The primary ossification of the human fetal ischium: CT, digital-image analysis, and statistics.

PURPOSES: Details concerning the normal growth of the pelvic girdle in the fetus are of importance in the early detection of congenital defects. This study was executed to quantitatively evaluate the primary ossification center of the ischium with relation to its linear, planar and volumetric parameters. MATERIALS AND METHODS: Using methods of CT, digital-image analysis, and statistics, geometrical dimensions of the ischium's primary ossification center in 42 spontaneously aborted human fetuses (21 ♂ and 21 ♀) aged 18-30 weeks were calculated. RESULTS: With no sex and laterality differences, the best fit growth dynamics for the ischium's primary ossification center were displayed by the following functions: y = - 10.045 + 0.742 × age ± 0.013 (R2 = 0.97) for its vertical diameter, y = - 5.212 + 0.385 × age ± 0.008 (R2 = 0.97) for its sagittal diameter, y = - 36.401 + 0.122 × (age)2 ± 45.534 (R2 = 0.96) for its projection surface area, and y = - 1052.840 + 368.470 × ln(age) ± 12.705 (R2 = 0.91) for its volume. CONCLUSIONS: Neither male-female nor right-left differences are found for any of the morphometric parameters of the ischium's primary ossification center. With relation to fetal ages in weeks, the ischium's primary ossification center grows proportionately in vertical and sagittal diameters, second-degree polynomially in projection surface area, and logarithmically in volume. The quantitative findings of the ischium's primary ossification center are considered age-specific reference data of relevance in the diagnostics of innate defects.

Fetal Development of the Human Obturator Internus Muscle With Special Reference to the Tendon and Pulley.

To examine the development of the tendon pulley of the obturator internus muscle (OI), we observed paraffin sections of 26 human embryos and fetuses (∼6-15 weeks of gestation). The OI was characterized by early maturation of the proximal tendon in contrast to the delayed development of the distal tendon. At 6 weeks, the ischium corresponded to a simple round mass similar to the tuberosity in adults. At 8 weeks, before development of the definite lesser notch of the ischium, initial muscle fibers of the OI, running along the antero-posterior axis, converged onto a thick and tight but short tendon running along the left-right axis. Thus, at the beginning of development, the OI muscle belly and tendon met almost at a right angle. At 10 weeks, the OI tendon extended inferiorly along the sciatic nerve, but the distal part remained thin and loose and it was embedded in the gluteus medius tendon. At 15 weeks, in association with the gemellus muscles, the distal OI tendon was established. The mechanically strong sciatic nerve was first likely to catch the OI muscle fibers to provide a temporary insertion. Next, the ischium developing upward seemed to push the tendon to make the turn more acute along the cartilaginous ridge. Finally, the gemellus muscle appeared to provide inferior traction to the OI tendon for separation from the gluteus medius to create the final, independent insertion. Without such guidance, the piriformis tendon first attached to the OI tendon and then merged with the gluteus medius tendon.

The developing juvenile ischium: macro-radiographic insights.

Despite the importance of the human pelvis as a weight-bearing structure, there is a paucity of literature that discusses the development of the juvenile innominate from a biomechanical perspective. This study aims to add to the limited body of literature pertaining to this topic through the qualitative analysis of the gross architecture of the human ischium during the juvenile period. Macro-radiographs of 55 human ischia ranging from 28 intra-uterine weeks to 14 years of age were examined using intensity-gradient color mapping to highlight changes in gross structural morphology with increasing age. A clear pattern of maturation was observed in the juvenile ischium with increasing age. The acetabular component and ramus of the ischium consistently displayed low bone intensity in the postnatal skeletal material. Conversely the posterior body of the ischium, and in particular the ischial spine and lesser sciatic notch, exhibited increasing bone intensity which first arose at 1-2 years of age and became more expansive in older cohorts. The intensity patterns observed within the developing juvenile ischium are indicative of the potential factors influencing the maturation of this skeletal element. While the low intensity acetabular fossa indicates a lack of significant biomechanical interactions, the posterior increase in bone intensity may be related to the load-bearing nature of the posterior ischium.

