Accessory Articulations Research Articles

Accessory Cuboid Facet Associated with Calcaneonavicular Coalitions

Category:Hindfoot; OtherIntroduction/Purpose:Though resection and soft tissue interposition is the mainstay of surgical treatment for symptomatic calcaneonavicular coalitions (CNCs) that fail conservative treatment, some consternation exists as to balancing adequacy of resection with violation of adjacent talonavicular and calcaneocuboid (CC) articulations. As better understanding of nearby articular anatomy might be helpful in determining extent of resection, this study aims to identify differences in the anatomy of the CC articulation between feet with and without CNCs.Methods:A retrospective radiographic analysis of patients with symptomatic CNCs presenting to a single tertiary care pediatric hospital from 2010-2019 was performed. Patients without computed tomographic (CT) or magnetic resonance imaging (MRI) were excluded. Using either CT or MRI and standardized anatomic landmarks, the length and morphology of the calcaneal and cuboid articular surfaces were documented at the CC joint. When bilateral imaging was available in patients with a unilateral coalition, measurements were also made on the uninvolved side to provide a cohort of normal controls for comparison.Results:81 CNCs in 55 patients were identified along with18 normal feet. Mean age was 11.7 years at the time of advanced imaging. In the coalition group, an accessory cuboid facet was identified articulating with the calcaneal portion of the coalition in 61/81 (75.3%) feet. The mean total length of the cuboid articular surface measured 28.6 mm (range, 22.4-34.9 mm). The average length of the accessory facet was 10.6 mm (range, 6.0-15.5 mm) while the length of the primary cuboid articulation with the calcaneus was 15.9 mm (range, 6.4-23.2 mm). Thus, the accessory facet comprised 37.2% of the cuboid articular surface in these patients. Patients without CNCs had a significantly larger primary cuboid articulation with the calcaneus of 21.6 mm (p<0.0001). An accessory cuboid facet was identified in only a single foot in the normal cohort.Conclusion:An accessory cuboid facet is present in over 75% of patients with CNCs and comprised nearly 40% of the proximal cuboid articular length. Moreover, significant differences in the shape of the cuboid portion of the CC joint were present in feet with and without CNCs. This information may be useful when planning the extent of CNC surgical resection as including the coalition side of the accessory articulation may have value in restoring hindfoot motion.

Segmented lordotic angles to assess lumbosacral transitional vertebra on EOS

PurposeTo test the vertical posterior vertebral angles (VPVA) of the most caudal lumbar segments measured on EOS to identify and classify the lumbosacral transitional vertebra (LSTV).MethodsWe reviewed the EOS examinations of 906 patients to measure the VPVA at the most caudal lumbar segment (cVPVA) and at the immediately proximal segment (pVPVA), with dVPVA being the result of their difference. Mann–Whitney, Chi-square, and ROC curve statistics were used.Results172/906 patients (19%) had LSTV (112 females, mean age: 43 ± 21 years), and 89/172 had type I LSTV (52%), 42/172 type II (24%), 33/172 type III (19%), and 8/172 type IV (5%). The cVPVA and dVPVA in non-articulated patients were significantly higher than those of patients with LSTV, patients with only accessory articulations, and patients with only bony fusion (all p < .001). The cVPVA and dVPVA in L5 sacralization were significantly higher than in S1 lumbarization (p < .001). The following optimal cutoff was found: cVPVA of 28.2° (AUC = 0.797) and dVPVA of 11.1° (AUC = 0.782) to identify LSTV; cVPVA of 28.2° (AUC = 0.665) and dVPVA of 8° (AUC = 0.718) to identify type II LSTV; cVPVA of 25.5° (AUC = 0.797) and dVPVA of − 7.5° (AUC = 0.831) to identify type III–IV LSTV; cVPVA of 20.4° (AUC = 0.693) and dVPVA of − 1.8° (AUC = 0.665) to differentiate type II from III–IV LSTV; cVPVA of 17.9° (AUC = 0.741) and dVPVA of − 4.5° (AUC = 0.774) to differentiate L5 sacralization from S1 lumbarization.ConclusionThe cVPVA and dVPVA measured on EOS showed good diagnostic performance to identify LSTV, to correctly classify it, and to differentiate L5 sacralization from S1 lumbarization.

