Surgical blade abstract
A surgical blade unit for receiving substantial cutting load and
adapted for use with a selected shaft-form handle that has, at its
distal end, an axially aligned blade-unit receiving opening. The
blade-unit includes a metal blade defining a working edge and a
load-transmitting, axially elongated metal support shank extending
from the edge, and a intermediate load-transferring member of synthetic
resin permanently molded about a proximal portion of the shank and
defining an attachment fitting adapted to engage in load-transferring
relationship with the handle. The proximal portion of the shank
extends through the intermediate member in the attachment fitting
region and is permanently embedded therein to define an elongated,
load-transferring interface therewith. The intermediate member has
substantial tensile and shear strength and is constructed and arranged
to receive via the attachment fitting the surgeon's forces on the
handle, and to receive via the substantial load-transferring interface,
forces from the proximal end of the shank attributable to the resistance
encountered by the metal blade, the substance of the intermediate
member being adapted to transfer the surgeon's forces to overcome
the resistance forces while maintaining the blade in fixed relationship
to said handle. In preferred aspects of the invention, the attachment
fitting comprises cooperatively acting threads on the handle and
a proximal portion of the intermediate member, the blade unit is
in the form of an arthroscopic retrograde blade, the unit being
sized to lie within a surgical cannula and having a working edge
disposed for reverse cutting.
Surgical blade claims
We claim:
1. A surgical blade unit for receiving substantial cutting load
and adapted for use with a selected shaft-form handle that has,
at its distal end, an axially aligned blade-unit receiving opening,
said blade unit comprising:
(a) a metal blade defining a working edge and a load-transmitting,
axially elongated metal support shank extending from said edge,
and
(b) an intermediate load-transferring member of synthetic resin
permanently molded about a proximal portion of said shank,
the distal extremity of said intermediate member being spaced proximally
from said working edge leaving said blade and a substantial length
of the distal portion of said shank exposed,
a proximal portion of said intermediate member defining an attachment
fitting adapted to engage in load-transferring relationship with
said handle,
the proximal portion of said shank extending through the intermediate
member substantially into the region of said attachment fitting
and being permanently embedded within said intermediate molded member
to define an elongated, load-transferring interface therewith,
said intermediate member being comprised of synthetic resin that
has substantial tensile and shear strength and being constructed
and arranged to receive via said attachment fitting the surgeon's
forces on said handle, and to receive via said substantial load-transferring
interface, forces from said proximal end of said shank attributable
to the resistance encountered by said metal blade, the substance
of said intermediate member adapted to transfer said surgeon's forces
to overcome said resistance forces while maintaining said blade
in fixed relationship to said handle.
2. A surgical blade unit for receiving substantial cutting load
and adapted for use with a selected shaft-form handle that has,
at its distal end, an axially aligned, internally threaded blade-unit
receiving opening,
said blade unit comprising:
(a) a metal blade defining a working edge and a load-transmitting,
axially elongated metal support shank extending from said edge,
(b) an intermediate load-transferring member of synthetic resin
permanently molded about a proximal portion of said shank,
the distal extremity of said intermediate member being spaced proximally
from said working edge leaving said blade and a substantial length
of the distal portion of said shank exposed,
a distal portion of said intermediate member being terminated in
a proximally directed, annular butt surface adapted to engage a
distally directed surface of said handle, and
a proximal portion of said intermediate member having a smaller
diameter than said distal portion and defining an attachment fitting
on its surface comprising a set of external threads adapted to match
and engage in load-transferring relationship with internal threads
of said handle,
the proximal portion of said shank extending through the intermediate
member in the region of said attachment fitting and being permanently
embedded within said intermediate molded member to define an elongated,
load-transferring interface therewith,
said intermediate member being comprised of synthetic resin that
has substantial tensile and shear strength and being constructed
and arranged to receive via said attachment fitting the surgeon's
forces on said handle, and to receive via said substantial load-transferring
interface, forces from said proximal end of said shank attributable
to the resistance encountered by said metal blade, the substance
of said intermediate member adapted to transfer said surgeon's forces
to overcome said resistance forces while maintaining said blade
in fixed relationship to said handle.
