Note: Descriptions are shown in the official language in which they were submitted.
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Pedicle Screw
The invention concerns a pedicle screw for implants for the correction and
stabilization
of the spinal column, with a head piece on the one axial end of a threaded
shaft, to which
a clamp piece can be connected which has a clamp receptacle for a rod that can
be fixed
to the head piece.
Pedicles of this type are known from actual practice which are intended to be
screwed
into the vertebra of a spinal column in order to allow it to carry out its
function in cases
of degenerative or traumatic diseases of the spinal column; this is achieved
by placing at
least one rod bridging several vertebrae along the spinal column and anchoring
it to the
spinal column. In order to align the rod precisely it is necessary to be able
to adjust the
position of the pedicle screw to the rod at least at the contact location,
taking into account
the anatomically correct position of the pedicle screw within the vertebra. In
practice
therefore, a large number of pedicle screws are kept on hand for surgery,
allowing the
various sizes of vertebrae to be taken into account, depending on their
position in the
cervical spine, the thoracic spine or the lumbar spine, which increases the
cost of
manufacture, stocking and provision for surgery.
Hence the aim of the invention is to design a pedicle screw of the type
mentioned at the
beginning in such a way as to avoid those disadvantages.
This aim is achieved by the invention of a pedicle screw of the type mentioned
at the
beginning in which a threaded bore is integrated into the clamp piece to
accommodate a
thread provided on the head piece.
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Thus, according to the invention, there is provided a pedicle screw for
implants for the
correction and stabilization of the spinal column, comprising a head piece
disposed on
one axial end of a threaded shaft, to which head piece a clamp piece can be
connected,
which clamp piece has a clamp receptacle for a rod that can be fixed in place
on the head
piece, wherein a threaded bore is formed in the clamp piece, to accommodate a
thread
that is associated with the head piece.
This design provides the advantage that the threaded shaft and its clamp piece
are
separate components that can be provided in different variants, so that
combining those
variants allows a large number of different pedicle screws to be put together.
The other
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advantage is that, without being hindered by the clamp piece, the threaded
shaft can be
inserted into the vertebra and its correct position verified, the clamp piece
with the
threaded bore only then being screwed onto the threaded shaft.
In this connection, within the framework of the invention it is advantageous
if the head
piece is shaped as a spherical head and the thread is located on the outside
of a threaded
retainer whose interior forms a ball socket for the spherical head. This
design allows a
flexible connection between the threaded shaft and the rod via the clamp
piece, so that the
rod can be precisely positioned due to the polyaxial alignment of the clamp
piece, with its
clamp receptacle relative to the axis of the threaded shaft.
In order to be able to screw the threaded shaft into the vertebra independent
of the clamp
piece, the design is such that, coaxially to the axis of the threaded shaft, a
non-spherical,
preferably polygonal tool receptacle is provided in the free end of the head
piece for a
tool to apply torque.
It is also advantageous if the threaded shaft has a coaxial guide receptacle
from which at
least one side channel leads to the circumference areaof the threaded shaft.
This guide
receptacle allows a bonding agent such as bone cement or other adhesive to be
pressed
into the bone opening where the pedicle screw is placed in the vertebra, thus
providing a
better loadbearing, early and durable seat of the pedicle screw in the
vertebra. In the
process care must be taken not to impair the mobility of the clamp piece
relative to the
threaded shaft, as the clamp piece may still be separated from the threaded
shaft so as not
to obstruct the application of the bonding agent and allowing clean work that
also permits
the removal of surplus bonding agent before screwing on the clamp piece. A
quick and
even distribution of the bonding agent is achieved by distributing the side
channel several
times evenly across the circumference of the threaded shaft or by staggering
it several
times in axial direction.
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It is also advantageous if the side channel leads into the circumference area
of the
threaded shaft, between the thread flights, since the thread edges remain
unaffected and
therefore will not have an adverse effect when the threaded shaft is screwed
in.
If the guide receptacle extends along the entire axial length of the threaded
shaft it is
possible to completely fill a bore channel positioned prior to screwing in the
threaded
shaft with bonding agent. In addition there is the very great advantage that
the pedicle
screw canulated through the continuous guide receptacle can also be used in a
"percutaneous" application within the framework of minimally invasive surgery
by first
introducing a guide wire into the operation site, on which the threaded shaft
with the
guide receptacle is strung to be guided to the correct position.