A new macronarian sauropod from the Upper Jurassic of Portugal

ABSTRACTThe Upper Jurassic of Portugal is relatively rich in sauropod remains. We describe a new sauropod specimen, which includes a partial tail, pectoral and pelvic girdle elements, and hind limb bones, from Praia de Valmitão (Praia da Amoreira-Porto Novo Formation, upper Kimmeridgian–lowermost Tithonian). This specimen constitutes the holotype of Oceanotitan dantasi, gen. et sp. nov., which shows a unique combination of characters, including the presence of anterior caudal vertebrae with a medial accessory articulation on the prezygapophysis; a circular, rough tuberosity on the medial surface of the scapula; an elliptical concavity on the ventral face of the scapula; an ischium that is shorter than the pubis; and a robust fourth trochanter located at the midline of the posterior face of the femur. Multiple phylogenetic analyses recover Oceanotitan dantasi within Titanosauriformes, with one resolving it at the base of Somphospondyli. This taxon shares several apomorphies with some Cretaceous somphospondylans and turiasaurs, such as the transverse furrow on the chevron articulations (shared with Tangvayosaurus and Phuwiangosaurus) and the ischium being shorter than the pubis (shared with Mierasaurus and somphospondylans). Oceanotitan might represent the oldest known somphospondylan, and its establishment increases the known diversity of the Late Jurassic–earliest Early Cretaceous sauropod fauna in the Iberian Peninsula, which also consists of turiasaurs, diplodocids and macronarians (non-camarasaurid, non-titanosauriform macronarians; camarasaurids; and brachiosaurids). This high diversity in sauropods suggests that this region might have played an important role during the Late Jurassic in the dispersal and diversification of several sauropod lineages between North America, Africa, and Europe, especially macronarians.

Quantifying Range of Motion and Stress Patterns at the Transitional Lumbosacral Junction: Pilot Study Using a Computational Model for Load-Bearing at Accessory L5-S1 Articulation.

Symptomatic or asymptomatic transitional anomalies at the lumbosacral junction are common occurrences in the population. Lumbosacral (L5-S1) accessory articulations are the most common presentations of transitional anomalies at this region. Such anatomical alterations are believed to be associated with biomechanical changes of load-bearing and movement restrictions leading to low back pain. This study attempts to use computational models of a normal and a lumbosacral transitional vertebrae (LSTV) accessory articulation to analyze and compare the range of motion and loading patterns at the lumbosacral articulations. Three-dimensional Finite Element computational models of normal and accessory L5-S1 articulated sacrum were created. These models were tested for range of motion and stress patterns generated at the lumbosacral articulations using similar loading and motion simulation to elicit different moments/excursions at the lumbosacral junctions. Compared to the normal variant, the transitional model exhibited different range of motion and divergent patterns of stress generation at the lumbosacral and accessory articulations with equal and physiological magnitudes of loading applied to both the models. The finite element modeling approach can be used for biomechanical investigations in LSTV variants. However, larger sample studies with different LSTV models may be required to statistically compare movement and loading patterns at LSTV-affected lumbosacral and sacroiliac junctions, and to recommend definitive treatment strategies in these situations.

A New Titanosaur Sauropod from the Upper Cretaceous of Patagonia, NeuquéN Province, Argentina

A new titanosaur sauropod from the Upper Cretaceous of Neuquen is described, Choconsaurus baileywillisi gen. et sp. nov. The species is represented by a nearly complete series of dorsal vertebrae as well as other parts of the skeleton. The material comes from the locality of Villa El Chocon and stratigraphically from the Huincul Formation, whose age has been estimated as upper Cenomanian. The new taxon presents many autapomorphic features, including the presence of a small notch on the dorsal margin of the posterior articular surface of the cervical centra, accessory articulations lateral to the hyposphene, which are more developed in the anterior dorsal vertebrae, midand posterior dorsal vertebrae with an accessory lamina placed between the posterior centrodiapophyseal and the accessory posterior centrodiapophyseal laminae, and a hyposphene on anterior caudal vertebrae. Phylogenetic analysis recovers Choconsaurus baileywillisi as a non-eutitanosaur titanosaur, taxa that are well represented in the lower Upper Cretaceous of Patagonia. Choconsaurus baileywillisi is, to date, the most complete non-eutitanosaur titanosaur.

