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.

Celsr3 is required in motor neurons to steer their axons in the hindlimb.

The cadherin Celsr3 regulates the directional growth and targeting of axons in the CNS, but whether it acts in collaboration with or in parallel to other guidance cues is unknown. Furthermore, the function of Celsr3 in the peripheral nervous system is still largely unexplored. Here we show that Celsr3 mediates pathfinding of motor axons innervating the hindlimb. In mice, Celsr3-deficient axons of the peroneal nerve segregate from those of the tibial nerve but fail to extend dorsally, and they stall near the branch point. Mutant axons respond to repulsive ephrinA-EphA forward signaling and glial cell-derived neurotrophic factor (GDNF). However, they are insensitive to attractive EphA-ephrinA reverse signaling. In transfected cells, Celsr3 immunoprecipitates with ephrinA2, ephrinA5, Ret, GDNF family receptor α1 (GFRα1) and Frizzled3 (Fzd3). The function of Celsr3 is Fzd3 dependent but Vangl2 independent. Our results provide evidence that the Celsr3-Fzd3 pathway interacts with EphA-ephrinA reverse signaling to guide motor axons in the hindlimb.

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.

Surgical anatomy of sensory portion of superficial fibular nerve for harvesting nerve grafts from fetuses.

The use of superficial fibular nerve (Sfn) as a potential donor nerve in nerve grafting has been introduced. The limited availability of donor nerves has paved the way for nerve allografting. We studied the sensory portion of Sfn in 60 limbs from 30 fetuses. Three distinct patterns of the nerve were designated as Types 1, 2, and 3 by us. Type 1 (66.67%) comprised Sfn piercing fascia cruris then branching into Mdn and Idn. Type 2 (21.67%) was a pattern where Sfn penetrated deep fascia then continued undivided over the dorsum of foot. Type 3 (11.67%) was where Mdn and Idn penetrated deep fascia independently. The study provided quantitative measurement data of the sensory portion of Sfn and its branching nerves with respect to osseous landmarks like the head of fibula and the malleoli. Such data may be of help in defining nerve segments suitable for harvesting in nerve grafts from fetuses.

Preliminary assessment of anatomical variability of nervus peroneus superficialis in the foetal period.

An assessment of the variability of the course and ramifications of the superficial peroneal nerve within the crus was made on a material of 33 foetuses of both sexes miscarried in the 6th month of foetal life. Particular attention was paid to the relation of the nerve under examination to the anterior intermuscular septum. To facilitate the analysis the material investigated was grouped into several types. The post mortem examination revealed that the nerve referred to followed a typical course within the shank in 54% of cases. At the same time in 15% of cases the examined nerve was split into two terminal branches within the fascial compartment of fibular muscles, leaving the fascia independently. In 19% of cases n. peroneus superficialis passes through the intermuscular septum to the anterior fascial compartment of the shank. Moreover, in 12% of cases the presence was demonstrated of n. peroneus superficialis accessorius passing together with n. peroneus profundus to the extensors chamber and further on into the medial cutaneous nerve of the foot.

Targeting of the EphA4 tyrosine kinase receptor affects dorsal/ventral pathfinding of limb motor axons.

The Eph family of tyrosine kinase receptors has recently been implicated in various processes involving the detection of environmental cues such as axonal guidance, targeted cell migration and boundary formation. We have inactivated the mouse EphA4 gene to investigate its functions during development. Homozygous EphA4 mutant animals show peroneal muscular atrophy correlating with the absence of the peroneal nerve, the main dorsal nerve of the hindlimb. This phenotype is also observed, although with a lower penetrance, in heterozygotes. During normal hindlimb innervation, motor axons converge towards the sciatic plexus region at the base of the limb bud, where they must choose between dorsal and ventral trajectories within the limb. Among the axons emerging from the sciatic plexus, dorsal projections show higher levels of EphA4 protein than ventral axons. In EphA4 mutant mice, presumptive dorsal motor axons fail to enter the dorsal compartment of the limb and join the ventral nerve. Our data therefore suggest that the level of EphA4 protein in growing limb motor axons is involved in the selection of dorsal versus ventral trajectories, thus contributing to the topographic organisation of motor projections.

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.

Conduction velocity and fibre diameter of the peroneal nerve in normal and growth retarded fetal sheep.

In this study we have examined structural and functional aspects of nerve fibre development in experimentally growth retarded fetal sheep following restriction of placental growth by carunclectomy in 5 ewes. Measurement of whole-nerve conduction velocity in the peroneal nerve showed, for the most rapidly conducting fibres, a significant slowing from the normal value of 50.3 +/- 1.8 m/s to 33.8 +/- 3.3 m/s (P less than 0.01). Histological examination of nerve sections revealed a deficit of large myelinated fibres in growth retarded fetuses which is consistent with the conduction velocity measurements.