Anatomy of a duplicated human foot from a limb with fibular dimelia.

At birth, a patient presented with a right lower limb featuring preaxial polydactyly and fibular dimelia with a complete absence of the tibia. Radiographic studies of the patient's foot revealed a duplicated tarsus with eight metatarsals and toes. The three preaxial toes were surgically removed at 1 year of age. A hallux and four normal-appearing postaxial toes remained. The foot was amputated when the patient was 3 years old. Dissection of the amputated foot revealed that the muscles of the dorsum were normal, except that the tendon of the extensor hallucis brevis muscle inserted into both the hallux and toe 2, rather than only into the hallux. The few abnormalities observed among the muscles on the plantar surface of the foot included absence of the insertions of the tibialis posterior and the abductor hallucis muscles. In addition, the two heads of the adductor hallucis muscle inserted abnormally into the medial (tibial) side of metatarsal 1, rather than into the lateral side. These various muscular anomalies, in addition to the mirror duplication of the foot with the presence of only a single metatarsal 1, leads us to propose that this metatarsal probably represents two lateral (fibular) halves that form a laterally duplicated bone. Although the dorsalis pedis artery was present on the dorsal surface of the foot, most of its derivatives were absent. This artery did give rise to a supernumerary medial branch that ended abruptly in the connective tissue (presumably postsurgical scar) at the medial border of the foot. This branch may have represented a duplicated dorsalis pedis artery associated with the duplicated preaxial portion of the foot. The arteries on the plantar surface of the foot were normal. Even though some anomalies in the pattern of the cutaneous innervation were observed, the nerves of the foot were largely normal. The gross and radiographic anatomy of this specimen and the radiographic anatomy of the leg suggest that some teratogenic event occurred when developmental specification reached the level of the future knee. The teratogenic event, which probably occurred early in the fifth week of development, may have caused damage that led to a lateral duplication of both the leg and the foot with the absence of some of the most medial structures. Teratology 60:272-282, 1999.

Confirmation of arterial deficiencies in a limb with necrosis following clubfoot surgery.

This study describes postoperative necrosis of the hallux and first ray in a child with clubfoot. Arteriography performed on this child's lower limbs demonstrated, in the operated leg, hypoplasia of both the anterior and posterior tibial arteries and failure of the dorsalis pedis artery to traverse the tarsus and complete the deep plantar arch. Previously, congenital vascular deficiency was suggested to predispose such operated limbs to necrosis. These findings confirm the association between vascular deficiency and necrosis. In this present study, the metabolic demands of wound healing were sufficient in a limb with vascular deficiency to cause localized distal hypoperfusion leading to cyanosis and necrosis of the hallux and medial foot.

Hematomas and limb skeletal malformations in chicken embryos following exposure to 5-fluoro-2-deoxyuridine.

Vascular injury or interruption may play a role in vertebrate limb teratogenesis. Since 5-fluoro-2'-deoxyuridine (FdU) can cause vascular injury in the murine limb and skull prior to the appearance of skeletal malformations in these structures, we studied the effects of this chemical on skeletal development in the chick embryo and noted any vascular injury. The yolk sacs of day three chick embryos (Hamburger and Hamilton states 17-19) were injected with solutions of vary concentrations of FdU in saline. The embryos developed until the 10th day of incubation when they were fixed for study. Uninjected, saline injected, and sham injected control embryos were similarly fixed. Upon gross inspection, frequent diffuse and saccular hematomas, as well as fluid-filled blisters, were noted in the limbs of embryos treated with FdU. After the embryos were fixed and cleared, and the skeletons stained, significant skeletal malformations were observed in these limbs. Bony elements of both the upper and lower limbs were affected in at least some of the embryos. The combination of FdU-induced hematomas and blisters with associated skeletal malformations in the same regions of some embryos suggests a relationship between these phenomena.

Embryonic hypertension following exposure to teratogenic doses of 5-fluoro-2'-deoxyuridine.