Morphometry of the sacrum and its implication on trans-sacral corridors using a computed tomography data-based three-dimensional statistical model

Background ContextTrans-sacral implants are increasingly used to treat fractures of the sacrum, especially for osteoporosis-associated fragility fractures. However, the complex and highly variable sacral anatomy limits their use. It is still not clear which morphologic characteristics are critical to determine the availability and dimensions of trans-sacral corridors. PurposeThis study aims to assess sacral anatomy and its influence on trans-sacral corridors. Study DesignThis study used a computed tomography (CT)-based three-dimensional (3D) statistical size and shape model of the sacrum with multiple morphometric measurements. Materials and MethodsA 3D statistical model was computed using clinical CT data of 92 intact pelvises (mean age 61.5 years). Multiple measurements of the sacrum and the trans-sacral corridors were taken. Descriptive statistics and linear regression were calculated. Shape and size were analyzed using principal component analysis. ResultsThe limiting craniocaudal diameter of the trans-sacral corridor was 13.1 mm (±5 mm) in S1 and 13.8 mm (±2.4 mm) in S2. In S1, the craniocaudal diameter correlated with larger sacral curvature (SC), pelvic incidence (PI), and cranially located auricular surfaces. The presence of an accessory articulation with L5 was associated with a larger trans-sacral corridor S1. In contrast, the craniocaudal diameter of the S2 corridor correlated with more caudally situated auricular surfaces and lower PI. The sacral shape, as demonstrated by the statistical model, was highly variable, which affected the size and availability of trans-sacral corridor S1. Important determinants of trans-sacral corridor S1 were the craniocaudal position of the auricular surfaces and the shape of the sacral ala, which were influenced by SC, sacral height, and PI. ConclusionsThe human sacrum is highly variable in size and shape. The dimensions of trans-sacral corridors depend on the sacral shape and specific morphologic characteristics. Understanding of morphologic variants helps with preoperative assessments of the trans-sacral corridors. When planning to use trans-sacral implants, because of variable sacral anatomy and dimensions of the trans-sacral corridors, thorough preoperative planning is mandatory.

Reassessing the affinities of vertebral remains from Permo-Triassic beds of Gondwana

The Sanga do Cabral Formation of southern Brazil has a rich fossil tetrapod assemblage and is suggested to have an Early Triassic age mainly based on the presence of the parareptile Procolophon trigoniceps. However, a Permo-Triassic age can be also suggested for this unit taking into account the presence of putative Permian taxa and some previous stratigraphic assessments. We describe here several large vertebrae from the Sanga do Cabral Formation that display a distinctive morphology that includes the presence of a transverse distance across postzygapophyses more than twice the transverse width of the centrum, and accessory articulation structures in the neural arch that remind the hyposphene and hypantrum present in some basal parareptiles and diadectomorphs. Vertebrae with a similar large size and morphology had been previously reported from the same locality as belonging to the genus Procolophon based on their parareptile appearance (mainly the presence of a swollen neural arch) and the fact that the vertebrae were collected at the same locality where a large fragmentary skull assigned to this taxon was found. However, these vertebrae lack a comparable consistent morphology with those of Procolophon and basic statistical analyses demonstrate that these vertebrae are significantly larger than those expected in the largest known Procolophon skulls of South Africa. The morphology of these vertebra is consistent with that present in seymouriamorphs, pareiasaurs and diadectomorphs, but the absence of exclusive diagnostic characters precludes an assure assignation to either of these taxa. According to their current stratigraphic range, seymouriamorphs are the most plausible postulation, as their younger representatives are known from Late Permian deposits of Russia, but the other candidates cannot be excluded. The presence of any representative of those groups in the Sanga do Cabral Formation would be important because: (1) they would represent the first and only known record of seymouriamorphs or diadectomorphs in Gondwana, regarding the characters that the described vertebrae share with these groups; (2) they would suggest a survivorship for pareisaurs up to the Latest Permian or through the Permian-Triassic boundary, according to geochronological data currently available for this unit; (3) they might also suggest a Late Permian age for at least part of the Sanga do Cabral Formation if the intraformational conglomerates that yielded the vertebrae resulted from the rejuvenation of older levels of the same unit, and they do not include reworking of stratigraphically older strata.

Letter to the Editor: Accessory articulation

Letter to the Editor: Accessory articulation

Pars inter-articularis and laminar morphology of the terminal lumbar vertebra in lumbosacral transitional variations

Background:Lumbo-sacral transitional variations are common in the general population. Structural inadequacies of the terminal lumbar vertebral pars interarticularis (PI) and lamina have often been implicated as important factors for lumbo-sacral instability.Aims:Quantifying dimensions of PI and laminae in terminal lumbar vertebrae associated with lumbosacral transitions and compare them with their normal counterparts.Materials and Methods:Fourth lumbar vertebrae in spines involved with complete sacralization of the fifth lumbar (L5) vertebrae and L5 vertebrae associated with lumbosacral accessory articulation were measured for the height, width and thickness of the PI and the laminae on both sides and compared to normal vertebrae.Results:Dimensions in sacralization associated terminal vertebrae were smaller than the normal. The height of the PI and the widths of laminae were observed to be significantly smaller in terminal lumbar segment in sacralized specimen. Lumbo-sacral accessory articulations demonstrated smaller overall dimensions of several parameters. Lamiane in the last lumbar segment associated with lumbo-sacral transitions demonstrate smaller dimensions compared to the normal ones. Sacralization results in maximum diminution of these parameters.Conclusions:Smaller PI may predispose spondylolysis and spondylolisthesis at lumbo-sacral junctions associated with transitional variations, and warrant special attention to avoid iatrogenic injuries.

