U.S. patent application number 13/612283 was filed with the patent office on 2013-03-14 for tool for use with a bone anchor, in particular for spinal surgery.
This patent application is currently assigned to Biedermann Technologies GmbH & Co. KG. The applicant listed for this patent is Lutz Biedermann, Michael Kegel, Wilfried Matthis. Invention is credited to Lutz Biedermann, Michael Kegel, Wilfried Matthis.
Application Number | 20130066386 13/612283 |
Document ID | / |
Family ID | 41073439 |
Filed Date | 2013-03-14 |
United States Patent
Application |
20130066386 |
Kind Code |
A1 |
Biedermann; Lutz ; et
al. |
March 14, 2013 |
TOOL FOR USE WITH A BONE ANCHOR, IN PARTICULAR FOR SPINAL
SURGERY
Abstract
A tool is provided for use with a bone anchor, wherein the bone
anchor has an anchoring section and a receiving portion for
receiving a rod to be connected to the anchoring section and a
locking element, the tool comprising a tip portion for engaging the
locking element; a mechanism to apply torque to the tip portion
comprising a drive shaft and a driven shaft coupled by a gear unit,
where the drive shaft has a different axis than the driven shaft,
and where the driven shaft comprises an engagement portion
configured to connect the driven shaft to the gear unit; and a
counter-holding portion for engaging the receiving part, wherein
the counter-holding portion is rotatable with respect to the tip
portion.
Inventors: |
Biedermann; Lutz;
(Vs-Villingen, DE) ; Matthis; Wilfried; (Weisweil,
DE) ; Kegel; Michael; (Tennenbronn, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Biedermann; Lutz
Matthis; Wilfried
Kegel; Michael |
Vs-Villingen
Weisweil
Tennenbronn |
|
DE
DE
DE |
|
|
Assignee: |
Biedermann Technologies GmbH &
Co. KG
|
Family ID: |
41073439 |
Appl. No.: |
13/612283 |
Filed: |
September 12, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12755360 |
Apr 6, 2010 |
|
|
|
13612283 |
|
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|
61167744 |
Apr 8, 2009 |
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Current U.S.
Class: |
606/86A |
Current CPC
Class: |
A61B 2090/031 20160201;
A61B 2090/064 20160201; A61B 17/8875 20130101; B25B 17/00 20130101;
A61B 17/7091 20130101; A61B 17/7082 20130101 |
Class at
Publication: |
606/86.A |
International
Class: |
A61B 17/56 20060101
A61B017/56 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 7, 2009 |
EP |
09 005 130.1 |
Claims
1. A tool for use with a bone anchor, the tool comprising: a tip
portion for engaging a locking element of the bone anchor; a
mechanism to apply torque to the tip portion, the mechanism
comprising a drive shaft and a driven shaft coupled by a gear unit,
wherein the drive shaft has a different axis than the driven shaft,
wherein the driven shaft comprises an engagement portion configured
to releasably connect the driven shaft to the gear unit; and a
counter-holding portion rotatable with respect to the tip
portion.
2. The tool of claim 1, wherein the gear unit is a reduction gear
unit, wherein the gear reduction is in the range of approximately
3:1 to 10:1.
3. The tool of claim 1, wherein the tip portion is releasably
connected to the driven shaft of gear unit.
4. A tool for use with a bone anchor, the tool comprising: a tip
portion for engaging a locking element of the bone anchor; a
mechanism to apply torque to the tip portion, the mechanism
comprising a drive shaft and a driven shaft coupled by a gear unit,
wherein the drive shaft has a different axis than the driven shaft,
wherein the gear unit comprises a worm drive; and a counter-holding
portion rotatable with respect to the tip portion.
5. The tool of claim 4, wherein the gear unit is a reduction gear
unit, wherein the gear reduction is in the range of approximately
3:1 to 10:1.
6. The tool of claim 4, wherein the tip portion is releasably
connected to the driven shaft of the gear unit.
7. The tool of claim 4, wherein the tip portion is one of a
plurality of different tip portions, each of which is configured to
be interchangeably connected to the driven shaft.
8. The tool of claim 1, wherein the drive shaft of the gear unit
comprises a handle.
9. The tool of claim 1, wherein the counter-holding portion
comprises an engagement portion configured to provide a positive
fit connection with the receiving portion.
10. The tool of claim 9, wherein the engagement portion has two
opposite flat surfaces.
