Notochordal cells in the adult intervertebral disc: new perspective on an old question

The intervertebral disc is a tissue positioned between each of the vertebrae that accommodates applied biomechanical forces to the spine. The central compartment of the disc contains the nucleus pulposus (NP) which is enclosed by the annulus fibrosus and the endplate cartilage.The NP is derived from the notochord, a rod-like structure of mesodermal origin. Development of the notochord is tightly regulated by interactive transcription factors and target genes. Since a number of these molecules are unique they have be used for cell lineage and fate mapping studies of tissues of the intervertebral disc. These studies have shown that in a number of species including human, NP tissue retains notochordal cells throughout life. In the adult NP, there are present both large and small notochordal cells, as well as a progenitor cell population which can differentiate along the mesengenic pathway. Since tissue renewal in the intervertebral disc is dependent on the ability of these cells to commit to the NP lineage and undergo terminal differentiation, studies have been performed to assess which signaling pathways may regulate these activities. The notch signaling pathway is active in the intervertebral disc and is responsive to hypoxia, probably through HIF-1a. From a disease viewpoint, it is hypothesized that an oxemic shift, possibly mediated by alterations in the vascular supply to the tissues of the disc would be expected to lead to a failure in notochordal progenitor cell activation and a decrease in the number of differentiated cells. In turn, this would lead to decrements in function and enhancement of the effect of agents that are known to promote disc degeneration.

Vertebral microanatomy in squamates: structure, growth and ecological correlates

The histological study of vertebrae in extant squamates shows that the internal vertebral structure in this group differs from that of other tetrapods. Squamate vertebrae are lightly built and basically composed of two roughly concentric osseous tubes--one surrounding the neural canal and the other constituting the peripheral cortex of the vertebra--connected by few thin trabeculae. This structure, which characteristically evokes that of a tubular bone, results from a peculiar remodelling process characterised by an imbalance between local bone resorption and redeposition; in both periosteal and endosteo-endochondral territories, bone is extensively resorbed but not reconstructed in the same proportion by secondary deposits. This process is particularly intense in the deep region of the centrum, where originally compact cortices are made cancellous, and where the endochondral spongiosa is very loose. This remodelling process starts at an early stage of development and remains active throughout subsequent growth. The growth of squamate centra is also strongly asymmetrical, with the posterior (condylar) part growing much faster than the anterior (cotylar) part. Preliminary analyses testing for associations between vertebral structure and habitat use suggest that vertebrae of fossorial taxa are denser than those of terrestrial taxa, those in aquatic taxa being of intermediate density. However, phylogenetically informed analyses do not corroborate these findings, thus suggesting a strong phylogenetic signal in the data. As our analyses demonstrate that vertebrae in snakes are generally denser than those of lizards sensu stricto, this may drive the presence of a phylogenetic signal in the data. More comprehensive sampling of fossorial and aquatic lizards is clearly needed to more rigorously evaluate these patterns.

Evaluation of fetal spine biometry between 11 and 14 weeks of gestation

This study was designed to establish a fetal spine nomogram for age 11 through 14 weeks of gestation and to document relations among fetal spine length, distance and angle. These parameters were prospectively measured during the first trimester of singleton pregnancies, along with nuchal translucency, over a 3-year period. A total of 430 fetuses were included in the study. The regression equations among fetal spine parameters and gestational age were as follows: Spine length (mm) = 1.116 x gestational age (days) - 59.169; spine distance (mm) = 1.079 x gestational age (days) - 59.038; head-spine angle = 0.740 x gestational age (days) + 4.735; spine length:spine distance ratio = -0.002 x gestational age (days) + 1.234. Prenatal age-specific reference intervals for fetal spine biometry between 11 and 14 weeks of gestation may assist in evaluation of fetuses investigated for genetic abnormalities that can be expressed by deviation in spine length, distance, or angle.

Tracking of bone mass and density during childhood and adolescence

CONTEXT

Whether a child with low bone mineral density (BMD) at one point in time will continue to have low BMD, despite continued growth and maturation, is important clinically. The stability of a characteristic during growth is referred to as "tracking."

OBJECTIVE

We examined the degree of tracking in bone mineral content (BMC) and BMD during childhood and adolescence and investigated whether tracking varied according to age, sexual maturation, and changes in growth status.

DESIGN

We conducted a longitudinal study with measurements at baseline and annually for 3 yr.

