BONE FASTETTER ASSEMBLY FOR BONE RETENl lOfWpPARATUS

FIELD OF THE INVENTION

[0001] The present invention relates to apparatuses that have utility in

connection with the retention of bone bodies in a desired spatial relationship. More

particularly, the invention concerns a pedicle screw assembly for an appliance that

maintains a desired spatial relationship among the vertebrae of a spine.

BACKGROUND OF THE INVENTION

[0002] A variety of devices are known for the fixation, internally or

otherwise, of bone bodies in humans and animals. In the case of the internal

fixation of the vertebrae of a spinal column, so that the vertebrae are maintained in a

desired spatial relationship with respect to one another, the devices often include

pedicle screw, or bone fastener, assemblies. These assemblies include a pedicle

screw, or bone fastener, that is anchored, typically by a threaded arrangement, into

the pedicle of each of the vertebrae that are to be maintained in a desired spatial

relationship. One or more appliances such as longitudinal supports, which may

comprise plates or rods, that extend longitudinally of the spinal column are

connected securely to the pedicle screw assemblies in a manner that allows the

vertebrae to be maintained in a desired alignment In order to achieve the desired

stability, the bone fasteners must be attached securely to the vertebrae and

connected firmly to the appliance

[0003] The B^ne fasteners may be connected directly to^he rods or plates,

or the connection between the bone fasteners and the rods may be accomplished by

the use of a connector or coupling member that forms a part of the appliance. In the

latter instance, the end of the bone fastener that is not attached to the vertebrae is

secured to one end of the coupling member and the other end of the coupling

member is secured to the rod or plate.

[0004] The secure placement of a rod with a rigid bone fastener, whether or

not a coupling member is used, or the placement of a plate between two or more

rigid screws is difficult for a variety of reasons. For example, the displacement or

angulation of the vertebrae may be such that the rigidity of the bone fastener and/or

coupling member, where a coupling member is used, prevents a secure connection

from being made among the components of the bone alignment system.

Additionally, installation is difficult because the rod or plate must align precisely with

all of the bone fasteners.

[0005] Although a bend can be made in the rod or plate in order that the

bone fasteners be firmly secured to the rod or plate, the possibility exits that

stresses can be created that cause the bone bodies or vertebrae to fracture or the

screws to loosen over time. This is even the case when rods having a degree of

flexibility are used. Thus it is important that bone fastener assemblies be provided

that minimize the likelihood of the establishment of undesirable stresses.

SUMMARY OF THE INVENTION

[0006] According to one aspect of the invention, a bone fastener assembly

comprises a bone fastener, an adjusting member and a securing fastener. The

bone fastener has an attaching portion for attaching the bone fastener to a bone or

bone part; a supporting portion; and a securing portion. The adjusting member is

supported by the supporting portion of the bone fastener and includes an opening

extending through it. The opening in the adjusting member is in registration with the

securing portion of the bone fastener. The adjusting member also includes an

engaging surface that is adapted to engage an appliance adjacent to an aperture in

the appliance. The supporting portion of the bone fastener and the adjusting

member are configured so that the adjusting member is supported by the supporting

portion of the bone fastener for universal movement relative to the supporting

portion of the bone fastener. The securing fastener has a first end that is adapted to

pass through the aperture in the appliance. The first end of the securing fastener

extends through the opening in the adjusting member and is secured to the securing portion of the bone fastener. A second end of the securing fastener has a bearing

surface that is adapted to bear against the appliance in opposition to the engaging

surface of the adjusting member, whereby the appliance may be securely fastened

to the bone fastener.

[0007] According to another aspect, the supporting portion of the bone

fastener includes a terminal portion and the adjusting member is sized so that the

engaging surface of the adjusting member extends beyond the terminal portion of

the supporting portion of the bone fastener in the direction of the appliance. With

this arrangement, thelerminal portion of the supporting portion ^" 3? the bone fastener

may be maintained out of contact with the appliance.

[0008] According to still another aspect, the attaching portion of the bone

fastener comprises a shank having a longitudinal axis extending from a bottom end

to a top end of the shank. The outer portion of the shank has threads that are

suitable for attaching the bone fastener to a bone or bone part. In a particular

aspect, the supporting portion of the bone fastener is positioned at the top end of

the shank. The supporting portion includes a spherical recess in which the

supporting portion of the bone fastener supports the adjusting member, and the

adjusting member, where it is supported by the supporting portion of the bone

fastener, has a complementary spherical surface.

[0009] According to yet another aspect, the securing portion of the bone

fastener comprises a threaded cavity and the outer portion of the securing fastener

includes threads that secure the securing fastener to the threaded cavity of the bone

fastener.

