The orientation of the articular facets of the zygapophyseal joints at the cervical and upper thoracic region.

Knowledge of the orientation of facet joints in the cervical and upper thoracic region is important for understanding the biomechanical properties and clinical conditions relevant to the neck. The study was undertaken on dry macerated bones from 30 adult male human vertebral columns. The orientation of the superior articular facets in relation to their inclination with the sagittal and transverse planes was examined between C3 and T3 vertebrae in each column. The linear dimensions of the superior articular facets and the width/height ratio were also calculated. The results show that all vertebrae at C3 level and 73% at C4 level displayed posteromedially facing superior articular facets. Similarly at T1 level (C7/T1 joint) and below, all columns showed posterolaterally facing superior articular facets. The level of change in orientation, from posteromedial to posterolateral facing superior facets, was not constant and occurred anywhere between C4 (C3/C4 joint) and T1 (C7/T1 joint). The change in orientation followed 2 different patterns, i.e. sudden or gradual. The C6 vertebra (C5/C6 joint) was the most frequent site to show the transition. The shape of the superior articular facets was circular to oval at C3, C4 and C5 levels and gradually changed to a transversely elongated surface at C7 and T1. These findings correlate well with various cervical movements and associated clinical conditions.

Location of the spinal nucleus of the accessory nerve in the human spinal cord.

The segmental extent and topography of the spinal nucleus of the accessory nerve (SNAN) was investigated in the adult human spinal cord. Transverse sections of segments between the lower medulla and C6 were stained with cresyl violet and the motor cell columns identified according to the numerical locations defined by Elliott (1942). The segmental extent and topography of the cervical part of column 2 resembled that previously described for the SNAN of primates.

Mechanism of change in the orientation of the articular process of the zygapophyseal joint at the thoracolumbar junction.

The orientation of the superior articular processes in thoracic and lumbar vertebrae differs. The present study was undertaken to investigate the possible mechanism for the change from a posterolaterally facing superior articular surface in the thoracic region to a posteromedially facing curved articular surface in the lumbar region. The material of the study consisted of dry macerated bones of 44 adult human vertebral columns. The orientation of the superior articular process and its relation to the mamillary tubercle (process) was examined between T9 and L5 vertebrae in each column. An abrupt change from the thoracic to lumbar type of articular process was observed in 3 columns (7 %). Forty-one (93 %) columns showed a gradual change extending over either 2 or 3 successive vertebrae. The present study suggests that the change in the orientation of the superior articular process, from the coronal to the sagittal plane (sagittalisation), occurs due to the change in the direction of weight transmission through zygapophyseal joints at the thoracolumbar junction. It was observed that the gradual sagittalisation of the superior articular process in the transitional zone brought it close to the mamillary tubercle which eventually fused with it. Thus the study suggests that the characteristic posteromedially facing concave superior articular process of lumbar vertebrae may have formed because of the fusion of the articular process and the mamillary tubercle.

A study of motoneuron groups and motor columns of the human spinal cord.

Eight normal human spinal cords were studied for motoneuron (Mn) groups and columns. Spinal segments (C1 to Coc.) were identified and embedded in paraffin wax. Serial cross sections were cut at 25 microm and stained by cresyl violet. Cross-sectional profiles of the spinal cord were traced for each segmental level and the outlines of the various Mn groups superimposed. These charts (maps) were used to examine intra and intersegmental changes in the relative positions of the columns. An attempt was made to provide topographical picture of Mn groups of individual segments. In the cervical region neuronal groups were more numerous but smaller and less distinct, while in the lumbosacral region they were fewer, larger and at many levels better circumscribed. The average number of Mn groups at any segmental level was 3-4 and never exceeded 5. C4, C5, C6, C7, L4, L5 and S1 contained numerous Mn groups. Maximum intrasegmental changes were noted at C3, C4, C7, T1, and S2, while at C5, C6, all thoracic, L1 L2 and L3, the pattern was constant throughout the segment. Eleven motor columns were traced in the human spinal cord. Column 1 belonged to the medial division and columns 2-11 to the lateral division of the ventral grey horn. Columns 1 and 2 were the most extensive as they were traceable from the lower medulla to S3 segment. Columns 3-8 were confined to cervical segments (including T1), while columns 9-11 were traced in lumbosacral segments. In general, motor columns followed a definite mode for their appearance and disappearance. Many of them showed rotation from a dorsal to a ventromedial direction.