SETTING

The Bone Mineral Density in Childhood Study was conducted at five clinical centers in the United States.

STUDY PARTICIPANTS

A total of 1554 girls and boys, ages 6-16 yr at baseline, participated in the study.

MAIN OUTCOME MEASURES

Whole body, spine, hip, and forearm BMC and BMD were measured by dual-energy x-ray absorptiometry, and age-, sex-, and race-specific Z-scores were calculated. Deviation from tracking was calculated as the Z-score at yr 3 minus baseline.

RESULTS

Correlations between Z-scores at baseline and yr 3 ranged from 0.76-0.88. Among children with a Z-score below -1.5 at baseline, 72-87% still had a Z-score below -1 after 3 yr. Age, sexual maturation, and deviations in growth status (P < 0.01) were associated with deviation from tracking; however, tracking was strongly evident even after adjusting for the effects of age, maturation, and growth.

CONCLUSIONS

Bone density showed a high degree of tracking over 3 yr in children and adolescents. Healthy children with low bone density will likely continue to have low bone density unless effective interventions are instituted.

Homeotic effects, somitogenesis and the evolution of vertebral numbers in recent and fossil amniotes

The development of distinct regions in the amniote vertebral column results from somite formation and Hox gene expression, with the adult morphology displaying remarkable variation among lineages. Mammalian regionalization is reportedly very conservative or even constrained, but there has been no study investigating vertebral count variation across Amniota as a whole, undermining attempts to understand the phylogenetic, ecological, and developmental factors affecting vertebral column variation. Here, we show that the mammalian (synapsid) and reptilian lineages show early in their evolutionary histories clear divergences in axial developmental plasticity, in terms of both regionalization and meristic change, with basal synapsids sharing the conserved axial configuration of crown mammals, and basal reptiles demonstrating the plasticity of extant taxa. We conducted a comprehensive survey of presacral vertebral counts across 436 recent and extinct amniote taxa. Vertebral counts were mapped onto a generalized amniote phylogeny as well as individual ingroup trees, and ancestral states were reconstructed by using squared-change parsimony. We also calculated the relationship between presacral and cervical numbers to infer the relative influence of homeotic effects and meristic changes and found no correlation between somitogenesis and Hox-mediated regionalization. Although conservatism in presacral numbers characterized early synapsid lineages, in some cases reptiles and synapsids exhibit the same developmental innovations in response to similar selective pressures. Conversely, increases in body mass are not coupled with meristic or homeotic changes, but mostly occur in concert with postembryonic somatic growth. Our study highlights the importance of fossils in large-scale investigations of evolutionary developmental processes.

The role of remodeling and asymmetric growth in vertebral wedging

BACKGROUND

Scoliosis with vertebral wedging is thought to be caused by asymmetric growth (Hueter-Volkmann law), but vertebral diaphyseal remodeling (Wolff's law) may also contribute to the deformity. We investigated whether vertebral wedging in scoliosis might involve both mechanisms.

METHODS

An external fixator was used to impose a 30 degrees scoliosis and compression of 0.1 or 0.2 MPa to the tails of 10 5-week-old and 20 14-week-old Sprague-Dawley rats for 6 weeks. The rats were divided into three groups of 10 animals each: Group 1: 5-week-old animals with 0.1 MPa compression; Group 2: 14-week-old animals with 0.1 MPa compression; Group 3: 14-week-old animals with 0.2 MPa compression. Vertebral wedging and diaphyseal curvature were measured from micro CT scans performed at weeks 1, 3, and 6. Wedging due to asymmetrical growth and remodeling was calculated from a Calcein label administered at week 3 and a Xylenol label at week 6.

RESULTS

The growth rate of the loaded vertebrae as a per cent of control vertebrae was 60% in Group 1, 40% in Group 2, and 30% in Group 3. The growth rate of control vertebrae in 14-week-old animals was 16% that of 5-week-old animals. The animals in all 3 groups developed a scoliosis with vertebral wedging that averaged 18.7 degrees in Group 1, 8.2 degrees in Group 2, and 10.1 degrees in Group 3. Asymmetric growth was much greater in Group 1 (5-week-old) animals. The ossified epiphyses became wedged and diaphyseal remodeling occurred in all groups.

CONCLUSIONS

The major contribution to the vertebral wedging was asymmetric growth in the 5-week-old animals and diaphyseal remodeling in the 14-week-old animals. The results support the concept that if appropriate loads can be applied to human vertebrae through minimally invasive techniques, scoliosis and vertebral wedging can be corrected without a spinal fusion in both adolescents and adults.

