Needle electrode assembly

A holder (16) for releasably holding needle electrodes (18). The holder (16) includes a body (26) having a base slidably mounted within the body. Depressing the base into the body (26) releases a gripping assembly (50) located within the body (26) allowing a needle electrode (18) inserted into the holder to be removed. Releasing the base (24) causes the gripping assembly to engage a needle electrode inserted into the holder. The gripping mechanism (50) includes a chuck (60) having an opening sized to receive the needle electrode (18). The chuck engages a ferrule (73) that depresses the jaws (70) of the chuck (68) radially inwardly with respect to each other to reduce the size of the opening in the chuck thus holding a needle electrode (18) inserted into the chuck (68).

FIELD OF THE INVENTION 
The present invention relates to needle electrode assemblies, specifically, 
the present invention relates to reusable needle electrode assemblies and 
holders. 
BACKGROUND OF THE INVENTION 
Needle electrodes are designed for use in neurological examinations using 
electronic monitoring equipment, namely electromyograph (EMG) equipment. 
The needle electrodes are connected to monitoring equipment and then 
inserted into a patient's muscle at the location that is to be stimulated 
or probed. As a needle electrode is inserted into a patient's body, both 
the electrode and operator may be exposed to bodily fluids carrying 
infectious diseases. Because of the danger associated with exposure to 
bodily fluids, the Food and Drug Administration (FDA) has stringent 
requirements regarding packaging, sterilization, reuse, disposal and 
testing performed using needle electrodes. 
FDA requirements have resulted in two basic types of needle electrodes 
being used in the marketplace. The first type of needle electrode 
generally used is a disposable electrode assembly including needle 
electrode, lead wires, and electrical connectors all joined to form a 
single unit. The electrode assemblies are generally sterilized and 
prepackaged for a one-time use by a physician. The physician opens the 
sterilized package, connects the needle electrode to the appropriate 
monitoring equipment, and inserts the needle electrode into a patient's 
muscle. After completing testing, the entire electrode assembly is 
disconnected from the monitoring equipment and discarded. 
Disposable needle electrode assemblies are fairly expensive and highly 
wasteful of resources due to their one-time use. Disposable electrode 
assemblies also add to the quantity of medical waste produced, increasing 
waste disposal costs. Because specific users require various length and 
diameter disposable needle electrode assemblies, users must stock large 
numbers of expensive needle electrode assemblies, adding to inventory 
overhead and storage costs. 
The second type of needle electrode assembly commonly available is a 
reusable needle electrode assembly designed to be sterilized after each 
use. Similar to disposable assemblies, reusable needle electrode 
assemblies are generally manufactured as single piece units including 
electrical connectors, leads, and needle electrodes. Reusable needle 
electrode assemblies are not as wasteful of resources; however, they are 
expensive and time-consuming to use due to the procedures necessary to 
sterilize the needle electrode assemblies prior to each use. As with 
disposable needle electrode assemblies, reusable needle electrode 
assemblies are generally manufactured as a single unit having a needle 
electrode of a specified diameter and length, making it necessary for a 
physician to keep a large stock of various needle diameter and lengths on 
hand, adding to inventory and storage costs. 
Some reusable needle electrode assemblies are designed with detachable 
needle electrodes. In such assemblies, an electrical housing and leads are 
formed as one unit and a needle electrode and an electrical connector used 
to connect the electrode to the leads are formed as a second unit. 
It would be advantageous to have a needle electrode assembly that is 
reusable and does not require expensive and time-consuming sterilization 
procedures after each use. It would also be beneficial to have a needle 
electrode assembly that allows different sizes and lengths of needle 
electrodes to be releasably attached to electrical connectors and leads to 
reduce fabrication costs and allow physicians to stock various sizes and 
lengths of needle electrodes, as opposed to stocking various sizes of 
needle electrode assemblies. 
The present invention is directed to reducing or eliminating some or all of 
the disadvantages of prior needle electrode assemblies discussed above. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a releasable and reusable needle 
electrode assembly for use with all types of neurological monitoring 
equipment is provided. The needle electrode assembly includes a holder 
capable of releasably holding needle electrodes of various sizes, shapes, 
and lengths. The needle electrode-holder of the present invention may be 
operated by placing the needle electrode holder in a single hand and then 
depressing the base of the holder to release or insert a needle electrode. 