3. The surgical blade unit of claim 2 wherein the body of said
intermediate member is resiliently deformable to the degree that,
without disturbing the load-transferring relationship of said intermediate
member with said shank, hand tightening of the threads of said blade
unit on said handle, and resultant compressional engagement of said
annular butt surface of said intermediate member with the distal
end surface of said handle, causes resilient stretching of the body
of said intermediate member between said butt-surface and said external
threads to produce a locking frictional engagement between said
thread and the internal threads of said handle thereby to prevent
rotation of said blade unit during surgical use.
4. The surgical blade unit of claim 1 or 2 wherein said blade unit
is in the form of an arthroscopic blade, said blade and intermediate
member being sized to lie within a surgical cannula.
5. The surgical blade unit of claim 1 or 2 wherein said blade unit
is a retrograde blade,
the working edge of said blade unit being disposed for operation
during reverse cutting.
6. A surgical blade unit for receiving substantial cutting load
and adapted for use in arthroscopic surgery with a selected shaft-form
handle that has, at its distal end, an axially aligned, internally
threaded blade-unit receiving opening,
said blade unit being sized to lie within a surgical cannula and
comprising:
(a) a metal retrograde blade defining a working edge disposed for
operation during reverse cutting and a load-transmitting, axially
elongated metal support shank extending from said edge,
(b) an intermediate load-transferring member of synthetic resin
permanently molded about a proximal portion of said shank,
the distal extremity of said intermediate member being spaced proximally
from said working edge leaving said blade and a substantial length
of the distal portion of said shank exposed,
a distal portion of said intermediate member being terminated in
a proximally directed, annular butt surface adapted to engage a
distally directed surface of said handle, and
a proximal portion of said intermediate member having a smaller
diameter than said distal portion and defining an attachment fitting
on its surface comprising a set of external threads adapted to match
and engage in load-transferring relationship with internal threads
of said handle,
the proximal portion of said shank extending through the intermediate
member in the region of said attachment fitting and being permanently
embedded within said intermediate molded member to define an elongated,
load-transferring interface therewith,
said intermediate member being comprised of synthetic resin that
has substantial tensile and shear strength and being constructed
and arranged to receive via said attachment fitting the surgeon's
forces on said handle, and to receive via said substantial load-transferring
interface, forces from said proximal end of said shank attributable
to the resistance encountered by said metal blade, the substance
of said intermediate member adapted to transfer said surgeon's forces
to overcome said resistance forces while maintaining said blade
in fixed relationship to said handle,
the body of said intermediate member being resiliently deformable
to the degree that, without disturbing the load-transferring relationship
of said intermediate member with said shank, hand tightening of
the threads of said blade unit on said handle, and resultant compressional
engagement of said annular butt surface of said intermediate member
with the distal end surface of said handle, causes resilient stretching
of the body of said intermediate member between said butt-surface
and said external threads to produce a locking frictional engagement
between said thread and the internal threads of said handle thereby
to prevent rotation of said blade unit during surgical use.
7. The surgical blade unit of claim 1 2 or 6 assembled with a
selected shaft-form handle,
the blade-unit receiving opening of said handle being configured
to receive the attachment fitting portion of said blade unit in
a close-fitting relationship,
whereby said intermediate member is restricted against lateral
expansion by the confining surfaces defining said opening.
8. The surgical blade unit of claim 1 2 or 6 wherein said synthetic
resin is sterilizable.
9. The surgical blade unit of claim 8 wherein said synthetic resin
is selected from the group consisting of nylon, acetal, polysulfone,
polyethylene and polypropylene.
10. The surgical blade unit of claim 1 2 or 6 wherein the distal
end of said intermediate member is tapered to facilitate entry of
said blade unit between close-lying portions of the body during
surgery.
