[Possibility of nerve lesions related to peripheral nerve blocks. A study of the human sciatic nerve using different needles].
When a needle tip comes too close to a nerve axon, the mechanical effect over the nerve membrane produces paresthesia. We examined the hypothetical mechanical damage of short bevel and long bevel needles over sciatic nerve bundles under scanning electron microscopy.


METHODS
We obtained samples of sciatic nerve from three patients of 68, 74 and 76 years old. These samples were fixed, dehydrated and coated with gold microfilm for their observation under scanning electron microscopy. Ten short bevel needles and ten long bevel needles were studied under the same microscopic technique. We interpolated microscopic images from sciatic nerve samples and different needle bevels at various angles to study the mechanical damage of these needles to nerve axons.


RESULTS
Sciatic nerve bundles were found 0.1 to 0.2 mm deep in the samples; information was given about the bevel length and angle of needles. The damage is perceptible under scanning electron microscopy, when the needle bevel is introduced 0.3-0.4 mm deep into the nerve bundle; here, the needle tip cuts through the perineurum, piercing the nerve bundle. At a depth of 1 mm, the lesion caused by short bevel needles is greater than that caused by long bevel needles. The type of epineural lesions caused by short bevel needles is also different from the ones caused by long bevel needles.


CONCLUSIONS
Lesions that affect superficially the epineurum can cause paresthesia by compression of nerve fascicles without damaging the axons. If the perineurm is damaged, the lession will also affect the blood-nerve barrier, leading probably to posterior sequels.
Reina
M A
MA
Servicio de Anestesiología del Hospital de Móstoles, Servicio de Anestesiología del Hospital Madrid Montepríncipe, Madrid. miguelangel.rei@terra.es
López
A
A
De Andrés
J A
JA
Machés
F
F
D000368:Aged; D004867:Equipment Design; D006801:Humans; D008855:Microscopy, Electron, Scanning; D008875:Middle Aged; D009339:Needles; D009407:Nerve Block / Q000009:adverse effects* / Q000295:instrumentation; D010292:Paresthesia / Q000209:etiology; D059348:Peripheral Nerve Injuries; D012584:Sciatic Nerve / Q000293:injuries* / Q000648:ultrastructure; D013314:Stress, Mechanical