphological anomalies, such as spinal synostosis, occipitalization, sacralization, and lumbarization, as well as the absence of the posterior vertebral arch, have been reported. Sequentially fused vertebral segments might result in spinal fusion, synostosis of the vertebrae, or blocked vertebrae. Movement limitations, early degenerative changes, and accompanying neurological abnormalities may all be brought on by the block vertebrae. The fusion may be whole or partial, acquired, or congenital. The cervical, lumbar, and thoracic vertebral levels are the most frequently affected by vertebral fusion, whether it is congenital or acquired. A systemic disorder, known as idiopathic diffuse idiopathic skeletal hyperostosis (DISH), is defined by distinctive ossification patterns that can run over at least three more vertebral levels or four successive vertebrae on their anterolateral aspect. Here, we present a series of spinal synostosis at various levels that were identified in museum specimens from our institution and that were associated with the clinical and developmental importance.

INTRODUCTION

The structure of a typical vertebra includes a vertebral arch on the posterior aspect with a foramen and a body in the anterior aspect. From the vertebral arch, two processes extend as two transverse processes and a single spinous process. A typical vertebra also has two superior and two inferior articular processes that make contact with the inferior and superior articular processes of neighboring vertebrae, respectively.[¹]

There have been the reports of a number of anatomical defects, including occipitalization, sacralization, lumbarization, lack of the posterior vertebral arch, and spinal synostosis.[²] Block spines, block vertebra, vertebral synostosis, or spinal fusion are the outcomes of the fusing of successive vertebral segments. These may in turn lead to restricted/limited movements, degenerative disc changes which are premature in nature and associated clinically visible neurological deficits. The synostosis may be complete or incomplete, acquired or congenital.[³] The fusion of vertebra whether congenital or acquired can occur at various levels that is thoracic, lumbar, and cervical vertebral levels in the order of increasing frequency. The term DISH was first used to characterize this syndrome by Resnick et al. in 1975, and it is currently the most often used word in the literature.[⁴] This systemic disorder, known as idiopathic diffuse skeletal hyperostosis, can affect the spine and peripheral enthuses is marked by distinctive ossification patterns. In the spine, the ossifications are often defined as running over at least three subsequent vertebral levels, or four consecutive vertebrae, along the anterolateral side.[⁵]

We hereby report a series of vertebral synostosis at different vertebral sites found in the departmental museum specimen of our college. These vertebral anomalies or irregularities are interesting not only to basic scientists and anatomists but also clinicians of various specialties' such as neurologists, orthopedicians, surgeons, and neurosurgeons.[²]

CASE SERIES

We are reporting six specimens of adult Indian human dried vertebrae which were fused at different levels after obtaining approval from Institution ethics committee. They were obtained from the departmental museums of human anatomy as well as forensic medicine and toxicology of KIMS, Bangalore. The vertebrae have been retrieved over nearly 30 years from bodies which were voluntarily donated for the purpose of research and teaching. The specimen had intact bodies and vertebral arches. However, gender could not be specified due to nonavailability of records. The specimens were subjected to detailed evaluation. Digital Vernier caliper (aerospace-150 mm × 0.02 mm) was used to take the measurements wherever possible, and measurements were recorded with up to two decimal places. The observations shown in Figure 1 and Figure 2 are summarized in Table 1 and described below [Figures 1 and 2].

Figure 1: Showing block vertebrae at different levels (Cases 1–6 shown from left to right)

Figure 2: Showing block vertebrae at different levels cervical/thoracic/lumbar/lumbosacral

Table 1: Site and extent of fusion of different parts of the vertebrae

1. Cervical synostosis: This was a case of upper six cervical vertebral fusions, starting from axis to C6-Fusion was seen at body, articular process and transverse processes. Anterior and posterior longitudinal ligaments were ossified which obscured the vertebral foramen, foramen transversarium, and exact extent of fusion. Hence, accurate measurements could not be taken. However, the spinous process remained unfused
2. Thoracic synostosis: This was a case of T7-T11 vertebral fusion – Fusion was evident at the anterior and anterolateral aspects of the body. Intervertebral disc region and posterior aspects of the body remained unfused. Articular process, transverse process, and spinous process were unfused. Anterior posterior diameter was reduced. The intervertebral foramen was precisely defined and the maximum diameter was around 1.0 cm on the right and 0.92 cm on the left side. The site of fusion and other features were typically suggestive of diffuse idiopathic skeletal hyperostosis
3. Thoracic Synostosis: Fusion of two typical thoracic vertebrae (exact vertebral levels could not be identified) showing fusion of their bodies only on the anterior aspect. Intervertebral disc region and posterior aspects of body remained unfused. Articular process, transverse process, and spinous process remained unfused. The intervertebral foramen was precisely defined in this case as well and the maximum diameter was 0.98 cm on the right and 0.90 cm on the left side
4. Lumbar synostosis: Three lumbar vertebrae were found to be fused between the bodies completely. Intervertebral foramen was well defined with the maximum diameter of 1.45 cm on the right side and 1.44 on the left side. Lamina and articular processes were partially fused to one another. Spinous process remained unfused
5. Lumbar synostosis: Two lumbar vertebrae were found to be fused between the anterior aspects of bodies. Intervertebral foramen was obscured with fusion of pedicles, lamina, and articular processes. Spinous process was also partially fused
6. Lumbosacral vertebral synostosis: Partial fusion of last 2 lumbar vertebras with sacrum. Fusion of bodies was more evident on the left side. Intervertebral foramen was well defined with the maximum diameter of 1.24 cm on the right side and 1.2 on the left side. Articular process, transverse process, and spinous process were unfused.