11. A surgical blade unit for receiving substantial cutting load
and adapted for use under high forces in arthroscopic surgery with
a selected shaft-form handle that has, at its distal end, an axially
aligned, internally threaded blade-unit receiving opening.
said blade unit being sized to lie within a surgical cannula and
comprising:
(a) a metal retrograde blade defining a working edge disposed for
operation during reverse cutting and a load-transmitting, axially
elongated metal support shank extending from said edge,
(b) an intermediate load-transferring member of synthetic resin
permanently molded about a proximal portion of said shank, a proximal
portion of said intermediate member defining an attachment fitting
adapted to engage in load-transferring relationship with said handle,
the proximal portion of said shank extending through the intermediate
member substantially into the region of said attachment fitting
and being permanently embedded within said intermediate molded member
to define an elongated, load-transferring interface therewith, and
the distal extremity of said intermediate member being spaced proximally
from said working edge leaving said blade and a substantial length
of the distal portion of said shank exposed,
at the distal extremity of said intermediate member, said shank
and said member being substantially coaxial,
the distal extremity of said shank supporting said working edge
disposed for reverse cutting being substantially coaxial with said
intermediate member, and
the intervening exposed distal portion of said shank lying on an
axis at an angle transverse to the axis of said intermediate member,
said intermediate member being comprised of synthetic resin that
has substantial tensile and shear strength and being constructed
and arranged to receive via said attachment fitting the surgeon's
forces on said handle, and to receive via said substantial load-transferring
interface, forces from said proximal end of said shank attributable
to the resistance encountered by said metal blade, the substance
of said intermediate member adapted to transfer said surgeon's forces
to overcome said resistance forces while maintaining said blade
in fixed relationship to said handle.
Surgical blade description
BACKGROUND OF THE INVENTION
This invention relates to surgical blade units for use within the
body and in particular to means for securing the portion of the
device within the body against displacement from a handle under
high force conditions.
It has long been recognized as desirable to employ handles and
replaceable blade units in place of one-piece surgical scalpels
to obtain the advantages of assured sharpness and sterility. Difficulties
have been encountered in prior designs under high force conditions,
especially where it is required that the unit be small. Particular
problems have been encountered in arthroscopic surgery, i.e. surgery
through a small puncture in the body in which the surgeon views
the operative site by means of an arthroscope inserted via another
puncture wound. The accidental detachment of a blade from a handle
under such conditions is very undesirable.
The problem has perhaps been most serious with respect to reverse
cutting involving pulling motions, such as retrograde scalpels in
arthroscopic surgery.
SUMMARY OF THE INVENTION
According to the invention, a surgical blade unit for receiving
substantial cutting load and adapted for use with a selected shaft-form
handle that has, at its distal end, an axially aligned blade-unit
receiving opening, comprises a metal blade defining a working edge
and a load-transmitting, axially elongated metal support shank extending
therefrom and an intermediate load-transferring member of synthetic
resin permanently molded about a proximal portion of the shank,
the distal extremity of the intermediate member being spaced proximally
from the working edge leaving the blade and a substantial length
of the distal portion of the shank exposed, a proximal portion of
the intermediate member defining an attachment fitting adapted to
engage in load-transferring relation with the handle, and the proximal
portion of the shank extending through the intermediate member in
the region of the attachment fitting and being permanently embedded
within the intermediate molded member to define an elongated, load-transferring
interface therewith. The intermediate member is comprised of synthetic
resin that has substantial tensile and shear strength and is constructed
and arranged to receive, via the attachment fitting, the surgeon's
forces on the handle, and to receive via the substantial load-transferring
interface, forces from the proximal end of the shank attributable
to the resistance encountered by the metal blade, the substance
of the intermediate member being adapted to transfer the surgeon's
forces to overcome the resistance forces while maintaining the blade
in fixed relationship to the handle.
According to one preferred aspect of the invention, the axially
aligned blade-unit receiving opening in the handle is internally
threaded, a distal portion of the intermediate member is terminated
in a proximally directed, annular butt surface adapted to engage
a distally directed surface of the handle, and a proximal portion
of the intermediate member has a smaller diameter than the distal
portion and defines a set of external threads adapted to match and
engage in load-transferring relationship with internal threads of
the handle.
