Note: Descriptions are shown in the official language in which they were submitted.
Z173935
INTEGRAL REA~ER APPARATU8
Cross-Reference to Rel~ted Application
B~c~LG~d of th~ Invention
This application is a continuation-in-part of U.S.
application serial no. 224,046, filed April 7, 1994, entitled
"Universal Modular Reamer System".
Field of the Invention
The invention relates to medullary reaming systems and to
flexible drive shafts therefor.
Description of the Prior Art
Medullary reamers are used to enlarge the medullary canals
of bone for various reasons. The medullary canals of bone
typically have some degree of curvature and, for this reason,
are almost always prepared with reamers having a flexible
shaft.
One type of prior flexible medullary reamer shaft consists
of a spiral or helically wound metal wire or strip which
comprises the shaft of the reamer. A disadvantage of this
type of shaft is that the reamer can be operated only in the
forward mode of rotation. If the reamer is reversed, which is
occasionally necessary in order to free a lodged reamer, for
example, the shaft unwinds, damaging the shaft. Another
disadvantage of this spiral shaft design is that the voids
between the shaft coils can trap blood and tissue, making it
extremely difficult to thoroughly and properly clean and
sterilize the shaft after use. Another disadvantage is that,
if the cutting head experiences unusually high resistance, the
driving torque will accumulate in the shaft as its coils close
and then, when it overcomes the resistance to the head, will
be released in a sudden burst, causing the cutting head to jump
or spin ahead rapidly in an uncontrolled fashion. Such
irregular movement of the cutting head may damage the bone.
Another type of medullary reamer shaft comprises a
plurality of parallel, flexible elements joined together at
~5 their opposite ends by means of a welded or soldered
connection. Such a shaft construction suffers from most of the
2173~35
same disadvantages as the helically coiled shaft described
above. Another disadvantage occurs in attempting to utilize
the central bore of the reamer to receive a long, small-
diameter guide wire, which had previously been inserted into
the medullary canal to act as a track for the advancing reamer.
Except at its respective ends, this parallel-element reamer
shaft lacks a well-defined and bordered central bore, making
it difficult to prevent the guide wire from exiting the reamer
in the area of the free standing shaft wires during the initial
positioning of the guide wire within the reamer.
To overcome many of these disadvantages, there has also
been provided a hollow tubular shaft formed of synthetic
plastic material or a fiber-reinforced composite material.
However, plastic shafts may lack the necessary torsional
~5 strength. Also, the reamer is autoclaved often and plastic
will ultimately fail. A disadvantage of fiber-reinforced
composite shafts is that, on failure, there is a danger that
fibers will enter the blood stream.
Also, in prior medullary reamers the cutting head has been
fixed to the flexible shaft by suitable welding or bonding.
But those attachment techniques require additional processing
or handling steps and can alter the properties of the materials
of which the joined parts are formed.
Summary of the Invention
It is a general object of the invention to provide an
improved medullary reaming apparatus which avoids the
disadvantages of prior systems while affording additional
structural and operating advantages.
An important feature of the invention is the provision of
a medullary reamer with a flexible drive shaft which provides
uniform transmission of energy to a cutting head in forward and
reverse directions and which is easy to clean.
In connection with the foregoing feature, a further
feature of the invention is the provision of a reamer shaft of
the type set forth which minimizes the risk of body
contamination.
2~ 7393~
Still another feature of the invention is the provision
of an integral reaming apparatus with a cutting head
permanently fixed on a flexible reamer shaft without altering
the properties of the materials of the joined parts.
In connection with the foregoing feature, another feature
of the invention is the provision of a method for forming the
reaming apparatus.
Certain ones of these and other features of the invention
are attained by providing a medullary rotational reaming
~0 apparatus comprising: an elongated flexible shaft having a
coupling portion at an end thereof, and an end member having
a hollow tubular coupling shank, the shank having a coupling
inner surface which is non-circular in transverse cross section
and is dimensioned to prevent free reception of the coupling
portion therein, the coupling portion being axially received
in press-fitted permanent engagement within the shank with the
coupling portion permanently deformed to the transverse cross
section of the coupling inner surface of the shank, whereby the
end member is fixed to the shaft solely by the press-fitted
engagement of the coupling portion in the shank.
