Determination and classification of cutaneous innervation of the dorsum of the foot in foetal cadavers.

BACKGROUND: The aim of this study is to determine cutaneous innervation of the dorsum of the foot on foetal cadavers. MATERIALS AND METHODS: In this study. 200 limbs from 100 embalmed foetuses (54 males and 46 females) were studied in Anatomy Laboratory. Contributions of medial, lateral and intermediate dorsal cutaneous nerves (MDCN, LDCN and IDCN) of the foot were identified. RESULTS: Cutaneous innervation of the dorsum of the foot was classified into five types. Type I (75%) where MDCN innervated medial border of the foot and second interdigital cleft; IDCN innervated third, fourth and fifth interdigital clefts; and LDCN innervated the lateral border of the foot. Type II (21%) where MDCN innervated medial border of the foot, second and third interdigital clefts; IDCN innervated fourth and fifth interdigital clefts; and LDCN innervated the lateral border of the foot. Type III (1.5%) where saphenous nerve innervated medial border of the foot; MDCN innervated second and third interdigital clefts; IDCN innervated fourth and fifth interdigital clefts; and LDCN innervated the lateral border of the foot. Type IV (1.5%) was similar to type I, with an extra connection between the MDCN and IDCN on the dorsum of the foot. Type V (1%) where superficial fibular nerve innervated medial border of the foot, and second, third and fourth interdigital clefts; and sural nerve innervated fifth interdigital cleft and lateral border of the foot. CONCLUSIONS: The present study provides a new classification for the cutaneous innervation of the dorsum of the foot.

Formation of the sural nerve in foetal cadavers.

The purpose of this study was to provide a morphologic description and assessment on the formation level of the sural nerve (SN) and its components. Also we aimed to reveal histological features of the SN components. An anatomical study of the formation of the SN was carried out on 100 limbs from 50 embalmed foetuses. The results showed that the SN was formed by the union of the medial sural cutaneous nerve (MSCN) and the peroneal communicating branch (PCB) in 71% of the cases (Type A); the MSCN and PCB are branches of the tibial and common peroneal nerve (CPN) or lateral sural cutaneous nerves (LSCN), respectively. Formation level of the SN was at the distal third of the leg in 43% of the cases, at the middle third of the leg in 46% of the cases, and at the upper third of the leg in 11% of the cases. The PCB originated in the CPN in 68% and the PCB originated in the LSCN in 3% of the cases. The SN was formed only by the MSCN in 20% of the cases (Type B). Type C was divided into four subgroups: in the first group the PCB and fibres of the posterior femoral cutaneous nerve joined the MSCN in 4% of cases; in the second group the MSCN, PCB, and sciatic nerve did not unite and coursed separately in 1% of cases; in the third group the SN arose directly from the sciatic nerve alone and the MSCN made a little contribution in 2% of cases; and in the fourth group the PCB, fibres of the sciatic nerve, and the MSCN formed the SN in 1% of the cases. The SN was formed only by the PCB in 1% of the cases (Type D). Distances of the formation level of the SN to the intercondylar line and the lateral malleolus were measured and also noted. A detailed knowledge of the anatomy of the SN and its contributing nerves are important in many interventional procedures.

Peculiarities of the sural nerve complex morphologic types in human fetuses.

The sural nerve is the most frequently used sensory nerve in nerve transplantation. It can be transplanted alone or together with the other elements of the neurovascular stalk within the superficial sural flap. The aim of this study was to define the morphologic types of the sural nerve complex, as well as to describe their specific characteristics. Microdissection was performed on 100 human fetuses (200 calves) after 10% formalin fixation. Five morphologic types of sural nerve complex with different incidence were defined. Two morphologic types dominated: type I (58.5%) in which the sural nerve was formed by merging of a fibular communicating branch and the medial sural cutaneous nerve, and type III (26%) in which the medial sural cutaneous nerve took over the function of the sural nerve. Other morphologic variations were less common.

Extent of nociceptive dermatomes in adult rats is not primarily maintained by axonal competition.