In preferred embodiments of this preferred aspect of the invention,
the body of the intermediate member is resiliently deformable to
the degree that, without disturbing the load-transferring relationship
of the intermediate member with the shank, hand tightening of the
threads of the blade unit on the handle, and resultant compressional
engagement of the annular butt surface of the intermediate member
with the distal end surface of the handle, causes resilient stretching
of the body of the intermediate member between the butt-surface
and the external threads to produce a locking frictional engagement
between these external threads and the internal threads of the handle,
thereby to prevent rotation of the blade unit during surgical use.
In preferred embodiments of the invention, where the surgical blade
unit is assembled with a selected shaft-form handle, the blade-unit
receiving opening of the handle is configured to receive the attachment
fitting portion of the blade unit in a close-fitting relationship,
whereby the intermediate member is restricted against lateral expansion
by the confining surfaces defining the opening; the blade unit is
in the form of an arthroscopic blade, the blade and intermediate
member being sized to lie within a surgical cannula of, e.g., 4
mm internal diameter; the blade unit is a retrograde blade, the
working edge of the blade unit being disposed for operation during
pulling motion; the synthetic resin is autoclavable and gamma irradiatable
for sterilization, preferably the synthetic resin is selected from
the group consisting of nylon, acetal copolymer, polysulfone; polyethylene
and polypropylene and the distal end of the intermediate member
is tapered to facilitate entry of the blade unit between close-lying
portions of the body during surgery.
According to a further aspect of the invention, where the blade
unit includes a retrograde blade, at the distal extremity of the
intermediate member, the shank and intermediate member are substantially
coaxial, the distal extremity of the shank supporting the working
edge disposed for reverse cutting is substantially coaxial with
the intermediate member, and the intervening exposed distal portion
of the shank lies on an axis at an angle transverse to the axis
of the intermediate member.
The invention thus provides a surgical blade unit which is simple,
yet may be securely attached and locked to a variety of different
handles for use under high force conditions, e.g. in the knee, and
which is adapted to receive forces applied by the surgeon to overcome
forces attributable to large resistances encountered by the blade,
with markedly reduced danger of separation.
DESCRIPTION OF THE PREFERRED EMBODIMENT
We turn to the structure, use and manufacture of the preferred
embodiment, first briefly describing the drawings.
DRAWINGS
FIG. 1 is a side view partially in section of a blade with a molded
member according to the invention;
FIG. 1a is a side view partially in section of a different blade
passing through a narrow diameter cannula into a surgical site;
FIG. 2 is a side view, partially in section, of a different blade
unit inserted in a handle, while FIGS. 2a and 2b are free body diagrams
showing the forces generated in the blade unit locking feature of
the invention and FIG. 2c is a graph of tension in the member over
length L when the blade is locked in the handle;
FIG. 3 is a diagrammatic view showing an instrument according to
the invention with accessories for arthroscopic surgery of the knee;
FIG. 4 is an isometric view of an insert according to the invention
in the holder package;
FIG. 5 is a free body diagram showing transfer of opposing forces
applied during use, while FIG. 5a is a similar view enlarged to
show lateral forces present in the assembled unit; and
FIG. 6 is a top view of a mold part with a retrograde blade blank
and mold insert in place according to the invention, while FIG.
6a is a side section view of the assembled mold for injection of
synthetic resin.
STRUCTURE
In FIG. 1 there is shown a surgical blade unit 10 adapted for
use with a selected shaft-form handle in high force conditions,
comprising blade 12 in this case a retrograde blade with elongated
metal shank 14 having a sharpened working edge 16 adapted for reverse
cutting, i.e. by pulling motion. Molded about proximal portion 18
of shank 14 is an intermediate load-transferring member 20 of rigid
synthetic resin material, e.g. nylon, acetal, polysulfone, polyethylene
or polypropylene selected for the characteristics discussed below.