The arrangement is also expediently organized in such a way that the threaded
bore is
located in the clamp base of the clamp piece and in that the clamp receptacle
allows a
ring to be placed on the head piece. This ring provides an improved contact
area for the
rod as well as the possibility of applying external pressure in order to press
the ring onto
head piece, thus ending the mobility of the head piece in relation to the
clamp piece.
In order to durably fix the rod in the clamp receptacle, a lid is connected to
the first leg of
the clamp piece by means of a joint. Within the framework of the invention it
is
preferable if a leg wing projects radially outward from the second leg of the
clamp piece
towards the side not facing the first leg, in which a threaded wing bore is
provided to
accommodate a securing screw that passes through an opening in the lid. This
embodiment has the advantage that the axis of the threaded wing bore does not
correspond identically to the axis of the threaded shaft or the axis of the
threaded bore,
but rather is laterally offset. This prevents torque being applied to the
threaded shaft
when the securing screw is screwed in, particularly when it reaches its firm
seat, through
which the seat of the threaded shaft in the vertebra could be loosened or
through which
the bonding agent pressed through the guide receptacle could be damaged during
the
setting process.
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During surgery, after determining the position and orientation of the pedicle
screw, it is
often necessary to make fine adjustments with respect to the position of the
vertebrae,
especially tractions or compressions. However, as long as the position of the
threaded
shaft in relation to the head piece is not load-bearingly determined, any
force applied to
the vertebrae frequently has no tractive or compressive effect, but rather
results in tilting
movements. Therefore, in order to durably and load-bearingly determine the
orientation
of the threaded shaft in relation to the clamp piece and at the same time
allow the rod to
rotate as well as a translatory displacement relative to the clamp piece, a
stamphead is
arranged between the lid and the head piece to clamp the head piece in the
clamp piece
when the lid is finally closed. Clamping the head piece in the clamp piece
determines and
secures the position of the threaded shaft relative to the clamp piece,
whereas the rod can
still be adjusted relative to the clamp piece. This allows a precise, even
iterative
alignment of the vertebrae during surgery.
Final determination of the clamp piece relative to the rod is achieved very
simply by
providing a screw receptacle in the lid to accommodate a fixing screw which
serves to
clamp the rod.
The stamphead is expediently formed by a ring leg formed at the ring so that
force is
applied to the ring for clamping the head piece not only by the rod but also
by the
stamphead, which with the ring forms a single piece. This also reduces the
number
components required to complete the pedicle screw.
In order to achieve an even introduction of force into the head piece, it is
possible to
provide two ring legs, each on opposite sides of the ring to encircle the rod
from both
sides.
In addition, for the precise transmission of force from the lid to the
stamphead it is
possible to provide a pressure strip on the clamp side facing the head piece
in order to
apply force to the stamphead.
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In order to provide a strong force for application to the stamphead, it is
advantageous if
the clamp piece's supporting surface for the stamphead is arranged at a
distance from the
joint, i.e. an increase in force can be achieved by means of a lever arm
formed by the lid
and the length of the lever arm provides an additional parameter for
determining the
clamping force.
The invention is described in more detail below by means of the embodiments
shown in
the drawings:
Fig. 1 shows a side view of the pedicle screw according to the invention,
Fig. 2 shows the section II-II from Fig. 1,
Fig. 3 shows a side view of the isolated threaded shaft with the head piece
shaped as
a spherical head,
Fig. 4 shows a perspective view of the threaded shaft from Fig. 3,
Fig. 5 shows the detail V from Fig. 3,
Fig. 6 shows a perspective view of the threaded retainer,
Fig. 7 shows a longitudinal section through the threaded retainer from Fig. 6,
Fig. 8 shows a perspective view of the ring,
Fig. 9 shows a longitudinal section through the ring from Fig. 8,
Fig. 10 shows a perspective view of the clamp piece,
Fig. 11 shows a longitudinal section through the clamp piece from Fig. 10,
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Fig. 12 shows a perspective view of the lid,
Fig. 13 shows a side view of the lid from Fig. 12,
Fig. 14 shows a perspective view of the safety screw,
Fig. 15 shows an exploded view of the pedicle screw,
Fig. 16 shows a longitudinal section through the upper area of a further
embodiment,
Fig. 17 shows a front view of the clamp piece with the lid of the further
embodiment,
Fig. 18 shows the section XVIII - XVIII from Figure 17,
Fig. 19 shows a perspective view of the modified ring of the further
embodiment,
Fig. 20 shows the section XX - XX from Figure 19,
Fig. 21 shows a perspective view of the lid of the modified embodiment, and
Fig. 22 shows the section XXII - XXII from Figure 21.