Relationship of sacral articular surfaces and gender with occurrence of lumbosacral transitional vertebrae

Research on lumbosacral transitional vertebra (LSTV) has yielded important information on the structural alterations of the sacrum associated with LSTV. Nevertheless, very little data are available on the relationship of a given type of LSTV with either a typical pattern of sacral morphology or its gender distribution in the population. To investigate the probable relationship between different variants of LSTVs with sacral morphology at the articular surfaces of the bone and the gender distribution of the anomalies in the population. Cross-sectional descriptive study involving dried human sacral bones and meta-analysis of data available related to LSTVs. Three hundred twenty sacra were screened for the presence of LSTV, the type of auricular surface, and facet joints in them. Samples were grouped against their sexes, type of the auricular surfaces present in them, the nature of facet joints, and the variety of LSTV (if present). Data on LSTV from reliable Internet databases were collected to account for the prevalence of LSTV in the population in terms of the types of the anomaly and their gender distribution. The detection rates of LSTV in the present study were similar to those observed in available literature. Accessory L5-S1 articulations and lumbarization of S1 were more commonly observed in the women. Sacralization was seen to be predominantly distributed in men. Higher auricular surfaces were associated with accessory articulations; lower auricular surfaces were present with partially separated S1 segment and in L5-S1 specimens. Morphology of the facets significantly altered in LSTV with accessory articulations. Different lumbosacral transitions share a stronger, definite, and specific patterns of relationship with certain sacral morphologies and gender. It is important to recognize the nuances of these connections so as to understand low back pain conditions in the setting of a typical sacral articular morphology or the sex of the individual.

Pedicular Anatomy of the First Sacral Segment in Transitional Variations of the Lumbo-Sacral Junction

The study aims to investigate the dimensions and angular orientations of the pedicles of the first sacral segment at the L5-S1 junctions affected by transitional variations. Measurement of parameters of the S1 pedicle and its orientation in sacra with (1) Accessory L5-S1 articulations, (2) Sacralisation of the L5, and (3) Lumbarisation of the first sacral segment, and comparing data with that observed in normal sacra. Lumbosacral fusion with instrumentation and screw fixation is commonly practiced to treat unstable L5-S1 junctions caused by a host of reasons. Though morphometric data pertaining to normal S1 pedicle structure is available in literature, it is hard to find such information regarding pedicles of first sacral segments associated with transitional variations. Transitional states at the lumbosacral junctions are often linked to development of L5-S1 instability. It thus becomes imperative to investigate S1 pedicular anatomy in context of these variations to prevent inadvertent surgical injuries and optimizing effects of screw placement in such sacral variations. S1 pedicle dimensions were measured in normal and L5-S1 transition affected sacra. Slope of the pedicle was measured with respect to the sagittal and the horizontal planes. Linear parameters were similar in the normal sacra and those with L5-S1 accessory articulations. Sacralisation reduced all dimensions including pedicle height, sagittal and transverse dimensions. Lumbarisation was associated with small length between the facet and the sacral promontory. Sacralisation reduced the sagittal angulation of the pedicles but substantially increased its downward slope. Lumbarised pedicles were more obtuse with the sagittal plane and less steep in front. S1 pedicle morphology and angulation in the first sacral segment are different from the normal in L5-S1 transitional situations and hence should be mapped accordingly in screw placements at the region in context of such common variations.