DISCUSSION

The anatomy of a typical vertebra includes a vertebral/neural arch, a foramen, a body, two lateral processes, and a single posteriorly extending spinous process. The body bears the majority of the force applied or weight that is placed on the vertebra. Vertebral body usually increased in size in the craniocaudal direction. The vertebral (spinal) canal, which houses the spinal cord, is formed by the arch and the back of the body. Bilateral lamina, or flat bone segments, make up the majority of the arch and link the transverse and spinous processes. Bilateral pedicles, or cylindrical bone processes, connect the arch to the body. A typical vertebra also has two superior and two inferior articular processes that make contact with the inferior and superior articular processes of neighboring vertebrae, respectively. A facet joint, sometimes called a zygapophyseal joint, is where the superior and inferior articular facets converge. These keep the vertebrae aligned, regulate the range of motion, and in some situations, support weight. Depending on the area of the spine, the spinous process extends posteriorly and frequently faces inferiorly from the vertebral arch and may partially or completely overlap the next adjacent vertebrae. Finally, symmetrically extending laterally from the vertebral arch are the two transverse processes.[¹]

The vertebral or the spinal column begins to develop from the 3^rd week of intrauterine life with the segmentation of the paraxial mesoderm which gives rise to paired somites on either side. Each somite comprises of a sclerotome and a derma-myotome which further can be subdivided into dermatome and a myotome. These somites initially begin in the cervical region and increase in the number in the craniocaudal direction. During the 5^th week of intrauterine life, the cells of the sclerotome present in the somites leave their parental adherence and move to the centrum or body of the vertebra first and then to the neural and costal processes. Each vertebral process on the posterior aspect gives rise to a pedicle which is cartilaginous, lamina, and lateral transverse process on both sides. The occurrences of the ossification centers are idiosyncratic. They begin at the 4^th month at T10 and L1 vertebral bodies and C2 and T1 neural process. They spread up and down the column from these regions.[⁶] Resegmentation is a process that occurs as each somite's sclerotome part develops. When the inferior half of each sclerotome develops and merges with the cephalic half of each subadjacent sclerotome, resegmentation takes place. Thus, the inferior half of one somite and the superior half of its neighbor combines to make each vertebra. The initial sclerotome segment's cephalic and caudal portions include mesenchyme cells that fill the gap between two precartilagenous vertebral centrums without proliferating. They assist in the development of intervertebral discs in this way.[⁷]

Failure of embryological spines to segment normally may result in fused vertebrae or blocked vertebrae because of a reduction in blood flow from the third to 8^th week of development.[⁸] Sacrum is an example for normal block or fused vertebra. Vertebral fusion abnormalities might develop as a result of further PAX-1 gene expression disruption.[⁹] Trauma, tuberculosis or other infections, as well as juvenile rheumatoid arthritis, are the main causes of the acquired fusion of vertebrae.[⁷] A systemic disorder known as diffuse idiopathic skeletal hyperostosis (DISH), which can affect the spine and peripheral enthuses, is marked by distinctive ossification patterns. In the spine, the ossifications are often defined as running along the anterolateral aspect in at least three successive vertebral levels or four contiguous vertebrae.[⁵]