Location of the phrenic nucleus in the human spinal cord.

Eight normal human spinal cords were studied. Spinal segments were identified and embedded in paraffin wax. Serial cross sections were cut at 25 microm and stained by cresyl violet. Motor columns were reconstructed adapting Elliott's (1942) methods. Motor columns were classified into the medial and lateral divisions and were numbered sequentially from medial to lateral at the level of C1. In the cervical cord, 8 motor columns were traced. Column 1, corresponding to the medial column, presented 3 subdivisions designated as 1a, 1b and 1c with ventral, dorsal and lateral positions respectively. Columns 1a and 1b extended throughout the cervical region while 1c was confined to 3rd, 4th and 5th cervical segments. At the level of C3, 1c was a discrete column situated lateral to 1a and 1b but at C4 and C5 it became displaced medially close to the medial margin of the ventral horn. In cross section, it presented smaller medial and large lateral part. With the help of clinical and developmental evidence an attempt was made to correlate column 1c with the phrenic nucleus.

Architecture of the cancellous bone of the human talus.

The trabeculae of the cancellous bone are formed along the direction of the lines of stresses to which a bone is subjected. The talus sustains the weight of the body and transmits the weight in different directions (i.e., the calcaneus and navicular). The aim of the present study was to investigate the architecture of the cancellous bone of the talus to understand the mechanism of transmission of force within the bone. Twenty-five dry, macerated tali of adult male humans were used to study the trabecular architecture. In a few bones, serial longitudinal (parasagittal), transverse (coronal), and horizontal sections were cut; in other bones, the trabecular bone was exposed by removal of cortical bone. Trabecular architecture was studied by dissection microscope and by taking radiographs of the slices. The body of the talus consisted of vertical, parallel plates arranged posteroanteriorly. This kind of orientation of the plates facilitates the transmission of weight, when the tibia rolls posteroanteriorly on the trochlear surface during walking. The trabecular architecture in the head of talus consisted of semiarched plates running parallel to each other. The vertical limb of these semiarched plates were situated above the middle and anterior calcaneal facets on the plantar surface of the head, whereas the horizontal limbs of the arches were deep to the navicular articular surface of the head. The vertical plates of the body and semiarched plates of the head were interconnected by a meshwork of irregularly arranged trabecular bone of the neck. The architecture of this meshwork was such that it could facilitate the change in the direction and nature of force. In conclusion, the part of compressive force, acting vertically downward on the body of the talus during standing, was converted to tensile force in the neck, and its direction was made perpendicular to enable this force to go toward the head of the talus. In a similar manner, the semiarched pattern of plates in the head facilitated the change in the direction of the force, at the end of the stance phase, from the downward (toward calcaneus) to the forward (toward navicular) direction.

The role of the vertebral laminae in the stability of the cervical spine.

The aim of this study was to determine the contribution of the vertebral laminae to the stability of the cervical spine since laminectomy may result in deformity of the neck. In 40 dry adult male cervical columns the weight-bearing areas of the inferior surfaces of the bodies and articular facets from C2 to C7 were measured and the means and S.D.S. calculated. In all columns the lamina index (height x thickness) of right and left halves of each lamina was calculated and summed at each cervical level. Means and S.D.S. were calculated for the series. The trabecular patterns in the laminae were studied in 6 of the columns. Results show that the laminae of C2 and C7 are heavily loaded, whilst the intervening ones are not. Thus laminectomy at C2 and C7 would tend to lead to instability, but between C3 and C6 this would be less likely. Significant segmental variation in weight transmission was not found for the facet joints.