Still other features of the invention are attained by
providing a method of forming a medullary rotational reaming
apparatus including an elongated flexible shaft having coupling
portions at the ends thereof and an end member having a hollow
tubular coupling shank with an inner surface, the method
comprising the steps of: shaping the inner surface of the
coupling shank to a non-circular transverse cross section, at
least the minimum transverse dimension of which is less than
the outer diameter of a coupling portion of the shaft, and
press-fitting a coupling portion of the shaft axially into the
shank so as to permanently deform the coupling portion of the
shaft to the transverse cross-section of the inner surface of
the shank, thereby to permanently fix the end member on the
shaft.
The invention consists of certain novel features and a
combination of parts hereinafter fully described, illustrated
21 73.935~
in the accompanying drawings, and particularly pointed out in
the appended claims, it being understood that various changes
in the details may be made without departing from the spirit,
or sacrificing any of the advantages of the present invention.
Brief Description of the Drawings
For the purpose of facilitating an understanding of the
invention, there is illustrated in the accompanying drawings
a preferred embodiment thereof, from an inspection of which,
when considered in connection with the following description,
the invention, its construction and operation, and many of its
advantages should be readily understood and appreciated.
FIG. 1 is a fragmentary, side elevational view of a reamer
of a medullary reaming system in accordance with a first
embodiment of the present invention, with portions broken away
and showing different positions in phantom to illustrate the
flexibility of the shaft;
FIG. 2 is a fragmentary, perspective view of the support
of the reaming system holding a plurality of cutting heads and
illustrating insertion of the reamer shaft;
FIG. 3 is an enlarged, fragmentary view in partial
vertical section showing the female connector of a cutting head
held on the support with the male connector on the shaft about
to be inserted;
FIG. 4 is an end view of the female connector taken along
the line 4-4 in FIG. 3;
FIG. 5 is an end view of the male connector taken along
the line 5-5 in FIG. 3;
FIG. 6 is a view similar to FIG. 3, illustrating the male
and female connectors in their coupled condition;
FIG. 7 is a view similar to FIG. 6, illustrating the
latching engagement of the male and female connectors after
removal from the support;
FIG. 8 is a fragmentary, side elevational view taken along
the line 8-8 in FIG. 7;
FIG. 9 is a sectional view taken along the line 9-9 in
FIG. 7;
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FIG. 10 is a fragmentary, perspective view of a reamer
with a fixed cutting head;
FIG. 11 is a fragmentary, side elevational view of a
reaming apparatus in accordance with another embodiment of the
invention, with portions broken away;
FIG. 12 is an enlarged, fragmentary, sectional view
showing the first stage of press-fitting the cutter head onto
the shaft of the apparatus of FIG. l;
FIG. 13 is a further enlarged, sectional view taken along
line 13-13 in FIG. 12;
FIG. 14 is an enlarged, fragmentary, sectional view
showing the completed press-fitted joint between the parts
shown in FIG. 12;
FIG. 15 is a further enlarged, sectional view taken along
~5 the line 15-15 in FIG. 14;
FIG. 16 is an enlarged, sectional view taken along the
line 16-16 in FIG. 11;
FIG. 17 is an end elevational view of another cutter head
of the present invention;
FIG. 18 is an enlarged, end elevational view of the cutter
head of the apparatus of FIG. 1; and
FIG. 19 is an end elevational view of another cutter head
of the present invention.
Description of the Preferred Embodiments
Referring to FIGS. 1 and 2, there is illustrated a reaming
system 10 in accordance with the present invention. The system
10 includes a reamer 11, comprising a cutting head 20 fixed to
the end of a flexible shaft 30, and a support 12 adapted for
holding a plurality of heads 20 in a support position for ready
~Q access by a user. Referring to FIG. 2, the support 12 includes
a bracket 13 which may be in the form of a flat plate having
a plurality of support notches 15 formed therein. Each of the
notches 15 has a part-circular inner end and a pair of parallel
notch edges 16 and 17 which have outwardly tapered portions 18
at their outer ends. Each of the cutting heads 20 has a head
body 21, which is a toothed or fluted cutting element having
2173Y35
an axial bore 2la therethrough. Integral with the head body
21 at its tail end is a coupling portion in the nature of a
female connector 22, which is preferably in the form of a
cylindrical tubular coupling shank 23. Referring also to FIGS.