11. A tool for use with a bone anchor, the tool comprising: a tip
portion for engaging a locking element of the bone anchor; a
mechanism to apply torque to the tip portion, the mechanism
comprising a drive shaft and a driven shaft coupled by a gear unit,
wherein the drive shaft has a different axis than the driven shaft,
a counter-holding portion rotatable with respect to the tip
portion; and a display member configured to indicate the value of
the applied torque, wherein the mechanism comprises a twistable
element and the display member indicates a twisting thereof,
wherein the display member comprises a first portion connected to a
first end of the twistable element and a second portion connected
to a second end of the twistable element, wherein the first portion
and the second portion are rotatable against each other when the
twistable element is twisted.
12. (canceled)
13. (canceled)
14. A tool for use with a bone anchor, the tool comprising: a tip
portion for engaging a locking element of the bone anchor; a
mechanism to apply torque to the tip portion, the mechanism
comprising a drive shaft and a driven shaft coupled by a gear unit,
wherein the drive shaft has a different axis than the driven shaft;
wherein the mechanism comprises a preset torque adapter configured
to be selectively connected to the tip portion, wherein the preset
torque adapter comprises a clutch mechanism having a set release
torque; and a counter-holding portion rotatable with respect to the
tip portion.
15. The tool according to claim 1, further comprising: a
counter-holding handle connected to the counter-holding portion;
and a drive shaft handle connected to the drive shaft, wherein the
drive shaft handle extends substantially perpendicular to the
counter-holding handle.
16. (canceled)
17. A tool according to claim 1, wherein the counter-holding
portion is selectively exchangeable with another counter-holding
portion, wherein the mechanism to apply torque to the tip portion
is selectively exchangeable with another mechanism to apply torque
to the tip portion, and wherein the tip portion is one of a
plurality of different tip portions, each of which is configured to
be interchangeably connected to the driven shaft.
18. A method of fastening a bone anchor with a tool, wherein the
tool comprises: a tip portion for engaging a locking element of the
bone anchor; a mechanism to apply torque to the tip portion, the
mechanism comprising a drive shaft and a driven shaft coupled by a
gear unit, wherein the drive shaft has a different axis than the
driven shaft, wherein the driven shaft comprises an engagement
portion configured to releasably connect the driven shaft to the
gear unit; and a counter-holding portion rotatable with respect to
the tip portion, the method comprising: selecting the bone anchor
comprising a receiving portion and the locking element for fixation
of a rod in the receiving portion; inserting the bone anchor into a
bone; inserting the rod into the receiving portion of the bone
anchor; engaging the receiving portion with an engagement portion
of the counter-holding portion; inserting the driven shaft
including the tip portion into the counter-holding portion;
mounting a housing onto the counter-holding portion, wherein the
housing comprises a driving handle for rotating the drive shaft,
the gear unit and a handle for holding the tool; and rotating the
drive shaft via the driving handle to screw in the locking
element.
19. The method of claim 18, further comprising applying a
predefined or set tightening torque.
20. The method of claim 18, wherein the step of mounting the
housing onto the counter-holding portion is performed before the
steps of engaging the receiving portion with the engagement portion
of the counter-holding portion and inserting the driven shaft
including the tip potion into the counter-holding portion.
21. The method of claim 20, further comprising applying a
predefined or set tightening torque.
22. The tool according to claim 1, wherein the gear unit comprises
a drive gear and a driven gear, and wherein the driven shaft
comprises an engagement portion configured to releasably connect
the driven shaft to the driven gear.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/755,360, filed Apr. 6, 2010, which claims
priority to and the benefit of European Patent Application No. 09
005 130.1 filed in the European Patent Office on Apr. 7, 2009, the
entire content of which is incorporated herein by reference. This
application also claims priority to and the benefit of U.S.
Provisional Application No. 61/167,744 filed in the US Patent and
Trademark Office on Apr. 8, 2009, the entire content of which is
incorporated herein by reference.
BACKGROUND
[0002] The invention relates to a tool for use with a bone anchor.
The bone anchor includes an anchoring section and a receiving part
for receiving a rod to be connected to the anchoring section and a
locking element. The tool is particularly applicable in spinal
surgery, for example for the fixation of a rod to pedicle
screws.