The role of posteriorly directed shear loads acting on a pre-rotated growing spine: a hypothesis on the pathogenesis of idiopathic scoliosis

Despite years of extensive research, the etiology of idiopathic scoliosis still has not been resolved. A hypothesis on the role of posteriorly directed shear loads was studied in several biomechanical and imaging studies. So far, it has been shown that: on the human erect spine these posteriorly directed shear loads act; these loads decrease the rotational stability of the spine vitro and in vivo; once rotation occurs, it logically follows an already built-in vertebral rotational pattern, that is pre-existent in the human spine; this pre-existent rotational pattern is related to organ anatomy, and not to handedness; certain areas in the female spine are more subject to posteriorly directed shear loads as certain areas in the female spine are more backwardly inclined. Although it is appreciated that the cause of idiopathic scoliosis is multi-factorial, we believe that the delicate upright spinal sagittal balance and the unique posteriorly directed shear loads acting on the erect human spine play a crucial role in the rotational stability of the human spine, and thus in the pathogenesis of idiopathic scoliosis.

Size and age estimates at sexual maturity for the little skate Leucoraja erinacea from the western Gulf of Maine, U.S.A

Size and age estimates at sexual maturity were determined for 162 male and 273 female little skates Leucoraja erinacea collected from the western Gulf of Maine. Maturity ogives suggest that 50% maturity in females occurs at age 9.5 years and 480 mm total length (LT), whereas 50% maturity in males occurs at a slightly younger age of 7.7 years and smaller size of 460 mm LT. Age estimates were made from 389 L. erinacea ranging in size from 93 to 570 mm LT. The index of average per cent error and age-bias plots indicated that the ageing methods were precise and non-biased. Additionally, annual periodicity of band formation was validated with oxytetracycline in eight individuals (three males and five females) ranging in age from 3 to 12 years. In conclusion, results from this study indicate that L. erinacea exhibits characteristics that make other elasmobranch populations highly susceptible to overexploitation.

Aetiology of idiopathic scoliosis: current concepts

The aetiology of the three-dimensional spinal deformity of idiopathic scoliosis (IS) is unknown. Progressive adolescent idiopathic scoliosis (AIS) that mainly affects girls is generally attributed to relative anterior spinal overgrowth from a mechanical mechanism (torsion) during the adolescent growth spurt. Established biological risk factors to AIS are growth velocity and potential residual spinal growth assessed by maturity indicators. Spine slenderness and ectomorphy in girls are thought to be risk factors for AIS. Claimed biomechanical susceptibilities are (1) a fixed lordotic area and hypokyphosis and (2) concave periapical rib overgrowth. MRI has revealed neuroanatomical abnormalities in approximately 20% of younger children with IS. A neuromuscular cause for AIS is probable but not established. Possible susceptibilities to AIS in tissues relate to muscles, ligaments, discs, skeletal proportions and asymmetries, the latter also affecting soft tissues (e.g. dermatoglyphics). AIS is generally considered to be multi-factorial in origin. The many anomalies detected, particularly left-right asymmetries, have led to spatiotemporal aetiologic concepts involving chronomics and the genome altered by nurture without the necessity for a disease process. Genetic susceptibilities defined in twins are being evaluated in family studies; polymorphisms in the oestrogen receptor gene are associated with curve severity. A neurodevelopmental concept is outlined for the aetiology of progressive AIS. This concept involves lipid peroxidation and, if substantiated, has initial therapeutic potential by dietary anti-oxidants. Growth saltations have not been evaluated in IS.

Spinal postural alignment variance according to sex and age in 7- and 8-year-old children

PURPOSE

Children's postural alignment undergoes many adjustments due to the changes in body proportions during the stages of growth. The objective of this study was to quantitatively characterize and analyze spinal postural standards in 7- and 8-year-old children to verify which of the differences found were correlated to age and sex.

METHODS

Two hundred thirty public school students (Amparo, São Paulo, Brazil) aged 7 to 8 years were divided into groups according to postural alignment, which were further subdivided by sex and age, for comparison. Digital photos of upright subjects were analyzed to evaluate posture. Lumbar and thoracic curvature, pelvic inclination, head posture, and lateral spine deviation were measured using CorelDraw (Ottawa, Canada) software guidelines and bone landmarks. Descriptive statistics and analysis of variance data analysis were utilized to verify differences among the groups. This was a cross-sectional, descriptive study.

