The lumbosacral transition: morphologic variations and their functional significance

The articular facet of a superior articular process of the sacrum is directed backward, inward, and upward with marked variations. 4 angles characterize the orientation of this facet: a) The relative angle of tilt: i.e. the angle between the articular facet and the upper end-plate of the sacrum, measured in a sagittal plane. b) The absolute angle of tilt: i.e. the angle between the articular facet and the horizontal plane, measured in a sagittal plane. c) The tilted part-angle of opening: i.e. the angle between the articular facet and the sagittal plane, measured in a plane parallel to the upper end-plate of the sacrum. d) The horizontal part-angle of opening: i.e. the angle between the articular facet and the sagittal plane, measured in a horizontal plane. These 4 angles are determined by characteristic straights within the articular facet and certain reference planes (upper end-plate of the sacrum, horizontal plane, sagittal plane). Only 2 intersecting straights suffice for an adequate determination of a geometrical plane; therefore, if we know the relative angle of tilt and the tilted part-angle of opening, we are able to construct or to calculate the absolute angle of tilt as well as the horizontal part-angle of opening by using the range of inclination of the sacrum. The shape as well as the orientation of the articular facets at the superior articular processes of the sacrum do not depend on the inclination of the pelvis nor on the inclination of the sacrum nor on the range of the lumbosacral angle. Only the absolute angle of tilt shows a reference to the inclination of the sacrum because the relative angle of tilt shows a certain constancy. The orientation of the articular facets is slightly influenced by static moments, but considerably determined by dynamical requirements. At spines with irregular numbers of praesacral vertebrae, the orientation of the lumbosacral articular facets do not differ from the orientation of these facets at spines with the regular number of 24 praesacral vertebrae. This, however, does not prove right at spines, that have a lumbosacral "transitional vertebra". Such lumbosacral transitional vertebrae detract much from the stability of the lumbosacral region of the spine.     

The biostatics of the human sacrum: is there a relationship between the sacral inclination and the spatial orientation of the upper articular process of the sacral plate?

The orientation of the superior articular processes with regard to the upper end-plate of the sacrum does not depend on the inclination of the sacrum. This assertion can be made by interpreting certain angles already described in literature and may be confirmed by a research following strict biomechanic principles: The orientation of the articular processes is put in relation to the direction of the forward shear brought upon by the Vth lumbar vertebra and caused by the inclination of the sacrum. This is achieved by measuring the angle between the articular facet and a plane normal to the mentioned forward shear. The result is that the size of this angle does not at all depend on the degree of the inclination of the sacrum.     

Shape and orientation of articular facets of cervical vertebrae (C3-C7) in dogs denoting axial rotational ability: an osteological study

Macerated cervical vertebrae of 139 adult and 39 juvenile dogs were assessed for morphological evidence of axial rotation, which is denoted by the shape and orientation of the articular facets. The potential effect of the presence of caudal costal foveae at C7 on facet geometry was also investigated. Four variations of caudal facet shape were evident, namely, plane, concave, convex and sigmoid. The earliest onset of change in shape from plane to curved was noticed in juvenile dogs who were older than 8 weeks. The incidence of curved facets denoting axial rotation ability was observed to increase on descending down the cervical spine. Concave caudal facets were more frequently present in males and in large dogs (P < 0.001), compared to Dachshunds and small breeds. The degree of concavity was not related to age but was associated with the transverse distance between the most medial aspects of the caudal and corresponding cranial facets (P < 0.05). In large breeds, the presence of concave caudal facets at C7 was inversely related to the presence of caudal costal foveae (P < 0.01). The effect of axial rotation is discussed in context with clinical literature suggesting that axial rotation might attribute to the development of the wobbler syndrome.     

Talar articular facets (facies articulares talares) in human calcanei

The variations of the talar articular facets in 176 calcanei were studied and classified. Three types were considered: type A = calcanei with two articular facets for the talar head, with four subtypes; type B = calcanei with one articular facet for the talar head, and two subtypes, and type C = unique articular facies in the superior surface of the calcaneus for the talus. We found 53% (94 cases) type B calcanei and 46% (82 cases) type A calcanei. No calcanei of type C were seen.     