Disc spaces, vertebral dimensions, and angle values at the lumbar region: a radioanatomical perspective in spines with L5–S1 transitions

Low-back pain (LBP) has been associated with lumbar spines of normal morphology as well as those with L5-S1 "transitional" vertebrae. It is hard to find literature that quantifies the overall morphological changes in lumbar spines as related to transitional states. The object of this study was to investigate lumbar spine changes resulting from the presence of these transitional states. The author quantified dimensions and angles and statistically compared the morphology of lumbar spines with or without L5-S1 transitions in the context of LBP. Anteroposterior and lateral radiographs were obtained from 50 patients suffering from LBP without transitional anomalies at the L5-S1 junction. These radiographs were compared with anteroposterior and lateral radiographs from patients suffering from LBP with L5-S1 transitional states involving accessory L5-S1 articulations, and with anteroposterior and lateral radiographs from patients with L5-S1 unilateral or bilateral fusions. Twelve linear dimensions from the anteroposterior views and 8 angles from the lateral radiographs were measured. The mean values of linear dimensions differed in 1) disc heights, 2) vertebral heights and widths, 3) pedicles and interpedicular distances, 4) angle values, and 5) overall configuration of the lumbar curvatures. The L5-S1 accessory articulations led to increased lordotic curves, L-5 vertebral heights, and pedicle and angular dimensions. The L5-S1 fusions were related to smaller disc heights at all spaces, short and wide L-5 pedicles, taller and less wide transverse processes, and overall straighter spines with the least measures for all lumbar angles. Dimensional differences provided in this study may help in placing instrumentation at the lumbar vertebrae and working on intervertebral disc replacements in spines with specific L5-S1 transitional anomalies.

Facet Dimensions, Orientation, and Symmetry at L5–S1 Junction in Lumbosacral Transitional States

Study analyses dimensions, angular orientations, and symmetry of articular facets at the L5-S1 junction associated with transitional anomalies comprising (1) L5-S1 accessory articulations; (2) complete sacralization of the L5 vertebrae; and (3) completely lumbarized S1 sacral segments. Data were compared with same parameters evaluated in normal sacrum. Investigating probable morphologic differences in facet joints at the normal and transition affected lumbosacral junctions. Facet joints at the L5-S1 play an important role in load sharing and imparting stability at this area as well as are involved in conditions such as isthmic spondylolysis, degenerative spondylolisthesis, and osteoarthritis, giving rise to low back pain situations. Several morphologic variations at the lumbosacral junction have been studied and inconsistently alluded to be associated with these painful conditions. Lumbosacral transitional anomalies, on the other hand, have also been linked to low back pain situations. L5-S1 transitions have been shown to be associated with altered L5-S1 articular morphology as well as load-sharing pattern at the region. The analysis of L5-S1 zygapophysial anatomy in context of transitional anomalies at this region has rarely been documented. Both the superior articulating facets in the normal as well as in transition associated sacra were measured for (1) height, (2) width, (3) surface area, and (4) angulation of the articular surfaces with reference to the midsagittal plane. Data were also analyzed to find structural asymmetry between the two sides. Facets demonstrated smallest linear dimensions, surface areas, and maximum coronal orientation in lumbarized specimens. Facets areas associated with accessory articulations were also smaller and coronally oriented. Sacralization induced insignificant alteration in the facet morphology. Asymmetry (tropism) was observed in facets predominantly associated with accessory L5-S1 articulations. L5-S1 transitions possess altered facet morphology. These alterations are possibly related to low back pain situations.

Morphological traits in sacra associated with complete and partial lumbarization of first sacral segment

Background context Transitional states of vertebrae at the lumbosacral junction are associated with low back pain. Lumbarization may present as partial (incomplete separation of S1–S2 bodies and their neural arches) or complete separation of the S1 from the S2 segment in a sacrum. Separation of S1 entails alteration of the anatomy at the lumbosacral junction that affects load bearing at the region. Purposes To 1) identify characteristic structural features in sacra associated with lumbarization of the S1 sacral element; 2) compare linear dimensions and surface areas in such sacra with that of the normal samples; 3) calculate relative contributions of different dimensions in the variant sacral corpuses by working out indices; and 4) analyze load bearing at these sacra in light of their altered morphology. Study design Three hundred thirty-two dried human sacra were measured for specific dimensions and surface areas. They were screened for partial or complete lumbarization of the S1 segment. Outcome measures All parameters and indices of the lumbarized specimen were compared with those in the normal sacra. Methods Seven linear dimensions and five surface areas were measured in 332 sacra. Nine indices were formulated from them. Sacra with partial or complete lumbarization of S1 were analyzed for all the parameters and evaluated for their morphological variations and traits. Results A total of 3.9% of sacra presented lumbarization, seven (2.1%) with partial and six (1.8%) with complete separation of the S1. Sacrum with partial lumbarization presented parameters similar to the normal variety. Auricular surfaces in these sacra were situated lower than normal with negligible contribution from the S1 segments. Parameters in sacral samples showing complete separation of S1 (with remaining S2-S5 segments) were smaller than normal dimensions except for some. These “baseline” (S2–S5) sacra transmitted load to the sacroiliac joints via the S2 and S3 elements. Four of six of these samples demonstrated unilateral or bilateral accessory facets between the transverse elements of the free S1 segment and the ala of the remaining sacrum (formed by S2). Significant load passed through the accessory articulations that abutted near the sacroiliac joints. A good number of these sacra showed highly attenuated laminae and at times presented incomplete fusion at the spines (spina bifida). Conclusions Lumbarization involved distinct anatomical alterations at the S1–S2 junctions. Partially lumbarized samples showed 1) gap (mean 1.43 mm) between S1 and S2 bodies; 2) incomplete separation between S1 and S2 neural arch elements with the S1 arches resembling lumbar laminae; 3) well-developed “baseline” (S2–S5) segments; and 4) “low-down” (positioned at S2–S3) auricular surfaces. Complete separation of S1 involved 1) smaller overall dimensions with diminished facet depth, sacral height, and facet area at S1; 2) auricular surface areas comparable to the normal and greater than those found in the partially lumbarized specimen; 3) large “baseline” (S2–S5) sacra with “high-up” auricular surfaces (positioned at S2–S3); 4) occasional S1–S2 accessory articulations; and 5) small zygapophyseal joints and attenuated sacral laminae with high sacral hiatuses associated at times, with “spina bifida.”