3, 4 and 7, the coupling shank 23 has an axial bore 24
therethrough with an enlarged-diameter counterbore 24a at its
distal end, the counterbore 24a being provided with parallel
flats 24b along diametrically opposite sides thereof.
Respectively formed in the coupling shank 23 at diametrically
~0 opposed locations adjacent to the flats 24b are lateral slots
or grooves 25 and 26, which are formed as chords of the
coupling shank 23 and are sufficiently deep to communicate with
the counterbore 24a adjacent to its inner end for,
respectively, defining radial apertures 27 and 28 (FIG. 7).
The lower sides of the slots or grooves 25 and 26, as viewed
in FIG. 7, form latch keeper shoulders 29 for a purpose to be
explained more fully below.
Referring also to FIGS. 5, 6, 8 and 9, the flexible shaft
30 is in the nature of a cylindrical tubular member having a
cylindrical outer surface 31 and an axial bore 32 therethrough.
The shaft 30 may have any desired length, depending upon the
particular application, but may typically be in the range of
from 12 to 20 inches. It is a significant aspect of the
invention that the shaft 30 is formed of a titanium alloy and,
~5 more specifically, of a nickel-titanium alloy of a type which
has considerable flexibility. Preferably, the nickel-titanium
alloy is "super elastic" alloy having a maximum recoverable
strain of approximately 8%, i.e., the material can be strained
up to 8% and will still elastically return to its original
configuration. There results a flexible shaft 30 which has
great torsional strength and yet provides the flexibility
necessary for medullary reaming operations. The monolithic
metal structure precludes any release of fibrous material or
the like in the event of failure of the shaft. In a
constructional model of the invention, the flexible shaft 30
is formed of a nickel-titanium alloy of the type sold by
2~ 7333~
Raychem under the designation TINEL~ Alloy BB.
The flexible shaft 30 is coupled at one end thereof by a
drive coupler or adaptor 33 to an associated source of
rotational drive power (not shown) for rotating the shaft 30
about its axis, all in a known manner. Integral with the shaft
30 at its other end and projecting axially therefrom is a
coupling structure in the nature of a male connector 35 of
reduced cross-sectional area, so that the connector 35
cooperates with the adjacent end of the shaft 30 to define
~0 therebetween an annular shoulder 35a. The male connector 35
is basically cylindrical in shape and has a pair of parallel
slots 34 extending thereacross at the distal end thereof as
chords thereof, thereby to form two diametrically flexible arms
36 and 37, respectively having flattened outer surfaces 36a and
37a along most of their length. The flattened surfaces 36a and
37a terminate short of the distal ends of the arms 36 and 37,
so as to define laterally outwardly projecting latch fingers
or tabs 38 or 39, respectively, on the arms 36 and 37.
In operation, a plurality of the cutting heads 20 are
preferably supported on the support 12, as illustrated in FIG.
2. The cutting heads 20 all have identical coupling shanks 23,
but may have different size head bodies 21. The coupling
shanks 23 are respectively received in the support notches 15.
The notch edges 16 and 17 are spaced apart a distance less than
the outer diameter of the coupling shank 23 and are
respectively received in the lateral slots or grooves 25 and
26 of the coupling shank 23, as is best illustrated in FIGS.
2, 3 and 6. The distance between the notch edges 16 and 17 is
such that, in this supported position, they will respectively
extend radially inwardly of the coupling shank 23 at least as
far as the flats 24b. It will be appreciated that, when the
cutting heads 20 are thus supported on the support 12, they are
effectively restrained against axial movement. While, in the
illustrated embodiment, the support 12 is oriented so that the
supported coupling shanks 23 are disposed substantially
vertically, it will be appreciated that other orientations
2173935
could be used for ease of access, depending upon the particular
application.
When a user wishes to attach a particular cutting head 20
to the flexible shaft 30, the male connector 35 is aligned
beneath the selected cutting head 20, as illustrated in FIGS.