The blade unit 10 is sized and configured to allow passage through
a narrow opening, e.g. for introduction on a handle 22 into the
body through a small diameter, d, e.g. 3 to 5 mm, cannula 24 as
shown in FIG. 1a, for arthroscopic surgery.
Shank 14 typically 2.3 inches in overall length, extends axially
completely through member 20 with the distal end supporting working
edge 16 exposed distally for a substantial length, typically about
1.2 inches for the retrograde blade shown, and end portion 26 projecting
proximally from member 20 typically about 0.1 inch.
Intermediate member 20 has a bullet-shaped head portion 28 with
maximum diameter, typically 0.16 inch, at the proximal annular surface
30 and terminates distally in hemisphere 32 of radius, r, typically
about 0.055 inch, which is substantially equal to one half the width,
W, typically about 0.110 inch, of blade shank 14 at point 34 where
it emerges from member 20. (This configuration provides maximum
strength in the relationship of intermediate member 20 to blade
12 at their intersection.) Smoothly sloped surface 36 between hemisphere
32 and annular surface 30 facilitates movement of the instrument
through constricted passages, e.g. within the body.
Proximal to head portion 28 member 20 has a smaller diameter,
typically about 0.135 inch, for entry into the handle opening, and
has an attachment fitting comprising external threads 38 defined
on its surface. Proximal shank portion 18 of blade 12 extending
axially beneath threads 38 completely through member 20 has surface
irregularities in the form of projections or scallops 40 along both
side surfaces 42 44 to create an elongated load-transferring interface
46 between member 20 and the metal blade shank. Shank portion 18
also serves to strengthen the threaded section of the member. Distally
of scallops 40 flanges 48 extend from shank 14 transversely to
blade axis, A, into the body of member 20 to further secure blade
12 against relative movement within member 20. (The flanges are
also understood to provide some slight additional load-transferring
between the blade and member.)
Referring now to FIG. 2 a different surgical blade unit 10' is
shown with meniscus surgical blade 12' having shank 14' and sharpened
blade edge 16'. The member 20 and proximal shank portion (not shown)
of the blade unit 10' are identical to that of device 10 shown in
FIG. 1. The overall length of this blade is typically about 2.07
inches.
In FIG. 2 device 10' is shown partially threaded into handle 22
which is a hollow rod with an axially aligned blade-receiving opening
50 having internal threads 52 sized and configured to securely receive
threaded portion 38 of member 20 over a length, L, typically about
0.27 inch, equal to at least three times the root diameter of member
20 in the area of the threads in order to establish a load-transferring
relationship between the handle and the member, and also to ensure
that the desired secure connection between the blade unit 10' and
handle 22 is achieved. (Only the threaded portion of handle 22 is
shown as the blade unit is adapted for attachment to any form of
manipulative device having a suitable coacting attachment means.)
After device 10' is threaded into handle threads 52 the predetermined
length L, proximally directed annular butt surface 54 of head portion
28 of member 20 engages upon the distal end surface 56 of handle
22. Referring also to the free body diagrams shown in FIGS. 2a and
2b, slight further relative rotation of blade unit 10', shown in
solid line, in handle 22 shown in dashed line, causes the relatively
fixed threads 38 of member 20 to resiliently deform slightly between
the threads 52 of metal handle 22 without disturbing the load-transferring
relationship of member 20 with shank 14'.
Hand tightening of blade unit 10' on handle 22 generates force,
H, due to the resultant compressional engagement of annular butt
surface 54 of member 20 on distal end surface 56 of handle 22 and
force, C, caused by the rotation of member threads 38 in the proximal
direction in relatively fixed threads 52 of handle 22. Coaction
of the forces causes resilient stretching of the body of member
20 between the butt surface 54 and the external threads 38 which
causes tension in threads 38 and produces a locking frictional relationship
between threads 38 of member 20 and the internal threads 52 of handle
22. The opposing forces exerted by the threads, shown representatively
in FIG. 2b by arrows T, resist rotation of the blade unit during
surgical use. As shown in FIG. 2c, the tension in threads 38 of
member 20 decreases in the proximal direction over length L when
the blade is locked in the handle.