The drawing shows a pedicle screw 1 for implants, comprising a threaded shaft
2 and a
clamp piece 3. At the one axial end of the threaded shaft 2 is a head piece 4
shaped as a
spherical head. The clamp piece 3 has a clamp receptacle 5 for a rod 6 that
can be fixed to
the head piece 4, the clamp base 7 in the clamp piece 3 having a threaded bore
8. The
clamp piece 3 also has two legs, a lid 11 being attached to the first leg 9 by
means of a
joint 10, and projecting radially outward from the second leg 12 towards the
side not
facing the first leg 9 is a leg wing 13 in which there is a threaded wing bore
14 to
accommodate a securing screw 16 that passes through an opening 15 in the lid
11.
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A thread is allocated to the head piece 4, namely on the outside of a threaded
retainer 26
whose interior forms a ball socket for the spherical head of the head piece 4,
and the
interior of the retainer may be designed as an inner cone or partial sphere.
In the free end of the head piece 4, coaxially to the axis 17 of the threaded
shaft 2, a non-
spherical tool receptacle 18 is incorporated through which a tool applies
torque to the
threaded shaft 2, by means of which the threaded shaft 2 can be screwed into a
vertebra.
The threaded shaft 2 also has a coaxial guide receptacle 19 from which several
axially
staggered side channels 20 spread evenly across the circumference and lead to
the
circumference area of the threaded shaft 2 and ending between the thread
flights 21. The
guide receptacle 19 extends along the entire axial length of the threaded
shaft 2, which at
its opposite end from the head piece 4 is provided with a self-cutting thread
(Fig. 5).
Figures 16 to 22 show an embodiment in which, between the lid 11 and the head
piece 4,
a stamphead 28 is arranged for clamping the head piece 4 in the clamp piece 3
when the
lid 11 is finally closed, the lid 11 also having a screw receptacle 23 to
accommodate a
fixing screw 27 for clamping the rod 6. The stamphead 28 is created by a ring
leg 24
provided on the ring 22, which according to an embodiment not shown in the
drawing
may be provided in duplicate on opposite sides of the ring 22 in order to
encircle the rod
6 from both sides.
Figure 22, in particular, shows that at the lid 11 on the side facing the head
piece 4 there
is a pressure strip 25 to apply force to the stamphead 28. The support area at
the lid 11, in
Figure 22 the pressure strip 25, is provided for the stamphead 28 at a
distance from the
joint 10.
The design of the pedicle screw 1 according to the invention allows, first of
all, the
threaded shaft 2 to be screwed into the vertebra and to be durably anchored
there by
means of bone cement, which is pressed through the guide receptacle 19 and the
side
channels 20. Then the clamp piece 3 is attached to the threaded shaft 2 by
screwing the
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clamp piece 3 with the threaded bore 8 onto the threaded retainer 26. With the
lid 11 of
the clamp piece 3 open, the rod 6 is then placed on a ring 22 and, when the
lid 11= is
closed, pressed by same onto the ring 22 and consequently onto the head piece
4 of the
threaded shaft 2, thus ending the potential movement of the clamp piece 3
relative to the
threaded shaft 2. The securing screw 16 locks the lid 11 and consequently the
rod 6 in the
first embodiment according to Figures 1 to 15.
The embodiment in Figures 16 to 22 provides increased variability as, firstly,
the
securing screw 16 can close the lid 11, thereby also ending the rotational
mobility of the
head piece 4 in relation to the clamp piece 3. The clamp piece 3 itself can
still be turned
relative to the rod 6, i.e. can be turned around its longitudinal axis and
also moved
parallel to that longitudinal axis. The fixing screw 27 eliminates these
movement options
when the pedicle screw 1 is in the desired position in relation to the
vertebra. It must be
ensured that the fixing screw 27 acts directly on the rod 6, which in turn
increases the
clamping of the head piece 4 via the ring 22.
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List of terms
1 Pedicle screw
2 Threaded shaft
3 Clamp piece
4 Head piece
Clamp receptacle
6 Rod
7 Clamp base
8 Threaded bore
9 First leg
Joint
11 Lid
12 Second leg
13 Leg wing
14 Threaded wing bore
Opening
16 Securing screw
17 Axis of the threaded shaft
18 Tool receptacle
19 Guide receptacle
Side channels
21 Thread flights
22 Ring
23 Screw receptacle
24 Ring leg
Pressure strip
26 Threaded retainer
27 Fixing screw
28 Stamphead