Relationship between the articular surface area of a bone and the magnitude of stress passing through it.

The present study investigates the relationship between the articular area of a bone and the magnitude of the stress it resists. An attempt was also made to find the correlation between the development of a bone and its articular area. The material of the study consisted of a large number of dry, macerated, adult male skeletons. The articular surface area of the bones was measured with the help of a planimeter. The magnitude of the force acting on the proximal articular surface of a bone is expected to go out of the bone through its distal articular surface in almost the same proportion. The present investigation is based on the assumption that if the articular area is related to the magnitude of stress, then the proximal and distal articular areas of a bone should also be correlated. A significant correlation was observed between the proximal and distal articular areas of axis vertebra; L4 and sacrum; and tibia-fibula and talus. This indicated that the stress resisted by proximal and distal articular areas was in the same proportion. Similarly, a significant positive correlation between bone index and articular area in ribs, tibia, and laminae of vertebrae indicated that the bone mass (development) runs parallel to the articular area. Thus, the present investigation could reveal that the articular area and bone development are related to the stress acting on the bone.

Trajectory architecture of the trabecular bone between the body and the neural arch in human vertebrae.

The cancellous structure of vertebrae has been studied to investigate the direction of trabeculae and thus the lines of stress. The trabecular bone of the pedicle, connecting the body to the lamina, differed in different regions of the vertebral column. At C2 level, it was found that trabeculae are involved in transfer of th column. At C2 level, it was found that trabeculae are involved in transfer of the compressive forces from the superior articular surface to the inferior articular process and body. Throughout the thoracic region, trabeculae in the pedicle were inclined anteriorly towards the body, indicating that compressive forces in the thoracic spine are transferred from the neural arch to the body. In the lower lumbar region, trabeculae run from the body towards the neural arch. Trabeculae in the thoracic transverse processes extend from the costal facet to the lamina, suggesting that weight brought by the ribs to the costotransverse articulations is transmitted to laminae through transverse processes.

A study of non-metric (qualitative) variation in Gujarati crania.

Three hundred and seventy adult skulls (284 crania of unknown sex, 58 males and 28 females) from Gujarat State of India were examined for the incidence of non-metric variants and compared with other populations to establish the distance between them. In general the Gujarati incidences are of similar order to those in other series. The mean measures of divergence between Gujarati and other populations were all statistically significant (P less than 0.001). The Gujarati differed most from Australian Aborigines, but only slightly from the Burma, Punjab and Egypt samples. From the same material side and sex dimorphism was also tested to ascertain that how far sides and sexes can be pooled in Indian sample for making comparison between populations. In Gujarati population out of 22 cranial variants only four show sex difference and in case of bilateral traits, none of the variant has shown significant (P less than 0.05) side to side difference.

Transmission of weight through the lower thoracic and lumbar regions of the vertebral column in man.

This study is an attempt to investigate the role of the neural arches in transmission of weight in the lower thoracic and the lumbar regions of the vertebral column. Based on simple mechanical principles of weight transmission, various parameters were chosen for measurements at each vertebral level. In 44 adult male dry vertebral columns measurements were made from T5 to L5 levels. The area of the inferior surface of the body at each vertebral level was compared with the area of the inferior articular facet, the cross sectional area of the laminae (lamina index), the pedicle index and the arch index. The inclination of the pedicles in relation to the body was also measured at each level. On the basis of the above measurements it was deduced that the compression force in the lower thoracic and lumbar regions is transmitted through two parallel columns, one anterior (formed by bodies and intervertebral discs) and one posterior (formed by successive articulations of laminae with each other at their articular facets). This study suggests that a considerable part of the weight of the upper limbs and the thoracic cage is transmitted through the ribs to the posterior column (laminae) through the costo-transverse articulations and ligaments. Because of the inclined position of the fifth lumbar vertebra, a significant part of the compressive force from the body is transmitted to the laminae in spite of the anterior inclination of the pedicles at this level. Because of the anterior concavity of the spine in the thoracic region, weight is transferred from the posterior to the anterior column through the inclined pedicles and in the lumbar region, where the concavity is posterior, a part of the compressive force of the anterior column is transmitted to the posterior. Thus, the compressive force in the curvilinear thoracolumbar column tends to deviate towards the line of gravity. The implications of these findings in relation to clinico-pathological disorders of the spine are discussed.