The needle electrode is inserted into the tip of the needle electrode 
holder while depressing the base of the needle electrode holder. Upon 
releasing the base of the needle electrode holder, the internal engagement 
mechanism of the needle electrode holder engages and holds the needle 
electrode in place. The needle electrode holder is in turn connected to 
leads that are connected to neurological monitoring equipment. 
One embodiment of the invention comprises a needle electrode assembly 
having a holder for releasably holding a needle electrode. The holder 
includes a body having a base slidably coupled to the body. A chuck is 
coupled to the base and includes an opening that is sized to receive and 
releasably hold a needle electrode. The chuck is adjustable between an 
engaged position in which the chuck engages a needle electrode and a 
released position in which the needle electrode may be freely removed by 
sliding the base with respect to the body. 
According to other aspects of the invention, a biasing means biases the 
chuck into the engaged position in which the chuck holds the needle 
electrode. The chuck is moved into the engaged position through the use of 
a ferrule that at least partially encircles the chuck. Slidably moving the 
base with respect to the body causes the chuck to move at least partially 
into and out of the ferrule thus moving the jaws of the chuck radially 
inwardly and outwardly, enlarging or reducing the size of the opening in 
the chuck. The tip of the holder includes a conically-shaped opening that 
helps to guide the needle electrode into the opening in the chuck. The 
body of the holder is shaped such that it may be held between the thumb 
and two fingers of a user's hand during operation. 
The needle electrode holder of the present invention allows a physician to 
purchase the required number of needle electrode holders and then purchase 
needle electrodes of various sizes and lengths. The needle electrodes may 
be releasably inserted into the needle electrode holder and subsequently 
discarded or sterilized depending upon the application. The needle 
electrode holder of the present invention may be used in combination with 
a needle electrode including a standoff mechanism that prevents the needle 
electrode holder from coming into contact with a patient's bodily fluid. 
Thus, the needle electrode holder of the present invention may be reused 
with different needle electrodes without being resterilized prior to every 
use. Use of the present invention should reduce medical costs by reducing 
the amount of medical waste that must be disposed of.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiment of a needle electrode assembly 10 including a 
needle electrode holder 16 according to the present invention is 
illustrated in FIG. 1. The needle electrode assembly 10 includes an 
electrical connector 12 that is configured to connect to neurological 
monitoring equipment, namely EMG monitoring equipment (not shown). The 
electrical connector 12 is connected to one end of an electrical lead 14. 
The other end of the electrical lead 14 is connected to the needle 
electrode holder 16 as described in more detail below. 
The needle electrode holder 16 is configured to releasably engage or 
disengage a needle electrode 18 that has been placed in the tip 28 of the 
needle electrode holder 16. The needle electrode holder 16 is configured 
to be held between the middle finger and thumb 21 of a user's hand and 
depressed with the index finger, as shown in FIG. 1. Depressing the base 
24 of the needle electrode holder 16 in the direction of the arrow 25 
causes the needle electrode holder to disengage, thus allowing the needle 
electrode 18 to be inserted into the conical tip 28 or to fall out of the 
tip as described in more detail below. Releasing the base 24 of the needle 
electrode holder 16 causes the needle electrode holder 16 to engage and 
grab a needle electrode 18 that has been inserted into the conical tip 28, 
thus holding the needle electrode for use during stimulation or probing. 
As shown in FIGS. 1 and 2, the electrode holder 16 is generally formed of a 
base 24 that is slidably mounted within a body 20 having a cylindrical 
interior 36. A conical tip 28 is rigidly attached to the end of the body 
16 opposite the base 24. 
The base 24 includes a flexible lead retainer 22 that extends out one side 
of the base. The retainer 22 includes a central passageway 34 that is 
sized to receive the electrical lead 14. The flexible lead retainer 22 
surrounds the electrical lead 14 and helps to prevent the electrical lead 
from being pulled away from the base 24, thus helping to prevent possible 
disconnection to the electrical lead. 