Models of the geometry of the human ankle bone pulley: two series of geometric models for demonstrating the biomechanics of the ankle joint

2 series of models demonstrate the geometrical shape of the human trochlea tali. We have changed step by step the shape of the 2 flanking articular facets of the trochlea, the course of the edges of the trochlea, and the length of their radii, and so we have found a model responding to the biomechanic conditions of the trochlea tali. The convex surface of this model (corresponding to the superior articular surface, i.e. the facies superior trochleae tali) is a torse, the medial flanking facet (corresponding to the medial articular facet of the trochlea, i.e. the facies malleolaris medialis) is a flat cone, the lateral flanking facet (corresponding to the lateral articular facet of the trochlea, i.e. the facies malleolaris lateralis) is a screwed (helicoidal) face. The resulting model shows the 2 completely different phases of motion in the ankle joint: During dorsiflexion (motion setting out from the neutral position towards the final position of dorsiflexion), the internal malleolus leads the talus, whereas the external malleolus is pushed outwards by the screwed lateral articular facet of the trocheal. The trochlea is moved like a hinge. In the final position of dorsiflexion, the malleoli tightly embrace the 2 flanking facets of the trochlea, whilst an obvious cleft appears dorsally and medially between the superior articular surface of the trochlea and the tibial roof (i.e. the facies articularis inferior tibiae). During plantarflexion (motion setting out from the neutral position towards the final position of plantarflexion), the external malleolus leads the talus, whereas the medial articular facet of the trochlea withdraws from the internal malleolus. The trochlea is moved like a screw. In the final position of plantarflexion, the superior articular surface of the trochlea closely contacts the tibial roof, whilst an obvious cleft appears between the medial articular facet of the trochlea and the internal malleolus.     

The relations between morphology, asymmetry of mutual articular facets, and range of movement, in the human hand joints

Surface area measurements were performed on the articular facets in the human hand joints in order to calculate the area-asymmetry (incongruency) between mutual articular facets in every one of the hand joints, and to learn about the relations between the asymmetry in the joint, the joint's morphology, and the range of movement exhibited by it. Several different trials have led to the conclusion that the asymmetry in a joint is strongly influenced by its morphological type (plane; sellar; condyloid; bicondylar). No such correlation was found between the asymmetry in a joint and its characteristic range of movement. The results contradict the intuitive assumption that the greater the incongruency in a joint, the wider the movement it can perform.     

Variations in the articular facets of the adult cuneiform bones

This study was carried out on 300 adult cuneiform bones (100 each of medial, intermediate and lateral cuneiform bones) for variations in their articular facets. The bones under study are from the Department of Anatomy, University of Jos, Nigeria. In each group, 75 were male and 25 female bones. The difference in the incidence of various patterns of articular facets in the different cuneiform bones between males and females as well as between right and left sides was found to be statistically significant.     

A NEW TITANOSAUR FROM WESTERN SÃO PAULO STATE, UPPER CRETACEOUS BAURU GROUP, SOUTH-EAST BRAZIL

Abstract: Material from a new titanosaur from the Bauru Basin (Bauru Group), Brazil is described and compared with well‐known titanosaurs. Adamantisaurus mezzalirai gen. et sp. nov. is based on six articulated anterior caudal vertebrae and two haemapophyses collected from the Adamantina Formation, which is considered to be Campanian–Maastrichtian? in age. Adamantisaurus mezzalirai is characterized by the following combination of characteristics: anterior caudal vertebrae with straight or slightly backwardly‐projecting neural spines with strongly expanded distal ends, stout prespinal lamina, very wide pre‐ and postzygapophyseal articular facets, and concave postzygapophyseal articular facets on anterior caudal vertebrae. Although our cladistic analysis has produced equivocal results, Adamantisaurus mezzalirai shares with DGM ‘Series B’ (Peirópolis titanosaur) and Aeolosaurus the presence of postzygapophyses with concave articular facets, and shares with DGM ‘Series B’ the presence of laterally expanded neural spines and stout prespinal lamina. Additionally, A. mezzalirai shares with DGM ‘Series’ C (other titanosaur from Peirópolis) the presence of short neural spines.     