The teratogenicity of 5-fluoro-2'-deoxyuridine (FdU) is well established. Previously, we have demonstrated that teratogenic doses of FdU produce hematomas and suggested that those hematomas produced skeletal malformations in chicken embryos. In this study, the cardiovascular effects of teratogenic doses of FdU in chicken embryos were studied. A dose of either 0.026 micrograms FdU or 0.030 micrograms FdU was injected into the yolk sacs of fertile chicken eggs containing embryos at Hamburger and Hamilton stages 17-19 of development. The embryos were then returned to the incubator. Aortic systolic and diastolic blood pressure, blood velocity and heart rate were measured at stages 21, 24 or 27 using a servonull system and Doppler ultrasound. In addition, mean arterial blood pressure, blood flow, and stroke volume were calculated from these data. Similar data were also recorded from uninjected and saline injected control embryos. Systolic and mean arterial blood pressures were significantly increased in FdU-treated embryos at stage 27. The other parameters measured or calculated were not significantly different from control embryos. Our study suggests that elevated systolic blood pressure in chicken embryos treated with FdU may lead to hematoma formation and subsequent birth defects.

Extent of duplication in lower-limb malformations suggests the time of the teratogenic insult.

Investigations of vertebrate limb development have suggested that a process called "specification" instructs the cells of the future limb as to which tissues they should form. This process proceeds in a wave-like manner, starting at the most proximal levels of the future limb and ending at its distal tip. Human limb specification probably occurs during the fourth and fifth weeks of development. It is proposed that human limb duplications result from errors of specification and, furthermore, that the more distal the duplication, the later the occurrence of the teratogenic event during the specification process. Therefore, among human lower limbs with duplications, one may be able to estimate the relative time of the teratogenic event by comparing the levels at which the duplications occur.

Somite pattern regulation in the avian segmental plate mesoderm.

Previous experimental evidence suggested that the avian segmental pattern is already specified in the apparently unsegmented paraxial (segmental plate) mesoderm, but is susceptible to modification and reconstitution. We explored capacities of embryos to alter the specified pattern and restore it after disruption. In control experiments, right segmental plates of chicken or Japanese quail embryos were removed after about 48 hours of incubation and immediately replaced. Hensen's node and the primitive streak were removed to halt further segmental plate formation and the embryos were cultured for about 18 hours more. Somite numbers on the operated and unoperated sides were nearly identical (r = 0.904, n = 31, P < 0.001); no species differences were noted. Right segmental plates of chicken hosts were then replaced with right segmental plates from quail donors. The numbers of somites formed by donors and grafts were not significantly correlated (r = 0.305, n = 30, P < 0.1), but the correlation between the graft and the host's unoperated side was significant (r = 0.666, n = 30, P < 0.001). The host is therefore able to alter the number of somites formed by the graft to one more compatible with the host's pattern. From orthostereoscopic reconstructions, it appeared that the location and size of somites could also be adjusted by the host. Similar results were obtained for tandem grafts of anterior halves of segmental plates and for grafts of minced segmental plates, though in the latter case contact with tissues near the midline was necessary for somite formation.

Magnetic resonance imaging study of the structure of the yolk in the developing avian egg.

Magnetic resonance imaging (MRI) techniques were used to study the morphology of the latebra and concentric rings seen in the yolk of White Leghorn eggs during development of the avian embryo. Previous studies of the macroscopic structure of avian yolk have revealed the latebra, a vase-shaped structure beneath the blastoderm composed of white yolk. The bulbous portion in the center of the yolk is termed the body of the latebra. The thinner portion extending toward the blastoderm is referred to as the neck of the latebra. As the neck of the latebra approaches the blastoderm, it flares out to become the nucleus of Pander. The remainder of the yolk often features alternating concentric layers of white and yellow yolk. These layers, which appear as rings in sections, are thought to represent the daily accumulation of yolk during oogenesis. In this study eggs were imaged with a single slice spin echo sequence using MRI parameters that maximized the visualization of the latebra and concentric rings in the egg yolk. Some experiments were conducted for 2 to 3 day periods with eggs kept in the bore of the magnet using a small incubator that was constructed using a temperature-controlled water pump. The concentric rings of the yolk and the body of the latebra flatten and become more elliptical during development. The neck of the latebra becomes shorter and disappears around the 7th day of incubation. The body of the latebra starts to become incorporated into the embryo at about the 7th day of incubation and usually disappears by the 13th day. The concentric rings are no longer visible as distinct entities at this time. Histochemical procedures carried out as a result of MRI findings indicate that the latebra is an iron-rich structure.

Consistent arterial abnormalities associated with a variety of congenital malformations of the human lower limb.