[0003] A known tool 100 is shown in FIGS. 19 and 20 in connection
with polyaxial screws 101 and 102, which are connected via a rod
103. The tool 100 includes a counter-holding portion 104 with a
handle 105 and a screw driver portion 106. The screw driver portion
106 is rotatable with respect to the counter-holding portion 104
and also comprises a handle 107. The screw driver portion 106 has a
tip portion (not shown) that engages a locking screw 108 of the
polyaxial screw 101 for fixation of the rod 103 within the
receiving portion 109. The counter-holding portion 104 engages the
receiving portion 109 and holds the receiving portion during
tightening of the locking screw 108. The tightening torque which is
necessary for finally tightening the locking screw 108 is typically
in the range of approximately 7 to 15 Nm. The counter-holding
portion 104 is advantageous in particular for counter-holding such
high tightening torques. However, since the counter-holding portion
acts at least partially onto the rod, the known tool is not
suitable for flexible rods, for example for rods made of an
elastomer material such as polycarbonate urethane (PCU), since the
loads would lead to deformations which may damage the rod. Further,
sensitive handling with two hands is difficult when applying high
tightening torques.
[0004] A tool which has a counter-holding portion that engages the
receiving portion of a bone anchor in a positive fit manner is
known from European Patent Application EP 1 726 264.
SUMMARY
[0005] An embodiment of the invention is a tool for use with a bone
anchor of the above described type where loads acting onto the bone
anchor and therefore onto the bone are reduced and which may allow
for a facilitated handling.
[0006] An embodiment of the tool includes a tip portion for
engaging a locking element of a bone anchor; a mechanism to apply
torque to the tip portion, wherein the mechanism to apply torque
includes a drive shaft and a driven shaft coupled by a gear unit,
and wherein the drive shaft has a different axis than the driven
shaft; and a counter-holding portion, wherein the tip portion is
rotatable with respect to the counter-holding portion.
[0007] A feature of the tool is that the tightening torque which
has to be applied manually by the surgeon is considerably reduced.
Therefore, the manually-applied fastening torque is small and
tightening of the locking screw can be performed smoothly.
[0008] The flow of forces is restricted to the locking element and
the tool, which implies that the force applied during a final
tightening is transferred directly from the locking element through
the receiving member to the counter-holding portion. This results
in an unloaded rod element. In addition, the tightening load is not
transferred into the bone by the bone anchor.
[0009] The tip portion of the screw driver portion of the tool may
be exchangeable. Therefore, a suitable tip portion can be selected
and the tool can be used for different kinds of locking
elements.
[0010] The applied fastening torque may be limited either by
observing a display indicating the applied torque and manually
stopping the application of torque or by using a preset torque
adapter that can be mounted together with the gear unit.
[0011] Principles and further features of the present invention
will become apparent by a detailed description of embodiments and
by means of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows a perspective view of an embodiment of the
tool.
[0013] FIG. 2 shows an enlarged portion of FIG. 1.
[0014] FIG. 3 shows a perspective exploded view of the tool.
[0015] FIG. 4 shows an enlarged portion of FIG. 3 with arrows
indicating the torque flow.
[0016] FIG. 5 shows a further enlarged portion of FIG. 3 with
arrows showing the torque flow.
[0017] FIG. 6 shows a sectional view of a lower portion of the
driven shaft of the tool.
[0018] FIG. 7 shows a side view of the lower portion of the driven
shaft according to FIG. 6.
[0019] FIG. 8 shows a sectional view of the lower portion of the
counter-holding portion of the tool.
[0020] FIG. 9 shows a side view of the counter-holding portion
according to FIG. 8.
[0021] FIG. 10 shows an enlarged perspective view of an upper
portion of the tool.
[0022] FIG. 11 shows an exploded perspective view of the upper
portion of the tool including the drive shaft.
[0023] FIG. 12 shows a plan view of the tool.
[0024] FIG. 13 shows a sectional view of the upper portion of the
tool.
[0025] FIGS. 14a to d show steps of assembling and applying the
tool.
[0026] FIG. 15 shows a schematic side view of the upper portion of
a further embodiment of the tool.
[0027] FIG. 16 shows a schematic sectional view of the further
embodiment shown in FIG. 15.
[0028] FIG. 17 shows a perspective view of a portion of a still
further embodiment of the tool in a not fully mounted
condition.
[0029] FIG. 18a shows a perspective view of a greater portion of
the still further embodiment of FIG. 17 in a mounted condition.
[0030] FIG. 18b shows an enlarged cross-sectional view along line
A-A shown in FIG. 18a
[0031] FIG. 19 shows a perspective view of a known tool.