The base 24 is slidably mounted within a cylindrical opening 88 in one end 
of the body 26 of the needle electrode holder 16. The conical tip 28 is 
rigidly attached to the opposite end of the body. The conical tip 28 
includes a cylindrical protrusion 30 that extends rearwardly from the 
large diameter end of the conical tip. The cylindrical protrusion 30 is 
sized to extend into and engage the cylindrical interior wall 31 of the 
end of the body 26. The conical tip 28 is attached to the body 26 by 
adhesive bonding or another commonly known method of attachment, e.g., 
threading the cylindrical protrusion 30 of the conical tip 28 into the 
cylindrical interior wall 31 of the body 26. The smaller diameter end of 
the conical tip 28, which is located opposite the body 26, includes a 
conical opening 38 that has its largest diameter adjacent the end of the 
tip and its smallest diameter interior from the end of the tip. The 
smallest diameter end of the conical opening 38 opens into a hollow 
cylindrical interior 70 of the conical tip. 
The base 24 is generally cylindrical and has an exterior diameter that is 
smaller than the interior diameter of the rear portion 86 of the body 26 
such that the base is free to slide within a cylindrical opening 88 
located at the rear of the body. Depressing the base 24 toward the body 26 
causes the base to slidably move into the cylindrical opening 88. The 
distance the base 24 may move into the body 26 is limited by a shoulder 89 
located at the forward end of the cylindrical opening 88. Releasing the 
base 24 results in the base being biased away from the body 26. The extent 
to which the base 24 may move away from the body while remaining within 
the cylindrical opening 88 is limited, as described below. 
The inward and outward movement of the base 24 causes an electrode gripping 
assembly 50 (FIG. 3) located within the cylindrical interior 36 of the 
body 26 to releasably engage or disengage the needle electrode 18. The 
structure and operation of the electrode gripping assembly 50 is best 
shown by FIGS. 3-6. The electrode gripping assembly 50 includes a stem 52 
that is connected at one end to a collet assembly 64. The stem 52 is a 
cylindrical tube having a recessed groove 54 extending around the 
circumference of the stem at the end of the stem opposite the collet 
assembly 64. Swaged connector 56 connects the other end of the stem to the 
collet assembly. In the preferred embodiment, the base 24 is formed of 
plastic that is injection molded around the end of the stem 52-opposite 
the collet assembly 64. The plastic resin forming the base 24 flows into 
the recessed groove 54 in the stem 52, helping to maintain the stem 52 
rigidly within the base. 
The collet assembly 64 is a cylindrical tube that includes a greater 
diameter raised portion 66 at the end of the collet assembly that is 
attached to the stem 52 by swaging. The raised portion 66 is sized to be 
received within an enlarged end of a passageway 57 that extends through 
the interior of the stem 52. After inserting the raised portion 66 of the 
collet assembly 64 into the passageway 57, the end 56 of the stem 52 is 
swaged over the raised portion 66 of the collet assembly (FIG. 4) in order 
to attach the stem to the collet assembly. 
The end of the collet assembly 64 opposite the raised portion 66 includes a 
conical three-jaw split chuck 68. The split chuck 68 is formed by slitting 
the cylindrical collet assembly 64 lengthwise along three equally spaced 
apart slots 69. The slots start from the front of the split chuck 68 and 
extend partially along the cylindrical tube toward the band 66. Thus three 
separate pieces or jaws 70 are formed, as best seen in the end elevational 
view of the chuck shown in FIG. 6. The exterior surface 71 of each jaw 70 
slopes outwardly from a point interior from the end of the collet assembly 
to form a conical shape having a greater diameter at the end of the split 
chuck than at a point interior from the end. 
The split chuck 68 includes an internal passageway 72 that extends through 
the center of the collet assembly 64. The passageway 72 is sized so that 
the needle electrode 18 may be placed within the split chuck 68 and 
engaged by the jaws 70 of the split chuck when the jaws are compressed as 
described below. The slots 69 in the split chuck 68 are of a sufficient 
width to allow the needle electrode to be inserted into the passageway 71 
when the jaws 70 are in an uncompressed position while allowing the jaws 
to engage and hold the needle electrode 18 when the jaws are in a 
compressed position as described below. 