A number of seemingly unrelated congenital deformities of the lower limb have been presented which include clubfoot, fibular deficiency, tibial aplasia, and diplopodia. Although the bony morphology in these limbs is quite different, they all share a strikingly similar arterial pattern, that being deficiency or absence of the anterior tibial artery, and of its derivative, the dorsal pedis artery. Since all of these diverse conditions share a similar aberrant arterial pattern, we suspect that the arterial changes are important in the pathogenesis of those conditions. Study of the soft tissue anatomy of these specimens suggests that the etiologic teratogenic event occurred early in embryonic development. In those limbs that contain the remnant of a missing structure, it is concluded that injury occurred after the mesenchyme was instructed to form that structure. These are termed "post-specification" defects. In those circumstances where limb duplication occurs, the injury affected the signal before instruction of mesenchyme to develop into a specific structure was completed and these abnormalities are termed "pre-specification" malformations. The musculotendenous and neurologic abnormalities seem to be reactive to the pre-existing bony pattern.

The anatomy of a human foot with missing toes and reduplication of the hallux.

Detailed dissection of a malformed human foot was performed so that the skeletal and soft tissue anomalies in the foot could be compared and contrasted with those found in three previous specimens that we have dissected. The specimen described here consisted of a foot with a reduplicated hallux and two missing toes. Study of the bones revealed a wide medial metatarsal that articulated with a reduplicated hallux. There were two complete lateral toes with normal bones. Two toes and their metatarsals were missing with no remnants. The arterial pattern was similar to those seen previously by us. The dorsalis pedis artery was absent and the plantar arch was abnormal in that it did not terminate with a dorsal anastomosis. There was an extra lateral branch of the medial plantar artery. The digital arteries to the missing toes were also missing. The nerves of the foot were normal with the exception of an extra lateral branch from the medial plantar nerve. As with the arteries, the nerves to the missing toes were also missing. The muscles and tendons on the dorsal surface of the foot were all present but several of the tendons were inserted in abnormal locations in apparent response to the abnormal bone pattern. Most of the muscles and tendons of the plantar surface were present with the exception of the flexor hallucis longus and brevis muscles. Several of the remaining tendons apparently were influenced by the abnormal skeletal pattern and the missing muscles to become inserted on or near the replicated phalanges of the hallux. The anatomy of this specimen suggests that the teratogenic event occurred when specification of the limb bud mesoderm cells had progressed to the level of the distal tarsus and was located in the region that normally would have formed the metatarsals and phalanges of Toes 2 and 3. Further, we propose that the association between skeletal anomalies and arterial deficiencies has aetiological significance. We hypothesise that the abnormal arterial pattern put the limb at risk of teratogenic damage by reducing the number of collateral blood supply routes and that some event, such as extravasation of blood or embolisation, compromised the blood flow in the remaining blood vessels. These events could have resulted in both general shortening of the limb and the specific defects observed in this foot.

Necrosis leading to amputation following clubfoot surgery.

Amputation after clubfoot surgery is a rare and catastrophic complication. This case report involves an amputation necessitated by postoperative necrosis on the medial side of the foot. To our knowledge, only one brief published report of necrosis following clubfoot surgery exists in the literature, and that report contains little clinical information. Although we know of several additional cases of necrosis following clubfoot surgery, the details of these cases remain unavailable to us for publication. The clubfoot deformity is almost always associated with vascular deficiencies involving the anterior tibial and dorsalis pedis arteries, as well as their derivatives. Since the area of necrosis in this case report coincided with the anatomic distribution of the derivatives of the congenitally reduced or absent dorsalis pedis artery, we suggest that insufficient blood flow to the dorsal and medial sides of the foot, and to the hallux contributed to the necrosis. In our opinion, the surgeon should assume that an abnormal vascular pattern, as described here, is present unless proven otherwise.

Arterial abnormalities in talipes equinovarus as assessed by angiography and the Doppler technique.

Preoperative angiography in 30 uncorrected clubfeet demonstrated abnormal vascular patterns in all but two limbs with hypoplasia or premature termination of the anterior tibial and medial plantar arteries in the remainder. Postoperative Doppler studies in nine of the limbs with abnormal vessels indicated that these arteries were present. We suggest that the continuous-wave Doppler technique is less useful for identifying major arteries than either dissection or angiography. Furthermore, arterial dysgenesis may play a role in the etiology of clubfoot. Since the posterior tibial artery usually provides the sole arterial supply to the foot, this vessel must be preserved at surgery and during subsequent ankle dorsiflexion.