The sequence of block vertebrae according to frequency of occurrence is C3-C2, C6-C5, L5-L4, and any region of the thoracic spine.[¹⁰] C2-C3 is a frequent location for cervical vertebral fusion, with a frequency of 0.4%–0.7% and no gender preference. Up to 70% of cervical vertebral synostosis has been linked to C2-C3 fusion with atlanto-axial articulation instability.[¹¹] From radiological evidence, three categories of spinal fusion have been cited in the literature. Single fusion of the cervical segment was seen in 25% of cases. The remaining presented as multiple fusions which included contiguous variety in 25% cases and noncontiguous variety in another 50% cases.[¹²] The vertebral body fusion alone or along with the vertebral arch may be complete or imperfect. Depending on the amount and location of the spinal fusion, different symptoms might occur.[³] The anterior-posterior measurement of the vertebral body is smaller and the height of the two fused vertebrae, including the intervertebral disc, is equal to the height of the two separate vertebrae bodies in congenitally fused vertebrae according to previous literature.[¹³] They exhibit the typical “wasp-waist” look. Intervertebral disc absence or its replacement by a radio-opaque line, smooth intervertebral foramina, a single spinous process for two vertebral bodies, and preservation of vertebral body height on roentgenographic inspection are all the signs of this condition.[¹⁰] Vertebral fusion that occurs at birth may be related to other systemic abnormalities. This may include scoliosis, spina bifida, hemi vertebrae, and sprengels deformity, among other aberrant spine curvatures. Other skeletal defects that may be related include basilar impression, cleft palate, club foot platybasia, and cervical ribs. In addition to these, malformations of the kidney, lungs, heart, and ear have also been reported.[¹³] Shortening of the trunk may be the result of acquired vertebral fusion. According to Butler, Scheuermann's vertebral osteochondritis is a condition that causes two vertebral bodies to fuse anteriorly due to the herniation of intervertebral disc tissues through the cartilage end plate.[¹⁴] The presence of fusion in cervical region may result in laxity of the ligaments between the occiput and the atlas, leading to the brainstem or spinal cord compression.[¹⁵]

Vertebral fusion or synostosis remains the trademark of Klippel − Feil syndrome, a triad consisting of short neck, limited mobility, and low hairline at the back. Various other syndromes associated with vertebral fusion are VACTERL (s) association which includes “Vertebral defects, anal atresia, cardiovasculardefects, tracheoesophageal anomalies, renal anomalies, and limb abnormalities,” segmentation syndromes with laryngeal malformations, Jarcho-Levin syndrome, and Joubert syndrome. They may also be associated with aplasia of the Mullerian duct, renal aplasia, somite dysplasia in the cervicothoracic region, trisomy 18, and diabetic embryopathy.

Block vertebra increase the bio-mechanical strain in the surrounding segments, which causes early regressive changes at adjacent motion segments. Other frequent side effects include discal tear, rupture of the transverse ligament, odontoid process fracture, and spondylitis.[¹⁶] Movement limitations, early degenerative changes, and accompanying neurological abnormalities may all be brought on by the block vertebrae. A greater risk of morbidity and death is associated with surgical surgery for block vertebra. If a cisternal or lumbar puncture is necessary, medical professionals should determine whether there is a chance of a blocked vertebra in the cervical and lumbar regions, respectively.[¹⁷]

The anomalies of the vertebra have been of interest to not only anatomists, clinicians who belong to various specialties such as neurologists, neurosurgeons, orthopedicians, and general surgeons but also evolutionists as well. In birds, the middle and lower spines are fused, and the sacrum is joined to the lumbar vertebrae, the backs of some thoracic vertebrae, and potentially the caudal vertebrae. The pygostyle, to which the tail feathers are joined, has fused caudal vertebrae, which improves flight control.[¹⁸] Thoracic and lumbar spines in mammals differ significantly from one another, with the former being typically rigid and the latter being flexible and tailored to the particular locomotor patterns. However, large apes such as chimpanzees, bonobos, and mountain gorillas do not have spines that are totally adapted for the upright posture.[¹⁹]

Fused vertebrae have clinical and embryological importance. The presenting clinical symptoms vary according to the degree and the exact location of vertebral amalgamation. Movement limitations, early degenerative changes, and related neurological abnormalities may result from them.

CONCLUSION

The findings of the aforementioned observation depict the occurrence of block vertebrae in the Indian context. We found more blocks at the lumbar level (3 specimens) in contrast to the cervical region (1 specimen) which may be an incidental occurrence, may be due differing lifestyle patterns or may have genetic basis. Further elaborate studies are thus suggested. The same can be compared to the observations in a different demographic profile. It will be helpful to identify alterations brought on by an accident, aging, or the progression of a degenerative condition through the early identification of these abnormalities in differing population. In addition, it will motivate patients to alter their lifestyles so they may resume regular lives.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Acknowledgments

In order to conduct anatomical research and education, the authors profoundly appreciate individuals who gave their bodies and those of their families to science. The outcomes of such observations might advance human understanding generally, which would subsequently enhance patient care. Therefore, we are very grateful for the donors and their families.[²⁰]