The jaws 70 of the split chuck 68 are compressed through the use of a 
cylindrical ferrule 62 that is placed around the exterior of the split 
chuck 68. The interior surface 73 (FIG. 4) of the cylindrical ferrule 62 
is conical and shaped to mate with the sloped surface 71 of the split 
chuck 68 when the ferrule is placed over the split chuck, as best seen in 
FIG. 4. 
As the cylindrical ferrule 62 is slidably moved toward the split chuck 68, 
the sloped interior surface 73 of the ferrule contacts the sloped exterior 
surface 71 of the split chuck. As the cylindrical ferrule 62 is moved 
further over the split chuck 68, the contact between the interior surface 
73 of the cylindrical ferrule and the exterior surface 71 of the split 
chuck pushes the three jaws 70 radially inwardly, decreasing the diameter 
of the passageway 72 through the split chuck 68. As the three jaws 70 are 
pushed together, they contact and grip the end of the needle electrode 18 
after it has been inserted into the passageway 72 as described below. 
A cylindrical coil spring 60 is located around the exterior of the stem 52. 
The front end of the spring 60 contacts a retaining clamp 29, located in 
the electrode body 26 adjacent to the end of the cylindrical portions 30 
of the conical tip 78, when the electrode gripping assembly 50 is placed 
within the electrode body. The opposite end of the spring 60 contacts a 
forward edge 73 of the base 24 after the electrode gripping assembly 50 
has been placed with the electrode body 16. The spring 60 biases the base 
24 away from the body 16 of the electrode holder such that the cylindrical 
ferrule 62 is maintained tightly around the split chuck 68, thus biasing 
the split chuck into an engaged position in which the jaws 70 of the chuck 
are forced together to engage a needle electrode 18 placed within the 
jaws. 
The mechanical interaction between the electrode gripping assembly 50 and 
the body 16 and base 24 of the electrode holder will now be described with 
reference to FIG. 2. As discussed above, the stem 52 of the electrode 
gripping assembly 50 is rigidly attached to the base 24. The combined 
electrode gripping assembly 50 and base 24 are slidably mounted within the 
interior 36 of the body 26. Specifically, the base 24 slides freely within 
the cylindrical opening 88 formed in the rear end of the body 26. The stem 
52 and collet assembly 64 extend through the interior 36 of the body 26 
and into the cylindrical interior 70 of the tip 28. 
The electrode gripping assembly 50 and, thus, the base 24 are prevented 
from moving rearwardly out of the body 26 by the retaining clamp 29, which 
encircles the collet assembly 64 just rearwardly of the ferrule 62. The 
retaining clamp 29 is inserted around the collet assembly 64 after the 
electrode gripping assembly 50 has been placed within the body 26 and 
before the conical tip 28 has been adhesively bonded to the front of the 
body. The retaining clamp 29 fits within the end of the body 26 opposite 
the end in which the base 24 is slidably mounted. The retaining clamp 29 
is prevented from moving rearwardly past a predetermined position within 
the interior 36 of the body 26 by a narrow shoulder 33 formed in the 
interior surface of the body. The forward side of the clamp 29 serves as a 
rearward stop to prevent rearward movement of the ferrule 62 past a 
predetermined position, thus maintaining the electrode gripping assembly 
50 within the body 26. As noted above, the rearward side of the retaining 
clamp 29 contacts the forward end of the biasing spring 60 thus allowing 
the biasing spring to bias the base 24 rearwardly away from the body 26. 
The electrode gripping assembly 50 is movable from an engaged position in 
which the jaws 70 of the split chuck 68 are compressed to engage the 
needle electrode 18 to a disengaged position in which the jaws of the 
split chuck are not compressed, thus allowing the needle electrode 18 to 
be removed from the needle electrode holder 16. In the engaged position, 
the stem 52 and base 24 are biased rearwardly by spring 60 in the 
direction of the arrow 90 (FIG. 2), such that the rearward edge of the 
cylindrical ferrule 62 contacts the front side of the clamp 29, thus 
preventing the ferrule from moving rearwardly. The biasing force provided 
by the spring 60 continues to bias the collet assembly 64 rearwardly, 
forcing the exterior surfaces 71 of the split chuck 68 into contact with 
the interior surface 73 of the ferrule 62, thus forcing the jaws 70 
together as described above. 
