U.S. patent number 3,630,204 [Application Number 05/049,301] was granted by the patent office on 1971-12-28 for blade for bone reamer.
Invention is credited to Meyer Fishbein.
United States Patent |
3,630,204 |
Fishbein |
December 28, 1971 |
BLADE FOR BONE REAMER
Abstract
A bone-cutting blade with a convex scraper edge, rotatable about
an axis which is in the plane of the blade and which intersects the
midpoint of the convex scraper edge, the convex scraper edge having
spaced notches therein, alternating with arcuate blade edge
segments, with segments one side of the midpoint of the arcuate
blade corresponding in position along the blade edge with notches
on the opposite side of the midpoint.
Inventors: |
Fishbein; Meyer (Los Angeles,
CA) |
Family
ID: |
21959104 |
Appl.
No.: |
05/049,301 |
Filed: |
June 24, 1970 |
Current U.S.
Class: |
606/81; 408/224;
408/228 |
Current CPC
Class: |
A61B
17/1666 (20130101); Y10T 408/906 (20150115); Y10T
408/9093 (20150115) |
Current International
Class: |
A61B
17/16 (20060101); A61b 017/32 (); B23b 051/10 ();
B23d 077/00 () |
Field of
Search: |
;128/305
;408/223,224,227,228 |
Foreign Patent Documents
|
|
|
|
|
|
|
1,020,421 |
|
Nov 1952 |
|
FR |
|
1,031,888 |
|
Mar 1953 |
|
FR |
|
Primary Examiner: Pace; Channing L.
Claims
I claim:
1. A rotary shearing blade for a rotary bone cutter adapted to
rotate it on an axis substantially in the plane thereof, comprising
a flat plate having a convex arcuate edge struck from a center
point on said axis of rotation, said arcuate edge being oppositely
beveled on opposite sides of its midpoint, the two halves of said
beveled arcuate edge, on opposite sides of said midpoint, having
spaced notches therein, alternating with beveled arcuate edge
segments, with segments on one of the halves corresponding
substantially in position along the arcuate edge with notches in
the other half, such that the segments on the two halves of the
arcuate edge coact to cut a continuous substantially hemispherical
surface of revolution when rotated on said axis, with each half
cutting a plurality of spaced zones thereof which intervene between
zones cut by the other half.
2. The subject matter of claim 1, wherein the beveled edge segment
on one arcuate edge half of the blade extends to the midpoint of
the arcuate blade edge, and is immediately adjoined, at said
midpoint, by an oppositely beveled edge segment on the other
arcuate edge half of the blade.
3. The subject matter of claim 1, wherein blade segments on each
side of the midpoint of the blade define and occupy zones about the
axis of rotation which at least meet adjacent zones defined and
occupied by notches on the opposite side of the midpoint of the
blade.
4. The subject matter of claim 3, with blade segments longer than
blade notches, in such arrangement that zones defined and occupied
by blade segments on each side of the midpoint of the blade at
least meeting zones defined and occupied by the blade notches on
opposite sides of the midpoint of the blade.
5. The subject matter of claim 4, wherein the zones occupied on
each side of the midpoint of the blade at least slightly overlap
zones defined and occupied by blade notches on opposite sides of
the midpoint of the blade.
Description
RELATED APPLICATION
This application discloses an improvement over a bone cutting blade
disclosed in my copending application filed Aug. 22, 1969, Ser. No.
852,226.
FIELD OF THE INVENTION
This invention relates generally to blades for rotary bone cutters,
particularly of the variety designed for forming a hemispherical
socket in a bone, e.g., in hip surgery.