Association of rudimentary sacral zygapophyseal facets and accessory and ligamentous articulations: Implications for load transmission at the L5‐S1 junction

Weight transmitted from the fifth lumbar vertebrae to the sacrum is distributed as three separate components between (a) the vertebral bodies anteriorly, (b) the transverse elements intermediately, and (c) the lumbosacral facet joints, posteriorly. The posterior components of the fifth lumbar vertebra share greater proportion of load in comparison with the posterior elements of the upper lumbar vertebral levels. This study focuses on rudimentary lumbosacral facet articulations and their possible effects on load sharing at this region. Twenty sacra bearing rudimentary articulations were collected for analysis. Sixteen of these sacra presented unilateral rudimentary facets, and the remaining four had facets that were bilaterally rudimentary. Thirteen of the sacra with unilateral rudimentary facets showed an accessory articulating area on the upper surface of the ala on the same side as the rudimentary zygapophyseal facet. The remaining three sacra (out of the 16) showed evidence of strong ligamentous attachments between the L5 and S1 transverse elements on the sides of the rudimentary facets. All the sacra with bilateral rudimentary facets demonstrated bilateral accessory L5-S1 articulations. These observations indicated that load transmission at lumbosacral junctions bearing a rudimentary facet joint is not normal and that their associations with strong L5-S1 lumbosacral ligamentous attachments or accessory articulations at the transverse elements serve a compensatory mechanism for load sharing.

Morphometric analysis and identification of characteristic features in sacra bearing accessory articulations with L5 vertebrae

Background context Occurrence of transitional vertebrae at the lumbosacral junction, especially accessory lumbosacral articulations (partial sacralization of the L5 vertebrae), is not uncommon. These transitional states are frequently associated with low back pain situations requiring surgical intervention. Purpose The study aimed to investigate the presence of distinct morphological features and structural peculiarities associated with these sacra. The features related to sacra bearing L5-S1 transitions might be significantly different from those of the normal sacra. This study tries to understand whether accessory L5-S1 articulations demonstrate altered mechanisms of load transfer as a result of structural changes at the L5–S1 junction. Study design Morphometric measurements of several linear dimensions and articular areas were obtained from 332 sacra. Thirty sacra demonstrated unilateral accessory facets on their ala. Twelve sacra showed bilateral accessory lumbosacral articulations. Indices were calculated based on the linear dimensions and on the surface areas of the bones to detect proportional contributions of the dimensions and surface areas to the overall structure of all the sacra. Outcome measures All the parameters obtained from the transitional sacra were compared with the same parameters worked out on 290 normal sacra. All parameters in the sacra bearing accessory articulations were statistically compared with parameters in the normal sacra. Method Seven linear dimensions and five surface areas were measured in 290 normal sacra. Thirty sacra bearing unilateral accessory articular facets and 12 sacra with bilateral accessory facets on their alae were measured for the same linear parameters and surface areas. Nine indices were calculated from these measurements in both the normal and transitional sacra and statistically verified. Results Analysis of the results indicated that sacra bearing accessory articulations, in comparison to the normal, carried their auricular surfaces at a higher level; possessed load bearing features mainly confined to the two upper sacral segments; showed lesser distances between the facet joints; showed smaller distance of the coronal plane of the facet joints from the posterior aspect of the S1 vertebral body; exhibited smaller and more coronally oriented facet joint surfaces; and exhibited smaller body width and height. The auricular surface area and superior surface of the body of S1 in these “transitional” sacra were similar in comparison to normal sacra. Linear dimensions in sacra with bilateral accessory articulations were smaller than the ones having unilateral accessory L5-S1 articulations. Conclusions Lumbosacral accessory articulations constituted the bulk of transitional variations at the junction. Accessory articulations were unilateral (9%) and bilateral (3%) with a total of 12% of all studied samples (n=332) demonstrating this type L5–S1 transition. Sacra with lumbosacral pseudoarticulations were associated with different anatomical features in contrast to normal sacra. Analysis of these structural differences with the normal variants may possibly help in understanding the biomechanical properties at these transitional sites. Evaluation of the relative proportions of dimensions within these bones may help plan surgical interventions or probably predict the pattern of abnormal weight bearing in these sacra.

