U.S. patent application number 11/876890 was filed with the patent office on 2009-04-23 for spinal implant.
Invention is credited to Marc Richelsoph.
Application Number | 20090105756 11/876890 |
Document ID | / |
Family ID | 40220186 |
Filed Date | 2009-04-23 |
United States Patent
Application |
20090105756 |
Kind Code |
A1 |
Richelsoph; Marc |
April 23, 2009 |
SPINAL IMPLANT
Abstract
A screw and rod fixation assembly includes a body member
including a screw seat for seating a screw head therein and a rod
seat for seating a rod therein. An adjustable locking ring applies
a locking force against the screw head seated in the screw seat and
a locking cap adjustably applies a locking force against a rod
seated in the rod seat. The adjustable screw locking ring and
locking cap function independent of each other. A method of fixing
the rod to the screw includes the steps of inserting a screw head
into a screw seat in one end of a body member and inserting a rod
into a rod seat in a second end of a body member and selectively
and independently adjusting a locking force on both the screw head
and the rod within the screw seat and rod seat, respectively.
Inventors: |
Richelsoph; Marc;
(Charlotte, NC) |
Correspondence
Address: |
KOHN & ASSOCIATES, PLLC
30500 NORTHWESTERN HWY, SUITE 410
FARMINGTON HILLS
MI
48334
US
|
Family ID: |
40220186 |
Appl. No.: |
11/876890 |
Filed: |
October 23, 2007 |
Current U.S.
Class: |
606/246 ;
606/103; 606/151; 606/264; 606/301; 606/305; 606/308 |
Current CPC
Class: |
A61B 2090/037 20160201;
A61B 17/7037 20130101; A61B 17/7035 20130101; A61B 17/7032
20130101 |
Class at
Publication: |
606/246 ;
606/103; 606/151; 606/264; 606/301; 606/305; 606/308 |
International
Class: |
A61B 17/70 20060101
A61B017/70; A61B 17/00 20060101 A61B017/00; A61B 17/56 20060101
A61B017/56; A61B 17/04 20060101 A61B017/04; A61B 17/58 20060101
A61B017/58 |
Claims
1. A screw and rod fixation assembly comprising: a body member
including a screw seat for seating a screw head therein and a rod
seat for seating a rod therein, adjustable rod locking means for
adjustably applying a locking force against a rod seated in said
rod seat; and adjustable screw locking means for adjustably
applying a locking force to a screw head seated in said screw seat,
said adjustable screw locking means being functionally independent
of said adjustable rod locking means.
2. An assembly as set forth in claim 1, wherein said body member
includes a first end having a pocket therein, said pocket including
outwardly flexible walls for receiving and retaining a screw head
therein, thereby defining said screw seat, said adjustable screw
locking means including a compressor member disposable over said
outwardly flexible walls for adjustably compressing said outwardly
flexible walls in locking engagement against the screw head.
3. An assembly as set forth in claim 2, wherein said screw seat
includes at least one slot therein provides outward flexibility to
said screw seat and thereby allowing a screw head to enter
therein.
4. An assembly as set forth in claim 2, wherein said compressor
member includes a locking ring having an internal bore defined by a
straight cylindrical wall, said first end of said body member
including an outer surface tapering outwardly when a screw head is
seated within said screw seat towards said first end, said internal
bore of said locking ring interacting with said outer surface to
selectively and adjustably compress said pocket about the screw
head as said locking ring is moved there along.
5. An assembly as set forth in claim 2, wherein said body portion
includes a second end including a base portion and two spaced arms
extending therefrom defining said rod seat, said adjustable rod
locking means including compressing means for adjustably and
selectively compressing said arms about a rod seated in said rod
seat to adjustably and selectively lock the rod in said rod
seat.
6. An assembly as set forth in claim 5, wherein said rod locking
means including an annular body portion having an internal bore for
receiving and retaining said arms therein, said arms being
outwardly flexible to allow outward deflection of said arms when a
rod is seated therein, said bore having a predetermined diameter
small than a diameter defined by a distance between an opposing
outer surface of said arms, whereby application of said body
portion about said arms selectively radially inwardly deflects said
arms to adjustably grip and lock the rod seated within said rod
seat.
7. An assembly as set forth in claim 6, including fixing means for
fixed locking said rod locking means in locked engagement with a
rod seated in said rod seat.
8. An assembly as set forth in claim 7, said arms include a
radially outwardly extending projection, said rod locking means
including a recess for mating engagement with said projections when
said rod locking means is in locking engagement with the rod seated
in said rod seat.
9. An assembly as set forth in claim 7, wherein said arms include
recesses therein and said rod locking means including radially
inwardly extending projections for mating engagement with said
recesses when said rod locking means is in locking engagement with
the rod seated in said rod seat.