BACKGROUND OF THE INVENTION
In hip surgery, the procedure known as cup arthroplasty includes
the reshaping of the acetabulum of the hip to provide a nicely
rounded cavity therein. This has been done in various ways
heretofore, and my aforesaid patent application discloses a rotary
cutter and blade for accomplishing this purpose in an improved
manner. The blade is a flat, tool steel plate, with an arcuate
shearing edge, and is rotated in the bone cavity to generate
hemispherical surface of revolution therein. An electric drill is
used to drive the holder for the blade, and it is the common
practice to use for this purpose self-contained battery power for
this drill, with the drill housing sealed against any possibility
of sparking such as might cause ignition of any explosive gases
that might be present in the operating room. Such drills are
generally of relatively low power and limited in torque; and in
some cases the bone in the region of the socket to be constructed
has become so dense and hardened that the torque available from a
drill of the type mentioned has been somewhat limited for the bone
condition encountered. For this reason particularly, but also
because a reduced torque requirement is always desirable, the
purpose of the present invention is to materially reduce the torque
requirement of the blade mentioned above.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention the arcuate cutting of the
earlier blade, mentioned hereinabove, is formed on opposite sides
of its midpoint with spaced notches, alternating with arcuate blade
edge segments, with the notches on one side of the midpoint
corresponding generally in position with the arcuate segments on
the opposite side of the midpoint. Together, the segments cover the
full area of the hemispherical cavity, but each arcuate half of the
blade engages and cuts along a series of segments whose summed
length is materially less, e.g., half, or somewhat more, of the
full length of the arcuate half of the blade. The overall torque
requirement to cut through the bone can thereby be reduced as much
as half; and with a given torque availability, the cutting force
availability can thus be doubled. With this improvement, relatively
lightly powered battery operated drills such as are now
commercially available, and such as are admirably suited to the
work because of compactness and low weight are capable of
generating the torque necessary to cut dense and hard bone easily
and satisfactorily.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view of a reamer in accordance with
the invention, with parts broken away;
FIG. 2 is a side elevational view of the cutter, in a position at
90.degree. from FIG. 1, parts being broken away;
FIG. 3 is a front elevational view of the cutter as seen from the
left toward FIG. 2;
FIG. 4 is a side elevational view, to double scale, of the blade of
the cutter of FIGS. 1-3;
FIG. 5 is a view of the blade, as seen looking toward the right in
FIG. 4;
FIG. 6 is a fragmentary perspective view of the central portion of
the cutter blade; and
FIG. 7 is a largely diagrammatic view showing the cutter blade in a
simple basic form.
DESCRIPTION OF A PREFERRED EMBODIMENT
In the drawings, a rotary bone cutter has a head 10 of
substantially hemispherical form with a convex front surface of
revolution 11, and a flat rearward surface 12. A hub 13 with a
reduced coaxial coupling pin 14 projects axially from surface 12.
Pin 14 is received in a socket 15 in the end of a somewhat tapered
shank 16, and is connected to the latter by a roll pin 17. Shank 16
is to be understood as adapted at its opposite end for coupling to
a rotary driver, preferably an electric surgical drill.
The center of curvature C of the convex front face of the head 10
is preferably spaced somewhat rearwardly of the rearward head
surface 12, so that while the head can be described as generally or
substantially hemispherical, its preferred form is just a trifle
under a full 180.degree. hemisphere.
The hemispherical head 10, and the hub 13, for approximately
three-fourths of the depth of the latter, are split longitudinally
on a diametrical plane, forming a diametrical slot 20, adapted to
receive the flat, tool steel blade 22. The blade 22 is shaped in
general resemblance to the head and hub, with alternating notches
and segments, its cutting edge being convex in form, as described
later, and with a shank 24 extending from its base edge 25, so as
to seat into the bottom of the slot 20. The hub is drilled and
tapped on the axis of the center C to receive a shoulder bolt 27,
and the blade 22 is drilled as at 28 to receive and be positioned
accurately by this bolt 27. Tightening of the bolt 27 clamps the
split head and knife in solid assembly. The blade may be quickly
removed and replaced by taking out and replacing the bolt 27.
The radius r of the convex blade edge 30, drawn from center C, is
slightly greater than that of the convex head surface 11, so that
the blade edge projects a slight marginal distance beyond the
latter for proper cutting, the cutting depth being controlled by
the proximity of the hemispherical surface 11. The blade edge is
oppositely beveled on opposite sides of its center or midpoint 31
to give a suitable clearance angle for each half of the blade, as
designated at 32 and 33, and so as to form two shear or scraper
edges 32' and 33', respectively. Rotation of the head spins the two
convex scraper edges against the cartilage and/or bone to take a
fine hemispherical shear type cut therein, which may be
progressively deepened as desired. The blade produces fine cuttings
or scrapings, which are disposed of as presently described. It will
be particularly noted that the curved blade edges 32' and 33' move
normally to the bone, and depth of cut is controlled to be uniform
along the entire blade edges by the uniform projection distance
thereof beyond the hemispherical guide surface 11. Maximized
cutting rate can be achieved with projection distance small enough
to avoid gouging or chatter.
Preferably, the blade slot 20 is bisected by a diametrical plane P
of the head, so that the two blade edges 32' and 33' are
equidistantly positioned, by distances equal to the half-thickness
of the blade, ahead of this diametrical plane. Maximum uniformity
of cutting by the two oppositely beveled half-lengths of the blade
is thereby achieved, and a highly uniform hemispherical socket
obtained.
