Spinal Needle

Abstract

A spinal needle comprising a hollow outer needle having a stylet removably insertable within it. The stylet forward end and the outer needle forward end cooperate to provide a generally closed piercing end having two side bevel faces and a heel face. The side bevel faces each form an acute angle with the longitudinal axis of said spinal needle and intersect at an acute angle to form a straight cutting edge lying in a plane including the longitudinal axis of said spinal needle and inclined thereto. The side bevel faces also intersect the outer needle surfaces to form curved cutting edges which intersect to form a point. The heel face is inclined at an angle to the longitudinal axis of the spinal needle and joins the side bevel faces remote from the point.

Description

This invention relates to spinal needles. In particular, it relates to an improved hollow spinal needle with a central stylet that can be inserted into the sub-arachnoid space of the vertebral canal with minimum stretching of the surrounding tissues.

The spinal cord and nerve roots lie within the vertebral canal surrounded by three membrane layers, dura mater, arachnoid and pia mater. The first two layers lie in close approximation at the perIphery of the canal while the pia mater overlays the spinal cord. The resultant space separating the first two from the third is termed the sub-arachnoid space and within it pass nerve roots and the circulating cerebrospinal fluid (CSF). It is within this region that many therapeutic and diagnostic maneuvers are carried out, i.e., lumbar puncture for manometery and CSF sampling, spinal anesthesia, myelography, etc.

In order to reach this space, a spinal needle must pass through several tissues of varying density, resistance and fiber orientation. The needle tip must puncture and penetrate the skin layers, then subcutaneous fat layer, interspinal ligament, ligamentum flavum, epidural space, dura mater, arachnoid and come to rest with the sub-arachnoid space with its entire beveled opening within this space.

Since the entire opening of the needle must lie within the sub-arachnoid space, the tip of a spinal needle must be shorter and so more sharply tapered than that of a standard hypodermic needle. A standard hypodermic needle is in general ground to have a bevel face at an angle of about 10.degree. to the logitudinal axis of the needle, but the end face of a spinal needle must have a steeper angle of about 18.degree.t. Since the force required to penetrate the patient's skin and underlying tissue is in proportion to this angle, a spinal needle requires greater force for insertion than a standard non-spinal needle. Since trauma to tissues and control of the spinal needle is related to this force, it is desirable to provide a spinal needle that can be inserted with reduced force, while still providing an opening that lies entirely within the spinal canal.

It is an object of this invention to provide a spinal needle that can be inserted with minimum force.

It is a further object to provide such a needle that can be inserted with a minimum of stretching or tearing of the tissue beyond the incision made by the cutting edge of the needle.

It is a still further object of the invention to provide such a needle that will provide a minimum danger of trauma when the needle is inserted and its stylet removed for use.

According to the invention, there is provided a novel spinal needle comprising a hollow outer needle and a stylet removably insertable within it. The stylet forward end and the outer needle forward end cooperate to provide a generally closed piercing end having two generally planar side bevel faces and a generally planar heel face. The side bevel faces each form an acute angle with the longitudinal axis of said spinal needle and intersect at an acute angle to form a straight cutting edge lying in a plane including the longitudinal axis of the spinal needle and inclined thereto. The side bevel faces also intersect the outer needle surfaces to form two curved cutting edges which intersect to form a point. The heel face is inclined at an angle to the longitudinal axis of the spinal needle and joins the side bevel faces and the straight cutting edge.

Other objects, features and advantages will appear from the following description of a preferred embodiment of the invention, taken together with the attached drawings thereof, in which:

FIG. 1 is a side elevation of the complete spinal needle of the invention, partially broken away to show the stylet;

FIG. 2 is a detail view of the locking means with the stylet partly removed from the outer needle;

FIG. 3 is an enlarged view of the piercing end of the spinal needle;

FIG. 4 is a view similar to FIG. 3 but rotated through 90.degree.;

FIGS. 5, 6 and 7 are views taken on the lines 5--5, 6--6, and 7--7 respectively of FIG. 3;

FIG. 8 is a view similar to FIG. 3 but viewed in the plane of one of the bevel faces;

FIG. 9 shows the shape of the cut made by the needle of the invention;

FIG. 10 shows the unstretched opening resulting from the cut of FIG. 9; and

FIG. 11 is a comparative graph of needle penetration forces.

Referring now to the drawing, and particularly to FIG. 1, the spinal needle 10 of the invention includes a hollow outer needle 12 with a forward end 14 and a hub 16. In the preferred embodiment, outer needle 12 has a uniform cylindrical bore 18 and a cylindrical outer surface 20.