10. An assembly as set forth in claim 1, wherein said rod seat
includes a substantively spherical inner surface.
11. A screw and rod fixation member comprising a body portion
including a first end having a screw seat for seating a screw head
therein and a second end including a rod seat for seating a rod
therein, said first end including a pocket therein having outwardly
flexible walls for receiving a screw head therein, thereby defining
said screw seat and a said second end including a base portion and
two spaced arms extending therefrom defining said rod seat, said
arms including a smooth outer surface and fixing means for
engagement with a rod locking member.
12. A fixation screw comprising a threaded portion for engagement
with base and a head pocket and a neck portion therebetween, said
screw head including multiple engagement surfaces for contacting
multiple areas of a spherical screw seat surface.
13. An assembly as set forth in claim 12, wherein said screw head
includes a radially outer cylinder surface having oppositely
disposed upper and lower tapered portions defining a diamond or
square, said tapered surfaces defining said multiple engagement
surfaces.
14. A method of fixing a rod to a screw by: inserting a screw head
into a screw seat in one end of a body member; inserting a rod into
a rod seat in a second end of the body member; and selectively and
independently adjusting a locking force on both the screw head and
rod within the screw seat and rod seat, respectively.
15. A method as set forth in claim 14, further including the step
of inserting the screw head into the screw seat and a locking ring
about the body portion and spaced from the outer surface of the
screw seat prior to surgery; and insert the rod with the rod seat
and independently and selectively apply a locking force of the
locking ring to the screw seat and rod locking member about an
outer surface of the rod seat during surgery.
16. A method as set forth in claim 15, further including the steps
of independently and adjustably forcing locking means on the
locking ring about the screw seat and on the rod locking member
about the rod seat.
17. A method of fixing a rod to a screw head by seating a screw
head having multiple contact points in a screw seat of a body
portion causing the screw head to interfere with and contact
multiple portions of the spherical seat creating sufficient
friction to lock the screw head in a desired position during rod
insertion while allowing the body portion to rotate relative to the
screw head.
18. A method as set forth in claim 17, further including the steps
of: fixing at least one screw in a bone; the screw seat as in claim
17, and adjusting the position of the rod seat relative to the
screw during seating of the rod into the screw seat.
19. A method as set forth in claim 17, including the step of
radially outwardly deflecting an outer surface of the screw seat
and forming an outwardly tapering outer surface and; disposing a
locking ring over the outwardly tapering surface to lock the screw
head in the screw seat.
20. A fixation screw assembly comprising a screw including a head
portion for engagement with a seat portion within a body member,
said head portion having a larger dimension than said seat portion
such that said screw head portion creates interference with the
body seat portion when seated therein.
21. An assembly of claim 20, whereby said interference of the
fixation screw head with said seat portion of the body forces said
body section around said screw head to be forced radially outwardly
creating a taper in an outer surface of an external lower portion
of said body member.
22. An implant comprising a body portion having a U shaped rod
receiving slot, said U shaped slot being smaller in width than the
width of a rod seated therein and having a seated condition when
the rod is seated within the U shaped channel such that the rod
forces arms of the U shaped slot radially outwardly creating a
taper, said taper at an open end of the U shaped slot being larger
in diameter and tapering to a smaller diameter at a base of said U
shaped slot.
23. The assembly of claim 22, wherein said taper created by the rod
seated in the U shaped slot contours around the rod when a locking
cap engages the larger diameter opening of the U shaped slot and
forces the arms of the U shaped slot inward around the rod.
24. The assembly of claim 23, wherein said U shaped slot is defined
by two arms, each of said arms having a distal end defining said
opening of said U shaped slot, each of said distal ends having a
baffled portion to allow ease of disposal of said locking cap over
said distal ends.
25. A method of retaining a rod in a U shaped slot of a body member
of a rod fixation assembly by inserting a rod into a rod seat that
is smaller in diameter than the rod while forcing the arms of the
rod seat radially outwardly to form an outer taper on the outside
surface of the rod seat, and disposing a rod locking cap over the
spread arms of the rod seat, the rod locking cap forcing the arms
radially inwardly and forcing the arms of the rod seat around the
rod.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention generally relates to spinal implants.
More particularly, the present invention relates to screw fixation
assemblies for use with bone fixation systems.
[0003] 2. Background Art
[0004] Polyaxial screw implants for assisting in fusion surgeries
have been in use for many years. Typically, polyaxial screw motion
implants allow motion of a body portion around a spherical screw
head to allow the assembly to pivot. When individual screw
assemblies are connected by a rod, it is common for the rod to be
out of alignment with all of the screw assemblies. This problem
increases in severity with an increasing number of screw assemblies
that the surgeon is trying to connect to the same rod. Pivoting
allows the assembly to compensate for this problem.