RESULTS

Mean values for the variables analyzed were calculated. For lumbar lordosis, 7-year-old boys showed 38.49 degrees +/- 15.32 degrees in comparison to all other groups (42.29 degrees +/- 7.13 degrees ). For thoracic kyphosis, the 7-year-old children presented 28.07 degrees +/- 7.73 degrees , and the 8-year-olds 30.32 degrees +/- 7.73 degrees . Pelvic inclination presented a mean value of 15.82 degrees +/- 5.46 degrees and single lateral spine deviation mean value of 3.48 degrees +/- 2.12 degrees .

CONCLUSION

For the sample studied, differences based on sex and age were found for some of the body segments analyzed. The values found in this study may contribute to improved physiotherapeutic treatment when associated with other aspects of the clinical assessment and symptomatology.

Axial and appendicular skeletal transformations, ligament alterations, and motor neuron loss in Hoxc10 mutants

Vertebrate Hox genes regulate many aspects of embryonic body plan development and patterning. In particular, Hox genes have been shown to regulate regional patterning of the axial and appendicular skeleton and of the central nervous system. We have identified patterning defects resulting from the targeted mutation of Hoxc10, a member of the Hox10 paralogous family. Hoxc10 mutant mice have skeletal transformations in thoracic, lumbar, and sacral vertebrae and in the pelvis, along with alterations in the bones and ligaments of the hindlimbs. These results suggest that Hoxc10, along with other members of the Hox10 paralogous gene family, regulates vertebral identity at the transition from thoracic to lumbar and lumbar to sacral regions. Our results also suggest a general role for Hoxc10 in regulating chondrogenesis and osteogenesis in the hindlimb, along with a specific role in shaping femoral architecture. In addition, mutant mice have a reduction in lumbar motor neurons and a change in locomotor behavior. These results suggest a role for Hoxc10 in generating or maintaining the normal complement of lumbar motor neurons.

Pinealectomy in the chicken: a good model of scoliosis?

The phenomenon of spinal deformity in the pinealectomized chicken has led researchers to postulate a disturbance of melatonin activity as a potential cause of adolescent idiopathic scoliosis (AIS). More recently, structural differences between curves seen in this model and those seen in scoliosis have been highlighted suggesting the deformities observed are not as similar as first thought. We examined melatonin levels, and the radiological and histological characteristics of scoliosis after pinealectomy in chickens. They underwent pinealectomy (P) at 2 days of age, sham surgery (S) or served as controls (C). Mean melatonin levels were 32.9 pmol/L (P), 175 pmol/L (S) and 227.3 pmol/L (C). Scoliosis developed in 75% of chickens after pinealectomy and 38% after a sham procedure. Nineteen percent of unoperated controls also developed scoliosis. A lower melatonin level was associated with the development of scoliosis (p < or = 0.001), but exceptions were seen with levels up to 265 pmol/L observed in one case. Most of the curves occurring spontaneously and after sham surgery and almost half after pinealectomy were short angular curves: distinct from those resembling idiopathic scoliosis. These occur over one or two segments and are characterized by marked apical wedging, frequently associated with subluxation or dislocation. The intervertebral joint in the chicken is more like a synovial joint histologically than an intervertebral disc. This study highlights important differences between the chicken and the human, and between their respective spinal deformities. Caution is advised when drawing conclusions regarding the pathogenesis of AIS from this model.

Continuous light affects mineralization and delays osteoid incorporation in vertebral bone of Atlantic salmon (Salmo salar L.)

In order to study the effects of photoperiod on fish bone, Atlantic salmon (Salmo salar L.) were exposed to two light regimes (natural and continuous light) from January until June. During the experimental period, several parameters related to the inorganic (minerals) and organic (osteoid) phases were measured. Changes in the organic phase were related to mechanical strength (yield-load) and the expression of the genes sonic hedgehog (shh) and collagen type I alpha 2 (col I). Co-variation between yield-load and the expression of both shh and col I were detected in both groups. It was also shown that fish on the continuous light regime had delayed activation of osteoid incorporation. Mineralization properties were measured with stiffness, mineral incorporation per day and expression of alkaline phosphatase (alp) and matrix Gla protein (mgp). Stiffness, mineral incorporation and gene expression followed the same trend in both light groups in late spring, whereas an increase in the expression of mgp and alp was detected in April, followed by significantly higher stiffness at last sampling in both light groups. These results indicate that constant light affects mineralization and delays osteoid incorporation in Atlantic salmon during the spring. However, in this experiment light treatment did not promote the development of vertebral deformities. Our results also suggest that shh can be used as a marker of osteoblast proliferation and col I a marker of osteoid incorporation, and that both alp and mgp expression could be associated with a rapid increase in mineralization in Atlantic salmon vertebrae.

