Surgery – Instruments – Electrical application
Reexamination Certificate
2000-02-15
2001-11-27
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Electrical application
C606S048000, C606S051000, C606S052000, C606S174000, C606S208000
Reexamination Certificate
active
06322561
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of art to which this invention relates is bipolar surgical instruments, in particular, an improved pivot screw design for bipolar surgical instruments.
2. Description of the Related Art
A technique used extensively in both open and endoscopic surgery is the controlling of bleeding using bipolar electrosurgical instrumentation. The control of bleeding during surgery accounts for a major portion of the time involved in surgery. In particular, bleeding that occurs when tissue is incised or severed can obscure the surgeon's vision, prolong the operation, and adversely effect the precision of cutting. Blood loss from surgical cutting may require blood infusion, thereby increasing the risk of harm to the patient.
Hemostatic electrosurgical techniques are known in the art for reducing bleeding from incised tissue prior to, during, and subsequent to incision. Electrosurgical cutting and coagulating instruments are used to perform such techniques. These instruments can be of a reusable type (which require cleaning and disinfecting or sterilizing before each use) or disposable (which are disposed of after a single use). Each type includes both monopolar and bipolar variations having at least one electrode. Radio frequency (RF) energy is conducted through this electrode to either a remote conductive body-plate (known as a grounding pad) in the case of monopolar instruments, or to a second, closely spaced conductive electrode in the case of bipolar instruments. In monopolar instruments electrical current travels from the electrode through the patient's body to the grounding pad. Bipolar instruments are typically connected to both poles of an electrosurgical generator, therefore current flow is typically limited to tissue adjacent to the working end of the bipolar instrument (where the two electrodes are located).
Bipolar electrosurgical instruments typically comprise two halves which pivot about a pivot means such as a pivot screw. However, pins and rivets are also utilized as the pivot means. Each halve comprises an electrode which needs to be electrically isolated from the other half. Isolation of the instrument halves is typically achieved by either coating a metallic pivot screw with an insulating material or fabricating the pivot screw entirely from an insulating material. In addition, surfaces of the two halves which are in sliding contact with each other are insulated, typically by coating the common surfaces with an insulating material, such as alumina oxide.
FIGS. 1 and 2
illustrate a bipolar surgical instrument of the prior art, and generally referred to as reference numeral
100
. The bipolar surgical instrument
100
typically comprises a first and a
30
second half
102
,
104
. Each half has a distal end
102
a
,
104
a
at which an end effector, such as scissor blades, are disposed. Each half also has a proximal end
102
b
,
104
b
at which an actuating means is disposed, such as finger loops
106
,
108
. Each instrument half comprises an electrode, whereby RF energy of differing polarity is supplied to each half through connector posts
110
,
112
disposed at the proximal end
102
b
,
104
b
of the instrument halves
102
,
104
. The two halves
102
,
104
engage in sliding contact at first and second pivot surfaces
114
,
116
and are fastened together at the pivot surfaces
114
,
116
by a fastening means, typically a pivot screw
118
disposed in a first and second bore
120
,
122
. The pivot screw has a head
118
a
and a first threaded portion
118
b
. The first bore
120
being in the first half
102
, the second bore
122
being in the second half
104
and opposing the first bore
120
.
To electrically isolate the two halves from each other, a layer of insulating material
124
is disposed between the first and second halves at their sliding surfaces. If the screw
118
is a conductive material, such as aluminum, it is further coated with an insulating material to electrically isolate the two instrument halves from each other. Additionally, the instrument is typically coated with an insulating material
126
in all portions other than the end effectors so as to insulate a user from electrical shock.
As can be seen in
FIG. 2
, the second bore
122
typically has a second threaded portion
128
, whereby the first bore
120
is typically sized as a through hole to accommodate easy passage of the first threaded portion
118
b
of the pivot screw
118
but which captures the head
118
a
of the pivot screw
118
. The screw
118
is disposed through the first bore
120
where the first threaded portion
118
b
engages with the second threaded portion
130
of the second bore
122
to provide a positive locking of the two halves.
Coated aluminum screws with an anodized coating are typically used in the art. While they have the advantage of being able to withstand the physical abuse typically encountered during surgery and processing (cleaning, disinfecting, and sterilizing), they suffer from a number of disadvantages. The most serious of which is the loss of portions of the coating due to rubbing contact between mating surfaces. Because the screw head
118
a
moves relative to the instrument half
102
, the screw coating is subject to wear. An uncoated portion of the screw or a chipped portion of the screw's insulating coating can lead to an eventual shorting across the screw and between the instrument halves. This will result in a very low resistance between instrument halves. Consequently, the voltage maintained between the instrument halves will not be sufficient to effect adequate hemostasis. The greater the worn portion is in size, the more significant the degradation of the hemostasis performance.
Ceramic coated screws, such as alumina oxide coated on aluminum, are also used as the pivot screw in a bipolar surgical instrument. However, ceramics are brittle and prone to chipping. As discussed, chipping of the insulating coating can lead to poor or inadequate hemostasis. Furthermore, ceramic coated screws do not easily thread into a mating female thread because of its high coefficient of friction. Impregnating, the screw with a material having a lower coefficient of friction, typically a polymer, helps with the latter problem. However, the impregnation does little to solve the former problem and adds significant costs to the fabrication of the screws.
Pivot screws fabricated entirely from ceramic or an impregnated ceramic also have their drawbacks. Ceramic screws are brittle and susceptible to failure when subjected to external forces caused by mishandling of the instrument. For instance, dropping the instrument from an instrument table to a hard operating room floor can result in the fracturing of the ceramic pivot screw, resulting in instrument failure.
Plastic screws have also been contemplated as pivot screws in bipolar surgical instruments. Like ceramic screws, plastic screws cannot withstand the impact stresses associated with mishandling the instrument, such as when the instrument is dropped onto a hard surface. Additionally, plastic screws cannot withstand expected torque levels experienced during normal use which is needed to adequately hold the two instrument halves together. Not only do plastic pivot screws suffer from being susceptible to failure from impact and torsional stresses, they can also fail electrically. Plastic screws have been found to fail from carbon tracking due to the high voltages used in bipolar electrosurgical instruments. Typically, the voltages run as high as 1,500 volts (peak to peak). At such elevated voltages, plastic screws can burn and/or melt causing catastrophic failure of the bipolar instrument.
Besides electrical conduction between instrument halves due to worn or chipped insulation on the screw
118
, electrical conduction can occur directly between instrument halves
102
,
104
as a result of exposed portions of the pivot surfaces
114
,
116
. If the insulating material
124
disposed on one or both of the pivot surfaces
114
,
116
i
Eggers Andrew
Eggers Philip
Wenzler Peter
Dvorak Linda C. M.
Ethicon Inc.
Kearney R
Scully, Scott, Murphy & Pressor
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