[0005] The main problems with polyaxial screws are package size and
implant locking. Most implants are fairly large in size in order to
allow enough force to be exerted against the spherical screw head
and rod without the implant flexing under the load. For all of
these implants, and a few that are small in size, the locking
component is complex and often involves the use of threads. Set
screws and threaded nuts are commonly used. Finding a thread inside
the implantation site is difficult and creates issues such as
cross-threading. Other concepts have been invented, but as a
combination of effective locking and small package size, room for
improvement exists.
[0006] In the majority of the prior art screw assemblies, the screw
head portion of the screw is spherical in form, such that it can
rotate in all directions. There are a few exceptions to the rule,
but the result is essentially the same. For example, U.S. Pat. No.
7,186,255 to Baynham et al. shows a screw portion having a
spherical head separated from the screw shank. However, once
assembled, the screw is no different than the other prior art. U.S.
Pat. No. 7,163,539 to Abdelgany et al. shows a screw with a partial
spherical head that has been hollowed. However, the concept is
still providing a spherical head. This approach also has
limitations in the amount of allowable rotation in all directions,
as the edges of the head contact the rod when the head is rotated.
U.S. Pat. No. 5,891,145 to Morrison et al. utilizes a polyaxial
screw head with a disk-like projection resting in a taper. This
complex design requires compression of the disk-like projection in
a taper. The difficulties in this are high because when the screw
head rotates, only a small portion of the disk-like projection is
in contact with the taper, thereby making it almost impossible to
lock the angulation of the screw in position.
[0007] U.S. Pat. No. 5,584,834 to Errico et al. discloses that a
taper is required on the exterior surface of an external ring to
engage and create sufficient pressure to lock a screw head. In
addition, this design is restricted to a curvate screw head. The
external locking collar is also tapered on its inside aspect and it
is a requirement of the design. U.S. Pat. No. 5,578,033 to Errico
et al. discloses a spherical head of a hook that is used in place
of a spherical head of a screw. The implant loads the rod component
from the side, with a locking collar sliding over a tapered lower
section. Both of these prior art Errico patents require the use of
a locking nut to lock the assembly in its final position. U.S. Pat.
No. 5,586,984 to Errico et al. discloses an external taper on a
body portion of a locking ring to clamp the tapered section against
a round screw head. This is also done by advancing a threaded
nut.
[0008] United States Publication No. 2007/0173819 to Sandlin et al.
shows a locking cap design to engage a tapered upper portion of a
body. A tapered portion can be used to cause contouring around a
rod, which has been shown in other prior art patents. The cap also
engages in such a way as to be fully locked or not locked at all.
There are no provisions for partial locking.
SUMMARY OF THE INVENTION
[0009] According to the present invention, there is provided a
screw and rod fixation assembly comprising a body member including
a screw seat for seating a screw head therein and a rod seat for
seating a rod therein. Adjustable rod locking means adjustably
applies a locking force against a rod seated in the rod seat. An
adjustable screw locking means adjustably applies a locking force
to a screw head seated in the screw seat. The adjustable screw
locking means is functionally independent of the adjustable rod
locking means.
[0010] The present invention further provides a screw and rod
fixation member including a body portion having a first end having
a screw seat for seating a screw head therein and a second end
including a rod seat for seating a rod therein. The first end
includes a pocket therein having outwardly flexible walls for
receiving a screw head therein, thereby defining a screw seat. The
second end includes a base portion and two spaced arms extending
therefrom defining a rod seat. The arms include a smooth outer
surface and fixing means for engagement with a rod locking
member.
[0011] The present invention also provides a fixation screw
including a threaded portion for engagement with a bone and a head
portion and a neck portion therebetween. The screw head includes
multiple engagement surfaces for contacting multiple areas of a
spherical screw seat surface.
[0012] The present invention provides a method of fixing a rod to a
screw by inserting a screw head into a screw seat in one end of a
body member and inserting a rod into a rod seat in a second end of
the body member. A locking force is selectively and independently
adjusted on both the screw head and the rod within the screw seat
and rod seat, respectively.
[0013] In addition, the present invention further provides a method
of fixing a rod to a screw head by seating a screw head having
multiple contact points in a screw seat of a body portion causing
the screw head to interfere with and contact multiple portions of
the spherical seat creating sufficient friction to lock the screw
head in a desired position during rod insertion while allowing the
body portion to rotate relative to the screw head.