[0032] FIG. 20 shows an enlarged portion of FIG. 19.
DETAILED DESCRIPTION
[0033] With reference to FIGS. 1 to 5, a tool according to one
embodiment comprises a screw driver portion, which includes a drive
shaft 1 as schematically shown by the dashed line in FIG. 1 and a
driven shaft 2 as shown in FIG. 3. The drive shaft 1 has a handle 3
at its free end projecting outside a housing 4. The drive shaft 1
and the driven shaft 2 enclose an angle of 90.degree. and are
connected by a reduction gear unit 5, which will be explained in
more detail below.
[0034] The tool further comprises a counter-holding portion 6,
which is fixedly connected to the housing 4 so that the driven
shaft 2 is rotatable with respect to the counter-holding portion 6.
At its free end opposite to the counter-holding portion 6, the
housing 4 comprises a handle 7 for holding the tool. The central
axis of the handle 7 extends substantially perpendicular to the
central axis of the handle 3 of the drive shaft 1. This allows a
convenient handling of the counter-holding portion.
[0035] The tool further has a display member 8, which may include
visual marks 9 for indicating the applied torque. The driven shaft
2 has, as can be seen in FIGS. 3, 4, 6 and 7, a tip portion 20 with
an engagement portion 21 for engagement with a locking element of a
bone anchor. Such a locking element can be, for example, a set
screw 108 (shown in FIG. 18) of a receiving portion 109 of a
polyaxial bone screw 102. The engagement portion 21 can have a
hexagon shape or a flathead, crosshead, square, hex socket or
Torx.RTM. shape, or any other shape adapted to the respective
engagement portion of the locking element. The tip portion is
connected via a plug connection member 22 to a main shaft portion
23 of the driven shaft 2. The main shaft portion 23 has, at its end
facing the tip portion 20, a section 24 with an enlarged outer
diameter and a recess for inserting the plug connection member 22.
The tip portion 20 has, at its end facing the main shaft portion
23, a recess for inserting a portion of the plug connection member
22. The plug connection member 22 may have a resilient portion 25,
which allows for the releasable holding of the tip portion 20 in
the main shaft portion 23. Further, the tip portion 20 and the main
shaft portion 23 are connected in a positive fit manner, such as,
for example, shown in FIG. 7 by means of
circumferentially-projecting portions 26 which engage in
circumferentially-arranged recesses 27 at the corresponding other
part.
[0036] A plurality of tip portions 20 may be provided with
different engagement portions 21, which can be interchangeably
connected to the main shaft portion 23. By means of the plug
connection member 22, the exchange of the tip portion 20 can be
easily made by hand. At its end facing the gear unit 5, the main
shaft portion 23 comprises an engagement portion 28 to be connected
with the gear unit 5.
[0037] The drive shaft 1 and the reduction gear unit 5 are now
explained with particular reference to FIGS. 3 and 10 to 13. In the
embodiment shown, the gear unit 5 includes a worm drive having a
worm 51 connected to the drive shaft 1 and a worm wheel 52. The
worm wheel 52 also is provided with an engagement portion 53 to be
engaged with the engagement portion 28 of the main shaft portion
23. A preferred gear transmission ratio for the application in
spinal surgery is around 3:1 or 10:1. The worm drive is
advantageous to transmit higher torques. A common feature of a worm
drive is that the direction of transmission from the drive shaft to
the driven shaft is not reversible. In surgery, this means that the
final tightening of the locking element can be performed
exactly.
[0038] As shown in FIGS. 3, 6 and 7, a display member 8 comprises a
tube portion 81, which is fixed at its lower end to the main shaft
portion 23 of the driven shaft 2 so that the tube portion 81
rotates with the driven shaft 2. At its end facing away from the
tip portion 20, the display member 8 comprises a lower ring-shaped
portion 82 with an enlarged diameter. The lower ring-shaped portion
82 carries a first visual mark 9a at its outer side. The visual
mark 9a can be of any type including bars, engravings etc. It is
configured to indicate a predefined tightening torque. The display
member 8 further comprises an upper ring-shaped portion 83, which
is connected to the worm wheel 52 and therefore to the main shaft
portion 23 of the driven shaft 2. The lower ring-shaped portion 82
and the upper ring-shaped portion 83 are rotatable against each
other. Between the two ring-shaped portions, a ring-shaped plate
member for facilitating gliding may be provided. Both the upper and
lower ring-shaped portions 83 and 82 have second visual marks 9b,
which indicate a zero position.