Changes in vertebral structure during growth of reared rainbow trout, Oncorhynchus mykiss (Walbaum): a new approach using modelling of vertebral bone profiles

Severe bone resorption of the vertebral body in reared rainbow trout was thought to be a dysfunction in mineral balance induced by increased growth rate in unfavourable rearing conditions. To verify this assumption, we sampled market-sized trout (c. 250 g) from 20 fish farms with different rearing conditions. Growth rate was also studied by sampling trout reared in three different water temperatures from fry to market-size. Transverse sections of vertebrae were microradiographed, then digitized. Total bone area (Tt-B.Ar.) and bone profiles were obtained using BONE PROFILER 3.23 software and a mathematical model was developed to statistically compare bone profiles using 12 parameters in four vertebra regions. Tt-B.Ar. and bone profiles were found to vary with rearing conditions and growing temperatures, indicating obvious influences of these factors on bone remodelling. However, vertebral resorption was found to be a general phenomenon. In trout from 190 to 235 mm in length, vertebrae underwent important remodelling resulting in large resorption of the middle area, while the transition and peripheral areas showed an increase in bone deposition. Changes in vertebra architecture seem to be a good compromise between the need to mobilize stored minerals during growth while maintaining vertebral biomechanical properties.

The role of spinal concave-convex biases in the progression of idiopathic scoliosis

Inadequate understanding of risk factors involved in the progression of idiopathic scoliosis restrains initial treatment to observation until the deformity shows signs of significant aggravation. The purpose of this analysis is to explore whether the concave-convex biases associated with scoliosis (local degeneration of the intervertebral discs, nucleus migration, and local increase in trabecular bone-mineral density of vertebral bodies) may be identified as progressive risk factors. Finite element models of a 26 degrees right thoracic scoliotic spine were constructed based on experimental and clinical observations that included growth dynamics governed by mechanical stimulus. Stress distribution over the vertebral growth plates, progression of Cobb angles, and vertebral wedging were explored in models with and without the biases of concave-convex properties. The inclusion of the bias of concave-convex properties within the model both augmented the asymmetrical loading of the vertebral growth plates by up to 37% and further amplified the progression of Cobb angles and vertebral wedging by as much as 5.9 degrees and 0.8 degrees, respectively. Concave-convex biases are factors that influence the progression of scoliotic curves. Quantifying these parameters in a patient with scoliosis may further provide a better clinical assessment of the risk of progression.

[Effect of staple on growth rate of vertebral growth plates in goat scoliosis]

OBJECTIVE

To further investigate the possible mechanism of the correction of scoliosis with Staple by quantifying the effect of Staple on growth rate of vertebral growth plates in goat scoliosis.

METHODS

Experimental scoliosis was created in 10 juvenile female goats by using unilateral pedicle screws asymmetric tethering. After 8-10 weeks, goats were divided randomly into Staple treated group (n=5) and control group (n=5). All tethers were removed in both groups and Staple group underwent anterior vertebral stapling with 4-5 shape memory alloy Staples along the convexity of the maximal curvature after posterior tether being removed. All goats were observed for an additional 8-13 weeks, the Cobb angle were measured to observe the correction of scoliosis. The fluorochromes Oxytetracycline and Calcein were administered respectively 18 and 3 days before death to label the ossifying front under the growth plates. Superior intervertebral disc of apical vertebra and two adjacent growth plates were completely harvested in all goats. All specimens were embedded with polymethyl methacrylate and sliced undecalcified. The growth rates of the vertebral growth plates were calculated by measuring the distance between the two fluorescent lines with fluorescence microscope.