DESCRIPTION OF THE DRAWINGS
[0014] Other advantages of the present invention are readily
appreciated as the same becomes better understood by reference to
the following detailed description when considered in connection
with the accompanying drawings wherein:
[0015] FIG. 1 is a side view of the present invention;
[0016] FIG. 2 is an exploded side view of the present
invention;
[0017] FIG. 3 is a side view of a partially exploded and partially
assembled view of the present invention;
[0018] FIG. 4 is a side view of the assembled invention;
[0019] FIG. 5 is a prospective exploded view of the present
invention;
[0020] FIG. 6 is a prospective view of the body member of the
present invention;
[0021] FIG. 7 is a prospective view of the body member of the
present invention as shown in FIG. 6 rotated 90.degree.;
[0022] FIG. 8 is a prospective view of the body member specifically
showing the screw seat portion;
[0023] FIG. 9 is a bottom prospective view of the body member
showing details of the screw seat;
[0024] FIG. 10 is a top prospective view of the body member;
[0025] FIG. 11 is a side prospective view of the body member;
[0026] FIG. 12 is a cross-sectional view of the body member;
[0027] FIG. 13 is a side view of the screw member made in
accordance with the present invention;
[0028] FIG. 14 is a prospective view of the inventive screw;
[0029] FIG. 15 is a prospective view showing the top portion of the
screw member;
[0030] FIG. 16 is a prospective view showing the top portion and
side portion of the rod locking member of the present
invention;
[0031] FIG. 17 is a side prospective view of the rod locking
member;
[0032] FIG. 18 is a prospective view of the locking ring of the
present invention;
[0033] FIG. 19 is a prospective view showing an opposite surface of
the locking ring shown in FIG. 18;
[0034] FIG. 20 is a prospective view of a second embodiment of the
locking ring made in accordance with the present invention;
[0035] FIG. 21 is a side view of the rod locking member and locking
ring of the present invention;
[0036] FIG. 22 is a prospective view showing the bottom surfaces of
the rod locking member and locking ring of the present
invention;
[0037] FIG. 23 shows an alternative embodiment of the rod locking
member;
[0038] FIG. 24 is an exploded side view of the assembly made in
accordance with the present invention;
[0039] FIG. 25 is a partially assembled side view of the present
invention;
[0040] FIG. 26 is a further assembled side view of the present
invention; and
[0041] FIG. 27 is a side view of a partially assembled assembly
made in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0042] In accordance with the present invention, a screw and rod
fixation assembly is generally shown at 10 in the figures. Most
generally, the assembly 10 includes a body member 100 including a
screw seat 119 for seating a screw head therein and a rod seat 116
for seating a rod 104 therein. An adjustable rod locking mechanism
in the form of a rod locking member 102 adjustably applies a
locking force against a rod 104 seated in the rod seat 116. An
adjustable screw locking mechanism in the form of a screw locking
ring 101 adjustably applies a locking force to a screw head seated
in the screw seat 119. The adjustable screw locking mechanism is
functionally independent of the adjustable rod locking mechanism.
Thus, in use, a practicing physician can independently adjust the
body member relative to the screw and, independently, relative to
the rod. This provides the physician with much more flexibility
during surgery, as described in more detail below.
[0043] More specifically and referring directly to the figures,
FIGS. 1-4 show solid models of the assembly 10. FIG. 1 shows the
assembly 10, wherein the screw 103 and rod 104 are inter-connected
and locked in place by the body member 100. The assembled screw and
rod form a compact structure with the assembly 10.
[0044] FIG. 2 shows the polyaxial screw assembly 10 partially
assembled and a rod 104 and locking cap 102 disengaged. The locking
ring 101 slides over the body member 100 and over side tabs 106
that extend radially outwardly from arm portions 108. The body
member 100 includes the arms 108 and a base portion 116, best shown
in FIG. 7, defining the rod seat. The arms 108 act as springs
allowing the locking ring 101 to radially inwardly push the arms
108. Once in position, the arms 108 spring back elastically. This
enables the locking ring 101 to be positioned under the side tabs
106, thereby preventing the locking ring 101 from unintentionally
sliding back off of the assembly 10. A lower lip 113 on the body
portion 100 prevents the locking ring 101 from traveling beyond a
desired locking point, as described in greater detail below.
[0045] The locking ring 101 is in a locked position as shown in
FIG. 3. The locking ring 101 is disposed over the outer surface of
the screw seat 119 and forced fully down and adjacent to or against
the lower lip 113. Based on variation and tolerances, contact with
the lip 113 is the maximum locking position. However, it is not
necessary for there to be contact with the lip 113 by the locking
ring 101 to have a locking action. Rather, the extent that the
locking ring 101 is disposed over the screw seat 119 adjustably
applies varying degrees of locking force on the screw head.