2 and 3, and is rotationally oriented so that the flexible arms
36 and 37 are, respectively, aligned beneath the flats 24b of
the coupling shank 23. The male connector 35 is then inserted
into the female connector 22 in the direction of the arrow in
FIG. 2 to the coupled condition illustrated in FIG. 6, wherein
the distal end of the coupling shank 23 bottoms against the
shoulder 35a on the shaft 30. It will be appreciated that the
arms 36 and 37 will flex to permit their insertion into the
counterbore 24a of the coupling shank 23 and, as was indicated
~5 above, the support bracket 13 will firmly hold the cutting head
20 against axial movement in response to this insertion. In
the coupled condition of FIG. 6, the latch fingers or tabs 38
and 39 will be respectively disposed opposite the lateral slots
or grooves 25 and 26 in the coupling shank 23, but will be
deflected out of those slots or grooves to an unlatching
condition shown in FIG. 6, wherein they are prevented from
engagement in the slots 25 and 26 by the notch edges 16 and 17
of the support bracket 13.
When the parts have been joined in the coupled condition
illustrated in FIG. 6, the user then pulls the flexible shaft
30 laterally outwardly to remove the cutting head 20 from the
support bracket notch 15. As the coupling shank 23 clears the
notch 15, the flexible arms 36 and 37 resiliently snap back to
their normal latching conditions, moving the latch fingers or
~30 tabs 38 and 39, respectively, into latching engagement with the
latch keeper shoulders 29, as illustrated in FIGS. 7-9, thereby
firmly latching the cutting head 20 to the flexible shaft 30.
It will be appreciated that, when it is desired to change
cutting heads, the user simply moves the coupling shank 23 of
the coupled cutting head 20 back into its supported position
in the corresponding notch 15 in the support bracket 13. As
21 7393~
the notch edges 16 and 17 reenter the lateral slots or groove
25 and 26 on the coupling shank 23 they deflect the flexible
arms 36 and 37 back to their unlatching conditions, illustrated
in FIG. 6, thereby permitting easy removal of the male
connector 35 from the female connector 22 for reattachment to
another cutting head 20.
It can be seen that the axial bore 32 through the flexible
shaft 30 continues through the male connector 35, and the axial
bore 24 through the coupling shank 23 is continuous with the
axial bore 2la through the cutting head body 21. Thus, when
the cutting head 20 is mounted on the flexible shaft 30, as is
illustrated in FIG. 1, there is a continuous axial bore through
the entire assembly, in standard fashion, for accommodating a
guide wire 40. In use, as the reamer 11 is passed through a
~5 medullary canal it is slid along the guide wire 40, which has
been preinserted in the canal, the guide wire 40 having an
enlarged knob 41 at its distal end sized so as not to pass
through the axial bore in the reamer 11, for purposes of
retrieving the reamer, all in a known manner.
While, in the preferred embodiment, the cutting heads 20
are removably coupled to the flexible shaft 30, it will be
appreciated that the flexible shaft of the invention could be
provided with a fixed cutting head. Thus, in FIG. 10 there is
shown a flexible shaft 50, which may be the same as the shaft
30 except that it lacks the male connector 35, and to which a
cutting head 60 is fixedly secured by any suitable means.
Indeed, it has been found desirable in certain
applications to utilize a reamer apparatus in which the cutter
head is fixed to the shaft. More specifically, it has been
found desirable that the ratio between the maximum outer
diameter of the cutting head and the outer diameter of the
shank of the cutting head be as large as possible in order to
maximize the clearance space between the cutter head blades,
so that the cut material can pass through these clearance
channels or flutes to the rear of the cutting head. If there
is insufficient clearance for pass-through of bone marrow or
2173~3~
other tissue, the cutting head tends to act as a piston and can
push the marrow out through a fracture site ahead of the
cutting head. These clearance channels or flutes between the
blades open at the outer surface of the cutting head shank, so
that the outer diameter of the cutting head shank determines
the depth of the clearance channels. Since the maximum outer
diameter of the cutting head blades is determined by the size
of the medullary canal to be reamed, the ratio between that
diameter and the outer diameter of the cutting head shank can
~0 be varied only by varying the shank diameter. Thus, in order
to maximize this ratio, the shank diameter must be minimized
and, accordingly, the outer diameter of the shaft to which the
shank is connected must, accordingly, be minimized. However,
in the modular embodiment of FIGS. 1-9, the shank diameter must
be large enough to properly accommodate the latch structure.
Thus, while the shaft diameter of the modular embodiment is
already smaller than in other commercially available scanners,
it could be made still smaller were it not for the latch
structure.