OPERATION
Referring now to FIG. 3 surgical instrument 58 with surgical blade
unit 10 is shown inserted on the end of handle 22 through narrow
cannula 24 into the patient's knee joint 60. At the same time, a
fiber optic device 62 introduces light to the interior of the joint
from light source 64 and returns a visual image along a separate
optical path. The image, in the preferred embodiment shown, is directed
to an eyepiece 66 through which the surgeon observes to control
his or her movements. (The image can also be recorded or can be
directed to a television screen.) During the operation the knee
is typically inflated by gas or fluid from source 68.
During the operative procedure, the patient may be anesthesized
and punctures made with a trocarring cannula at points about the
joint for introduction of the fiber optic device 62 the cannula
24 for instrument 58 and the inflation source 68.
The surgical nurse opens a sealed, sterile package containing a
sterile holder 70 (FIG. 4) and surgical blade unit 10" having
a blade with a standard side-facing working edge 16" and dumps
the holder and blade unit onto a sterile field. The blade unit 10"
is then assembled with a handle, which typically has been sterilized
by autoclaving and hand tightened until blade unit 10" is locked
onto the handle 22.
Referring back to FIG. 3 the instrument is inserted through cannula
24 into knee joint 60. The surgeon positions the retrograde blade
with the sharpened edge 16 beyond the tissue he wishes to cut, e.g.
cartilage within the knee. The bullet-shaped head portion 28 of
blade unit 10 facilitates positioning as it eases the enlarged handle
portion into more constricted areas of the joint. Furthermore, by
selection of special low friction polymers for the member, e.g.
Celcon.RTM. acetal copolymer supplied by Celanese Plastics Materials
Co. of Chatham, NJ, Delrin.RTM. acetal polymer supplied by E. I.
DuPont de Nemours & Co. of Wilmington, Del., the head portion
moves more easily, e.g. than metal, through the tissue.
Referring also to FIG. 5 once the cutting edge is positioned relative
to the tissue to be cut (not shown), the surgeon draws instrument
58 proximally, shown representatively by dashed arrows D, to move
sharpened edge 16 through the tissue. By cutting in the proximal
direction, force R, shown by dashed arrows, is exerted in the distal
direction to urge cutting blade unit 10 out of handle 22. This is
a critical point of failure for standard metal collets and other
collets not having the features of the subject unit, i.e. an intermediate
member to transfer the opposing loads between the handle and the
metal blade, the forces being shown representatively in FIG. 5 by
solid arrows.
The load generated by drawing forces D applied by the surgeon to
handle 22 is transferred into member 20 the intermediate member,
through the load-transferring relationship established between internal
handle threads 52 and external member threads 38. The load of force
D, carried through the body of member 20 is then transferred into
shank proximal portion 18 of blade 12 through the elongated load-transferring
interface 46 between the member 20 and the shank, and finally through
metal blade shank 14 to cutting edge 16 to overcome the load of
resistance force R, transferred from cutting edge 16 to handle 22
by the same means operating in the opposite direction. Referring
to FIG. 5a, any axial movement of proximal portion 18 of shank 14
within member 20 requires that the material of the member expand
laterally in the area of threads 38 to allow passage of projecting
scallops 30. However, when the blade unit is assembled with a handle,
the tightly confining inner surface of handle 22 restricts lateral
expansion of the member to further prevent separation of the blade
from the handle. Also, the closeness of the projections to the outer
surface of member 20 in the area of the threads prevents any significant
inward deflection of the threads due to the compressional or resistance
forces applied.
In tests, sterilized instruments of this design have withstood
opposing forces of up to 50 pounds.
Also, while only retrograde blades (and also surgical hooks and
saws) have configurations in which high distal draw-out forces are
repeatedly applied, blades with side and end cutting edges, e.g.
as shown in FIGS. 2 and 4 may also become wedged or jammed and
may have to withstand considerable forces in the distal direction
while the surgeon attempts to dislodge them.