Nociceptive innervation territories of individual peripheral and spinal nerves in the skin of the rat hind paw were investigated. In addition, the hypothesis that competitive interactions among the axons from adjacent dorsal root ganglia (DRG) play an important role in maintenance of dermatomal extent in adult animals was tested. The area of innervation territories of individual spinal and peripheral nerves was determined by nociceptive pinch test of the skin after extirpation of adjacent DRGs or transection of adjacent peripheral nerves, respectively. Positions of nociceptive dermatomes and innervation territories of peripheral nerves were similar to the territories innervated by the C-fibers described earlier by dye extravasation technique. In contrast, our results convincingly demonstrated substantial overlap of nociceptive (probably A delta) fibers from adjacent dermatomes in which the autonomous innervation areas were only about one-half of the maximal areas. Nociceptive territories of peripheral nerves overlapped, too. Accordingly, we could find no autonomous innervation area of the sural nerve. Two weeks after extirpation of adjacent DRGs, the area of each of the isolated dermatomes L3, L4, and L5 increased only by about 10%, and it did not change detectably during the next 6 months. The results of our study (a) support the view that innervation fields supplied by the nociceptive (probably A delta) fibers are greater and display more overlap than those supplied by the C-fibers of the same nerve and (b) suggest that axonal competition for innervation territory is not decisive for maintenance of dermatomal borders in the adult rat.

Anatomia cirugica do nervo sural / Surgical anatomy of the sural nerve

O nervo sural e comumente utilizado como enxerto nas reconstrucoes de nervos porque apresenta acesso facil e sequela minima, apos sua retirada. Apesar de apresentar constancia na sua localizacao topografica, as variacoes anatomicas do nervo sural sao frequentes. Assim, foram dissecadas 38 pernas em 19 cadaveres visando determinar o padrao de formacao do complexo nervo sural. Os dados obtidos foram divergentes da literatura, quando a frequencia de ocorrencia dos dois padroes classificamente conhecidos (Padrao I e II). Alem disso, tambem foi possivel identificar dois outros padroes (Padrao III e IV) de formacao do nervo sural, que ainda nao havia sido descrito previamente. O Padrao I, no qual o servo sural e proveniente da uniao do nervo cutaneo sural medial e do nervocomunicante poroneal, foi encontrado em 21 por cento dos casos. A frequencia na literatura e de 65,6 por cento a 80 por cento. O Padrao II, no qual o nervo sural origina-se a partir do nervo cutaneo sural medial com frequencia na literatura de 20 a 34,2 por cento, foi identificado em 52,6 por cento dos casos...

A morphometric study of human fetal sural nerve.

A morphometric study was performed on sural nerves from human fetuses at 15 to 36 weeks postovulation. There were no myelinated fibres at 15 and 16 weeks, but by 21 weeks there were 5,000/mm2, rising to 25,000/mm2 at 36 weeks. During the fetal period, the mean myelin lamellar count trebled and the g ratio (axon diameter: total fibre diameter) decreased from 0.90 to 0.75, although the axon diameter of myelinated fibres did not increase. The smallest myelinated axon diameter was 0.63 micron, whereas the largest unmyelinated axon in a 1:1 relationship with a Schwann cell was 2.83 micron, suggesting that axon size is unlikely to be the only stimulus for myelination. The density of unmyelinated axons that were the sole occupants of a Schwann cell fell considerably between 23 and 33 weeks, while the ratio of total unmyelinated axons to myelinated fibres decreased from 82:1 at 21 weeks to 6:1 at 36 weeks. Data for Schwann cell nuclear density and percentages of fibres cut through the nucleus are also presented.

Changes of the ratio between myelin thickness and axon diameter in the human developing sural nerve.

Axon caliber and myelin sheath thickness of individual nerve fibers were evaluated in the developing human sural nerve using three different methods of measurement: 1. ocular micrometer evaluation of large fibers, 2. photographic enlargements for evaluating large numbers of nerve fibers of all sizes, and 3. electron microscopic enlargements for more precise measurements in selected nerves. The average axonal diameter doubles from 5 months gestation to about 5 years of age. Large fiber group axons increase, during the same period, by a factor of 3--3.5 with a slight decrease thereafter. The myelin thickness increases more slowly, but continuously, between 5 months gestation until the age of 14. This asynchronous development of axons and myelin sheaths results in a statistically significant change of the ratio between axonal caliber and myelin thickness. The slope of the regression line is steeper in older than in younger individuals, and the correlation coefficient increases during development of the nerve.