RESULTS

Nine (5 in Staple treated group and 4 in control group) of 10 tethered goats had progressive scoliotic curves of significant magnitude after 8-10 weeks of tethering. In Staple treated group, the Cobb angles were (34.8 +/- 12.4) degrees at the instant after treatment, and (15.6 +/- 11.7) degrees 8-13 weeks after treatment; showing statistically significant difference (P < 0.05). In the control group, the Cobb angles were (49.3 +/- 18.0) degrees at the instant after treatment, and (49.0 +/- 17.6) degrees 8-13 weeks after treatment; showing no statistically significant difference (P > 0.05). In Staple treated group, the growth rate of growth plate in the concavity (3.27 +/- 0.96) microm/d was higher than that in convexity (1.84 +/- 0.52) microm/d (P < 0.05), while the growth rate of the concavity did not differ significantly from that of the convexity in control group (P > 0.05).

CONCLUSION

Staple can significantly alter the growth rates of two sides of vertebrae in scoliosis with the growth rate of concavity exceeding the one of convexity, which results in correction of deformity.

[Digital skeletal age and histological evaluation for residual spine growth potential in idiopathic scoliosis]

OBJECTIVE

To ascertain the correlation between histological grades (HGs) of vertebral growth plates and Risser grades in idiopathic scoliosis (IS) patients; to identify whether digital skeletal age (DSA) is a reliable indicator for accurate evaluation of the spinal residual growth potential.

METHODS

Twenty eight Chinese female patients were available for this study. Superior and inferior growth plates were obtained at each level when anterior approach surgeries were performed. Histological examinations were conducted after the specimens were processed. The patients were evaluated by DSA stages in this study. Correlations between histological grades, menarchal status, and chronological age were analyzed.

RESULTS

There was a negative correlation between the following: HGs and DSA stages in 28 cases (r = -0.541, P = 0.003), and HGs and menarchal status in patients in DSA stage III (r = -0.591, P = 0.006). Statistical significance of growth activity of growth plates was found between patients in DSA-stage II and those in DSA-stage III (P = 0.014).

CONCLUSIONS

DSA may be a reliable indicator for predicting the spinal residual growth potential in IS patients, but it should be correlated with menarchal status and chronological ages.

Evaluation of tail biopsy collection in laboratory mice (Mus musculus): vertebral ossification, DNA quantity, and acute behavioral responses

A preferred method to genotype genetically engineered mice is through collection of distal tail tissue (tail biopsy) followed by DNA isolation. Currently, general or local anesthesia (or both) is recommended for biopsy after 3 wk of age, the time after which tail vertebrae are considered to be ossified. Our objective was to rigorously evaluate vertebral development, DNA content, and acute behavioral responses at different ages by harvesting tail biopsies of different lengths. We evaluated laboratory mice from 5 inbred strains and 1 outbred stock at each of 12 ages (3 to 42 d of age). Biopsies of 5-, 10-, and 15-mm lengths were obtained. Vertebrae were graded according to level of ossification by using complementary modalities of high-resolution microradiography, microcomputed tomography, and histology. Vertebral development progressed at different rates among the strains, with mature tail vertebrae containing endplates detectable in the tail of some strains by 10 d of age. Within the distal 2 mm of tail, end plates were not identified before 21 d of age. DNA yield (DNA weight/tissue weight) was greatest from the 5-mm biopsy harvest. Acute behavioral responses to biopsy varied by age and strain, and these differences were associated with vertebral maturation. Vertebral development progressed most rapidly in C57BL/6 mice, which also demonstrated the highest response rate to biopsy, whereas BALB/c mice had slower vertebral development and were less responsive. These findings support the collection of minimal lengths of tail tissue from mice at ages younger than 17 d, unless anesthesia or analgesia is provided.

Unilateral pedicle screw epiphysiodesis of the neurocentral synchondrosis. Production of idiopathic-like scoliosis in an immature animal model

BACKGROUND

The neurocentral synchondrosis plays a role in the growth of the spine. The goal of this study was to determine whether asymmetric epiphysiodesis of this synchondrosis creates a scoliotic deformity in a growing-animal model and to correlate curve magnitude with the degree of closure of the synchondrosis.

METHODS

Two-month-old pigs were assigned to three groups. In the control group, two animals received a sham operation without pedicle screw fixation; in the single-screw group, three animals were treated with a single right transpedicular screw placed across the neurocentral synchondrosis from T7 to T14; and in the double-screw group, three animals were treated in the same way as the previous group except that two screws were placed in each pedicle. The animals were killed at six months, and radiographs and axial computed tomography images of the spine were obtained. Histomorphometric analyses were performed to grade the synchondrosis at each level.