Referring now to FIGS. 11-16 and 18 there has,
accordingly, been provided an integral reamer apparatus 110
including a flexible shaft 111 having permanently fixed thereto
a cutting head 120 and a rotational drive coupling element 130.
More particularly, the elongated flexible shaft 111 is a
hollow, tubular shaft of circularly cylindrical cross section
with an axial cylindrical bore therethrough and may be formed
of the same material as the shaft 33, described above in
connection with FIG. 1. The shaft 111 has a cylindrical outer
surface 112 and has coupling portions 113 and 114,
respectively, at the opposite ends thereof, these coupling
portions preferably being beveled, as at 115 and 116, at the
adjacent ends of the shaft 111.
The cutting head 120 includes a head body 121 provided at
one end thereof with an elongated, circularly cylindrical
coupling shank 122 having a cylindrical outer surface 123. An
axial bore 124 is formed through the entire cutting head 120,
217393~
including the body 121 and the shank 122, in a known manner.
The body 121 is provided with a plurality of equiangularly
spaced-apart cutting blades 125 which extend laterally
outwardly and are spaced apart by clearance channels or flutes
126, the rear ends of which open at the outer surface 123 of
the shank 122.
Formed inside the shank 122 is a coupling surface 127
which is non-circular in transverse cross section. The
coupling surface 127 preferably has a quadrilobular shape, and
lo is formed by initially forming a counterbore 127a in the shank
122 having a diameter slightly greater than that of the axial
bore 124 and slightly less than that of the outer surface 112
of the shaft coupling portions 113 and 114. Then four
equiangularly spaced-apart lobes 128 are formed in the
counterbore 127a. Preferably, the lobes 128 are arcuate in
shape and are formed by machining the counterbore 127a of the
shank 122 by any suitable process to respectively form the four
lobes. The coupling surface 127 thus formed defines a shoulder
127b at its inner end where it joins the axial bore 124.
Formed in the outer end of the shank 122 is a counterbore
129 having a circular cylindrical diameter slightly greater
than the maximum across-lobe transverse dimension of the
coupling surface 127, and slightly greater than the outer
diameter of the flexible shaft 111, being joined to the
coupling surface 127 by a bevel which defines a frustoconical
surface 129a.
The rotational drive coupling element 130 is similar to
the drive coupler or adaptor 33, described above in connection
with FIG. 1, having an axial bore 131 extending therethrough
and having a cylindrical outer surface 132 at the forward end
thereof (the right-hand end, as viewed in FIG. 11). Formed
inside the forward end of the coupling element 130 is a
coupling surface 133 which is substantially identical in cross
section to the coupling surface 127 described above, and is
formed in the same manner, resulting in a quadrilobular cross-
sectional shape including four equiangularly spaced-apart lobes
2173~
134 (see FIG. 16). Formed in the forward end of the coupling
surface 133 is a circularly cylindrical counterbore 135, which
is dimensioned identically to the counterbore 129, described
above, in the cutting head shank 122. The counterbore 135 is
beveled at its inner end, as at 136 (FIG. 11) to form a
frustoconical surface defining a juncture with the coupling
surface 133.
It is a fundamental aspect of the invention that the
coupling portions 113 and 114 of the flexible shaft 111 are,
respectively, press-fitted into engagement with the cutting
shank 122 of the cutting head 120 and with the rotational drive
coupling element 130. More specifically, referring to FIG. 12,
in assembling the cutting head 120 on the coupling portion 113
of the shaft 111, the coupling portion 113 is first inserted
~5 into the counterbore 129 in the direction of the arrow. The
dimensions of the parts permit free insertion into the
counterbore 129, this insertion being aided and guided by the
bevel 115 on the coupling portion 113 and a slight chamfer at
the entry end of the counterbore 129. However, as was
indicated above, the coupling portion 113 cannot be freely
inserted into the coupling surface 127 and must be press-fitted
therein. In particular, the parts are pressed together with
a force F, as indicated by the arrow in FIG. 12, to force the
coupling portion 113 into the coupling surface 127. The value
of the force F is dependent on the relative shapes and
dimensions of the parts and is sufficient to achieve a coupling
with adequate torsional strength for the intended application.