[0010] According to a further aspect, the opening in the adjusting member

extends from a first end at the engaging surface of the adjusting member to a

second end that abuts the threaded cavity in the securing portion of the bone

fastener. The second end of the opening is larger than the first end of the opening

in the adjusting member. According to a particular aspect, the opening in the

adjusting member has the shape of a frustrum of a cone.

[0011] According to another aspect, the bone fastener assembly fastens the

appliance to bone bodies and the apparatus retains the bone bodies in a desired

spatial relationship. The apertures in the appliance are located where the appliance

is attached to the bo?Wbodies. The bearing surface of the secδWhg fastener has a

generally convex configuration That ^" engages a complementary concave surface in

the appliance.

[0012] According to still another aspect, the appliance comprises a coupling

member having a first portion and a second portion and an elongated member such

as a rod or plate. The first portion of the coupling member is secured to the bone

fastener assembly and the second portion of the coupling member is connected to

the elongated member.

[0013] According to all the foregoing aspects, the combined rotational and

translatioπal degrees of freedom provided by the adjusting member and securing

fastener permit the bone fastener to remain firmly fixed but easily attached to the

appliance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The detailed description of the present invention that follows is

presented with reference to the accompanying drawings wherein the same

reference numerals denote the same elements in the several views and wherein:

[0015] Fig. 1 is a perspective view of an apparatus comprising the bone

fastener assembly and appliance of an embodiment of the invention;

[00161 Fig. 2 is an exploded view of the bone fastener and assembly

depicted in Fig. 1 ; and

[0017] Fig. 3 is a cross-sectional view through the line 3-3 of Fig.1 .

DETAILED DESCRIPTION OF THE INVENTION

[0018] Referring first to Fig. 1 of the drawings, there is shown in an

assembled state apparatus for use in retaining bone bodies, such as spinal

vertebrae, in a desired spatial relationship. The apparatus includes an appliance,

indicated generally at 10, for aligning bone bodies, and a bone fastener assembly,

indicated generally at 30, for fastening the appliance to one of the bone bodies.

[0019] in the embodiment of the invention shown in Fig. 1 , the appliance

comprises a coupling member, indicated generally at 12, and an elongated member

or fixation rod 26. The coupling member 12 has a first portion, indicated generally

at 13, that is secured to the bone fastener assembly 30 and a second portion,

indicated generally at 14, that is connected to the rod 26. Typically, for the purpose

of stabilizing the vertebrae in a spinal column so that the vertebrae are retained in a

desired spatial relationship, a respective coupling member 12 and an associated

bone fastener assembly 30 secured to the respective coupling member are provided

for each of the vertebrae to be stabilized. Each of the coupling members 12 is

connected to the rod 26 which serves to retain the vertebrae in a desired spatial

relationship.

[0020] There are a variety of means known in the art for connecting a

coupling member, such as the coupling member 12, to a fixation rod, such as rod

26, and many of these known means can be adapted to the apparatus of the present

invention. In the embodiment of the invention illustrated in the drawings, the

coupling member 12 includes two individual substantially identical halves consisting

of a top half 23 and a bottom half 24. The second portion 14 of each of the top and

bottom halves 23 an^4 are inclined away from the first portion^ of the top and

bottom halves, respectively, so as to form a yoke 15. A grommet 25 is located

within the yoke 15. The inside of the yoke may include a recess in which the

grommet 25 is positioned. The rod 26 extends through an opening 27 in the

grommet, the opening being equal to or slightly smaller than the diameter of the rod

26 so that the grommet will be in good contact with the rod. The rod 26 is finally

secured to the coupling member 12 at such time as the bone fastener assembly 30

is secured to coupling member as is described in further detail below.

[0021] Turning now to a description of the bone fastener assembly 30, the

bone fastener assembly includes a bone fastener, indicated generally at 32, an

adjusting member, indicated generally at 44, and a securing fastener, indicated

generally at 50. The bone fastener 32 has an attaching portion 33 for attaching the

bone fastener to a bone or bone part, such as the pedicle of a vertebra. In the

embodiment of the invention shown in the drawings, the attaching portion 33

comprises a shank having a longitudinal axis extending from the bottom end of the

shank, indicated generally at 34, to the top end of the shank just before the top end,

indicated generally at 35, of the bone fastener. The outer portion of the shank has

threads suitable for attaching the bone fastener 32 to a bone or bone part such as

the pedicle of a vertebra. Thus, typically as an initial step in a procedure for

aligning and retaining spinal vertebrae in a desired spatial relationship, a respective

bone fastener 32 is screwed into each of the vertebrae to be aligned. For that

purpose, the top end 35 of the bone fastener 32 is provided with a hexagonally

shaped circumference so that the bone fastener can be securely gripped by a

fastening tool, such as a wrench, and the bone fastener screwed into the vertebrae.