Lumbar anomalies in the Shanidar 3 Neandertal

Recent examination of the Shanidar 3 remains revealed the presence of anomalous bilateral arthroses in the lumbar region. This paper describes this developmental anomaly, as well as several degenerative changes and offers potential etiologies.The Shanidar 3 remains represent an adult male Neandertal, approximately 35–50 years of age, dating to the Last Glacial. Although the partial skeleton is fragmentary, preserved elements include an almost complete set of ribs, portions of all thoracic vertebrae, all lumbar vertebrae, and the sacrum. Vertebral articulations from S1–T1 can be confidently assigned. The vertebra designated L1 is well preserved but lacks transverse processes. Instead, well defined bilateral articular surfaces, rather than transverse processes, are located on the pedicles. The skeletal elements associated with the anomalous L1 articulations were not recovered.The most likely interpretation is that the arthroses in question represent the facets for a 13th pair of ribs, a rare condition in modern hominid populations. Such lumbar developmental anomalies are an infrequent expression of a larger complex of cranial-caudal border shifting seen in the vertebral column. These shifts result in a change in the usual boundaries between the distinctive vertebral regions and are responsible for the majority of variability present in the vertebral column.     

How do we stand? Variations during repeated standing phases of asymptomatic subjects and low back pain patients

An irreproducible standing posture can lead to mis-interpretation of radiological measurements, wrong diagnoses and possibly unnecessary treatment. This study aimed to evaluate the differences in lumbar lordosis and sacrum orientation in six repetitive upright standing postures of 353 asymptomatic subjects (including 332 non-athletes and 21 athletes – soccer players) and 83 low back pain (LBP) patients using a non-invasive back-shape measurement device.In the standing position, all investigated cohorts displayed a large inter-subject variability in sacrum orientation (∼40°) and lumbar lordosis (∼53°). In the asymptomatic cohort (non-athletes), 51% of the subjects showed variations in lumbar lordosis of 10–20% in six repeated standing phases and 29% showed variations of even more than 20%. In the sacrum orientation, 53% of all asymptomatic subjects revealed variations of >20% and 31% of even more than 30%.It can be concluded that standing is highly individual and poorly reproducible. The reproducibility was independent of age, gender, body height and weight. LBP patients and athletes showed a similar variability as the asymptomatic cohort. The number of standing phases performed showed no positive effect on the reproducibility. Therefore, the variability in standing is not predictable but random, and thus does not reflect an individual specific behavioral pattern which can be reduced, for example, by repeated standing phases.     

The axial skeleton of the labyrinthodont Eogyrinus attheyi

An articulated length of vertebral column is used as a basis for the reconstruction of the salient features of the axial skeleton of the embolomerous anthracosaur Eogyrinus attheyi Watson, together with other material, including the holotype, in the Hancock Museum, Newcastle upon Tyne.
The trunk vertebrae are typically emboloinerous, with disoshaped notochordal pleuro-centra, firmly attached by broad facets to this neural arches, and much thinner intercentra. Regional variation is chiefly concerned with the span of the transverse processes, which diminishes posteriorly, and the associated separation of the two heads of each rib. A longitudinal series of trunk ribs, of diminishing length from the mid-trunk backwards, is reconstructed.
Eogyrinus has a normal tetrapod sacrum with one characteristic sacral rib. The first few caudal vertebrae bear ribs of unusual form, (of which four are preserved in sequence in the articulated specimen. The fifth caudal intercentrum bears the first and largest haemal arch and the pleurocentrum of the seventh caudal is distinguished by marked muscle origins presumably for the caudifemoral muscles.
The probability that Eogyrinus, like the few other embolomeres known, had an unusually long vertebral column for a labyrinthodont, is supported by an orthometric comparison using Romer's data on the American form Archeria.     

Incidence of squatting facets on the talus of Indians (Agra region).

230 adult Indian tali (from Agra region) were studied for the incidence of squatting facets. Extension of medial articular facet was observed in all the cases. Medial extension of trochlea was observed in 37% of cases; lateral extension of trochlea in 71.6% of cases, lateral squatting facets in 43.5% of cases and medial squatting in 8.6% of cases. The present data are compared with that of other workers.     