After surgery is complete and the severed tissue fragments have
been removed from the joint, the cannulas and other instruments
are removed and the punctures closed.
MANUFACTURE
Referring now to FIG. 6 the surgical blade unit is manufactured
by placing a formed metal blade 12 with the shank proximal portion
18 in the forming cavity 72 defined by mold part 74 and part 76
(FIG. 6a). Cavity 72 has first and second ports, 78 and 80 respectively.
Port 78 is sized and adapted to tightly engage about the intermediate
portion of shank 14 to form a substantially leak-proof seal. Port
78 also aligns blade 12 along axis A of the device. Port 80 is sized
and adapted for connection of injection source 82 of the desired
polymeric material to cavity 72. The proximal end portion 26 of
shank 14 lies adjacent to port 80.
Mold insert 84 shown also in FIG. 6a, extends between mold parts
74 76 through the corresponding indent 86 defined in the side surface
42 of shank proximal end 26. The surface of end defining indent
86 engages about insert 84 to resist movement of the blade 12 in
the axial direction with the flow of synthetic resin from injection
source 82.
The synthetic resin material is selected to have the characteristics
of being injection moldable, having good tensile and shear strength
at the load transferring interface 46 between the member 20 and
the scallops 40 and at the threads 38 52 (for Celcon.RTM. M90 material,
tensile strength is 13700 8000 and 5000 lbs./in..sup.2 at -40.degree.
F., 73.degree. F. and 160.degree. F. respectively; and shear strength
is 7700 6700 and 5700 lbs./in..sup.2 at 73.degree. F., 120.degree.
F. and 160.degree. F., respectively), being compressible under hand
pressure (the compressive stress of Celcon.RTM. M90 is 4500 lb./in..sup.2
at 1% deflection and 16000 lb./in..sup.2 at 10% deflection), and
generating tight friction with the opposed threads of the handle
for locking the blade into the handle.
For insertion into the body, the material must be FDA approved,
and be sterilizable, e.g. by autoclaving or irradiation, and also,
for easy movement through constricted openings in the tissue, the
material should have the characteristic of low surface friction.
Forms of nylon, acetal copolymer, polysulfone, polyethylene and
polypropylene polymers have these characteristics.
Mold part 88 is positioned about the distal end of blade 12 to
further align the blade in the mold cavity and also provide an abutting
surface 90 to further prevent axial movement of blade 12 with the
flow of synthetic resin into the cavity.
After the blade 12 is positioned in the mold, the mold parts are
closed under pressure and the mold parts lock blade 12 in position.
Synthetic resin material is injected from source 82 in liquid form
at high pressure through port 80 to fill cavity 72.
As the synthetic resin in cavity 72 cools, it permanently contracts
about shank 14 of blade 12 forming load transferring interface 46
and exerting hoop-tension forces to hold the shank 14 tightly within
the molded member 20. When the resin has sufficiently cooled, the
mold is opened and the surgical blade unit 10 of blade 12 and member
20 is ejected.
OTHER EMBODIMENTS
Other embodiments of the invention are within the following claims.
For example, other surgical blade units, e.g. surgical hooks or
saws, may be fitted with a member according to the invention for
securing to a handle. The blade blank can have other forms, e.g.
round. The blade units may be provided in sterile or non-sterile
packaging. Also, mold parts corresponding to part 78 shown in FIG.
6 may be used with other configurations to perform the same purpose.
Also, because the sharpened edge is positioned outside the mold
during the operation, the blades may be presharpened prior to molding.
In some blade configurations, e.g. the retrograde and meniscus blades
(12 FIG. 1; 12' FIG. 2 respectively), the edge is protected by
adjacent masses of the blade. In other configurations, e.g. as shown
in FIG. 4 the edge should be protected, e.g. with a piece of soft
tubing. The attachment fitting of the blade unit to the handle may
be achieved by other means, e.g. without the tensioned-thread locking
feature of the preferred embodiment described above. |