A stylet 22 is removably inserted within hollow outer needle 12; stylet 22 has a hub 24 and a forward end 26, and is uniformly cylindrical of a size to fit closely within bore 18. The extreme forward position of stylet 22 within needle 12 is determined by the engagement of stop surfaces 28 and 30 on needle hub 16 and stylet hub 24 respectively. When surfaces 28 and 30 engage one another, stylet 22 is in its forward position, and end 26 of stylet 22 is flush with end 14 of needle 12 to form a generally closed piercing end 32. The angular orientation of stylet 22 with respect to needle 12 is determined by locking means comprising a boss 34 on stylet hub 24 and a slot 36 on needle hub 16. Stop surfaces 30 and 28 can engage one another only when boss 34 fits into slot 36, limiting stylet 22 to a single longitudinal and angular position flush with respect to needle 12 in the extreme forward position.

Referring now particularly to FIGS. 3 through 8, in accordance with the invention, the generally closed piercing end 32 of spinal needle 10 has two side bevel faces 40 and 42. The plane of each side bevel face forms with the longitudinal axis 44 of needle 10 an acute angle 46, which may be about 15.degree. to 21.degree., and is about 18.degree. in the preferred embodiment (FIG. 8). Bevel faces 40 and 42 intersect one another to include between them an acute angle 48, which may be about 55 to 85.degree., and is about 75.degree. in the preferred embodiment (FIGS. 6 and 7).

Side bevel face 40 intersects outer needle surface 20 to form a curved cutting edge 50, and side bevel face 42 intersects surface 20 to form a curved cutting edge 52. Edges 50 and 52 intersect to form a point 54, having an included angle 56 (FIG. 4). The intersection of side bevel faces 40 and 42 forms a straight cutting edge 58 leading away from point 54, and forming with axis 44 an angle 60 (FIG. 3) which is determined by the angles 46 and 48. Each side bevel face has a rounded end 70 remote from point 54.

Piercing end 32 of spinal needle 10 further has a heel face 62, forming with axis 44 a shallow angle 64, of about 15 to 21 degrees and preferably about 18 degrees and joining bevel faces 40 and 42 at equal angles. Heel face 62 has a pointed forward end 72 which joins cutting edge 58 to limit the extent of straight cutting edge 58 remote from point 54. Piercing end 32 has a dimension defined as the distance 73 from point 54 to the projection 74 of the opposite outer needle surface, measured in a plane containing cutting edge 58. Cutting edge 58 extends from one-half to three-quarters of distance 73 before being terminated by heel face 62 at pointed end 72. In the preferred embodiment, the length of cutting edge 58 is about two-thirds of distance 73.

In use, spinal needle 10 is inserted into the sub-arachnoid space of the vertebral canal with stylet 22 in its extreme forward position, as determined by stop means 30 and 28, and oriented as determined by locking means 34 and 36. In entering the skin and tissue of a patient, curved cutting edges 50 and 52 create a curved incision 70 (FIG. 9), while straight cutting edge 58 creates a straight incision 72 extending away from curved incision 70 and connecting with it. As needle 10 is inserted to make this incision, flaps 74 and 76 are folded away from the incision lines, leaving an unstretched opening 78 (FIG. 10) that is very nearly fully circular. Thus, the needle piercing end 32 is admitted up to the point of intersection of cutting edge 58 and heel face 62 without any stretching of the skin and tissue, and only moderate stretching is necessary to admit the full cross-section of the needle, the presence of heel face 62 greatly reducing the possibility of trauma without substantially increasing needle penetration forces. Once needle 10 is fully inserted, stylet 22 may be removed, leaving outer neeele 12 in place with its opening fully within the sub-arachnoid space. Fluid may then be removed or injection into the sub-arachnoid space as desired.

The graph of FIG. 11 illustrates the much reduced penetration forces needed with the spinal needle of the invention, as compared to a conventional spinal needle of the same gauge, the reduction in point penetration being especially significant, as well as the gradually increasing force until heel penetratin occurs.