Complete sacralization of L5 vertebrae: traits, dimensions, and load bearing in the involved sacra

Background Context Spines with sacralized fifth lumbar vertebrae are quite commonly encountered. Sacralizations represent a transitional state at lumbosacral junctions and are more susceptible to degenerative changes resulting from the altered load-bearing patterns at these regions. Purpose The present study is an attempt to analyze the morphology of sacra with complete and partially fused (sacralized) L5 vertebrae and compare it with those observed in normal sacra. Study Design/Setting Measurements of dimensions and articular surface areas were recorded in samples bearing sacralized L5 vertebrae and in normal sacra. Relative contributions of dimensions and surface areas on the bone were worked out by calculating indices. Comparison with the normal sacra was expected to yield significant differences. Outcome Measures Means of all linear parameters and indices were compared between sacralized and normal samples and between the fused and unfused sides of unilaterally sacralized specimens. Unpaired Student t test was applied to assess the differences in the values. Methods Seven linear dimensions and five surface areas were measured in 330 sacra. Nine indices were formulated from them. Sixteen (4.8%) sacra presented with bilateral completely fused L5 vertebrae with the first sacral segments. Four (1.2%) showed unilateral complete unification of sacra with the transverse process of the L5 vertebra above. Parameters were compared between the normal and sacralized samples and also between the two varieties of sacralized specimen. Results Sacra with fused L5 possessed significantly smaller heights than the normal ones if the fused L5 vertebra was excluded from the measurements. On inclusion of the L5, these sacra presented a grossly reduced distance between the zygapophyseal facets, a greater distance of the coronal plane of the facet joints from the posterior aspect of the L5, a narrower interauricular distance, slightly increased body width at the top of the sacrum (now L5), a comparable auricular surface area (with inclusion of the fusion of L5 transverse process at the lateral mass) to the normal ones, attenuated facet area, and occasionally, small intervertebral space between L5 and S1. The unilaterally fused variety exhibited overall smaller dimensions. None of these sacra showed accessory articulations at their ala. The auricular surfaces in these sacra spanned from mid-L5 to mid-S2 segments. The fusion of L5 increased the sacral height, width, and auricular surface. The auricular surfaces appeared to be situated “low-down” in context of the six (including L5) sacral segments. Conclusions Sacralization of L5 vertebra entails morphological alterations in the sacrum. The remnants of the original sacra in these specimens presented grossly diminished parameters. Sacralization of L5 possibly represents a structural and biomechanical adjustment to compensate for reduced joint interfaces associated with smaller sacra. It may correspond to one end of the transitional “spectrum,” the other end being defined by lumbarization of the S1 sacral segment.

Not just a pretty face: anatomical peculiarities in the postcranium of Rebbachisaurids (Sauropoda: Diplodocoidea)