[0039] As can be seen in FIGS. 10 and 13, the housing 4 comprises a
recess 41 to allow inspection of the visual marks 9a and 9b that
indicate the applied torque.
[0040] With regard to FIG. 3, the handle 7 may be fixedly attached
to the housing 4, for example by screwing as shown in FIG. 13. The
housing 4 further has on its end opposite to the handle 7 a
projection with fixation means, for example of the type of a
thread, to connect the housing 4 to the counter-holding portion 6.
The counter-holding portion 6 has on its end facing the housing 4
connection means 61 for connecting the counter-holding portion 6
fixedly to the housing 4. The counter-holding portion 6 further
includes a main tube portion 62, shown in FIG. 3, the diameter of
which is such that the driven shaft 2 and the tube portion 81 can
be arranged and freely rotate therein. Further, the counter-holding
portion 6 comprises an end section 63, as shown in FIGS. 3 and 5.
The end section 63 is hollow so that the tip portion 20 extends
through the end section 63. The end section 63 has at its free end
an engagement portion 64. The engagement portion 64 is configured
to engage the receiving portion 109 of the bone anchor. The
engagement section 64 has a square or rectangular inner contour
that is adapted to the outer contour of the receiving portion 109.
In the embodiment shown, the receiving portion 109 has two opposed
flat outer surfaces 110 as shown for example in FIG. 5. The
engagement section 64 has inner flat surfaces 65 on two opposing
sides, as shown in FIGS. 8 and 9, that are configured to correspond
with the two flat outer surfaces 110 on the receiving portion 109.
In addition, the engagement portion 64 has on each of the other two
sides a recess 66 where the rod 103 can be guided through. The end
section 63 further has on each of the sides that include the inner
flat surface 65 a recess 67, which allows for visualization of the
inserted tip portion 20.
[0041] In the embodiment shown, the end section 63 is fixedly
connected to the end tube portion 62. However, the end section 63
may also be releasably attached thereto so as to allow fixation of
different end sections 63 with an engagement portion 64 adapted to
the shape and size of the receiving portions 109. Hence, the
engagement portion 64 may have any shape that provides for a
positive fit connection with the receiving portion 109 without
acting onto the rod 103.
[0042] Use of an embodiment of the tool is now explained with
reference to FIGS. 14a to d. FIG. 14a schematically shows a bone
anchor which is in this example a polyaxial bone screw 101
comprising a receiving portion 109 and a set screw 108 for fixation
of the rod (not shown) in the receiving portion 109. The rod 103 is
shown in FIG. 2. The bone anchor 101 is inserted into the bone, and
then the rod 103 is inserted into the receiving portion 109.
Thereafter the set screw 108 is inserted into the receiving portion
109. The engagement portion 64 of the counter-holding portion 6 of
the tool engages the receiving portion 109 as shown in FIG. 14b.
Thereafter, as shown in FIG. 14c, a driven shaft 2 including a tip
portion 20 is inserted into the counter-holding portion 6. Next, as
shown in FIG. 14d, a housing 4 with a handle 3, a reduction gear
unit 5 and a handle 7 is mounted. In this condition, by rotating
the drive shaft by means of the handle 3 the set screw is screwed
in. When the set screw 108 abuts the rod and is blocked thereby and
the drive shaft 1 is further rotated, the main shaft portion 23 of
the driven shaft 2 becomes twisted by the torque which is
introduced by the worm wheel 52 via the engagement portions 53 and
28. The upper ring-shaped portion 83, which is fixedly connected to
the upper end of the main shaft portion 23, is rotated by the worm
wheel 52 as long as the handle 3 is rotated by the surgeon. The
lower ring-shaped portion 82 is connected with the lower end of the
main shaft portion 23 via the tube portion 81. Because the lower
end of the main shaft portion 23 does not rotate any more when the
set screw 108 is blocked by the rod 103, the ring-shaped portion 82
is not rotated any more when the set screw 108 is blocked. Hence,
the upper ring-shaped portion 83 rotates with respect to the lower
ring-shaped portion 82 while the main shaft portion is twisted. By
rotating the handle 3 until the upper visual mark 9b is aligned
with the lower visual mark 9a, a predefined tightening torque is
applied. Because of the gear unit 5, a final tightening of the set
screw is possible even with a manual application of low tightening
torque.