Claims

What is claimed is:

1. A spinal needle comprising

a hollow outer needle having an outer surface

a stylet removably insertable within said hollow outer needle

said stylet forward end and said outer needle forward end cooperating in the extreme forward position of said stylet to provide a generally closed piercing end

said generally closed piercing end having two generally planar side bevel faces and a generally planar heel face

said side bevel faces each forming an acute angle with the longitudinal axis of said spinal needle and intersecting one another at an acute angle to form a straight cutting edge inclined to the longitudinal axis of said spinal needle and lying in a plane including the longitudinal axis of said spinal needle

said side bevel faces intersecting said outer needle surface to form two curved cutting edges which intersect to form a point

said heel face being inclined at an angle to the longitudinal axis of said spinal needle and joining said side bevel faces and said straight cutting edge,

said closed piercing end having a dimension defined as the distance from said point to the projection of said opposite outer needle surface, measured in a plane containing said straight cutting edge,

said cutting edge extending from one-half to three-quarters of said dimension.

2. A spinal needle as claimed in claim 1 wherein

said side bevel faces intersect one another at an angle of 55.degree. to 85.degree..

3. A spinal needle as claimed in claim 1 wherein

said heel face is inclined at an angle of 15.degree. to 21.degree. to said longitudinal axis.

4. A spinal needle comprising

a hollow outer needle having a forward end with a cylindrical bore and cylindrical outer surface

a stylet removably insertable within said hollow needle to an extreme forward position and fitting closely within said bore

said stylet forward end and said outer needle forward end cooperating in said extreme forward position to provide a generally closed piercing end

said generally closed piercing end having two generally planar side bevel faces and a generally planar heel face

said side bevel faces each forming an acute angle of 15.degree. to 21.degree. with the longitudinal axis of said spinal needle and intersecting one another at an acute angle of 55.degree. to 85.degree. to form a straight cutting edge inclined to the longitudinal axis of said spinal needle and lying in a plane including the longitudinal axis of said spinal needle

said side bevel faces intersecting said outer needle surface to form curved cutting edges which intersect to form a point

said closed piercing end having a dimension defined as the distance from said point to the projection of said opposite outer needle surface, measured in a plane containing said straight cutting edge,

said heel face being inclined at a shallow angle to the longitudinal axis of said spinal needle and joining said side bevel faces and said cutting edge remote from said point to define the length of said straight cutting edge as about one-half to three-quarters of said dimension.

5. A spinal needle as claimed in claim 4 wherein

said heel face is inclined at an angle of 15.degree. to 21 degrees to said longitudinal axis.

6. A spinal needle comprising

a hollow outer needle having a hub and a forward end, said forward end having a cylindrical bore and cylindrical outer surface

a stylet removably insertable within said hollow needle to an extreme forward position and having a hub and a cylindrical forward end and fitting closely within said bore

said stylet forward end and said outer needle forward end cooperating in said extreme forward position to provide a generally closed piercing end

locking means for limiting said inserted stylet to a single predetermined angular position with respect to said outer needle in said extreme forward position

said generally closed piercing end having two generally planar side bevel faces and a generally planar heel face

said side bevel faces each forming an identical acute angle of 15.degree. to 21.degree. with the longitudinal axis of said spinal needle and intersecting one another at an actue angle of 55.degree. to 85.degree. to form a straight cutting edge inclined to the longitudinal axis of said spinal needle and lying in a plane including the longitudinal axis of said spinal needle

said side bevel faces intersecting said outer needle surface to form curved cutting edges which intersect to form a point

said closed piercing end having a dimension defined as the distance from said point to the projection of said opposite outer needle surface, measured in a plane containing said straight cutting edge,

said heel face being inclined at an angle of 15.degree. to 21.degree. to the longitudinal axis of said spinal needle and joining said side bevel faces at equal angles thereto remote from said point to define said straight cutting edge as about one-half to three-quarters of said dimension.

7. A spinal needle comprising

a hollow outer needle having an outer surface

a stylet removably insertable within said hollow outer needle

said stylet forward end and said outer needle forward end cooperating in the extreme forward position of said stylet to provide a generally closed piercing end

said generally closed piercing end having two generally planar side bevel faces and a generally planar heel face

said side bevel faces each forming an acute angle with the longitudinal axis of said spinal needle and intersecting one another at an acute angle to form a straight cutting edge inclined to the longitudinal axis of said spinal needle and lying in a plane including the longitudinal axis of said spinal needle

said side bevel faces intersecting said outer needle surface to form two curved cutting edges which intesect to form a point, each said side bevel face including a rounded end remote from said point,

said heel face being inclined at an angle to the longitudinal axis of said spinal needle and joining said side bevel faces, said heel face having a pointed forward edge joining said straight cutting edge,

said closed piercing end having a dimension defined as the distance from said point to the projection of said opposite outer needle surface, measured in a plane containing said straight cutting edge,

said cutting edge extending from one-half to three-quarters of said dimension.