[0046] Once the locking ring 101 is in the locked position, the
screw 103 is locked in position relative to the body member 100,
thereby preventing rotation of the screw head 122 relative to the
body member 100. The bottom portion of the rod 104 is shown to be
above the locking ring 101 and not in contact therewith. It is not
a restriction of the present invention to have contact or not to
have contact between the rod 104 and locking ring 101. However, the
locking ring 101 can be adjusted relative to the outer surface of
the screw seat 119 to adjust the locking force of the locking ring
thereon. This places the screw head 122 in a pre-locking condition
wherein a compressing force of the screw seat 119 on the screw head
122 can be adjusted. When some force is exerted on the head of the
screw to limit the screw motion, the rod may be pushed against the
locking ring, thereby placing it in contact with the locking ring.
Full locking can move the locking ring below the bottom of the rod,
thus avoiding contact therebetween.
[0047] FIG. 4 shows the body member 100 including extended tabs
100A, which extend through the central bore of the locking cap 102.
The tabs 100A are broken away after locking the rod to the body
member, but are included in the preferred embodiment of the present
invention to assist and guide the locking cap 102 into a proper
position. The extended tabs 100A also assist in introducing and
guiding the rod 104 into the rod seat 116. Side tabs 106 extending
from arm portion 108 can be biased radially inwardly when the
locking cap 102 is pushed downward and return biased radially
outwardly into openings 133 in the locking cap 102 to assist in
securing the locking cap in a locked condition.
[0048] Each of the components of the present invention are shown in
FIG. 5. The body member 100 includes the screw seat 119 described
above, the head 122 of the screw 103 snapping into the screw seat
119. This allows the screw head to be one size regardless of the
thread size of the screw. The locking ring 101 is capable of
sliding down over the body member 100 after the head 122 of the
screw 103 is in place. After the rod 104 is introduced into the
extended tabs 100A and pushed down against the rod seat 116 in the
body member 100, the locking cap 102 is disposed over the arms 100A
and locked in place as described above.
[0049] FIGS. 6-13 show details of the body member 100. The locking
ring 101 engages surface 150 of the body member 100, which can be
cylindrical or tapered. The locking cap 102 engages arms 108, which
can also be cylindrical or tapered. If one of the surfaces is
tapered and the other is cylindrical, then a transition zone is
created between the two surfaces at 105, which simply allows for a
transition of varying diameters in geometry. In addition, the
surface 150 can be larger in diameter than the body member 100. In
this situation, the transition zone 105 forms a small tapered
region. Side tabs 106 extend outwardly from the body member 100,
since these tabs 106 are attached to the wall of the body member
100, (defined by the arms 108 and rod seat 116), the remaining wall
is thin enough to be elastic, thereby allowing the side tabs 106 to
be able to spring inwards and outwards. Raising or lowering the
tabs 106 on the arms 108 of the body member 100 relative to the
base of the body member 100 changes the stiffness of the spring
action.
[0050] To allow the locking cap 102 the ability to slide over the
side tabs 106 and compress the flexible tab portion, a chamfer or a
radius (preferably a chamfer) 107 is machined or formed into the
top of the side cap 106. The extended tabs 100A are only present
during the placement of the rod 104 into the rod seat 116 and
locking of the implant. Once this is accomplished, the tabs 100A
are snapped off and removed from the assembly 10. To accomplish
this, a groove 109 forms a stress riser such that sufficient
pressure on the extended tab 100A will allow the tab 100A to be
snapped off of the body member 100. To assist in holding onto the
body member 100 during introduction of the rod 104, as well as to
provide attachment points for pre-locking and locking of the
implant, holes or openings 110 in the extended tabs 100A are
provided. To assist the locking cap 102 onto the extended tabs 106,
a radius or chamfer 111 is provided in the ends thereof. The top of
the extended tabs 105 can be flat, rounded, or any other
appropriate form. However, as the locking cap extends above the
level of the groove 109, a flat surface is preferred. This prevents
any edges of the snapped off portion from being able to contact
soft tissue. Accordingly, the body members provided with a first
end including the screw seat and a second end including the rod
seat.
[0051] To allow a curved rod 104 to fully seat within the body
member 100, a section of the body member 100 at the bottom of the
U-shaped seat is relieved, thereby forming the rod seat 116. A hole
117 allows a screw driver to pass through the polyaxial screw body
member 100 into the screw 103 so that the screw 103 can be turned
after it is inserted into the body member 100. At least one slot
118 allows the body member 100 to spread sufficiently to allow the
screw head 122 to enter into the screw seat 119. Additional slots
121 can be added to provide additional spring to the body member
100 to allow better opening and closing around the screw head 122
during screw head insertion and locking. The screw seat 119 is
spherical in shape. A chamfer 120 breaks the edge at the screw seat
opening.