While the arrow implies that the cutting head 120 is held
stationary, this is simply for purposes of illustration, and
it will be appreciated that either part or both parts could be
moved. Initial entry is facilitated by the bevel 115 on the
coupling portion 113 and by the frustoconical portion 129a at
the entry end of the coupling surface 127. Because of the
different transverse cross-sectional shapes of the parts and
the relative dimensions thereof, the outer surface of the
coupling portion 113 is deformed, as at 140 (FIG. 15), to
21 73~3S
conform to the cross-sectional shape of the coupling surface
127 and fill the lobes 128. This press-fitted insertion
continues until the leading end of the coupling portion 113
bottoms at the inner end of the coupling surface 127, as
illustrated in FIG. 14. When the parts have thus been joined,
the deformed outer surface 140 mates with the coupling surface
127 and has formed thereon lobes 141 which mateably fill the
lobes 128. Thus, the parts are fixedly and permanently secured
together to form a joint of great strength, having equally high
~0 torsional strength in either rotational direction of the
reamer.
The coupling portion 114 at the other end of the shaft 111
is joined to the rotational drive coupling element 130 in
exactly the same manner, being press-fitted into the coupling
surface 133 and deformed to conform to and mate with the
coupling surface 133, as indicated in FIG. 16. More
particularly, the outer surface of the coupling portion 114 is
deformed, as at 145, defining lobes 146 which mate with the
lobes 134 of the coupling surface 133.
It is a significant aspect of the invention that, by
reason of this attachment technique, the outer diameter of the
coupling portions 113 and 114 of the shaft 111 and, therefore,
the outer diameter of the coupling shank 122 of the cutting
head 120 can be minimized. Accordingly, the ratio between the
maximum outer diameter D2 of the cutting head 120 and the shank
diameter Dl can be maximized. It will be appreciated that the
cutting head 120 is provided in a variety of sizes to
accommodate different reaming applications. For example,
cutting heads might be provided with maximum outer diameters
which vary from about 5 mm to about 22 mm. Since the flute
depth is limited by the shank diameter of the cutting head,
which is in turn limited by the shaft diameter, on small-sized
cutting heads a smaller diameter shaft may be used so as to
maintain a sufficient difference between the maximum outer
diameter and shank diameter of the cutting head and thereby
maintain adequate flute depth. In constructional models of the
2~ 7333~
invention, with cutting heads having a diameter D2 from 5 mm
to 7.5 mm, a flexible shaft having an outer diameter of 0.150
inch (3.8 mm) has been used, while with cutting heads having
a diameter D2 from 8 mm to 22 mm, a flexible shaft with an
outer diameter of 0.200 inch (S mm) has been used. This
results in ratios of D2/D1 varying from about 1.2 for the 5
mm cutting head to about 3.2 for the 22 mm cutting head.
The cutting head 120 illustrated in FIG. 11 is a four-
bladed head, which is of medium size. The number of blades
preferably varies, depending upon the size of the cutting head.
In FIG. 17 there is illustrated a small cutting head 150 having
three blades 155, while in FIG. 19 there is illustrated a large
cutting head 160 having five blades 165.
In a constructional model of the invention, the cutting
head 120 is formed of a suitable stainless steel, with the body
121 thereof preferably provided with a titanium nitride
coating. The stainless steel material is selected so that the
relative elastic properties of the parts are such that, upon
insertion of the coupling portion 113 of the shaft 111 into the
shank 122, the coupling portion 113 will be deformed and not
the shank 122.
From the foregoing, it can be seen that there has been
provided an improved reaming system which has a reamer with a
flexible shaft and fixed cutting head and drive coupling
element of great torsional strength, while minimizing the
chance of contamination and, at the same time, optimizes the
ratio between the maximum and shank outer diameters of the
cutting head.
While particular embodiments of the present invention have
been shown and described, it will be obvious to those skilled
in the art that changes and modifications may be made without
departing from the invention in its broader aspects.
Therefore, the aim in the appended claims is to cover all such
changes and modifications as fall within the true spirit and
scope of the invention. The matter set forth in the foregoing
description and accompanying drawings is offered by way of
- 2173~3~
illustration only and not as a limitation. The actual scope
of the invention is intended to be defined in the following
claims when viewed in their proper perspective based on the
prior art.