Soft tissue anomalies in a patient with congenital tibial aplasia and talo-calcaneal synchrondrosis.

We have carried out the third in a series of anatomical dissections of amputated congenitally deformed human limbs in an attempt to determine the etiological relationship between the bony and soft tissue anomalies. This specimen consisted of a limb with congenital tibial aplasia and an adducted foot with five toes. The arterial and nerve patterns were reminiscent of those seen previously by us. The arteries were characterized by absence of the anterior tibial artery and an incomplete plantar arch. The superficial peroneal nerve terminated at the ankle. Extra branches from the sural, deep peroneal, and medial plantar nerves supplied branches to the dorsum of the foot. There were two extra muscles in the leg. The remaining muscles were normal, with the exception that most muscles normally inserting on the plantar surface of the foot inserted instead into a common tendon sheet. The tibia was replaced by a tendinous band, and the talus and calcaneus were united by a complete synchondrosis. The contralateral limb clinically appeared to have a clubfoot. The combination of an absent anterior tibial artery and an incomplete plantar arch is consistent with our theory that a reduced number of vessels puts the embryonic limb at increased risk of congenital defects due to the reduction in the number of collateral blood routes. Some event, such as extravasation of blood or embolization, may concurrently or subsequently compromise blood flow in the remaining vessels. We have previously observed abnormal arterial patterns similar to that described above in limbs having absence of the tibia and in other patients having clubfeet. The presence of abnormal arterial patterns in a limb with absence of the tibia and a contralateral limb with clubfoot suggests that absent tibia and clubfoot may be etiologically related.

Morphological and experimental studies of the somitomeric organization of the segmental plate in snapping turtle embryos.

The segmental plate mesoderm of snapping turtle embryos (Chelydra serpentina) was examined with stereoscanning electron microscopy imaging. A metameric pattern was detected along the entire length of the segmental plates. This pattern consisted of a tandem sequence of mesodermal units, called somitomeres. Each somitomere was oval to cubic in shape and the processes of the constituent mesodermal cells tended to be arranged in concentric rings about the centre of the somitomere. Several experiments from a previous study (Packard, 1980b) of snapping turtle segmental plates were repeated, but, instead of culturing the explants and observing the numbers of somites that formed, the explants were fixed immediately for scanning electron microscopy and the number of somitomeres was counted. The segmental plates were found to contain an average of 6.5 +/- 0.7 somitomeres, which is almost identical to the average number of somites formed by such segmental plates when cultured (6.6 +/- 1.2). Furthermore, the number of somitomeres was identical in right and left explants removed from the same embryo, and the number of somitomeres was consistent regardless of the length of the segmental plate. Both of these observations are identical to those made previously for somite formation in culture. This association between numbers of somitomeres and somites strongly suggests that one gives rise to the other. Finally, it was demonstrated that for each somite formed by a segmental plate in culture, the segmental plate contained one less somitomere. This showed in a direct manner that turtle somitomeres become somites. It was concluded that the segmental plate mesoderm of snapping turtle embryos is already segmented, and that the 'segmentation' seen under a dissecting microscope is actually the final stage of somitomere differentiation into an epithelial somite.

Morphogenesis of the cranial segments and distribution of neural crest in the embryos of the snapping turtle, Chelydra serpentina.