The bone fastener 3?may also be fastened to a vertebra by means other than a

threaded connection as will be understood by those skilled in the art.

[0022] The bone fastener 32 also includes both a supporting portion 40 that

is positioned at the top end 35 of the shank and a securing portion 37. The

supporting portion 40 includes a spherical recess 41 in the embodiment of the

invention illustrated in the drawings. The adjusting member 44 is supported by the

supporting portion 40 of the bone fastener 32 in the spherical recess 41 of the

supporting portion 40 and has a complementary spherical surface 45 where the

adjusting member 44 is supported by the supporting portion 40 of the bone fastener.

[0023] The securing portion 37 of the bone fastener 32 comprises a

threaded cavity for receiving the securing fastener 50 which is provided with threads

51 that secure the securing fastener to the threaded cavity. The adjusting member

44 has an opening 46 that extends through the adjusting member and is in

registration with the threaded cavity of the securing portion 37 of the bone fastener

32.

[0024] From the foregoing description, it will be understood that the

supporting portion 40 of the bone fastener 32 and the adjusting member 44 are

configured so that the adjusting member 44 is supported by the supporting portion

40 of the bone fastener 32 for universal movement relative to the supporting portion

of the bone fastener. Thus, the concave spherical recess 41 of the supporting

portion 40 of the bone fastener and the convex spherical surface 45 of the adjusting

member 44 allow for the adjusting member to be universally pivoted within spherical

recess 41 .

[0025] The adjusting member 44 includes an engaging surface 47 that,

essentially, is flat and engages the underside 17 of the first portion 13 of the

coupling member 12. As discussed in greater detail below, it is important that there

be good contact between the engaging surface 47 of the adjusting member and the

underside 17 of the first portion 13 of the coupling member 12. To provide such

contact, any angularity that exists between the engaging surface 47 and the

underside 17 of the coupling member when the bone fastener assembly is being

secured to the coupling member 12 can be corrected by appropriate pivoting of the

adjusting member 44 in the spherical recess 41 of the supporting portion 40 of the

bone fastener 32. In this connection, as can be seen in Fig. 3, the adjusting

member 44 is sized so that the engaging surface 47 of the adjusting member

extends sufficiently beyond the terminal portion 42 of the supporting portion 40 of

the fastener in the direction of the underside 17 of the coupling member 12 so that

the terminal portion 42 is maintained out of contact with the underside 17 of the

coupling member. Otherwise, good contact between the engaging surface 47 and

the coupling member 12 would be compromised.

[0026] It can be seen from Figs. 2 and 3 that the opening 46 in the adjusting

member 44 extends from a first end at the engaging surface 47 of the adjusting

member to a second end that abuts the threaded cavity of the securing portion 37 of

the bone fastener. The second end of the opening 46 is larger than the first end of

the opening so that the opening will remain in registration with the threaded cavity of

the securing portion 37 of the bone fastener regardless of any anticipated

adjustment of the adjusting member 44 in the spherical recess 41. In the

embodiment of the invention illustrated in the drawings, the opening 46 has the

shape of a frustrum oTa cone. This arrangement insures tnat the securing fastener

50 will be able to pass through opening 46 and be secured within the threaded

cavity in the securing portion 31 of the bone fastener 32 without interfering with any

adjustment of the adjusting member 44.

[0027] The first portion 13 of the coupling member 12 of the appliance 10

includes an elongated aperture 18 in the top half 23 and the bottom half 24 of the

coupling member 12 which enables the coupling member to be fastened to the bone

fastener 32 through the instrumentality of the securing fastener 50. The securing

fastener has a first end 52 that passes through aperture 18 and extends through the

opening 46 in the adjusting member 44. The first end 52 of the securing fastener 50

is secured to the securing portion 37 of the bone fastener 32 by means of the

threads 51 on the securing fastener and the threads in the cavity in the securing

portion 37.