[0043] The tool may be preassembled or assembled before or during
surgery.
[0044] The visual mark 9a can be applied when calibrating the
tool.
[0045] The angle of 90.degree. between the drive shaft 1 and the
driven shaft 2 provides a convenient handling.
[0046] As shown in FIGS. 4 and 5, the torque flow is such that the
torque is transmitted from the driven shaft to the set screw and is
redirected by the end section 63 of the counter-holding portion.
Therefore, no forces are conducted via the rod 103 back to the
receiving portion 109, which could loosen the anchoring section in
the bone.
[0047] The upper portion of a further embodiment of the tool is
shown in FIGS. 15 and 16. The tool differs from the tool of the
previous embodiment in that a preset torque adapter 90 is provided,
which limits the applicable torque to a specific predefined value.
The preset torque adapter 90 is arranged in a housing 4', which can
be releasably connected to the main shaft portion 23 of the driven
shaft. The preset torque adapter 90 has a shaft portion 91 which
can be coupled to the main shaft portion 23 to transfer the torque.
The preset torque adapter further has a recess 92 on the side
opposite to the shaft portion 91 in which a shaft 53' engages.
Shaft 53' is fixidly connected to the worm wheel 52 of the gear
unit 5. The recess 92 may be a square recess, hexagon recess, or
any other recess by means of which torque can be transferred from
the shaft portion 53' to the torque adapter 90. The torque adapter
90 has in its interior a clutch mechanism (not shown) which has a
defined release torque. For example, the clutch mechanism can be a
slipping clutch. If the applied torque exceeds the predefined
torque, the torque is no longer transferred from the shaft portion
53' via the torque adapter 90 to the main shaft portion 23.
[0048] As shown in FIGS. 15 and 16, the housing 4' also contains
the gear unit 5. It may be closed by a closure 45 with or without
an additional handle. Further, the housing 4' can be connected to
the counter-holding portion 6 via a screw, a press fit, or any
other connection 46. The whole unit including the gear unit and the
torque adapter can be selectively connected instead of the housing
with the gear unit and the display unit according to the previous
embodiment.
[0049] As shown in FIG. 16, the housing 4' has a lower
sleeve-shaped portion 400 that has an inner conically-shaped
section 400a and the counter-holding portion 6 has at the free end
of the main tube portion 62 an end portion 600 with an outer
complementary conically-shaped portion 600a that is introduced into
the sleeve-shaped portion 400 so that the housing 4' and the
counter-holding portion 6 are connected at the conical portions by
means of a friction fit. A nut element 700 is screwed onto the
sleeve-shaped portion 400 to secure the parts against each
other.
[0050] As shown in FIGS. 17, 18a and 18b a still further embodiment
of the tool differs from the previous embodiments mainly by the
type of connection between the housing 4' and the counter-holding
portion 6. The housing 4' has a lower sleeve-like portion 401 with
an outer thread 402 which cooperates with a corresponding inner
thread of the nut member 700. The inner wall of the sleeve-shaped
portion 401 comprises a plurality of coaxial recesses 403 like a
Torx.RTM.-wrench that cooperates with a correspondingly-shaped end
portion 601 of the counter-holding portion 600 to provide a
positive-fit connection. Thereby, a safe connection is guaranteed
even in the case of large torques to be transferred. Furthermore,
the positive-fit connection is advantageous in view of a modular
tool that allows the surgeon to easily exchange the components such
as the counter-holding portion or the housing portion with gear.
For example, the upper portion of the tool can be provided as
several individual different upper portions comprising either
different gear units and/or preset torque adapters and/or different
display members. They can be selectively connected to the
counter-holding portion. In a similar manner, different
counter-holding portions that are used for different screws can be
provided and selectively connected to the upper portion.
[0051] The embodiment shown in FIGS. 17, 18a and 18b has, for
example, different handle portions 3' and 7' for the drive shaft
and the counter-holding portion 6, respectively.
[0052] Various modifications of the tool are conceivable. The gear
unit need not be a worm drive. It could also be realized by a
planetary gear unit, in particular with coaxial drive shaft and
driven shaft. Any other reduction gear unit may be used also.
[0053] The counter-holding portion and the tip portion may be
exchanged such that the counter holding portion is at the center
and the tip portion of the screw driver is surrounding it.
[0054] The counter-holding portion and the tip portion can be
adapted in their shape to various shapes of receiving portions and
locking elements.
* * * * *