Alongside each knife edge 32' and 33', the head 10 is formed with a
trough, passage, or groove 40. As will be seen, each of these
grooves extends from a point just beyond the midpoint of the blade,
back past said midpoint and angularly down or back alongside the
opposite half of the blade. The groove opens to the blade on one
side, and intersects the convex surface 11 on the other, in a
curved line 42, opening through a discharge notch 44 in the back
surface 12 of the head, adjacent its periphery.
It will be seen especially from FIG. 3, that the groove 40,
positioned immediately in advance of the scraping edge of the
blade, receives and gathers scrapings and cuttings from the blade,
and that these will pack into, flow along, and be continuously
discharged from the groove 40 and its exit notch 44 in the back of
the head 10 during the operation of the drill.
Irrigation is not required, and since the cuttings and scrapings
pass continuously out of the cutter and the bone cavity being
formed, there is no need for the surgeon to stop his work to clean
out the cutter.
Irrigation is not required, and since the cuttings and scrapings
pass continuously out of the cutter and the bone cavity being
formed, there is no need for the surgeon to stop his work to clean
out the cutter.
The cutter as heretofore described, excepting for brief reference
to the blade notches is disclosed in my aforementioned application.
For a basic understanding of the present invention, please refer to
the diagrammatic FIG. 7 of this application. The arcuate, convex
edge 30 of the blade 22 is divided into two halves by a midpoint 31
coinciding with the axis of rotation A-A'. The convex edge 30 is
shown to subtend somewhat less than 180.degree. of angle about the
center C of the edge 30, and, for simple example, each half of the
edge 30, on opposite sides of midpoint 31, has two arcuate segments
50, alternating with two notches 51. The segments will be
understood to be oppositely beveled on opposite side of the
midpoint 31, as explained in connection with FIGS. 1- 6. The
segments in this simple example are of the same lengths as the
notches 51, though in the preferred example, FIGS. 1- 6, the
segments 50 exceed the notches in length by substantially 2to 1. As
seen in simple basic example of FIG. 7, the first segment 50 of the
lower half of the blade edge 30 has one end at the midpoint 31. It
is followed by a notch 51, then a second segment 50, and a second
notch 51. (More segments and notches are desirable in practice.)
The upper half of the blade edge 30 beings at midpoint 31, with a
notch 51, followed by a segment 50, a second notch 51, and a second
segment 50. Thus, a segment on one-half of the convex blade edge
corresponds in position along the arc with a notch in the other
half. It will be clear that if the blade is rotated on axis A-A',
the cutting segments on one half will cut spaced bands in the
hemispherical bone cavity, and the cutting segments on the other
half will cut the remaining or intervening "bands," so that a
complete substantially hemispherical cut will be made. It is
convenient to adopt as a definition for these "bands," that used in
works on Solid Geometry, i.e., "the portion of the surface of a
sphere included between two parallel planes is called a "zone." The
two ends of each segment and of each notch of each blade half thus
define a "zone." And for the simple example of FIG. 7, these zones
Z meet edge to edge along parallel planes such as p in FIG. 7. The
zone defined and occupied by each segment on each blade half thus
meets and fits precisely between adjacent zones defined notches on
the other blade half. If, however, the segments are of greater
lengths than the notches, as in FIG. 1-6, the zones for the
segments slightly overlap the zones defined by the notches. There
is thus a factor of safety assuring that cutting will occur
continuously about the complete hemisphere.
Turning now to the preferred embodiment of FIGS. 1-6, it will be
immediately observed that a larger number of segments 50 and
notches 51 have been used, and also, as suggested hereinabove, that
the segments 50 have been made substantially double the length of
the notches 51. Also, as will be clear from the drawings, the zones
defined by the segments at least slightly overlap the zones defined
by the notches in the opposite half of the convex blade. Clean
cutting and stable nonchattering cutting, with assurance of cutting
continuously, without leaving a narrow strip of bone between
successive segments on the two halves of the blade, are thereby
achieved.
A further improvement in the region of the midpoint 31 of the
convex blade is also employed. Note that the segment 50 (FIG. 5) at
the midpoint of the blade is above the midpoint for most of its
length, but extends for a short portion 50a of its length below the
midpoint 31, and that this last mentioned portion of the segment
has an opposite bevel from the remainder of the segment. The
segment, thus divided into two oppositely beveled portions, assures
clean cutting at the center.
It will be clear that various changes in design in the number,
length, location, and arrangement of the segments or teeth 50 and
the notches or gaps 51 may be made within the broad scope of the
invention. The present blade, which performs successfully, has a
center-to-center spacing angle, from notch to notch, of 18.degree.
15', and the notches are substantially 0.10 inch in length along
the arc. The blade is double scale in the patent drawings in FIGS.
5 and 6 (prior to reduction in printing).
* * * * *