Rebbachisauridae are poorly known ‘bizarre’ sauropods with two nearly complete skeletons collected: Limaysaurus tessonei and Nigersaurus taqueti. Whereas the latter taxon allowed the understanding of their cranial novelties, other species show some peculiarities in the postcranium. L. tessonei, Rebbachisaurus garasbae and a new form (MMCH-Pv-49) from Villa El Chocón, Patagonia, exhibit peculiar pectoral girdles and the loss of the hyposphene–hypantrum accessory articulations in their amphiplathyan dorsal vertebrae. Actually, the postzygapophyses are not only devoid of hyposphenal locks but also additionally show a curved postzygapophyseal eave that allows a sliding over the corresponding structure of the anterior side of the neural arch, a curved concave and elongated platform continuous along both prezygapophyses: the prezygapophyseal shelf. As the ‘ball and socket’ opisthocoelous centra in macronarians optimised mobility, the ‘U-eaves and shelf complex’ of rebbachisaurids permitted wider movements between successive vertebrae. While in titanosaurs the increased mobility occurred related to the centrum shape, in rebbachisaurids it is related to a complex system in the neural arch. Furthermore, whereas macronarians show large centra, rebbachisaurids underwent a minimisation of the centrum. These changes in both sauropod lineages probably had an outstanding relevance in the diversity and ecological roles that sauropods experienced in Cretaceous terrestrial ecosystems.

Coronal oblique turbo STIR imaging of the sacrum and sacroiliac joints at routine MR imaging of the lumbar spine

The objective of the study was to evaluate the clinical impact of coronal oblique imaging of the lumbrosacral junction and the sacrum at initial presentation for MR imaging of the lumbar spine in patients presenting with low back pain or sciatic pain. Two hundred and sixty consecutive patients attending for MRI of the lumbar spine underwent simultaneous coronal oblique turbo short tau inversion recovery (STIR; TR 2500, TE 40, TI 150, echo train length 7, number of scan acquisitions 2) imaging of the sacrum and the sacroiliac joints with a field of view of 30-cm and 3-mm slices (acquisition time 3 min and 20 s). Images were reviewed by two experienced radiologists to determine the cause of back pain, with and without images of the sacrum and sacroiliac joints. The added value of the additional sequence was assessed. Correlation was made with surgery, response to nerve root injection or clinical follow-up at 3 months. Subgroup analysis was performed to determine if patient stratification according to sex or symptoms would be useful. In total, in 19 of 260 patients (7.3%), abnormalities were identified at coronal STIR imaging. In 7 of 260 patients (2.7%), pathology was identified in the sacrum thought to account for back pain, altering the diagnosis made on the standard sequences. These diagnoses were sacroiliitis (n=2), sacral stress fracture (n=1), degenerative sacroiliac joints (n=1), degenerative accessory articulation between the lumbar spine and the sacrum (n=1), Tarlov cyst of nerve root (n=1) and retroverted uterus causing sciatic pain (n=1). Patient stratification according to sex or the presence or absence of sciatic symptoms was not useful in predicting the added benefit of the additional sequence. Routine coronal STIR imaging of the sacrum as part of lumbar spine MRI improves assessment of patients presenting with low back pain or sciatica in only a small number of patients.

Adriosaurus and the affinities of mosasaurs, dolichosaurs, and snakes

The poorly-known, long bodied, limb-reduced marine lizard Adriosaurus suessi Seeley, 1881, is reassessed. Adriosaurus and a number of other marine lizards are known from Upper Cretaceous (Upper Cenomanian-Lower Turonian) marine carbonate rocks exposed along the Dalmatian coast of the Adriatic Sea, from Komen, Slovenia, to Hvar Island, Croatia. A revised vertebral count reveals 10 cervical, 29 dorsal, and at least 65 caudal vertebrae. The projections previously interpreted as hypapophyses are instead transverse processes. Openings on the anterior part of the skull, previously described as external nares, are probably internal nares. Important features not noted previously include accessory articulations on all presacral vertebrae, pachyostosis of dorsal vertebrae and ribs, and the presence of two pygal vertebrae. Phylogenetic analysis of 258 osteological characters and all the major squamate lineages suggests that Adriosaurus and dolichosaurs are successive sister-taxa to snakes. This is consistent with their long-bodied, limb-reduced morphology being intermediate between typical marine squamates (e.g., mosasaurs) and primitive marine snakes (pachyophiids). The analysis further reveals that up to five successive outgroups to living snakes (pachyophiids, Adriosaurus, dolichosaurs, Aphanizocnemus, and mosasauroids) are all marine, suggesting a marine (or at least, semi-aquatic) phase in snake origins. These phylogenetic results are robust whether multistate characters are ordered or unordered, thus refuting recent suggestions that snakes cluster with amphisbaenians and dibamids (rather than aquatic lizards) if multistate characters are left unordered. Also, the recent suggestion that Pachyrhachis shares synapomorphies with advanced snakes (macrostomatans) is shown to be poorly supported, because the reinterpretations of the relevant skull elements are unlikely and, even if accepted, the character states proposed to unite Pachyrhachis and advanced snakes are also present in more basal snakes and/or the nearest lizard outgroups, and are consequently primitive for snakes.