A NEW GENUS OF ICHTHYOSAUR FROM THE LOWER CRETACEOUS OF WESTERN CANADA

Abstract:  A new fauna of Lower Cretaceous (Albian) ichthyosaurs, which includes at least one new genus and species, was recovered from deposits of the Loon River Formation at Hay River, Northwest Territories, Canada. All Cretaceous ichthyosaurs have been referred to a single genus, Platypterygius . The Loon River Formation material, however, does not satisfy the diagnosis for Platypterygius , and it is distinctive enough to warrant the erection of a new genus and species of ichthyosaur. Maiaspondylus lindoei gen. et sp. nov. is distinguished from other ichthyosaurs by an extensive overlapping contact of the jugal and the maxilla; marginal teeth with smooth crowns, fluted cementum, lingual curvature and implantation in a dental groove; and humerus with isomorphic proximal and distal ends, featuring three distal articular facets in which the medial articular facet is smaller than the lateral facets. The holotype and referred material is described here, and the relationship of Maiaspondylus to other ophthalmosaurs is discussed.     

Relationships between geometry and kinematic characteristics in the temporomandibular joint

Motions of the temporomandibular joint (TMJ) involve both translation and rotation; however, there may be substantial variations from one human to another, and these variations present significant difficulties when designing TMJ prostheses. The disc-condyle glides along the temporal bone and the condyle centre describe a curve that depends on the individual morphology. This study analyses disc-condyle rotatory and translatory displacements moving all along the temporal bone facets which are mainly composed of two areas: the articular tubercle slope (ATS) and the preglenoid plane separated by the articular tubercle crest. Displacements were quantified using 3D video analysis, and this technique was computer-assisted. From a population of 32 volunteers, we were able to establish a correlation between the kinematic characteristics of the joint and the disc-condyle trajectories. This study quantifies the geometrical characteristics of the ATS and their inter-individual variations, which are useful in TMJ prosthesis design.     

Contribution of postnatal collagen reorientation to depth-dependent mechanical properties of articular cartilage

The collagen fibril network is an important factor for the depth-dependent mechanical behaviour of adult articular cartilage (AC). Recent studies show that collagen orientation is parallel to the articular surface throughout the tissue depth in perinatal animals, and that the collagen orientations transform to a depth-dependent arcade-like structure in adult animals. Current understanding on the mechanobiology of postnatal AC development is incomplete. In the current paper, we investigate the contribution of collagen fibril orientation changes to the depth-dependent mechanical properties of AC. We use a composition-based finite element model to simulate in a 1-D confined compression geometry the effects of ten different collagen orientation patterns that were measured in developing sheep. In initial postnatal life, AC is mostly subject to growth and we observe only small changes in depth-dependent mechanical behaviour. Functional adaptation of depth-dependent mechanical behaviour of AC takes place in the second half of life before puberty. Changes in fibril orientation alone increase cartilage stiffness during development through the modulation of swelling strains and osmotic pressures. Changes in stiffness are most pronounced for small stresses and for cartilage adjacent to the bone. We hypothesize that postnatal changes in collagen fibril orientation induce mechanical effects that in turn promote these changes. We further hypothesize that a part of the depth-dependent postnatal increase in collagen content in literature is initiated by the depth-dependent postnatal increase in fibril strain due to collagen fibril reorientation.     

Comparison of contact pressures measured at the sacrum of young and elderly subjects

Contact (interface) pressure measurements were made between the sacrum of groups of young and elderly subjects lying upon two special mattresses used to prevent pressure sores. One mattress was an alternating air pressure mattress, the other a foam mattress. Contact pressures were measured using a hydraulic sensor taped directly to the skin over the sacrum. All mean pressures and ‘pressure impulses’ (total applied pressure per standard time period) appeared higher when measured among the elderly subjects. Compared with the pressures measured from young subjects, the maximum contact pressures were significantly higher (p < 0.05) on both mattresses, with the pressure impulse higher while lying upon the foam mattress (p < 0.05).     

Relationships between geometry and kinematic characteristics in the temporomandibular joint

Motions of the temporomandibular joint (TMJ) involve both translation and rotation; however, there may be substantial variations from one human to another, and these variations present significant difficulties when designing TMJ prostheses. The disc–condyle glides along the temporal bone and the condyle centre describe a curve that depends on the individual morphology.

This study analyses disc–condyle rotatory and translatory displacements moving all along the temporal bone facets which are mainly composed of two areas: the articular tubercle slope (ATS) and the preglenoid plane separated by the articular tubercle crest. Displacements were quantified using 3D video analysis, and this technique was computer-assisted.