Joint shape morphogenesis precedes cavitation of the developing hip joint.

The biology and mechanobiology of joint cavitation have undergone extensive investigation, but we have almost no understanding of the development of joint shape. Joint morphogenesis, the development of shape, has been identified as the 'least understood aspect of joint formation' (2005, Birth Defects Res C Embryo Today 75, 237), despite the clinical relevance of shape morphogenesis to postnatal skeletal malformations such as developmental dysplasia of the hip. In this study, we characterise development of early hip joint shape in the embryonic chick using direct capture 3D imaging. Contrary to formerly held assumptions that cavitation precedes morphogenesis in joint development, we have found that the major anatomical features of the adult hip are present at Hamburger Hamilton (HH)32, a full day prior to cavitation of the joint at HH34. We also reveal that the pelvis undergoes significant changes in orientation with respect to the femur, despite the lack of a joint cavity between the rudiments. Furthermore, we have identified the appearance of the ischium and pubis several developmental stages earlier than was previously reported, illustrating the value and importance of direct capture 3D imaging.

The evolution, development and skeletal identity of the crocodylian pelvis: revisiting a forgotten scientific debate.

Unlike most tetrapods, in extant crocodylians the acetabulum is formed by only two of the three skeletal elements that constitute the pelvis, the ilium, and ischium. This peculiar arrangement is further confused by various observations that suggest the crocodylian pelvis initially develops from four skeletal elements: the ilium, ischium, pubis, and a novel element, the prepubis. According to one popular historical hypothesis, in crocodylians (and many extinct archosaurs), the pubis fuses with the ischium during skeletogenesis, leaving the prepubis as a distinct element, albeit one which is excluded from the acetabulum. Whereas the notion of a distinct prepubic element was once a topic of considerable interest, it has never been properly resolved. Here, we combine data gleaned from a developmental series of Alligator mississippiensis embryos, with a revised interpretation of fossil evidence from numerous outgroups to Crocodylia. We demonstrate that the modern crocodylian pelvis is composed of only three elements: the ilium, ischium, and pubis. The reported fourth pelvic element is an unossified portion of the ischium. Interpretations of pelvic skeletal homology have featured prominently in sauropsid systematics, and the unambiguous identification of the crocodylian pubis provides an important contribution to address larger scale evolutionary questions associated with locomotion and respiration.

Avian pelvis originates from lateral plate mesoderm and its development requires signals from both ectoderm and paraxial mesoderm.

The pelvic girdle is composed of three skeletal elements: ilium, pubis, and ischium. In comparison with other parts of the postcranial skeleton, its development is not well known to date. To elucidate the embryonic origin of the avian pelvic girdle and the signaling centers that control its development, we have performed extirpation and quail-to-chick grafting experiments. The results reveal that the entire pelvic girdle originates from the somatopleure at somite levels 26 to 35. No somitic cell contribution to skeletal elements of the pelvis has been detected. Removal of the surface ectoderm covering the lateral plate mesoderm has revealed that ectodermal signals control the development of the pelvic girdle, especially the formation of the pubis and ischium. The impaired development of the ischium and pubis correlates with the downregulation of Pax1 and Alx4, two transcription factors that control the normal development of the ischium and pubis. Although of somatopleural origin, the development of the ilium depends on somitic signals. Insertion of a barrier between somites and somatopleure disrupts the expression of Emx2 and prevents normal development of the ilium but does not affect the expression of Pax1 or Alx4 and the development of the pubis and ischium. Thus, the development of the ilium, but not of the pubis and ischium, depends on somitic and ectodermal signals.

Fetal bony pelvis in the bladder exstrophy complex: normal potential for growth?