The electrode gripping assembly 50 is released by depressing the base 24 
inwardly toward the body 26 against the biasing force provided by the 
spring 60 such that the base 24 slidably moves within the cylindrical 
opening 88 in the direction opposite the arrow 90. As the base 24 moves 
into the body 26, the stem 52 and thus collet assembly 64 moves forward 
within the interior of the body 26 and the conical tip 28. As the split 
chuck 68 moves forward, the ferrule 62 also moves forward until the 
forward edge of the ferrule contacts a shoulder 74 formed in the interior 
of the cylindrical cavity 70, thus preventing the ferrule from moving 
forward any further. As the split chuck 68 continues to move forward, the 
jaws 70 move out of the ferrule 62 allowing the jaws to move radially 
apart, thus increasing the diameter of the passageway 72. As the diameter 
of the passageway 72 increases, the needle electrode 18 is free to move 
into or out of the needle electrode holder 16. 
A needle electrode 18 may be inserted into the needle electrode holder 16 
while the base 24 is depressed by inserting it through the conical opening 
38 into the split chuck 68. The conical opening 38 helps to guide the 
needle electrode in the passageway 72. The base 24 may then be released 
allowing the biasing force of the spring 60 to force the base rearwardly, 
thus compressing the jaws 70 around the needle electrode as described 
above. 
In the preferred embodiment, the stem 52 and collet assembly 64 are formed 
of an electrically conductive material. A conductor 91 that forms part of 
the electrical lead 14 is attached to the rear portion of the stem 52 by 
crimping, soldering, or other means of attachment, thus establishing an 
electrical path from the lead to the needle electrode 18. 
In operation, the user inserts a needle electrode by depressing the base 24 
(i.e., moving the base 24 toward the body 26), sliding a needle electrode 
18 into the tip 28 and releasing the base 24. To dispose of a used needle 
electrode 18, the user holds the needle electrode 18 and needle electrode 
holder 16 over a disposal receptacle and depresses the base 24, allowing 
the needle electrode 18 to fall into the disposal receptacle. 
The present invention allows various diameters, lengths, and types of 
needle electrodes to be used within a standard needle electrode holder. A 
physician may stock the present invention along with a large variety of 
needle electrodes as opposed to stocking a large quantity of various sizes 
and lengths of disposable needle electrode assemblies, thus reducing 
storage and overhead costs. The present invention may also be reused, 
thereby reducing medical waste and disposal costs. 
If the needle electrode holder 16 is contaminated by a patient's bodily 
fluids, it may be sterilized using commonly known and used sterilization 
procedures. The present invention may be used with either monopolar or 
dipolar needle electrodes by making minor electrical modifications as 
readily accomplished by someone of ordinary skill in the art. 
The present invention may be used with needle electrodes of varying sizes, 
lengths, and configurations; however, it is advantageous to use the 
present invention with a needle electrode 18 that includes a stand-off 
section 100 designed to off-set the tip 28 of the needle electrode from a 
patient's body. The stand-off section 100 shown in FIG. 2 is a Z-shaped 
bend in the needle electrode 18. The distal portion 102 of the Z-shaped 
bend contacts a patient's skin and prevents the needle electrode 18 from 
being inserted beyond a predetermined position. The proximal portion 104 
of the Z-shaped bend contacts the tip 28 of the needle electrode holder 
once the needle electrode 18 is fully inserted into the needle electrode 
holder. Using a needle electrode having a stand-off section 100 as shown 
helps to prevent the needle electrode holder from becoming contaminated by 
contact with the surface of a patient's body or the patient's bodily 
fluids. 
While the preferred embodiment of the invention has been illustrated and 
described, it will be appreciated that, within the scope-of the appended 
claims, various changes can be made therein without departing from the 
spirit and scope of the invention.