RESULTS

A scoliotic curve was seen in none of the animals in the control group, in one of the three in the single-screw group, and in all three in the double-screw group (30 degrees, 42 degrees, and 42 degrees). Vertebral rotation in the axial plane occurred toward the screw side and was significantly greater in the double-screw group (mean, 15.2 degrees) than in the single-screw (mean, 6.1 degrees) and control (0 degrees) groups (p < 0.001). There was no difference in morphology between the left and right pedicles in the control group. The left pedicle was 9% longer than the right (screw-treated) pedicle in the single-screw group, and it was 22% longer than the right pedicle in the double-screw group. Closure of the neurocentral synchondrosis was greatest in the double-screw group (>75% closure) compared with the single-screw group (<50% closure) (p < 0.0001) and the control group (no closure) (p < 0.0001), and closure correlated with the magnitude of the coronal curve (p = 0.001).

CONCLUSIONS

Unilateral transpedicular screw fixation that traverses the neurocentral synchondrosis in a growing-pig model can produce asymmetric growth of the synchondrosis to create scoliosis with the convexity on the side of the screw fixation. Double pedicle screws provided a greater epiphysiodesis effect on the neurocentral synchondrosis, which correlated with a greater degree of scoliosis.

Computed tomographic morphometry of thoracic pedicles: safety pedicle parameter measurement of the Chinese immature thoracic spine

Our objective was to quantify the morphometric characteristics of the pedicles of the Chinese immature thoracic spine. A total of 120 patients aged 5-14 years underwent standard thoracic computed tomography (CT). The patients were grouped according to age: group 1 (5-8 years of age), group 2 (9-11 years of age) and group 3 (12-14 years of age). Images were reformatted, and multiplanar reconstructions were used to attain images of thoracic pedicles on sagittal, coronal and transverse planes. The measurements included the inner and outer pedicle diameters on the transverse plane, pedicle sagittal diameter, pedicle length and the pedicle angle on the transverse. (1) Pedicle diameters on the transverse plane decreased gradually from T1 to T4 and increased gradually from T5 to T12. The shortest transverse diameter of the thoracic pedicle was T4 or T5. (2) The sagittal diameter was significantly larger than the transverse diameter except at T1. (3) The length of the pedicle from the posterior cortex to the anterior cortex of the vertebra increased from T1 to T12. (4) The pedicle angle decreased gradually from T1 to T8 and became negative below the level of T10. The length of the pedicle changed with age significantly, but the pedicle angle changed with age insignificantly. The success of transpedicular fixation requires a better understanding of morphological features at different ages and reasonable selection of the diameter, length and direction of the pedicle screws based on X-ray and CT films.

Skeletal morphology and maturation of male Gambusia holbrooki exposed to sewage treatment plant effluent

Sewage effluent has been identified as a major source of endocrine disrupting chemicals (EDCs) in the aquatic environment. The modified hemal spines (modified skeletal structures important in reproduction) of mosquitofish, Gambusia spp. have been shown to be under androgenic control and to be affected by exposure to estrogen. The current study aimed to investigate the effects of two sewage treatment plants (STPs) in Sydney, Australia on the morphology of hemal spines in populations of Gambusia holbrooki and on the ability of the fish to reach sexual maturity. The effluent from the two STPs had different effects on the hemal spines of males. At St. Marys differences in hemal spine morphology between fish upstream and downstream of the STP were not attributable to effluent from the STP. At Quakers Hill, results suggest that the effluent is generally estrogenic to G. holbrooki. There was a decrease in the proportion of males that were morphologically mature downstream of both STPs indicating potential population level effects that were associated with the presence of the STPs.

[Selective dorsal T1-T6 fusion of the thoracic spine and effects on thorax growth: experimental study in prepuberal New Zealand White rabbits]

PURPOSE OF THE STUDY

The purpose of this study is to assess the consequences brought by selective dorsal arthrodesis of thoracic spine (T1-T6) to the growth of spine and thoracic volume in operated and sham-operated New Zealand White rabbits, between prepubertal age and the end of somatic growth, through the study of computerised tomography (CT) scans periodically carried out on them after arthrodesis surgery.

MATERIAL AND METHODS

Nine female rabbits were subjected to surgery for selective dorsal arthrodesis of the upper thoracic spine and three were sham-operated. Surgery was performed at age nine weeks, before the onset of puberty. Two "C"-shaped titanium bars were placed beside the spinous processes of the thoracic vertebrae to obtain a selective posterior arthrodesis of the first six thoracic vertebrae. Under general anesthesia, three CT scans were performed, 10 (t1), 55 (t2) and 139 (t3) days after surgery. Measures were obtained by Myrian Pro software for three different groups: group 1 with complete fusion, group 2 with incomplete fusion, group 3 sham-operated.