Recent studies of the heads of vertebrates have shown a primitive pattern of segmentation in the mesoderm and neural plate not previously recognized. The role of this pattern in the subsequent distribution of cranial crest and the development of branchial arches and cranial nerves, may resolve century-old arguments about the evolution of vertebrate segmentation. In this study, we examine the early embryonic development of the cranium of a primitive amniote, the snapping turtle, with the SEM. We show that the paraxial mesoderm cranial to the first-formed somites is segmented and that this pattern is based on somitomeres, similar to those described in the embryos of chick and mouse. Seven contiguous pairs of somitomeres comprise the "head mesoderm"; the first pair of somites actually arise from the eighth pair of somitomeres added to the axis. Cranial somitomeres are associated with specific brain regions, in that the first pair lie adjacent to prosencephalon, the second and third pair are adjacent to the mesencephalon, and the fourth, fifth, sixth, and seventh pair of somitomeres lie adjacent to individual neuromeres of the rhombencephalon. Prior to the closure of the anterior neuropore, cranial neural crest cells first emerge from the mesencephalon and migrate onto the second and third somitomeres. Shortly thereafter, neural crest cells emerge at more caudal levels of the rhombencephalon, beginning at the juncture of the fifth and sixth somitomeres. Eventually, neural crest originating from the mesencephalon spreads caudally as far as the fourth somitomere, leaving a gap in crest emigration adjacent to the fifth somitomere. The otic placode develops from the surface ectoderm covering the sixth and seventh somitomeres, and the adjacent rhombencephalic neural crest moves around the cranial and caudal edge of the placode. At more caudal levels, rhombencephalic crest cells merge with cervical crest populations to form a continuous sheet over the somites. By the time the anterior neuropore closes, some of the mesencephalic crest cells return from the paraxial mesoderm to spread onto the rostral wall of the optic vesicle and future telencephalon. The segmentation of the mesoderm and patterned distribution of cranial neural crest seen in snapping turtle embryos, further strengthens the argument that the heads of amniotes are derived from a common metameric pattern established early during gastrulation.

The anatomy of a congenitally short limb with clubfoot and ectrodactyly.

Previous studies have shown an association between an abnormal arterial pattern and bony malformations of the human lower limb. We have dissected and performed arteriography on a congenitally short limb with ectrodactyly in order to examine the relationship between arterial pattern and bony anomalies in another type of deformity. The bony anomalies were a combination of short femur, tibia and fibula, clubfoot with tarsal synostoses, metatarsal absence, ectrodactyly, and a bifid hallux. The arterial pattern was characterized by deficiency of the anterior tibial artery and absence of the plantar arch. Major muscular anomalies were noted in the foot only; the muscles of the missing toe were absent and any muscles that normally cross the midventral line were either missing or failed to cross the midline. The superficial peroneal nerve failed to enter the dorsum of the foot and its sensory distribution was assumed by an extra branch of the sural nerve. The most severe abnormalities of the bones, muscles, arteries, and nerves occurred near the midventral line of the foot. We hypothesize that the abnormal arterial pattern put the limb at risk of teratogenic damage by reducing the number of collateral blood supply routes. We suggest that some event, such as extravasation of blood or embolization, compromised the blood flow in the remaining blood vessels and that this event resulted in both a general shortening of the limb and the specific defects observed in the foot. We interpret the anatomy to be consistent with the vascular teratogenic event occurring near the midline of the foot during the fifth week of embryonic development.

Arterial anatomy of chicken embryo and hatchling.

The arterial pattern in chicken hatchlings was investigated by microangiography and microscopic analysis of cleared specimens. The hatchling arterial pattern was found to resemble strongly the pattern that has been described for the adult chicken. Several minor variations in this pattern were found which were probably due to species, strain, or age differences. We also investigated the arterial pattern in chicken embryos aged 4.5 to 21 days of incubation. The hatchling pattern was fully developed by approximately 8 days of incubation. Some similarities were found to exist between the embryonic pattern in the chicken embryo and that described for the human embryo.

An experimental study of the somitomeric organization of the avian segmental plate.

The segmental plate mesoderm of chicken and Japanese quail embryos HH stages 9 to 16 was studied with scanning electron microscopy (SEM) imaging. The segmental plates were found to exhibit a metameric pattern consisting of tandemly stacked somitomeres. It was found that the numbers of somitomeres in segmental plates removed from the same embryo were nearly identical. Furthermore, the number of somitomeres in a segmental plate was found to be quite consistent (10.0 +/- 1.5) and independent of the length of the segmental plate. These results are very similar to those obtained in previous experimental studies in which "prospective somites" were detected in avian segmental plates. Further experiments showed that for each somite that is formed by a cultured segmental plate-containing explant, the somitomere complement of the segmental plate is reduced by one. It was concluded that the segmental plate mesoderm is already organized into a metameric pattern consisting of somitomeres and that the somitomeres undergo further morphogenesis to become somites. The specification of the somite pattern in birds may occur at the level of Hensen's node and the cephalic primitive streak.