OBJECTIVES: To provide the first look at the bony histologic features of fetuses with the exstrophy complex, specifically evaluating the endochondral ossification, stage of development, and microscopic potential for normal growth. METHODS: Three fetuses between 28 and 30 weeks of gestation, one with classic bladder exstrophy, one with cloacal exstrophy, and one control, were obtained from France. The bony pelves were dissected and preserved in formalin, and multiple representative sections were sliced from all pelvic areas: pubis, ischium, ilium, and sacrum. These slices were sequentially processed as slides, stained with hematoxylin-eosin, and evaluated microscopically for histologic changes, developmental stage, and degree of endochondral ossification. RESULTS: All slides from the three specimens showed cartilage analogue with endochondral ossification. Histologically the exstrophy specimens were identical to the control and appeared completely normal; bone development was occurring at an expected rate with the potential for continued normal growth. CONCLUSIONS: These new findings illustrate that fetal bone in the exstrophy complex displays normal microscopic growth patterns and unhindered endochondral ossification at 28 weeks of gestation, well beyond the embryologic period. With no evident microscopic bony defect, the gross bony anomalies in exstrophy should be surgically correctable, leading us to conclude that early reapproximation of the physiologic shape of the pelvis could lead to more normal gross bone growth, decreased shortage of bone, and a more appropriate distribution of the mechanical and developmental forces on a closed, normally functioning pelvic ring.

[Expression of sexual dimorphism in the fetal pelvic girdle]. / Expression du dimorphisme sexuel sur le bassin du foetus.

The objective of this study was to analyse the development of the foetal pelvis in order to define normal anatomic reference values as a function of gender and gestational age. The study population included 500 stillborn foetuses between the gestational ages of 18 and 41 weeks. Those foetuses without known demographic histories were strictly excluded. For each case studied, an AP radiograph was performed with the following parameters measured by two independent observers: pelvic width, inter-iliac width, inter-sciatic nodes, inter-pubic width and bi-ischial width. The correlation between these radiographic measurements and the gestational age as well as the gender was analysed. The result indicated that the inter-ischiatic distance is significantly greater in the female foetus after the 26-27th week of gestation (P < 0.0062). Standard growth for the female and the male foetal pelvis is proposed with potential application in the study of normal and pathological development of the foetus.

MR imaging of the ischiopubic synchondrosis.

The ischiopubic synchondrosis (IPS) is a temporary joint, occurring in childhood prior to fusion of the ischial and pubic bones. On conventional radiographs this tumor-like appearance is a well known normal anatomic variant, however, there are no reports in the literature of the appearance of IPS on MRI. Therefore the purpose of this study was to evaluate typical magnetic resonance features of the IPS. All pelvic MRIs from 1/1992 to 4/1998 of children ranging in age from 4 to 16 years, who were scanned for reasons other than bone disorders, were retrospectively investigated. Twenty-eight children were included and the morphologic appearance of IPS on MRI was evaluated. Seventeen (61%) of these 28 children had the following findings of IPS on MRI. Listed in order of frequency we found signal alteration of the ischiopubic fusion zone [hyperintense on T(2) with fat-saturation (89%) or STIR (74%), hypointense on T(1) (71%)], fibrous "bridging" (68%) [hypointense band on all sequences in perpendicular orientation to the axis of the inferior pubic ramus], fusiform swelling (68%), signal alteration of the adjacent soft tissue (57%) and irregular margins (56%). In 10 children contrast enhanced scans were available for evaluation, showing contrast enhancement of the bone marrow in 83.3% and of the adjacent soft tissue in 66.7%. Fusiform swelling of the ischiopubic fusion zone, signal alteration and contrast enhancement of both the bone marrow and the adjacent soft-tissue are characteristic features of the IPS on MRI, which may be due to mechanical stress at this temporary joint. These features are nonspecific and may resemble tumor, infection or trauma. Fibrous "bridging" was the only finding on MRI, which has not been described for any other entity and thus, it seems to be a characteristic MRI-feature.