[0052] To prevent the locking ring 101 from sliding off the body
member 100, the lower lip 113 is provided, as discussed above. A
blend radius 114 on the lower edge of the lip 113 provides a smooth
transition in the case where the implant comes into contact with
bone, while the polyaxial screw assembly is being positioned.
[0053] FIGS. 14-16 show the polyaxial screw 103 of the present
invention and various details of its construction. The screw 103
includes a threaded portion 124 for engagement with bone, a neck
portion 123, which is generally smooth and cylindrical, and a head
section 122. The screw head 122 includes a basically cylindrical
shape having an upper tapered portion 127 and a lower tapered
portion 126. In FIG. 15, the basic form of the screw head is a
diamond or square, depending on the specific measurements of the
features of the screw head 122, of which the undesired portions are
removed. This creates a very compact head design with two specific
regions 126, 127 for contact with the spherical seat 119. The screw
103 includes a tapered end 125, which creates sharp threads at the
intersection of the taper and the first few threads. These threads
assist in self-tapping or cutting of the threads into the bone
during screw insertion. It is common to machine grooves into the
tapered tip 125 and/or threads 124 to create additional edges for
screw self-tapping.
[0054] FIG. 16 shows one method of providing a feature for allowing
a screw driver to connect with the screw 103. In the top surface of
the screw 129, a hexagon is machined into the surface 131 to a
sufficient depth to thereby allow a screw driver to engage the
hexagon and not slip out. A chamfer 130 aids in guiding the screw
driver into the screw head hexagon.
[0055] The locking cap 102 is shown in FIGS. 17 and 18 and includes
a cylindrical portion having an internal bore or hole 135. This
bore 135 can be cylindrical or tapered. U-shaped slots 134 are cut
into the side of the locking cap 102, thereby allowing the locking
cap to clear the rod 104. To secure the locking cap 102 as well as
provide for additional positive locking to the body member 100,
slots or holes 133 are provided. These slots or holes 133 provide
sufficient clearance to allow the side tabs 106 to slide into the
slots or holes 133. A radius 132 on the top of the locking cap 102
provides a smooth surface for tissue contact.
[0056] The polyaxial screw locking ring 102, shown in FIG. 19,
includes a cylindrical ring shape having an internal bore 139,
which can be a straight cylindrical bore or a tapered bore. The top
surface of the locking ring 137 is designed to contact the lower
edge of the locking cap 136 during assembly locking. It is possible
to lock the rod and screw with the body member without the two
components touching, since both locking means are independent.
However, it is preferable to have contact such that when the
locking cap 102 is placed on the body member 100, the locking cap
102 pushes the locking ring 101 into the proper locking position.
To avoid any sharp edges in contact with the bone when the locking
ring 101 is in the fully locked position, a radius 138 is provided
to smooth the edge. This edge could alternatively be chamfered. The
bottom 140 of the locking ring 101, in maximum locking position,
can contact the lip 113, as described above. It is not necessary
for this to occur to have maximum locking of all components.
[0057] It is also possible to have an alternative structure of the
locking ring 101 such that a portion of the locking cap 102 engages
more directly with the locking ring 101. FIG. 21 shows a groove
machined or formed into the internal bore 139. This groove 142
having a bore larger than the internal bore 139, creates a ledge
141. As shown in FIGS. 22 and 23, the lower surface of the locking
cap 102 includes a corresponding feature 143 to fit in mating
contact with the groove 142 within the locking ring. During
locking, the small extension 143 slides within the groove 142 and
the locking ring. This prevents the lower portion of the locking
cap 102 from flexing outwardly, as the arms on each side of the
u-shaped rod seat is held by the extension and groove arrangement.
It is also possible to accomplish this function through other
means, such as having the lower surface of the locking cap tapered,
such that the smaller end of the taper extends in the direction of
the locking ring. The locking ring would then have a corresponding
tapered feature, such that when the two components contact each
other, the male taper of the locking cap would engage the female
taper of the locking ring, thereby creating the same effect of the
radially extending lip.
[0058] FIGS. 11 and 12 show the assembly drawings of the polyaxial
screw 103. It is possible to insert the screw 103 into the body
member 100 prior to surgery and the remainder of the components
added after, or with the screw already inserted into the polyaxial
body member 100. When the polyaxial body member 100 and screw 103
are provided assembled, it is preferable to also have the locking
ring 101 in the unlocked position already disposed on the body
member 100. This simplifies the implant for the surgeon, as the rod
and the locking cap are the only components that need to be
introduced after the screw assembly is attached to the bone. FIG.