[0028] A second end 53 of the securing fastener 50 has a bearing surface

54 that bears against the topside 19 of the first portion 13 of the coupling member

12 of the appliance 10. The bearing surface 54 bears against the coupling member

in opposition to the engaging surface 47 of the adjusting member 44 whereby the

appliance 10 is securely fastened to the bone fastener 32. As noted above, any

angularity between the underside 17 of the coupling member 12 and the engaging

surface 47 of the adjusting member 44 will be corrected by appropriate pivoting of

the adjusting member 44 in the spherical recess 41 of the supporting portion 40 of

the bone fastener 32. However, in that instance because the securing fastener 50

will be aligned with the longitudinal axis of the shank 33 of the bone fastener, the

securing fastener 50 will engage the coupling member 12 at an angle. To provide

good contact betweerTϊhe bearing surface 54 and the coupling member 12 under

such circumstances, the bearing surface 54 has a convex spherical configuration

and the perimeter 21 of aperture 18 in the top half 23 of the coupling member 12

which engages the bearing surface 54 is provided with a complementary concave

spherical surface. Similarly, the perimeter 20 of aperture 18 in the bottom half 24 of

trie-coupling member 12 which also engages the bearing surface 54 is provided with

a concave complementary concave spherical surface. Although the securing

fastener 50 is depicted in the Figures with a slotted drive mechanism, other types of

drive mechanisms, such as mechanisms familiar to those skilled in the art may be

employed.

[0029] The invention, as illustrated in Figs. 1 through 3, depicts the

engaging surface 47 of the adjusting member 44 and the underside 17 of the

coupling member 12 as being perpendicular to the longitudinal axis of the shank 33

of the fastener 32. However, rarely will that be case and, as indicated in the

foregoing description of the invention, an angularity will exist between the underside

17 of the coupling member 12 and the longitudinal axis of the shank and that

angularity will be compensated for by the adjusting member 44. Thus, in order to

install the apparatus of the invention for the purpose of retaining a plurality of

vertebrae in a desired spatial relationship, typically, a respective bone fastener 32

will be screwed into each of the vertebrae. With existing technology, it is not

possible to. attach the bone fasteners to the vertebrae so that no angularity exits

between the mutually engaging surfaces of each of the bone fasteners 32 and

respective coupling members 12; and as has been described above, the angularity

is compensated for by the pivoting of each adjusting member 44 in the spherical

recess 41 of a respective supporting portion 40 of a bone fastener 32. This

adjustment places the engaging surface 47 of the adjusting member in a parallel,

rather than angular, relationship with the underside 17 of the coupling member 12.

The opening 46 in the adjusting member 44 is sufficiently large that such adjustment

of the adjusting member 44 will not place the opening 46 out of registration with the

threaded cavity in the securing portion 37 of the bone fastener. Consequently, the

securing fastener 50 is able to pass through the opening 46 in the adjusting member

44 and be secured in the threaded cavity in the securing portion 37 of the bone

fastener.

[0030] For aligning the vertebrae in their desired orientation, the fact that

the aperture 18 is elongated allows the distance between the fixation rod 26 and the

bone fastener assembly 30 to be adjusted. Once the proper distance is established,

the securing fastener 50 is tightened in the threaded cavity in the securing portion

37 of the bone fastener. Tightening of the securing fastener 50 will cause the

engaging surface 47 of the adjusting member 44 to come into contact with the

underside 17 of the coupling member 12 whereby the adjusting member 44 will pivot

in the spherical recess 41 of the supporting portion 40 of the bone fastener 32,

resulting in full contact between the engaging surface 47 and the underside 17 of

the coupling member 12. Additionally, the convex bearing surface 54 of the

securing fastener 50 will engage and bear on the complementary concave surfaces

of the perimeters 20 and 21 of the aperture 18. In the embodiment of the invention

shown in the drawings, the convex bearing surface 54 of the securing fastener 50,

the surface 45 of adjusting member 44, spherical recess 41 and the concave

spherical surfaces 20 and 21 all have a common center of rotation so that forces

applied by the securing fastener are normal to the engaging surfaces of the various

elements of the bone fastener assembly and appliance. This procedure is carried

out with each bone fastener assembly and a respective coupling member until the

apparatus is completely secured so as to retain the vertebrae in a desired spatial

relationship. Tightening of the securing fastener 50 also will cause the yoke 15 to

compress the grommet 25 and securely attach the coupling member 12 to the rod

26.

[0031] Although the invention has been described in relation to the use of a

rigid rod 26 so that an essentially immovable stabilizing apparatus is provided, rods

may be employed that possess a degree of flexibility such that limited movement of

the apparatus can take place once it is installed. Additionally, the appliance to

which the bone fastener assembly of the invention is applied can be other than a rod

and coupling member. For example, a plurality of the bone fastener assemblies

attached to bone bodies can be secured directly to a plate provided with

cooperating apertures and the bone bodies to which the assemblies are attached thereby retained in a desired spatial relationship.

[0032] The foregoing description and discussion of the invention has been

presented for purposes of illustration and to facilitate the presentation of aspects of

the invention. The foregoing is not intended to limit the invention to those aspects.

Although the description of the invention has included discussions of certain

variations and modifications, other variations and modifications may become

apparent to those skilled in the art and it is intended that the scope of the invention

as set forth in the claims below be inclusive of such variations and modifications.