A study of weight transmission through the cervical and upper thoracic regions of the vertebral column in man.

The role of the neural arch in weight transmission in the cervical and upper thoracic regions of the vertebral column has been investigated. Measurements at the levels of C2, C4, C6, C7, T1 and T5 vertebrae were made in 44 adult male vertebral columns. At each level, the area of the inferior surface of the body was compared with the area of the inferior articular facets, the pedicle index and the arch index; inclination of the pedicle in relation to the body was also measured. On the basis of these studies it was found that at C2 level the compressive force acting on the superior articular surfaces was transmitted to the inferior surface of the body and to the two inferior articular facets. From C2 to C7, compressive force is transmitted through three parallel columns - one anterior, formed by the bodies and intervertebral discs, and two posterior, formed by the articulations of the articular processes on either side. Due to the posterior curvature in the cervical region, the posterior columns here sustain more of the compressive force. From C7 level downwards, the compressive force is transmitted through two columns, i.e. one anterior formed by the bodies and intervertebral discs and one posterior formed by successive articulations of the laminae. Below C7 level, compressive force from the posterior column is partly transferred to the anterior column through the pedicles at T1 and T2. In the upper thoracic region, due to the anterior curvature, the main part of the compressive force is transmitted through the anterior column, which sustains even greater compressive force than is suggested by body area, with resulting increased stress.

A study of sutural bones in different morphological forms of skulls.

117 adult human skulls were classified for three morphological forms, i.e. dolichocephalic, mesocephalic and brachycephalic, and were examined for the presence of sutural bones in each form. Sutural bones occur in each forms of the skulls with no statistically significant differences. This finding is interpreted as indicating that sutural bones are not formed secondary to stress, otherwise the incidence of the sutural bones would have been differed in different morphological forms of skulls.

A study of sutural bones in Gujarati (Indian) crania.

370 adult crania were examined to find the incidence of sutural bones in Gujarati (Indian) crania and to compare it with other populations to establish the distance between them. The mean measure of difference between Indian and other populations was statistically significant. Comparison of cranial capacity in skulls with and without sutural bones showed no significant difference, and this is interpreted as indicating that sutural bones are not formed secondary to stress.

Anatomical symmetry in the hind limbs and spinal motoneurons in frogs.

The weight of muscles and bones of the right and left hind limbs has been studied in 60 frogs. In the first ten frogs studied, the number and size of motoneurons of the seventh, eighth and ninth lumbar spinal segments (which give origin to the sciatic nerve) were studied on both sides. This was done to ascertain the relationship between motoneuron size and limb dominance. No statistically significant difference was observed in the weights of the right and left hind limbs indicating that frogs do not show one-sided hind limb dominance. This result stands in marked contrast to a previous report of asymmetry in bone weight in frogs. Similarly no significant difference was observed in the numerical distribution of neurons and their size between the two sides of the spinal cord.

The ossification of the membraneous part of the squamous occipital bone in man.

The membranous part of the squamous occipital bone, above the highest nuchal line, develops from two pairs of centres and an occasional third pair, pre-interparietal, which may develop anterior to the interparietal centres. Previously it was considered that the pre-interparietal bone is found at the lambda, anterior to the interparietal, which is also a common site for the formation of sutural bones. In this study, on the basis of anomalies observed in a large series of skulls, sutural bones at the lambda are differentiated from the bone developed from the pre-interparietal centres. A separate pre-interparietal bone is identified by its shape and position. It is present behind the lambda within the territory of the membranous occipital bone.