26 shows the assembly with the locking ring 101 in the unlocked
position. This allows the screw head 122 to pivot freely. FIG. 27
shows the locking ring 101 in the fully locked position, which
prevents screw head rotation.
[0059] The above-described assembly provides a body member 100
including a U-shaped slot defining the rod seat for accepting the
rod 104 and the spherical screw seat 119 for accepting the screw
head 122 of the screw 103. By using a predominantly cylindrical
screw head 122 cut from a diamond or square shaped as described
above, the overall height of the assembly 10 can be significantly
reduced without comprising and possibly improving screw head
locking. The reasoning behind this is the problem of the minimal
contact of the standard prior art spherical screw head in a
spherical seat. No matter how precise the machining of the screw
head and the spherical seat, the two are never exactly the same.
Thus, a gap exists between the two except at very specific
locations, which represent only a fraction of the surface area of
the screw head. By utilizing the diamond shape of the present
invention with the points cut off, a cylinder is formed having two
chamfers. The chamfers are matched closely to an angled tangent of
the circle defined by the spherical screw head seat. This creates a
flat surface within the ark, but is fairly close to matching since
the overall contact area is relatively small. This design provides
for four edges to further enhance engagement with the spherical
wall of the screw head seat. It is also possible to use a curvate
surface in place of the chamfer to still create a relative edge.
This curvate surface need not be spherical in an attempt to match
the sphere of the screw head seat, but can be a portion of an oval
as well. The smaller the chamfered or curvate surface is, the
sharper the edge contact between the screw and the body member
spherical seat. Since rotation of the screw head within the seat of
the body is a key part of the design, the ideal balance of smooth
rotation and sufficient locking is created by allowing sufficient
distance between the two circular lines of contact at the top and
bottom of the cylindrical screw head. An alternative implant option
is effectively creating a tapered surface that the diamond shape is
sharper towards one side. Therefore, it is not necessary that the
chamfers on the top and bottom of the cylinder be equal to achieve
locking.
[0060] The screw seat including the slots therein allows sufficient
flexibility for the screw 103 to enter from the bottom of the body
member 100. Entering from the bottom of the body member 100 avoids
restrictions on what diameter screw thread can be used without
having to create a two-part screw where the head is separate from
thread and mechanically attaching them together after the head is
inserted into the body member. Thus, any major thread diameter is
possible.
[0061] The present invention also addresses another issue, wherein
the implant assembly rotates freely such that holding the implant
rod in the desired position without a screw assembly rotating is
very difficult in situ. By utilizing a screw head 122 that is large
enough to interfere and contact the spherical seat 119 of the
present invention, sufficient friction can be created between the
screw head 122 and the screw seat 119 to hold the screw head 122 in
position while still allowing the surgeon the ability to rotate the
body member 100 relative to the screw 103 as needed. This greatly
assists in alignment of the rod seat 116 with the rod 104. In
addition, and more significantly, interference between the screw
head 122 and the spherical seat 119, spreads the outer surface of
the screw seat by opening at the slots. This in effect creates a
radially outwardly extending taper on the outside of the lower
portion of the body member without having the machine into the body
member.
[0062] As described above, the locking ring 101 is basically a
cylinder designed to slide over the body member and compress the
outer surface of the screw seat against the screw head in order to
lock the screw head seat in place. The cylinder of the locking ring
has an internal bore, which can have a straight cylindrical wall,
which is easier to machine and measure than a small tapered wall.
As there is already a taper created on the outer surface of the
screw head seat due to the interference of the screw head with the
spherical seat, there is no need to taper the inner aspect of the
locking ring. By pressing the locking ring 101 down and over the
outer aspect of the spherical screw seat, the locking ring 101
engages the created taper, thereby compressing the spherical seat
against the screw head to securely lock the screw 103 in the
desired position. As described above, the locking ring 101 can be
adjusted to adjust the locking force. This adjustment can be done
totally independent of the application and locking of the locking
cap 102 over the rod 104.
[0063] The section of the arm 108 below the extended tabs 106 are
relatively thin in cross-section and are thereby quite flexible. By
placing side tabs that extend outwardly from the arms, the arms can
be used as a spring to allow the side tabs to easily move inward
and outward. The locking cap 102 can slide over the arms and the
flexible nature of the arms allow the side tabs to flex inwardly
and then outwardly to engage slots or holes 133 in the locking cap.
These features can be inversed, such that the body member includes
holes or slots and the locking cap includes tabs or pins. Also, the
flexibility of the arms is relative to the length of the moment
arm, such that less force is required to push the side tab inward,
the farther it is away from the bottom rod seat 116 of the u-shaped
channel.