From a population of 32 volunteers, we were able to establish a correlation between the kinematic characteristics of the joint and the disc–condyle trajectories. This study quantifies the geometrical characteristics of the ATS and their inter-individual variations, which are useful in TMJ prosthesis design.     

Matrix disruptions, growth, and degradation of cartilage with impaired sulfation

Diastrophic dysplasia (DTD) is an incurable recessive chondrodysplasia caused by mutations in the SLC26A2 transporter responsible for sulfate uptake by chondrocytes. The mutations cause undersulfation of glycosaminoglycans in cartilage. Studies of dtd mice with a knock-in Slc26a2 mutation showed an unusual progression of the disorder: net undersulfation is mild and normalizing with age, but the articular cartilage degrades with age and bones develop abnormally. To understand underlying mechanisms, we studied newborn dtd mice. We developed, verified and used high-definition infrared hyperspectral imaging of cartilage sections at physiological conditions, to quantify collagen and its orientation, noncollagenous proteins, and chondroitin chains, and their sulfation with 6-μm spatial resolution and without labeling. We found that chondroitin sulfation across the proximal femur cartilage varied dramatically in dtd, but not in the wild type. Corresponding undersulfation of dtd was mild in most regions, but strong in narrow articular and growth plate regions crucial for bone development. This undersulfation correlated with the chondroitin synthesis rate measured via radioactive sulfate incorporation, explaining the sulfation normalization with age. Collagen orientation was reduced, and the reduction correlated with chondroitin undersulfation. Such disorientation involved the layer of collagen covering the articular surface and protecting cartilage from degradation. Malformation of this layer may contribute to the degradation progression with age and to collagen and proteoglycan depletion from the articular region, which we observed in mice already at birth. The results provide clues to in vivo sulfation, DTD treatment, and cartilage growth.     

A chondral modeling theory revisited

The mechanical environment of limb joints constantly changes during growth due to growth-related changes in muscle and tendon lengths, long bone dimensions, and body mass. The size and shape of limb joint surfaces must therefore also change throughout post-natal development in order to maintain normal joint function. Frost's (1979, 1999) chondral modeling theory proposed that joint congruence is maintained in mammalian limbs throughout postnatal ontogeny because cartilage growth in articular regions is regulated in part by mechanical load. This paper incorporates recent findings concerning the distribution of stress in developing articular units, the response of chondrocytes to mechanically induced deformation, and the development of articular cartilage in order to expand upon Frost's chondral modeling theory. The theory presented here assumes that muscular contraction during post-natal locomotor development produces regional fluctuating, intermittent hydrostatic pressure within the articular cartilage of limb joints. The model also predicts that peak levels of hydrostatic pressure in articular cartilage increase between birth and adulthood. Finally, the chondral modeling theory proposes that the cell-cell and cell-extracellular matrix interactions within immature articular cartilage resulting from mechanically induced changes in hydrostatic pressure regulate the metabolic activity of chondrocytes. Site-specific rates of articular cartilage growth are therefore regulated in part by the magnitude, frequency, and orientation of prevailing loading vectors. The chondral modeling response maintains a normal kinematic pathway as the magnitude and direction of joint loads change throughout ontogeny. The chondral modeling theory also explains ontogenetic scaling patterns of limb joint curvature observed in mammals. The chondral modeling response is therefore an important physiological mechanism that maintains the match between skeletal structure, function, and locomotor performance throughout mammalian ontogeny and phylogeny.     

Orientational analysis of the ultrastructural architecture of the fibrous base of human articular cartilage

An equivalent well reproduced reliable method of quantitative morphological orientational analysis has been chosen. Determination of the character, predominant direction and degree of orientation of the structural elements have been foreseen. Computer morphological orientational analysis of the fibrous architectonics of the human articular cartilage makes it possible to present a quantitative characteristics of peculiarities in its structural organization along the distance from the articular surface up to the subchondral bone. Certain objective data obtained confirm existance of three layers in the cartilage having various construction of the fibrous base: superficial layer with a predominant orientation of the collagenous fibrils in parallel with the articular surface; central--nonoriented; deep layer--with a radial orientation of fibrils. The method of orientational analysis applied can be used for quantitative characteristic of the fibrous base architectonics of any part of the locomotor apparatus in the human being and animals.