RESULTS

The total dorsal and ventral lengths of thoracic vertebral bodies in the spinal segment T1-T6 was smaller in group 1 and group 2 than in group 3, whereas no differences were observed between the three groups in the T7-T12 segment. The average of the dorsoventral/laterolateral thoracic diameter ratio at fused levels was less than 1 in group 1 as well as in group 2; on the contrary, in group 3 it was greater than 1. The sternum and lung volume grow less.

CONCLUSIONS

Vertebral arthrodesis in the treatment of progressive idiopathic scoliosis in prepubertal patients is not ideal, but is still a choice in treating major deformities of the spine. Postoperative assessment of spinal deformity is essential, feasible and recordable through CT scans. Dorsal arthrodesis in prepubertal rabbits changes thoracic growth patterns. In operated rabbits, the dorsoventral thoracic diameter grows more slowly than the laterolateral thoracic diameter. The sternum, the total lengths of thoracic vertebral bodies in the spinal segment T1-T6 and lungs grow less. The Crankshaft phenomenon is evident at the fused vertebral levels where there is a reduction of thoracic kyphosis.

[Experimental investigations on the growth of the vertebral column after dorsal spondylodesis (author's transl)]

To investigate the question which growth processes take place in dorsally stiffened vertebral regions, 4 vertebral segments each were dorsally fused in twenty-one pigs, using Harrington's distraction system in 20 cases. X-ray examination and histological measurements conducted with the aid of fluorochromosequential markings showed a more or less pronounced growth of the vertebral bodies and of the fusion mass in all animals. As a rule, the sequence of vertebral bodies overgrows the fusion mass in longitudinal direction, which always results in lordosis of the stiffened region. The longitudinal growth of the vertebral bodies, and even more so of the fusion mass, decreases with increasing postoperative observation time. The fusion mass shows actual internal growth which proceeds partly in diffuse manner in all directions, in the region of the clefts, i.e. as spondyloschisis, in some cases also in the same direction as with enchondral ossification associated with columnar chondrification. The growth of the fused mass does not depend on the formation of a pseudoarthrosis, although it is probably quantitatively promoted by pseudarthroses. The stimulus to longitudinal growth of the fused mass originates from the growing vertebral bodies, with probably varying influence of tensile and compressive forces.

[Initial experiences with subcutaneous Harrington distraction without spondylodesis in scoliosis]

We report on a special method in the treatment of scoliosis using subcutaneous Harrington-distraction without spondylodesis. We operated 14 patients in all who were between 7 and 12 years old, in average 10 2/12 years Indication is made if scoliosis is extremely progressive, if Cobb's measure is above 50 degrees, after unsuccessful conservative treatment also including orthosis and physiotherapy, or if patients appeared to late in our department. In this technique only two incisions to make are necessary to place the Harrington roots to the cranial and caudal end of the scoliosis curve. The Harrington root can be 'needled' in subcutaneously. When in times of further growth the amount of correction gets noticeably lost the cranial hook could be tightened or the Harrington root could be changed easily. We need an orthosis (Cheneau or Milwaukee) for after treatment until in a final operation with spinal fusion is made. This method has showed good results although we had to cope with a bad prognostic starting position.

Dissociation of somatic growth from segmentation drives gigantism in snakes

Body size is significantly correlated with number of vertebrae (pleomerism) in multiple vertebrate lineages, indicating that change in number of body segments produced during somitogenesis is an important factor in evolutionary change in body size, but the role of segmentation in the evolution of extreme sizes, including gigantism, has not been examined. We explored the relationship between body size and vertebral count in basal snakes that exhibit gigantism. Boids, pythonids and the typhlopid genera, Typhlops and Rhinotyphlops, possess a positive relationship between body size and vertebral count, confirming the importance of pleomerism; however, giant taxa possessed fewer than expected vertebrae, indicating that a separate process underlies the evolution of gigantism in snakes. The lack of correlation between body size and vertebral number in giant taxa demonstrates dissociation of segment production in early development from somatic growth during maturation, indicating that gigantism is achieved by modifying development at a different stage from that normally selected for changes in body size.