[0064] The locking cap 102 is basically a ring having an internal
bore 103 as shown in FIGS. 21 and 23. The cap 102 includes U-shaped
openings 105 being disposed about the rod 104 and grooves or slots
to slide and fit over the side tabs of the body member 100. As
described above, this can be varied by allowing the slots to change
the pins or tabs and the body features were inversed. The internal
bore can be straight or tapered. However, by allowing interference
with the rod, the arms of the U-shaped slot will naturally move
outwardly creating a taper. By using a chamfer at the top of the
arm just below the snap off point, the spread arms have a feature
to allow the locking cap to slide onto the arms, which without the
chamfer would be spread larger than the diameter of the locking
cap. By pressing the locking cap downwardly, the arms compress
around the rod, thereby securely locking it into position. In
addition, the locking cap can include a central clip 200 that can
be used to provide additional force against the rod. This locking
clip is sufficiently flexible to compensate for contoured rods.
[0065] Overall, the present invention allows for independent
locking of the rod and screw. By locking the locking ring 101 into
the locking position, the screw head is fixed. However, without the
locking cap in place, a rod 104 is free to move relative thereto.
This is an extremely helpful feature in certain surgical
procedures, wherein screw head rotation would not be desirable. It
also allows a polyaxial screw to work as if it is a fixed screw.
The locking ring 101 can also be used to increase friction against
the screw head without fully locking the screw head by not pressing
it downward into its final locking position.
[0066] The locking cap 102 possesses the same function of
adjustability in that force can be applied against the rod 104
without fully locking the rod 104 in position. As the locking cap
102 engages the arms 108 of the U-shaped slot in the body member
100, forces apply to the rod 104. The further the locking cap 102
moves towards the final locking position, the more force is applied
against the rod 104. The body member 100 can also be provided more
than one side tab, thereby forming a ratchet effect, such that
varying locking loads to the rod 104 control than better moderated
by the surgeon, yet still locked in those positions.
[0067] In view of the above, the present invention provides a
method of fixing a rod to a screw by inserting a screw head into a
screw seat in one end of a body member, inserting a rod into a rod
seat in a second end of the body member, and then selectively and
independently adjusting a locking force on both the screw head and
rod within the screw seat, respectively. More specifically, the
screw head is inserted into the screw seat and a locking ring is
disposed about the body portion and space from the outer surface of
the screw seat prior to surgery. The rod is inserted within the rod
seat and independently and selectively locking forces apply to the
locking ring about the screw seat and the rod locking cap member
about an outer surface of the rod seat during surgery.
[0068] The present invention further provides the method of fixing
the rod to the screw head by seating the screw head having multiple
contact points in a screw seat of a body portion causing the screw
head to interfere with and contact multiple portions of the
spherical seat creating sufficient friction to lock the screw head
in a desired position during rod insertion while also allowing the
body portion to rotate relative to the screw head.
[0069] Throughout this application, various publications, including
United States patents, are referenced by author and year and
patents by number. Full citations for the publications are listed
below. The disclosures of these publications and patents in their
entireties are hereby incorporated by reference into this
application in order to more fully describe the state of the art to
which this invention pertains.
[0070] The invention has been described in an illustrative manner,
and it is to be understood that the terminology, which has been
used is intended to be in the nature of words of description rather
than of limitation.
[0071] Obviously, many modifications and variations of the present
invention are possible in light of the above teachings. It is,
therefore, to be understood that within the scope of the appended
claims, the invention can be practiced otherwise than as
specifically described.
REFERENCES
U.S. Patents
[0072] U.S. Pat. No. 7,186,255 [0073] U.S. Pat. No. 7,163,539
[0074] U.S. Pat. No. 5,891,145 [0075] U.S. Pat. No. 5,584,834
[0076] U.S. Pat. No. 5,586,984 [0077] U.S. Pat. No. 5,578,033
U.S. Publications
[0077] [0078] 2007/0173819 [0079] 2007/0233086 [0080] 2007/0173819
[0081] 2007/0157543 [0082] 2007/0123867 [0083] 2007/0118123 [0084]
2007/0055242 [0085] 2007/0055235 [0086] 2006/0276789 [0087]
2006/0271047 [0088] 2006/0241603 [0089] 2006/0241599 [0090]
2006/0235393 [0091] 2006/0235392 [0092] 2006/0235385 [0093]
2006/0200133 [0094] 2006/0173456 [0095] 2006/0149240 [0096]
2006/0149233 [0097] 2006/0100622 [0098] 2006/0100621 [0099]
2006/0058788 [0100] 2006/0036252 [0101] 2006/0036242 [0102]
2005/0261687 [0103] 2005/0222570
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